Bermuda

SUMMARY 1. The term “interspecific territorialism” is defined. 2. Examples are given of interspecific territorialism between (a) members of the chat genus Oenanthe (leucopyga, lugens, monacha, oenanthe, and pleschanka); (b) oenanthids and a female Monticola solitarius; and (c) the shrikes Lanius collurio and L. nubicus. 3. An encounter between a Robin Erithacus rubecula and a pair of Stonechats. Saxicola torquata is described. 4. It is contended that common outline and mannerisms are more important than common plumage characters in stimulating these interspecific reactions. 5. Interspecific territorialism is apparently one of the means evolved to eliminate the effect of competition between closely allied species with a similar ecology.

@article{doi101111j1474919x1951tb05443x,
    author = "Simmons, K. E. L.",
    title = "INTERSPECIFIC TERRITORIALISM",
    year = "1951",
    journal = "Ibis",
    abstract = "SUMMARY 1. The term “interspecific territorialism” is defined. 2. Examples are given of interspecific territorialism between (a) members of the chat genus Oenanthe (leucopyga, lugens, monacha, oenanthe, and pleschanka); (b) oenanthids and a female Monticola solitarius; and (c) the shrikes Lanius collurio and L. nubicus. 3. An encounter between a Robin Erithacus rubecula and a pair of Stonechats. Saxicola torquata is described. 4. It is contended that common outline and mannerisms are more important than common plumage characters in stimulating these interspecific reactions. 5. Interspecific territorialism is apparently one of the means evolved to eliminate the effect of competition between closely allied species with a similar ecology.",
    url = "https://doi.org/10.1111/j.1474-919x.1951.tb05443.x",
    doi = "10.1111/j.1474-919x.1951.tb05443.x",
    openalex = "W4240743867"
}

Observations of unrelated but ecologically comparable species of sunbirds, Nectariniidae, derived from Malaysia, and honeyeaters, Meliphagidae, derived from Australia in the interstitial region of the eastern Indonesian islands, indicate that these birds of identical size and similar food habits, are at least in partial competition. A study of the behavior of these birds in the territory of one of the species indicates an unequal numerical ratio between the species and dominant, aggressive behavior by the scarcer species (honeyeater). It is suggested that the behavioral activity of aggressiveness may in itself serve to limit successful reproduction in addition to other phenomena such as clutch size or nesting success of which so far nothing is known. Any activities of a social or behavioral nature which may serve to limit the reproductive rate of the species may, therefore, have a considerable absolute survival value.

@article{doi101086282064,
    author = "Ripley, S. Dillon",
    title = "Competition between Sunbird and Honeyeater Species in the Moluccan Islands",
    year = "1959",
    journal = "The American Naturalist",
    abstract = "Observations of unrelated but ecologically comparable species of sunbirds, Nectariniidae, derived from Malaysia, and honeyeaters, Meliphagidae, derived from Australia in the interstitial region of the eastern Indonesian islands, indicate that these birds of identical size and similar food habits, are at least in partial competition. A study of the behavior of these birds in the territory of one of the species indicates an unequal numerical ratio between the species and dominant, aggressive behavior by the scarcer species (honeyeater). It is suggested that the behavioral activity of aggressiveness may in itself serve to limit successful reproduction in addition to other phenomena such as clutch size or nesting success of which so far nothing is known. Any activities of a social or behavioral nature which may serve to limit the reproductive rate of the species may, therefore, have a considerable absolute survival value.",
    url = "https://doi.org/10.1086/282064",
    doi = "10.1086/282064",
    openalex = "W2086726887"
}

@article{doi101086282065,
    author = "Hutchinson, G. Evelyn and MacArthur, Robert H.",
    title = "Appendix on the Theoretical Significance of Aggressive Neglect in Interspecific Competition",
    year = "1959",
    journal = "The American Naturalist",
    url = "https://doi.org/10.1086/282065",
    doi = "10.1086/282065",
    openalex = "W1974409144"
}

In summary, then, our general conclusions are: (1) Populations of producers, carnivores, and decomposers are limited by their respective resources in the classical density-dependent fashion. (2) Interspecific competition must necessarily exist among the members of each of these three trophic levels. (3) Herbivores are seldom food-limited, appear most often to be predator-limited, and therefore are not likely to compete for common resources.

@article{doi101086282146,
    author = "Hairston, Nelson G. and Smith, Frederick E. and Slobodkin, Lawrence B.",
    title = "Community Structure, Population Control, and Competition",
    year = "1960",
    journal = "The American Naturalist",
    abstract = "In summary, then, our general conclusions are: (1) Populations of producers, carnivores, and decomposers are limited by their respective resources in the classical density-dependent fashion. (2) Interspecific competition must necessarily exist among the members of each of these three trophic levels. (3) Herbivores are seldom food-limited, appear most often to be predator-limited, and therefore are not likely to compete for common resources.",
    url = "https://doi.org/10.1086/282146",
    doi = "10.1086/282146",
    openalex = "W2004827430",
    references = "beauchamp1932competitive, doi101101sqb195702201017, doi101101sqb195702201021, doi101111j155856461957tb02883x, doi101111j174966321948tb39854x, doi1023071395, doi1023071485, doi1023071931600, doi1023071943584, doi1023072240"
}

@article{crowell1961the,
    author = "Crowell, Kenneth",
    title = "THE EFFECTS OF REDUCED COMPETITION IN BIRDS",
    year = "1961",
    journal = "Proceedings of the National Academy of Sciences",
    url = "https://doi.org/10.1073/pnas.47.2.240",
    doi = "10.1073/pnas.47.2.240",
    number = "2",
    openalex = "W2073818755",
    pages = "240-243",
    volume = "47"
}

@article{doi1023071933500,
    author = "Connell, Joseph H.",
    title = "The Influence of Interspecific Competition and Other Factors on the Distribution of the Barnacle Chthamalus Stellatus",
    year = "1961",
    journal = "Ecology",
    url = "https://doi.org/10.2307/1933500",
    doi = "10.2307/1933500",
    openalex = "W1973688100",
    references = "beauchamp1932competitive, connell1961effects, doi101017s0025315400009073, doi101017s002531540001047x, doi1023071665, doi1023071851, doi1023071931034, doi1023071931600, doi1023071950746, doi1023072256872, doi1023072273"
}

@article{ripley1961aggressive,
    author = "Ripley, S. Dillon",
    title = "Aggressive Neglect as a Factor in Interspecific Competition in Birds",
    year = "1961",
    journal = "The Auk",
    url = "https://doi.org/10.2307/4082274",
    doi = "10.2307/4082274",
    number = "3",
    openalex = "W2317709984",
    pages = "366-371",
    volume = "78",
    references = "doi101086282064, doi101086282065, doi101111j1474919x1951tb05443x, doi1023071932731, doi105281zenodo16226952"
}

@article{crowell1962reduced,
    author = "Crowell, Kenneth L.",
    title = "Reduced Interspecific Competition among the Birds of Bermuda",
    year = "1962",
    journal = "Ecology",
    url = "https://doi.org/10.2307/1932042",
    doi = "10.2307/1932042",
    number = "1",
    openalex = "W2034637962",
    pages = "75-88",
    volume = "43",
    references = "doi101002jmor1050500106, doi101086282070, doi101086282106, doi10114912429992, doi101163036551653x00024, doi1023071931600, doi1023071932254, doi1023074510687"
}

@misc{crowell1962reduced1,
    author = "Crowell, K. L",
    title = "Reduced interspecific competition among the birds of Bermuda",
    year = "1962",
    howpublished = "Ecology, v. 43, p. 75-88",
    note = "talkorigins\_source = {true}; raw\_reference = {Crowell, K. L., 1962, Reduced interspecific competition among the birds of Bermuda: Ecology, v. 43, p. 75-88.}"
}

@article{doi1023071932042,
    author = "Crowell, Kenneth L.",
    title = "Reduced Interspecific Competition among the Birds of Bermuda",
    year = "1962",
    journal = "Ecology",
    url = "https://doi.org/10.2307/1932042",
    doi = "10.2307/1932042",
    openalex = "W2034637962",
    references = "doi101002jmor1050500106, doi101086282070, doi101086282106, doi10114912429992, doi101163036551653x00024, doi1023071931600, doi1023071932254, doi1023074510687"
}

Adaptive radiation has been defined as the evolutionary divergence of members of a phyletic line into different niches or adaptive zones (Mayr, 1963:633). Although it has been customary to think of adaptive radiation solely in terms of species or races, a growing body of evidence indicates that some degree of radiation occurs also within populations, as individuals come to occupy different subniches or adaptive subzones, subdividing and, perhaps, expanding the total niche or zone utilized by the population. Probably all species show some degree of ecological variation, either polymorphic or continuous. But this phenomenon is being studied in only a few groups of organisms, notably in Drosophila, in which chromosomal polymorphism has been interpreted as a. means of adaptation of populations to heterogeneous environments (Dobzhansky, * 1961, 1963, 1965). Theoretical bases for research on ecological variation in animal populations have been provided by Ludwig (1950), Levene (1953)) da Cunha and Dobzhansky (1954), Dempster (1955), Li (1955), Carson (1959), and Levins (1962, 1963). In birds, as in other vertebrates, the sexes usually differ in size if not also in proportions of body parts, including those used in feeding (Amadon, 1959); and, especially where the degree of sexual dimorphism, which is a form of polymorphism (Ford, 1961: 12), is marked, it seems probable that the morphological divergence has ecological significance in adapting the sexes to different subniches. However, there is only an occasional reference in the literature to sexual dimorphism in relation to niche utilization (e.g., Pitelka, 1950; Rand, 19.52), and, in general, the whole problem of ecological variation in populations has been neglected by vertebrate ecologists. The primary purpose of this report is to present evidence of an adaptive function of sexual dimorphism in size in woodpeckers by relating degrees of morphological dimorphism and sexual divergence in foraging behavior in two melanerpine species, the strongly dimorphic Hispaniolan Woodpecker (Centurus striatus) of Haiti and the Dominican Republic and the moderately dimorphic Golden-fronted Woodpecker (Ce&zmus awifrons) of continental North and Central America. In addition, the paper surveys other evidence that sexual dimorphism in birds is related to differential niche utilization. Finally, some evolutionary aspects of sexual dimorphism and ecological variation are considered.

@article{doi1023071365712,
    author = "Selander, Robert K.",
    title = "Sexual Dimorphism and Differential Niche Utilization in Birds",
    year = "1966",
    journal = "Ornithological Applications",
    abstract = "Adaptive radiation has been defined as the evolutionary divergence of members of a phyletic line into different niches or adaptive zones (Mayr, 1963:633). Although it has been customary to think of adaptive radiation solely in terms of species or races, a growing body of evidence indicates that some degree of radiation occurs also within populations, as individuals come to occupy different subniches or adaptive subzones, subdividing and, perhaps, expanding the total niche or zone utilized by the population. Probably all species show some degree of ecological variation, either polymorphic or continuous. But this phenomenon is being studied in only a few groups of organisms, notably in Drosophila, in which chromosomal polymorphism has been interpreted as a. means of adaptation of populations to heterogeneous environments (Dobzhansky, * 1961, 1963, 1965). Theoretical bases for research on ecological variation in animal populations have been provided by Ludwig (1950), Levene (1953)) da Cunha and Dobzhansky (1954), Dempster (1955), Li (1955), Carson (1959), and Levins (1962, 1963). In birds, as in other vertebrates, the sexes usually differ in size if not also in proportions of body parts, including those used in feeding (Amadon, 1959); and, especially where the degree of sexual dimorphism, which is a form of polymorphism (Ford, 1961: 12), is marked, it seems probable that the morphological divergence has ecological significance in adapting the sexes to different subniches. However, there is only an occasional reference in the literature to sexual dimorphism in relation to niche utilization (e.g., Pitelka, 1950; Rand, 19.52), and, in general, the whole problem of ecological variation in populations has been neglected by vertebrate ecologists. The primary purpose of this report is to present evidence of an adaptive function of sexual dimorphism in size in woodpeckers by relating degrees of morphological dimorphism and sexual divergence in foraging behavior in two melanerpine species, the strongly dimorphic Hispaniolan Woodpecker (Centurus striatus) of Haiti and the Dominican Republic and the moderately dimorphic Golden-fronted Woodpecker (Ce\&zmus awifrons) of continental North and Central America. In addition, the paper surveys other evidence that sexual dimorphism in birds is related to differential niche utilization. Finally, some evolutionary aspects of sexual dimorphism and ecological variation are considered.",
    url = "https://doi.org/10.2307/1365712",
    doi = "10.2307/1365712",
    openalex = "W2084499670",
    references = "crowell1961the, crowell1962reduced, doi101086281792, doi101111j155856461963tb03295x, doi101111j155856461963tb03296x, doi101537ase188722495, doi1023071931600, doi1023071931976, doi1023071932042, doi1023072407089, doi1023072407090, doi104159harvard9780674865327, doi105962bhltitle110063, doi105962bhltitle27468, doi107312rens91062, openalexw1595343243, openalexw1973833797, openalexw2128666103"
}

The land and fresh-water birds of the southwest Pacific islands derive mainly from New Guinea and offer a favorable situation for studying ecological consequences of island invasions. The reduction of competition on species-poor islands permits some colonizing species to expand their niches spatially, by occupying altitudinal bands, types of habitats, and/or vertical strata of the forest from which they are excluded by other species on species-rich islands. Expansions to higher altitudes, or from second-growth into forest, are especially frequent. Other colonists become more abundant in the same type of habitat preferred on New Guinea. Instances of a change in diet are rare. Changes in foraging technique are noted mainly for those colonists that have been isolated long enough to have undergone morphological divergence. Approximately half of the colonizing populations experience no niche shift.

@article{doi101073pnas672529,
    author = "Diamond, Jared M.",
    title = "Ecological Consequences of Island Colonization by Southwest Pacific Birds, I. Types of Niche Shifts",
    year = "1970",
    journal = "Proceedings of the National Academy of Sciences",
    abstract = "The land and fresh-water birds of the southwest Pacific islands derive mainly from New Guinea and offer a favorable situation for studying ecological consequences of island invasions. The reduction of competition on species-poor islands permits some colonizing species to expand their niches spatially, by occupying altitudinal bands, types of habitats, and/or vertical strata of the forest from which they are excluded by other species on species-rich islands. Expansions to higher altitudes, or from second-growth into forest, are especially frequent. Other colonists become more abundant in the same type of habitat preferred on New Guinea. Instances of a change in diet are rare. Changes in foraging technique are noted mainly for those colonists that have been isolated long enough to have undergone morphological divergence. Approximately half of the colonizing populations experience no niche shift.",
    url = "https://doi.org/10.1073/pnas.67.2.529",
    doi = "10.1073/pnas.67.2.529",
    openalex = "W2081071692"
}

The concepts by which MacArthur and Wilson have transformed the science of ecology in the past decade, and the results of ecological studies such as mine on New Guinea bird communities, have implications for conservation policies. For example, primary tropical rain forest, the most species-rich and ecologically complex habitat on earth, has for millions of years served as the ultimate evolutionary source of the world's dominant plant and animal groups. Throughout the tropics today, the rain forests are being destroyed at a rate such that little will be left in a few decades. When the rain forests have been reduced to isolated tracts separated by open country, the distribution of obligate rain forest species will come to resemble bird distributions on New Guinea land-bridge islands after severing of the land bridges. The smaller the tract, the more rapidly will forest species tend to disappear and be replaced by the widespread second-growth species that least need protection (13). This ominous process is illustrated by Barro Colorado Island, a former hill in Panama that became an island when construction of the Panama Canal flooded surrounding valleys to create Gatun Lake. In the succeeding 60 years several forest bird species have already disappeared from Barro Colorado and been unable to recolonize across the short intervening water gap from the forest on the nearby shore of Gatun Lake. The consequences of the species-area relation (Fig. 1) should be taken into consideration during the planning of tropical rain forest parks (13). In a geographical area that is relatively homogeneous with regard to the fauna, one large park would be preferable to an equivalent area in the form of several smaller parks. Continuous nonforest strips through the park (for example, wide highway swaths) would convert one rain forest "island" into two half-size islands and should be avoided. If other considerations require that an area be divided into several small parks, connecting them by forest corridors might significantly improve their conservation function at little further cost in land withdrawn from development. Modern ecological studies may also be relevant to the understanding of human populations. For instance, during a long period of human evolution there appear to have been not one but two coexistent hominid lines in Africa, the Australopithecus robustus-A. boisei ("Zinjanthropus") line, which became extinct, and the Australopithecus africanus-A. habilis line, which led to Homo sapiens (27). The need to maintain niche differences between these lines must have provided one of the most important selective pressures on the ancestors of modern man in the late Pliocene and early Pleistocene. Thus, any attempt to understand human evolution must confront the problem of what these ecological segregating mechanisms were. To what extent were contemporaneous species of the two lines separated by habitat, by diet, by size difference, or by foraging technique, and were their local spatial distributions broadly overlapping or else sharpened by behavioral interactions as in the case of the Crateroscelis warblers of Fig. 6? To take another example, there are striking parallels between the present distributions of human populations and of bird populations on the islands of Vitiaz and Dampier straits between New Guinea and New Britain. Some of these islands were sterilized by cataclysmic volcanic explosions within the last several centuries. The birds that recolonized these islands have been characterized as coastal and small-island specialists of high reproductive potential, high dispersal powers, and low competitive ability, unlike the geographically closer, competitively superior, slowly dispersing, and breeding birds of mainland New Guinea (10, 11, 13). It remains to be seen whether the people of the Vitiaz-Dampier islands, the Polynesians, and other human populations that colonize insular or unstable habitats also have distinctive population ecologies.

@article{doi101126science1794075759,
    author = "Diamond, Jared M.",
    title = "Distributional Ecology of New Guinea Birds",
    year = "1973",
    journal = "Science",
    abstract = {The concepts by which MacArthur and Wilson have transformed the science of ecology in the past decade, and the results of ecological studies such as mine on New Guinea bird communities, have implications for conservation policies. For example, primary tropical rain forest, the most species-rich and ecologically complex habitat on earth, has for millions of years served as the ultimate evolutionary source of the world's dominant plant and animal groups. Throughout the tropics today, the rain forests are being destroyed at a rate such that little will be left in a few decades. When the rain forests have been reduced to isolated tracts separated by open country, the distribution of obligate rain forest species will come to resemble bird distributions on New Guinea land-bridge islands after severing of the land bridges. The smaller the tract, the more rapidly will forest species tend to disappear and be replaced by the widespread second-growth species that least need protection (13). This ominous process is illustrated by Barro Colorado Island, a former hill in Panama that became an island when construction of the Panama Canal flooded surrounding valleys to create Gatun Lake. In the succeeding 60 years several forest bird species have already disappeared from Barro Colorado and been unable to recolonize across the short intervening water gap from the forest on the nearby shore of Gatun Lake. The consequences of the species-area relation (Fig. 1) should be taken into consideration during the planning of tropical rain forest parks (13). In a geographical area that is relatively homogeneous with regard to the fauna, one large park would be preferable to an equivalent area in the form of several smaller parks. Continuous nonforest strips through the park (for example, wide highway swaths) would convert one rain forest "island" into two half-size islands and should be avoided. If other considerations require that an area be divided into several small parks, connecting them by forest corridors might significantly improve their conservation function at little further cost in land withdrawn from development. Modern ecological studies may also be relevant to the understanding of human populations. For instance, during a long period of human evolution there appear to have been not one but two coexistent hominid lines in Africa, the Australopithecus robustus-A. boisei ("Zinjanthropus") line, which became extinct, and the Australopithecus africanus-A. habilis line, which led to Homo sapiens (27). The need to maintain niche differences between these lines must have provided one of the most important selective pressures on the ancestors of modern man in the late Pliocene and early Pleistocene. Thus, any attempt to understand human evolution must confront the problem of what these ecological segregating mechanisms were. To what extent were contemporaneous species of the two lines separated by habitat, by diet, by size difference, or by foraging technique, and were their local spatial distributions broadly overlapping or else sharpened by behavioral interactions as in the case of the Crateroscelis warblers of Fig. 6? To take another example, there are striking parallels between the present distributions of human populations and of bird populations on the islands of Vitiaz and Dampier straits between New Guinea and New Britain. Some of these islands were sterilized by cataclysmic volcanic explosions within the last several centuries. The birds that recolonized these islands have been characterized as coastal and small-island specialists of high reproductive potential, high dispersal powers, and low competitive ability, unlike the geographically closer, competitively superior, slowly dispersing, and breeding birds of mainland New Guinea (10, 11, 13). It remains to be seen whether the people of the Vitiaz-Dampier islands, the Polynesians, and other human populations that colonize insular or unstable habitats also have distinctive population ecologies.},
    url = "https://doi.org/10.1126/science.179.4075.759",
    doi = "10.1126/science.179.4075.759",
    openalex = "W2082049451",
    references = "doi101073pnas5161207, doi101073pnas6951109, doi101086282454, doi101086282738, doi101111j1469185x1965tb00815x, doi101111j155856461963tb03295x, doi101722611310, doi1023071931976, doi1023071934090, doi1023072407089, doi104159harvard9780674865327"
}

We suggest that the "predation" and "competition" hypotheses of community organization and species diversity are complementary. Maintenance of high diversity by competition appears to be relatively more important at higher trophic levels, while maintenance of high diversity by predation seems relatively more important at lower trophic levels. Further, predation is probably the dominant organizing interaction in trophically complex communities, while competition is probably the dominant organizing interaction in trophically simple communities. These hypotheses are supported on a local scale by experimental studies in the rocky intertidal communities of New England and the West Coast. A probable consequence of its greater temporal heterogeneity (i.e., a less stable, less predictable, and more stressful environment) is that the East Coast is trophically more simple and has an increased incidence of competitive exclusion. As a result, diversity is lower on the East Coast compared with the West Coast. A similar interpretation is possible for differences in diversity along other gradients of temporal heterogeneity such as the shallow to deep-sea soft-sediment communities. In structurally simple environments, competition reduces diversity through competitive exclusion. On the other hand, predation first increases and then decreases diversity in spatially simple environments, presumably because refuges are few and hence overexploitation of a resource is more probable. In structurally complex environments, competition may increase diversity through increased habitat specialization. Such environments undoubtedly have more refuges and reduce predator foraging efficiency, both of which may allow the coexistence of more species. Predator-mediated escapes by primary producers from herbivores may explain the apparent importance of interspecific competition in certain primary producer associations.

@article{doi101086283073,
    author = "Menge, Bruce A. and Sutherland, John P.",
    title = "Species Diversity Gradients: Synthesis of the Roles of Predation, Competition, and Temporal Heterogeneity",
    year = "1976",
    journal = "The American Naturalist",
    abstract = {We suggest that the "predation" and "competition" hypotheses of community organization and species diversity are complementary. Maintenance of high diversity by competition appears to be relatively more important at higher trophic levels, while maintenance of high diversity by predation seems relatively more important at lower trophic levels. Further, predation is probably the dominant organizing interaction in trophically complex communities, while competition is probably the dominant organizing interaction in trophically simple communities. These hypotheses are supported on a local scale by experimental studies in the rocky intertidal communities of New England and the West Coast. A probable consequence of its greater temporal heterogeneity (i.e., a less stable, less predictable, and more stressful environment) is that the East Coast is trophically more simple and has an increased incidence of competitive exclusion. As a result, diversity is lower on the East Coast compared with the West Coast. A similar interpretation is possible for differences in diversity along other gradients of temporal heterogeneity such as the shallow to deep-sea soft-sediment communities. In structurally simple environments, competition reduces diversity through competitive exclusion. On the other hand, predation first increases and then decreases diversity in spatially simple environments, presumably because refuges are few and hence overexploitation of a resource is more probable. In structurally complex environments, competition may increase diversity through increased habitat specialization. Such environments undoubtedly have more refuges and reduce predator foraging efficiency, both of which may allow the coexistence of more species. Predator-mediated escapes by primary producers from herbivores may explain the apparent importance of interspecific competition in certain primary producer associations.},
    url = "https://doi.org/10.1086/283073",
    doi = "10.1086/283073",
    openalex = "W2052231134",
    references = "connell1961effects, doi101086282272, doi101086282379, doi1023071942321, doi1023071942327, doi1023071950746"
}

This paper analyzes patterns of bird species diversity on an elevational transect of the Cordillera Vilcabamba, Peru. Major changes in climate and vegetation are encompassed by the transect which extended from the Apurimac Valley floor at 500 m to the summit ridge of the range at >3,500 m. Four vegetation zones are easily discerned–lowland rain forest, montane rain forest, cloud forest, and elfin forest. In progressing upwards there is a monotonic trend toward decreasing canopy stature and reduced number of plant strata. The vegetation gradient provided the opportunity to examine the relation between bird species diversity and habitat complexity in an entirely natural setting. The decrease in forest stature with elevation was closely paralleled by decreasing avian syntopy (the total number of bird species cohabiting the forest at a given elevation). Bird species diversity was shown to be highly correlated with foliage height diversity, using either four or five layers in the foliage height diversity calculation (r =.97), and less well correlated using three layers, as defined previously by MacArthur (r =.84). At this superficial level the trend in bird species diversity seemed to be adequately explained as a response to the vegetation gradient. This preliminary conclusion was found to be illusory when the elevational trend in syntopy was reexamined separately for three major trophic subdivisions of the fauna. The number of insectivores decreased 5.2—fold from the bottom to the top of the gradient, frugivores decreased by a factor of 2.3, and nectarivores showed no change. It was now clear that the diversity in each of these trophic categories was responsive to environmental influences other than, or in addition to, the gradient in habitat structure. Additional factors implicated by the available evidence are competitive interactions with other taxa at the same trophic level, changing composition of the resource base as a function of elevation, and declining productivity at high elevations. Analysis of netted bird samples revealed an unexpected diversity maximum in the lower cloud forest zone. The immediate cause of this was a relaxation of the vertical stratification of foraging zones, such that an anomalously large fraction of the species present entered the nets. The excess diversity was found to consist almost entirely of insectivores. Several factors appear to contribute to the ultimate causes of the diversity maximum: greater patchiness of the montane forest due to the rugged topography, a higher density of foliage near the ground, and possibly increased resource productivity. A correlation between diversity and density in the netting results suggested a causal connection mediated via resource levels. The conclusion in that diversity is a complex property that is responsive to many types of influences beyond simply the structure of the habitat.

@article{doi1023071936921,
    author = "Terborgh, John",
    title = "Bird Species Diversity on an Andean Elevational Gradient",
    year = "1977",
    journal = "Ecology",
    abstract = "This paper analyzes patterns of bird species diversity on an elevational transect of the Cordillera Vilcabamba, Peru. Major changes in climate and vegetation are encompassed by the transect which extended from the Apurimac Valley floor at 500 m to the summit ridge of the range at >3,500 m. Four vegetation zones are easily discerned–lowland rain forest, montane rain forest, cloud forest, and elfin forest. In progressing upwards there is a monotonic trend toward decreasing canopy stature and reduced number of plant strata. The vegetation gradient provided the opportunity to examine the relation between bird species diversity and habitat complexity in an entirely natural setting. The decrease in forest stature with elevation was closely paralleled by decreasing avian syntopy (the total number of bird species cohabiting the forest at a given elevation). Bird species diversity was shown to be highly correlated with foliage height diversity, using either four or five layers in the foliage height diversity calculation (r =.97), and less well correlated using three layers, as defined previously by MacArthur (r =.84). At this superficial level the trend in bird species diversity seemed to be adequately explained as a response to the vegetation gradient. This preliminary conclusion was found to be illusory when the elevational trend in syntopy was reexamined separately for three major trophic subdivisions of the fauna. The number of insectivores decreased 5.2—fold from the bottom to the top of the gradient, frugivores decreased by a factor of 2.3, and nectarivores showed no change. It was now clear that the diversity in each of these trophic categories was responsive to environmental influences other than, or in addition to, the gradient in habitat structure. Additional factors implicated by the available evidence are competitive interactions with other taxa at the same trophic level, changing composition of the resource base as a function of elevation, and declining productivity at high elevations. Analysis of netted bird samples revealed an unexpected diversity maximum in the lower cloud forest zone. The immediate cause of this was a relaxation of the vertical stratification of foraging zones, such that an anomalously large fraction of the species present entered the nets. The excess diversity was found to consist almost entirely of insectivores. Several factors appear to contribute to the ultimate causes of the diversity maximum: greater patchiness of the montane forest due to the rugged topography, a higher density of foliage near the ground, and possibly increased resource productivity. A correlation between diversity and density in the netting results suggested a causal connection mediated via resource levels. The conclusion in that diversity is a complex property that is responsive to many types of influences beyond simply the structure of the habitat.",
    url = "https://doi.org/10.2307/1936921",
    doi = "10.2307/1936921",
    openalex = "W2102729100",
    references = "doi1023071934090"
}

That niches of competitors in ecological communities are shaped by mutual coevolution, which thus allows many species to coexist, is a commonly-held view. Two species must live together consistently to coevolve, so since predators (or parasites) are dependent upon their prey, they will necessarily co-occur with them and so should coevolve. In contrast, competing species, which are not dependent on each other, need not consistently co-occur or coevolve. Increased diversity, by reducing the consistency of co-occurrence, also reduces the chance of coevolution. To demonstrate coevolutionary divergence of competitors one must show: 1) that divergence has actually occurred: this has been done for some fossil sequences but not for any extant competitors; 2) that competition, rather than some other mechanism, is responsible; and 3) that it has a genetic basis. To demonstrate 2) and 3) for natural populations requires appropriate field experiments, which are suggested in the paper. This has been done, in part, in only one case. Thus the notion of coevolutionary shaping of competitors' niches has little support at present. Theory and evidence suggest that it is probable only in low diversity communities.

@article{doi1023073544421,
    author = "Connell, Joseph H.",
    title = "Diversity and the Coevolution of Competitors, or the Ghost of Competition Past",
    year = "1980",
    journal = "Oikos",
    abstract = "That niches of competitors in ecological communities are shaped by mutual coevolution, which thus allows many species to coexist, is a commonly-held view. Two species must live together consistently to coevolve, so since predators (or parasites) are dependent upon their prey, they will necessarily co-occur with them and so should coevolve. In contrast, competing species, which are not dependent on each other, need not consistently co-occur or coevolve. Increased diversity, by reducing the consistency of co-occurrence, also reduces the chance of coevolution. To demonstrate coevolutionary divergence of competitors one must show: 1) that divergence has actually occurred: this has been done for some fossil sequences but not for any extant competitors; 2) that competition, rather than some other mechanism, is responsible; and 3) that it has a genetic basis. To demonstrate 2) and 3) for natural populations requires appropriate field experiments, which are suggested in the paper. This has been done, in part, in only one case. Thus the notion of coevolutionary shaping of competitors' niches has little support at present. Theory and evidence suggest that it is probable only in low diversity communities.",
    url = "https://doi.org/10.2307/3544421",
    doi = "10.2307/3544421",
    openalex = "W2125389285",
    references = "doi101016b9780127114422x50016, doi101038269471a0, doi101071zo9540009, doi101086282070, doi101111j109583121972tb00690x, doi101126science19943351302, doi101146annureves06110175002011, doi1023071942161, doi1023072479933, doi105962bhltitle56234, openalexw1500291103, openalexw2962874606"
}

We studied the relations between bird distribution and abundance and habitat characteristics at a regional scale of investigation, using surveys conducted over three consecutive years on 14 plots at nine locations in the shrubsteppe of the northwestern Great Basin of North America. Bivariate and multivariate analyses revealed no large suites of bird species that were correlated in their distribution and abundance, and few associations existed between pairs of species, suggesting that bird populations in this system vary largely independently of one another. Both bivariate and multivariate correlational analyses between birds and habitat physiognomy indicated that the bird species that were widely distributed in this shrubsteppe system had few significant associations with habitat features, while species with more localized distributions did exhibit habitat affinities, most notably with a suite of characters associated with the occurrence of rocky outcrops. Bird species whose primary distributions and habitat affinities lie in grassland regions to the east demonstrated the greatest degree of correlation with features of habitat physiognomy in this shrubsteppe region, increasing in abundance as vegetation coverage and stature increased and horizontal heterogeneity of habitats decreased. Some bird species, however, exhibited no correlations with the habitat features we measured, and multivariate analyses comparing variation in the bird abundances with variation in features of habitat physiognomy accounted for <17% of the overall variation in the bird abundance matrix. Consideration of coverages of different species of shrubs, however, generally produced more significant correlations with variations in bird abundances, especially for the widespread shrubsteppe species. Attributes of avian community structure varied among the locations surveyed. Variations in the abundance of Brewer's Sparrows, the most abundant species at most sites, accounted for 86% of the variation in total avian density. Species diversity was negatively correlated with total density (presumably because of the overwhelming influence of one species on density) but positively correlated with species richness. Richness variations, in turn, were a consequence of variations in the abundances of several locally distributed shrubsteppe species or grassland species. Richness decreased with increasing horizontal habitat heterogeneity and general vegetation sparseness, but increased with increasing structural diversity of the habitat. Variations in avian community biomass were largely a function of abundances of the widespread or peripheral species; none of the local shrubsteppe forms that contributed so much to species richness was correlated with total biomass variations. We compare the findings of these regional—scale analyses with those of a continental—scale study that included a habitat spectrum ranging from shrubsteppe through tallgrass prairies. Bird species exhibited different patterns of habitat correlations on the two spatial scales. In particular, the characteristic shrubsteppe species showed strong correlations with features of habitat physiognomy in the continental analysis, but in the regional study such associations were generally lacking and these birds instead were correlated with the coverages of various shrub species. This suggests that at a large scale, between—habitat level of analysis these birds may respond to some elements of general habitat configuration, but their within—habitat responses may be more strongly associated with details of habitat floristics. These results complicate studies of avian community/habitat relationships: complete understanding of ecological patterns apparently requires knowledge of vegetational floristics as well as physiognomy; the response of birds to habitat characteristics, and the habitat features that are important, may differ at different scales of spatial resolution. At both spatial scales, however, a substantial portion of the variation in avian abundance remains unexplained after consideration of habitat features. Relatively few significant correlations thus emerge, increasing the probability that those that are revealed may well be spurious, and reinforcing the view that biotic interactions such as competition probably play a minor role in structuring these communities.

@article{doi1023072937305,
    author = "Wiens, John A. and Rotenberry, John T.",
    title = "Habitat Associations and Community Structure of Birds in Shrubsteppe Environments",
    year = "1981",
    journal = "Ecological Monographs",
    abstract = "We studied the relations between bird distribution and abundance and habitat characteristics at a regional scale of investigation, using surveys conducted over three consecutive years on 14 plots at nine locations in the shrubsteppe of the northwestern Great Basin of North America. Bivariate and multivariate analyses revealed no large suites of bird species that were correlated in their distribution and abundance, and few associations existed between pairs of species, suggesting that bird populations in this system vary largely independently of one another. Both bivariate and multivariate correlational analyses between birds and habitat physiognomy indicated that the bird species that were widely distributed in this shrubsteppe system had few significant associations with habitat features, while species with more localized distributions did exhibit habitat affinities, most notably with a suite of characters associated with the occurrence of rocky outcrops. Bird species whose primary distributions and habitat affinities lie in grassland regions to the east demonstrated the greatest degree of correlation with features of habitat physiognomy in this shrubsteppe region, increasing in abundance as vegetation coverage and stature increased and horizontal heterogeneity of habitats decreased. Some bird species, however, exhibited no correlations with the habitat features we measured, and multivariate analyses comparing variation in the bird abundances with variation in features of habitat physiognomy accounted for <17\% of the overall variation in the bird abundance matrix. Consideration of coverages of different species of shrubs, however, generally produced more significant correlations with variations in bird abundances, especially for the widespread shrubsteppe species. Attributes of avian community structure varied among the locations surveyed. Variations in the abundance of Brewer's Sparrows, the most abundant species at most sites, accounted for 86\% of the variation in total avian density. Species diversity was negatively correlated with total density (presumably because of the overwhelming influence of one species on density) but positively correlated with species richness. Richness variations, in turn, were a consequence of variations in the abundances of several locally distributed shrubsteppe species or grassland species. Richness decreased with increasing horizontal habitat heterogeneity and general vegetation sparseness, but increased with increasing structural diversity of the habitat. Variations in avian community biomass were largely a function of abundances of the widespread or peripheral species; none of the local shrubsteppe forms that contributed so much to species richness was correlated with total biomass variations. We compare the findings of these regional—scale analyses with those of a continental—scale study that included a habitat spectrum ranging from shrubsteppe through tallgrass prairies. Bird species exhibited different patterns of habitat correlations on the two spatial scales. In particular, the characteristic shrubsteppe species showed strong correlations with features of habitat physiognomy in the continental analysis, but in the regional study such associations were generally lacking and these birds instead were correlated with the coverages of various shrub species. This suggests that at a large scale, between—habitat level of analysis these birds may respond to some elements of general habitat configuration, but their within—habitat responses may be more strongly associated with details of habitat floristics. These results complicate studies of avian community/habitat relationships: complete understanding of ecological patterns apparently requires knowledge of vegetational floristics as well as physiognomy; the response of birds to habitat characteristics, and the habitat features that are important, may differ at different scales of spatial resolution. At both spatial scales, however, a substantial portion of the variation in avian abundance remains unexplained after consideration of habitat features. Relatively few significant correlations thus emerge, increasing the probability that those that are revealed may well be spurious, and reinforcing the view that biotic interactions such as competition probably play a minor role in structuring these communities.",
    url = "https://doi.org/10.2307/2937305",
    doi = "10.2307/2937305",
    openalex = "W2012588930",
    references = "doi101086282531"
}

In a strictly defined sample of competition studies using controlled field experiments, covering 215 species and 527 experiments, competition was found in most of the studies, in somewhat more than half of the species, and in about two-fifths of the experiments. In most of these experiments interspecific competition was not distinguished from intraspecific competition. In the few studies in which the two were separated, interspecific competition was the stronger form in about onesixth of all experiments done. When competition was demonstrated, intraspecific competition was as strong or stronger than interspecific in three-quarters of the experiments. Some evidence from this literature survey suggests that negative results may be underrepresented, so that the absolute values of these figures may be too high. Since this bias should apply also to studies of all taxa, habitats, or other interactions it should not greatly affect estimates of the relative prevalence of competition. Since these estimates come from field experiments open to other influences such as predators, grazers, weather, disturbances, etc., they should provide a fair approximation of the relative prevalence of interspecific and intraspecific competition in natural ecological communities. The prevalence of competition in these studies varied. Marine organisms showed consistently higher frequencies of competition than terrestrial ones as did large-sized organisms as compared to smaller ones. Plants, herbivores, and carnivores showed similar frequencies of competition in all habitats compared. The incidence of competition varied considerably from year to year and place to place. In some categories, evidence concerning competition is sparse. More studies are needed of all freshwater species, marine vertebrates, parasites, effects on resource partitioning, and particularly the relative strengths of interspecific versus intraspecific competition. When both members of a pair were studied and some competition found, only one member was affected in well over half the experiments. Such strong asymmetrical competition is not always consistent in direction; reversals in the rank order of competitive superiority have been demonstrated by field experiments and direct observations. Some positive interactions were found. These may have been a consequence of actual positive influences or of negative ones acting indirectly through other species. The latter may also apply to some of the negative interactions interpreted as competition in these studies. If only the input and output of an experiment are known, it is difficult to decide what mechanism produced the observed effect. While many of the experiments probably have been correctly interpreted, the present survey illustrates how difficult it is to produce a clear and unambiguous demonstration of interspecific competition.

@article{doi101086284165,
    author = "Connell, Joseph H.",
    title = "On the Prevalence and Relative Importance of Interspecific Competition: Evidence from Field Experiments",
    year = "1983",
    journal = "The American Naturalist",
    abstract = "In a strictly defined sample of competition studies using controlled field experiments, covering 215 species and 527 experiments, competition was found in most of the studies, in somewhat more than half of the species, and in about two-fifths of the experiments. In most of these experiments interspecific competition was not distinguished from intraspecific competition. In the few studies in which the two were separated, interspecific competition was the stronger form in about onesixth of all experiments done. When competition was demonstrated, intraspecific competition was as strong or stronger than interspecific in three-quarters of the experiments. Some evidence from this literature survey suggests that negative results may be underrepresented, so that the absolute values of these figures may be too high. Since this bias should apply also to studies of all taxa, habitats, or other interactions it should not greatly affect estimates of the relative prevalence of competition. Since these estimates come from field experiments open to other influences such as predators, grazers, weather, disturbances, etc., they should provide a fair approximation of the relative prevalence of interspecific and intraspecific competition in natural ecological communities. The prevalence of competition in these studies varied. Marine organisms showed consistently higher frequencies of competition than terrestrial ones as did large-sized organisms as compared to smaller ones. Plants, herbivores, and carnivores showed similar frequencies of competition in all habitats compared. The incidence of competition varied considerably from year to year and place to place. In some categories, evidence concerning competition is sparse. More studies are needed of all freshwater species, marine vertebrates, parasites, effects on resource partitioning, and particularly the relative strengths of interspecific versus intraspecific competition. When both members of a pair were studied and some competition found, only one member was affected in well over half the experiments. Such strong asymmetrical competition is not always consistent in direction; reversals in the rank order of competitive superiority have been demonstrated by field experiments and direct observations. Some positive interactions were found. These may have been a consequence of actual positive influences or of negative ones acting indirectly through other species. The latter may also apply to some of the negative interactions interpreted as competition in these studies. If only the input and output of an experiment are known, it is difficult to decide what mechanism produced the observed effect. While many of the experiments probably have been correctly interpreted, the present survey illustrates how difficult it is to produce a clear and unambiguous demonstration of interspecific competition.",
    url = "https://doi.org/10.1086/284165",
    doi = "10.1086/284165",
    openalex = "W1998245410",
    references = "doi101016b9780127114422x50016, doi101086282146, doi101086282478, doi101086283073, doi101086284133, doi101111j109583121972tb00690x, doi101126science185414527, doi1023071933500, doi1023071935707, doi1023071942404, doi1023071942484, doi1023071942563, openalexw2077454220"
}

The object of this study was to determine whether interspecific competition modified local geographic distribution, after taking into account the effect of habitat structure. The tendencies for 14 passerine birds to have positive or negative associations were examined, using 7861 sample points in seven native forests on the islands of Hawaii, Maui, and Kauai. All birds were at least partly insectivorous and were fairly common in forested areas, although some fed chiefly on nectar or fruit. Species—pairs were classified as primary or secondary potential competitors based on general dietary similarity. To evaluate the association between species and to account for the effect of individual species habitat preferences, partial correlations were computed for each species—pair in a study area from the simple correlations between the species and 26 habitat variables plus two quadratic terms to represent nonlinearity. The partial correlations represented a short—term ("instantaneous") assessment of the strength of competitive interactions, and did not reflect the accumulation of competitive displacement through time. Of 170 partial correlations in the analysis, only 10 indicated significant negative association. The general pattern was of positive association (76 significantly positive partials), which probably resulted from flocking and from attraction of birds to areas of resource superabundance. Two species showed consistent patterns of negative partial correlations over several adjacent study areas, the Japanese White—eye/Iiwi in montane Hawaii, and the Japanese White—eye/Elepaio in windward Hawaii; both patterns could be reasonably attributed to direct competition. Species—pairs were grouped by the native or exotic status of the component species. Native/exotic pairs had a significantly greater proportion of negative partial correlations (37%) than either native/native pairs (8%) or exotic/exotic pairs (0%). This pattern was consistent across the seven study areas and appeared to reflect the occurrence of interspecific competition along a broad and diffuse ecological "front" between a co—evolved native avifauna and recently introduced exotic species. The role of competition in the pattern was corroborated by the significantly higher proportion of negative partial correlations among species—pairs of primary potential competitors than among those of secondary potential competitors. Our results suggested that °47% of the primary potential competitors among native/exotic species—pairs may experience at least small depressions in local population density due to competition. Although the negative correlations were for the most part small (average negative r = 0.06), one species could eventually replace another as spatial displacement accumulated through time. The Japanese White—eye appeared to have a principal role in native/exotic interactions, with 62% of the partial correlations between it and native primary potential competitor species being negative. Noteworthy implications were that (1) it was important to account for the habitat responses of individual species when studying the role of interspecific competition in modifying small—scale geographic distribution; (2) competition was frequently sporadic in its geographic occurrence and in the species affected, thus supporting Wiens' (1977) theory of competition; and (3) as a consequence, the role of interspecific competition in modifying distribution may be difficult to detect statistically with small data sets.

@article{mountainspring1985interspecific,
    author = "Mountainspring, Stephen and Scott, J. Michael",
    title = "Interspecific Competition Among Hawaiian Forest Birds",
    year = "1985",
    journal = "Ecological Monographs",
    abstract = {The object of this study was to determine whether interspecific competition modified local geographic distribution, after taking into account the effect of habitat structure. The tendencies for 14 passerine birds to have positive or negative associations were examined, using 7861 sample points in seven native forests on the islands of Hawaii, Maui, and Kauai. All birds were at least partly insectivorous and were fairly common in forested areas, although some fed chiefly on nectar or fruit. Species—pairs were classified as primary or secondary potential competitors based on general dietary similarity. To evaluate the association between species and to account for the effect of individual species habitat preferences, partial correlations were computed for each species—pair in a study area from the simple correlations between the species and 26 habitat variables plus two quadratic terms to represent nonlinearity. The partial correlations represented a short—term ("instantaneous") assessment of the strength of competitive interactions, and did not reflect the accumulation of competitive displacement through time. Of 170 partial correlations in the analysis, only 10 indicated significant negative association. The general pattern was of positive association (76 significantly positive partials), which probably resulted from flocking and from attraction of birds to areas of resource superabundance. Two species showed consistent patterns of negative partial correlations over several adjacent study areas, the Japanese White—eye/Iiwi in montane Hawaii, and the Japanese White—eye/Elepaio in windward Hawaii; both patterns could be reasonably attributed to direct competition. Species—pairs were grouped by the native or exotic status of the component species. Native/exotic pairs had a significantly greater proportion of negative partial correlations (37\%) than either native/native pairs (8\%) or exotic/exotic pairs (0\%). This pattern was consistent across the seven study areas and appeared to reflect the occurrence of interspecific competition along a broad and diffuse ecological "front" between a co—evolved native avifauna and recently introduced exotic species. The role of competition in the pattern was corroborated by the significantly higher proportion of negative partial correlations among species—pairs of primary potential competitors than among those of secondary potential competitors. Our results suggested that °47\% of the primary potential competitors among native/exotic species—pairs may experience at least small depressions in local population density due to competition. Although the negative correlations were for the most part small (average negative r = 0.06), one species could eventually replace another as spatial displacement accumulated through time. The Japanese White—eye appeared to have a principal role in native/exotic interactions, with 62\% of the partial correlations between it and native primary potential competitor species being negative. Noteworthy implications were that (1) it was important to account for the habitat responses of individual species when studying the role of interspecific competition in modifying small—scale geographic distribution; (2) competition was frequently sporadic in its geographic occurrence and in the species affected, thus supporting Wiens' (1977) theory of competition; and (3) as a consequence, the role of interspecific competition in modifying distribution may be difficult to detect statistically with small data sets.},
    url = "https://doi.org/10.2307/1942558",
    doi = "10.2307/1942558",
    number = "2",
    openalex = "W1966764972",
    pages = "219-239",
    volume = "55",
    references = "doi101086284165, doi101093aesa492190, doi101198tech2005s303, doi1023071267833, doi1023071932254, doi1023072344930, doi1023072530180, openalexw1500291103, openalexw1989371375, openalexw2109228066"
}

@incollection{crossref1988bermuda,
    title = "BERMUDA",
    year = "1988",
    booktitle = "1988–1989",
    url = "https://doi.org/10.1515/9783112420621-028",
    doi = "10.1515/9783112420621-028",
    pages = "211-213"
}

@article{crossref1999bermuda,
    title = "Bermuda",
    year = "1999",
    journal = "Trusts \& Trustees",
    url = "https://doi.org/10.1093/tandt/5.6.17",
    doi = "10.1093/tandt/5.6.17",
    number = "6",
    pages = "17-18",
    volume = "5"
}

Resource competition is thought to play a major role in driving evolutionary diversification. For instance, in ecological character displacement, coexisting species evolve to use different resources, reducing the effects of interspecific competition. It is thought that a similar diversifying effect might occur in response to competition among members of a single species. Individuals may mitigate the effects of intraspecific competition by switching to use alternative resources not used by conspecific competitors. This diversification is the driving force in some models of sympatric speciation, but has not been demonstrated in natural populations. Here, we present experimental evidence confirming that competition drives ecological diversification within natural populations. We manipulated population density of three-spine sticklebacks (Gasterosteus aculeatus) in enclosures in a natural lake. Increased population density led to reduced prey availability, causing individuals to add alternative prey types to their diet. Since phenotypically different individuals added different alternative prey, diet variation among individuals increased relative to low-density control enclosures. Competition also increased the diet-morphology correlations, so that the frequency-dependent interactions were stronger in high competition. These results not only confirm that resource competition promotes niche variation within populations, but also show that this increased diversity can arise via behavioural plasticity alone, without the evolutionary changes commonly assumed by theory.

@article{doi101098rspb20060198,
    author = "Svanbäck, Richard and Bolnick, Daniel I.",
    title = "Intraspecific competition drives increased resource use diversity within a natural population",
    year = "2006",
    journal = "Proceedings of the Royal Society B Biological Sciences",
    abstract = "Resource competition is thought to play a major role in driving evolutionary diversification. For instance, in ecological character displacement, coexisting species evolve to use different resources, reducing the effects of interspecific competition. It is thought that a similar diversifying effect might occur in response to competition among members of a single species. Individuals may mitigate the effects of intraspecific competition by switching to use alternative resources not used by conspecific competitors. This diversification is the driving force in some models of sympatric speciation, but has not been demonstrated in natural populations. Here, we present experimental evidence confirming that competition drives ecological diversification within natural populations. We manipulated population density of three-spine sticklebacks (Gasterosteus aculeatus) in enclosures in a natural lake. Increased population density led to reduced prey availability, causing individuals to add alternative prey types to their diet. Since phenotypically different individuals added different alternative prey, diet variation among individuals increased relative to low-density control enclosures. Competition also increased the diet-morphology correlations, so that the frequency-dependent interactions were stronger in high competition. These results not only confirm that resource competition promotes niche variation within populations, but also show that this increased diversity can arise via behavioural plasticity alone, without the evolutionary changes commonly assumed by theory.",
    url = "https://doi.org/10.1098/rspb.2006.0198",
    doi = "10.1098/rspb.2006.0198",
    openalex = "W2120385174",
    references = "doi101111j109583121972tb00690x, doi1018900012965820020832936milrs20co2"
}

Biological invasions can change ecosystem function, have tremendous economic costs, and impact human health; understanding the forces that cause and maintain biological invasions is thus of immediate importance. A mechanism by which exotic plants might displace native plants is by increasing the pressure of native consumers on native plants, a form of indirect interaction termed "apparent competition." Using experimental exclosures, seed addition, and monitoring of small mammals in a California grassland, we examined whether exotic Brassica nigra increases the pressure of native consumers on a native bunchgrass, Nassella pulchra. Experimental plots were weeded to focus entirely on indirect effects via consumers. We demonstrate that B. nigra alters the activity of native small-mammal consumers, creating a gradient of consumption that dramatically reduces N. pulchra establishment. Previous work has shown that N. pulchra is a strong competitor, but that it is heavily seed limited. By demonstrating that consumer pressure is sufficient to curtail establishment, our work provides a mechanism for this seed limitation and suggests that, despite being a good competitor, N. pulchra cannot reestablish close to B. nigra within its old habitats because exotic-mediated consumption preempts direct competitive exclusion. Moreover, we find that apparent competition has a spatial extent, suggesting that consumers may dictate the rate of invasion and the area available for restoration, and that nonspatial studies of apparent competition may miss important dynamics.

@article{doi1018900702231,
    author = "Orrock, John L. and Witter, Martha S. and Reichman, O. J.",
    title = "APPARENT COMPETITION WITH AN EXOTIC PLANT REDUCES NATIVE PLANT ESTABLISHMENT",
    year = "2008",
    journal = "Ecology",
    abstract = {Biological invasions can change ecosystem function, have tremendous economic costs, and impact human health; understanding the forces that cause and maintain biological invasions is thus of immediate importance. A mechanism by which exotic plants might displace native plants is by increasing the pressure of native consumers on native plants, a form of indirect interaction termed "apparent competition." Using experimental exclosures, seed addition, and monitoring of small mammals in a California grassland, we examined whether exotic Brassica nigra increases the pressure of native consumers on a native bunchgrass, Nassella pulchra. Experimental plots were weeded to focus entirely on indirect effects via consumers. We demonstrate that B. nigra alters the activity of native small-mammal consumers, creating a gradient of consumption that dramatically reduces N. pulchra establishment. Previous work has shown that N. pulchra is a strong competitor, but that it is heavily seed limited. By demonstrating that consumer pressure is sufficient to curtail establishment, our work provides a mechanism for this seed limitation and suggests that, despite being a good competitor, N. pulchra cannot reestablish close to B. nigra within its old habitats because exotic-mediated consumption preempts direct competitive exclusion. Moreover, we find that apparent competition has a spatial extent, suggesting that consumers may dictate the rate of invasion and the area available for restoration, and that nonspatial studies of apparent competition may miss important dynamics.},
    url = "https://doi.org/10.1890/07-0223.1",
    doi = "10.1890/07-0223.1",
    openalex = "W2017000066"
}

Island environments typically share characteristics such as impoverished biotas and less-seasonal climates, which should be conducive to specific adaptations by organisms. However, with the exception of morphological studies, broad-scale tests of patterns of adaptation on islands are rare. Here, I examine reproductive patterns in island birds worldwide. Reproductive life histories are influenced by latitude, which could affect the response to insularity; therefore, I additionally test this hypothesis. Island colonizers showed mostly bi-parental care, but there was a significant increase in cooperative breeding on islands. Additionally, I found support for previous suggestions of reduced fecundity, longer developmental periods and increased investment in young on islands. However, clutch size increased with latitude at a rate nearly five times faster on the mainland than on the islands revealing a substantially stronger effect of insularity at higher latitudes. Latitude and insularity may also interact to determine egg volume and incubation periods, but these effects were less clear. Analyses of reproductive success did not support an effect of reduced nest predation as a driver of reproductive change, but this requires further study. The effect of latitude detected here suggests that the evolutionary changes associated with insularity relate to environmental stability and improved adult survival.

@article{doi101098rspb20111785,
    author = "Covas, Rita",
    title = "Evolution of reproductive life histories in island birds worldwide",
    year = "2011",
    journal = "Proceedings of the Royal Society B Biological Sciences",
    abstract = "Island environments typically share characteristics such as impoverished biotas and less-seasonal climates, which should be conducive to specific adaptations by organisms. However, with the exception of morphological studies, broad-scale tests of patterns of adaptation on islands are rare. Here, I examine reproductive patterns in island birds worldwide. Reproductive life histories are influenced by latitude, which could affect the response to insularity; therefore, I additionally test this hypothesis. Island colonizers showed mostly bi-parental care, but there was a significant increase in cooperative breeding on islands. Additionally, I found support for previous suggestions of reduced fecundity, longer developmental periods and increased investment in young on islands. However, clutch size increased with latitude at a rate nearly five times faster on the mainland than on the islands revealing a substantially stronger effect of insularity at higher latitudes. Latitude and insularity may also interact to determine egg volume and incubation periods, but these effects were less clear. Analyses of reproductive success did not support an effect of reduced nest predation as a driver of reproductive change, but this requires further study. The effect of latitude detected here suggests that the evolutionary changes associated with insularity relate to environmental stability and improved adult survival.",
    url = "https://doi.org/10.1098/rspb.2011.1785",
    doi = "10.1098/rspb.2011.1785",
    openalex = "W2170904075",
    references = "doi101093oso97801985464120010001, doi101111j1474919x1947tb04155x, doi1015159781400881376, doi1023072937160, doi1023075403, doi105281zenodo16204874, doi105860choice295104, openalexw3086315876, openalexw3144712972"
}

Populations facing novel environments can persist by adapting. In nature, the ability to adapt and persist will depend on interactions between coexisting individuals. Here we use an adaptive dynamic model to assess how the potential for evolutionary rescue is affected by intra- and interspecific competition. Intraspecific competition (negative density-dependence) lowers abundance, which decreases the supply rate of beneficial mutations, hindering evolutionary rescue. On the other hand, interspecific competition can aid evolutionary rescue when it speeds adaptation by increasing the strength of selection. Our results clarify this point and give an additional requirement: competition must increase selection pressure enough to overcome the negative effect of reduced abundance. We therefore expect evolutionary rescue to be most likely in communities which facilitate rapid niche displacement. Our model, which aligns to previous quantitative and population genetic models in the absence of competition, provides a first analysis of when competitors should help or hinder evolutionary rescue.

@article{doi101098rstb20120085,
    author = "Osmond, Matthew M. and de Mazancourt, Claire",
    title = "How competition affects evolutionary rescue",
    year = "2012",
    journal = "Philosophical Transactions of the Royal Society B Biological Sciences",
    abstract = "Populations facing novel environments can persist by adapting. In nature, the ability to adapt and persist will depend on interactions between coexisting individuals. Here we use an adaptive dynamic model to assess how the potential for evolutionary rescue is affected by intra- and interspecific competition. Intraspecific competition (negative density-dependence) lowers abundance, which decreases the supply rate of beneficial mutations, hindering evolutionary rescue. On the other hand, interspecific competition can aid evolutionary rescue when it speeds adaptation by increasing the strength of selection. Our results clarify this point and give an additional requirement: competition must increase selection pressure enough to overcome the negative effect of reduced abundance. We therefore expect evolutionary rescue to be most likely in communities which facilitate rapid niche displacement. Our model, which aligns to previous quantitative and population genetic models in the absence of competition, provides a first analysis of when competitors should help or hinder evolutionary rescue.",
    url = "https://doi.org/10.1098/rstb.2012.0085",
    doi = "10.1098/rstb.2012.0085",
    openalex = "W2115726271",
    references = "crowell1961the, doi101038246015a0, doi101038nature09670, doi101086282505, doi101086282697, doi1015159780691209418, doi1023071525780, doi1023072529912, doi102307jctvx5wbbh, doi105962bhltitle27468, openalexw2145250129"
}

Interference competition may lead to a tragedy of the commons in which individuals driven by self-interest reduce the fitness of the entire group. We investigated this hypothesis in Allenby's gerbils, Gerbillus andersoni allenbyi, by comparing foraging behaviors of single vs. pairs of gerbils. We recorded strong interference competition within the foraging pairs. Competition reduced the amount of time the gerbils spent foraging, as well as foraging efficiency since part of the foragers' attention was directed toward detecting competitors (apparent predation risk). Single gerbils harvested significantly more food than the combined efforts of two gerbils foraging together. Competition reduced the success of both individuals within a pair by more than 50%, making this a case of the tragedy of the commons where each individual's investment in competition reduces the success of all individuals within the group, including its own. Despite their great costs, competitive behaviors will be selected for as long as one individual achieves higher fitness than the other. In nature, interspecific interactions, such as predation risk, may act to reduce and regulate the deleterious effects of intraspecific competition.

@article{doi1018901401301,
    author = "Berger‐Tal, Oded and Embar, Keren and Kotler, Burt P. and Saltz, David",
    title = "Everybody loses: intraspecific competition induces tragedy of the commons in Allenby's gerbils",
    year = "2014",
    journal = "Ecology",
    abstract = "Interference competition may lead to a tragedy of the commons in which individuals driven by self-interest reduce the fitness of the entire group. We investigated this hypothesis in Allenby's gerbils, Gerbillus andersoni allenbyi, by comparing foraging behaviors of single vs. pairs of gerbils. We recorded strong interference competition within the foraging pairs. Competition reduced the amount of time the gerbils spent foraging, as well as foraging efficiency since part of the foragers' attention was directed toward detecting competitors (apparent predation risk). Single gerbils harvested significantly more food than the combined efforts of two gerbils foraging together. Competition reduced the success of both individuals within a pair by more than 50\%, making this a case of the tragedy of the commons where each individual's investment in competition reduces the success of all individuals within the group, including its own. Despite their great costs, competitive behaviors will be selected for as long as one individual achieves higher fitness than the other. In nature, interspecific interactions, such as predation risk, may act to reduce and regulate the deleterious effects of intraspecific competition.",
    url = "https://doi.org/10.1890/14-0130.1",
    doi = "10.1890/14-0130.1",
    openalex = "W2102859043",
    references = "ripley1961aggressive"
}

Island environments share distinctive characteristics that offer unique opportunities to investigate parallel evolution. Previous research has produced evidence of an island syndrome for morphological traits, life-history strategies and ecological niches, but little is known about the response to insularity of other important traits such as animal signals. Here, we tested whether birds' plumage colouration is part of the island syndrome. We analysed with spectrophotometry the colouration of 116 species endemic to islands and their 116 closest mainland relatives. We found a pattern of reduced brightness and colour intensity for both sexes on islands. In addition, we found a decrease in the number of colour patches on islands that, in males, was associated with a decrease in the number of same-family sympatric species. These results demonstrate a worldwide pattern of parallel colour changes on islands and suggest that a relaxation of selection on species recognition may be one of the mechanisms involved.

@article{doi101111ele12588,
    author = "Doutrelant, Claire and Paquet, Matthieu and Renoult, Julien P. and Grégoire, Arnaud and Crochet, Pierre‐André and Covas, Rita",
    title = "Worldwide patterns of bird colouration on islands",
    year = "2016",
    journal = "Ecology Letters",
    abstract = "Island environments share distinctive characteristics that offer unique opportunities to investigate parallel evolution. Previous research has produced evidence of an island syndrome for morphological traits, life-history strategies and ecological niches, but little is known about the response to insularity of other important traits such as animal signals. Here, we tested whether birds' plumage colouration is part of the island syndrome. We analysed with spectrophotometry the colouration of 116 species endemic to islands and their 116 closest mainland relatives. We found a pattern of reduced brightness and colour intensity for both sexes on islands. In addition, we found a decrease in the number of colour patches on islands that, in males, was associated with a decrease in the number of same-family sympatric species. These results demonstrate a worldwide pattern of parallel colour changes on islands and suggest that a relaxation of selection on species recognition may be one of the mechanisms involved.",
    url = "https://doi.org/10.1111/ele.12588",
    doi = "10.1111/ele.12588",
    openalex = "W2297257352",
    references = "doi101098rspb20111785"
}

Behavioral interference between species can influence a wide range of ecological and evolutionary processes. Here, we test foundational hypotheses regarding the origins and maintenance of interspecific territoriality, and evaluate the role of interspecific territoriality and hybridization in shaping species distributions and transitions from parapatry to sympatry in sister species of North American perching birds (Passeriformes). We find that interspecific territoriality is pervasive among sympatric sister species pairs, and that interspecifically territorial species pairs have diverged more recently than sympatric noninterspecifically territorial pairs. None of the foundational hypotheses alone explains the observed patterns of interspecific territoriality, but our results support the idea that some cases of interspecific territoriality arise from misdirected intraspecific aggression while others are evolved responses to resource competition. The combination of interspecific territoriality and hybridization appears to be an unstable state associated with parapatry, whereas species that are interspecifically territorial and do not hybridize are able to achieve extensive fine- and coarse-scale breeding range overlap. In sum, these results suggest that interspecific territoriality has multiple origins and impacts coexistence at multiple spatial scales.

@article{doi101111evo14068,
    author = "Cowen, Madeline C. and Drury, Jonathan P. and Grether, Gregory F.",
    title = "Multiple routes to interspecific territoriality in sister species of North American perching birds",
    year = "2020",
    journal = "Evolution",
    abstract = "Behavioral interference between species can influence a wide range of ecological and evolutionary processes. Here, we test foundational hypotheses regarding the origins and maintenance of interspecific territoriality, and evaluate the role of interspecific territoriality and hybridization in shaping species distributions and transitions from parapatry to sympatry in sister species of North American perching birds (Passeriformes). We find that interspecific territoriality is pervasive among sympatric sister species pairs, and that interspecifically territorial species pairs have diverged more recently than sympatric noninterspecifically territorial pairs. None of the foundational hypotheses alone explains the observed patterns of interspecific territoriality, but our results support the idea that some cases of interspecific territoriality arise from misdirected intraspecific aggression while others are evolved responses to resource competition. The combination of interspecific territoriality and hybridization appears to be an unstable state associated with parapatry, whereas species that are interspecifically territorial and do not hybridize are able to achieve extensive fine- and coarse-scale breeding range overlap. In sum, these results suggest that interspecific territoriality has multiple origins and impacts coexistence at multiple spatial scales.",
    url = "https://doi.org/10.1111/evo.14068",
    doi = "10.1111/evo.14068",
    openalex = "W3045491597",
    references = "drury2020competition"
}

Costly interactions between species that arise as a by-product of ancestral similarities in communication signals are expected to persist only under specific evolutionary circumstances. Territorial aggression between species, for instance, is widely assumed to persist only when extrinsic barriers prevent niche divergence or selection in sympatry is too weak to overcome gene flow from allopatry. However, recent theoretical and comparative studies have challenged this view. Here we present a large-scale, phylogenetic analysis of the distribution and determinants of interspecific territoriality. We find that interspecific territoriality is widespread in birds and strongly associated with hybridization and resource overlap during the breeding season. Contrary to the view that territoriality only persists between species that rarely breed in the same areas or where niche divergence is constrained by habitat structure, we find that interspecific territoriality is positively associated with breeding habitat overlap and unrelated to habitat structure. Furthermore, our results provide compelling evidence that ancestral similarities in territorial signals are maintained and reinforced by selection when interspecific territoriality is adaptive. The territorial signals linked to interspecific territoriality in birds depend on the evolutionary age of interacting species, plumage at shallow (within-family) timescales, and song at deeper (between-family) timescales. Evidently, territorial interactions between species have persisted and shaped phenotypic diversity on a macroevolutionary timescale.

@article{drury2020competition,
    author = "Drury, Jonathan P. and Cowen, Madeline C. and Grether, Gregory F.",
    title = "Competition and hybridization drive interspecific territoriality in birds",
    year = "2020",
    journal = "Proceedings of the National Academy of Sciences",
    abstract = "Costly interactions between species that arise as a by-product of ancestral similarities in communication signals are expected to persist only under specific evolutionary circumstances. Territorial aggression between species, for instance, is widely assumed to persist only when extrinsic barriers prevent niche divergence or selection in sympatry is too weak to overcome gene flow from allopatry. However, recent theoretical and comparative studies have challenged this view. Here we present a large-scale, phylogenetic analysis of the distribution and determinants of interspecific territoriality. We find that interspecific territoriality is widespread in birds and strongly associated with hybridization and resource overlap during the breeding season. Contrary to the view that territoriality only persists between species that rarely breed in the same areas or where niche divergence is constrained by habitat structure, we find that interspecific territoriality is positively associated with breeding habitat overlap and unrelated to habitat structure. Furthermore, our results provide compelling evidence that ancestral similarities in territorial signals are maintained and reinforced by selection when interspecific territoriality is adaptive. The territorial signals linked to interspecific territoriality in birds depend on the evolutionary age of interacting species, plumage at shallow (within-family) timescales, and song at deeper (between-family) timescales. Evidently, territorial interactions between species have persisted and shaped phenotypic diversity on a macroevolutionary timescale.",
    url = "https://doi.org/10.1073/pnas.1921380117",
    doi = "10.1073/pnas.1921380117",
    number = "23",
    openalex = "W3015731989",
    pages = "12923-12930",
    volume = "117",
    references = "doi101016jbiocon200905006, doi101016jtree201707004, doi101038nature11631, doi101086343873, doi101093vevey016, doi101111j14679868200500503x, doi101126science1157704, doi101214ss1177011136, doi1018637jssv033i02, openalexw1549853756, openalexw2097360283"
}

Theorists have identified several mechanisms through which species that compete exploitatively for resources could coexist. By contrast, under the current theory, interference competitors could coexist only in rare circumstances. Yet, some types of interference competition, such as interspecific territoriality, are common. This mismatch between theory and nature inspired us to model interference competition in an eco-evolutionary framework. We based the model on the life cycle of territorial birds and ran simulations to examine whether natural selection could rescue a superior interference competitor from extinction without driving a superior exploitative competitor extinct. We found that coexistence between interference competitors can occur over a wide range of ecologically plausible scenarios, and up to the highest levels of resource overlap. An important caveat is that coexistence requires the species to co-evolve. Reductions in population size and levels of genetic variation could destabilise coexistence between interference competitors, and thereby increase extinction rates over current estimates.

@article{doi101111ele14091,
    author = "Grether, Gregory F. and Okamoto, Kenichi W.",
    title = "Eco‐evolutionary dynamics of interference competition",
    year = "2022",
    journal = "Ecology Letters",
    abstract = "Theorists have identified several mechanisms through which species that compete exploitatively for resources could coexist. By contrast, under the current theory, interference competitors could coexist only in rare circumstances. Yet, some types of interference competition, such as interspecific territoriality, are common. This mismatch between theory and nature inspired us to model interference competition in an eco-evolutionary framework. We based the model on the life cycle of territorial birds and ran simulations to examine whether natural selection could rescue a superior interference competitor from extinction without driving a superior exploitative competitor extinct. We found that coexistence between interference competitors can occur over a wide range of ecologically plausible scenarios, and up to the highest levels of resource overlap. An important caveat is that coexistence requires the species to co-evolve. Reductions in population size and levels of genetic variation could destabilise coexistence between interference competitors, and thereby increase extinction rates over current estimates.",
    url = "https://doi.org/10.1111/ele.14091",
    doi = "10.1111/ele.14091",
    openalex = "W4292549857",
    references = "drury2020competition"
}

Significant changes in the environment have the potential to affect bird species abundance and distribution, both directly, through a modification of the landscape, habitats, and climate, and indirectly, through a modification of biotic interactions such as competitive interactions. Predicting and mitigating the consequences of global change thus requires not only a sound understanding of the role played by biotic interactions in current ecosystems, but also the recognition and study of the complex and intricate effects that result from the perturbation of these ecosystems. In this review, we emphasize the role of interspecific competition in bird communities by focusing on three main predictions derived from theoretical and empirical considerations. We provide numerous examples of population decline and displacement that appeared to be, at least in part, driven by competition, and were amplified by environmental changes associated with human activities. Beyond a shift in relative species abundance, we show that interspecific competition may have a negative impact on species richness, ecosystem services, and endangered species. Despite these findings, we argue that, in general, the role played by interspecific competition in current communities remains poorly understood due to methodological issues and the complexity of natural communities. Predicting the consequences of global change in these communities is further complicated by uncertainty regarding future environmental conditions and the speed and efficacy of plastic and evolutionary responses to fast-changing environments. Possible directions of future research are highlighted.

@article{doi103390d14100857,
    author = "Guillaumet, Alban and Russell, Ivory",
    title = "Bird Communities in a Changing World: The Role of Interspecific Competition",
    year = "2022",
    journal = "Diversity",
    abstract = "Significant changes in the environment have the potential to affect bird species abundance and distribution, both directly, through a modification of the landscape, habitats, and climate, and indirectly, through a modification of biotic interactions such as competitive interactions. Predicting and mitigating the consequences of global change thus requires not only a sound understanding of the role played by biotic interactions in current ecosystems, but also the recognition and study of the complex and intricate effects that result from the perturbation of these ecosystems. In this review, we emphasize the role of interspecific competition in bird communities by focusing on three main predictions derived from theoretical and empirical considerations. We provide numerous examples of population decline and displacement that appeared to be, at least in part, driven by competition, and were amplified by environmental changes associated with human activities. Beyond a shift in relative species abundance, we show that interspecific competition may have a negative impact on species richness, ecosystem services, and endangered species. Despite these findings, we argue that, in general, the role played by interspecific competition in current communities remains poorly understood due to methodological issues and the complexity of natural communities. Predicting the consequences of global change in these communities is further complicated by uncertainty regarding future environmental conditions and the speed and efficacy of plastic and evolutionary responses to fast-changing environments. Possible directions of future research are highlighted.",
    url = "https://doi.org/10.3390/d14100857",
    doi = "10.3390/d14100857",
    openalex = "W4304175320",
    references = "drury2020competition"
}

Charles Darwin proposed his ‘principle of divergence’ to account for changes in traits that could promote speciation and coexistence of diverse forms through occupation of different niches to reduce interspecific competition. We explore interspecific foraging behaviour overlap in Fiji’s forest birds, and address two main questions: (1) Is there vertical stratification of foraging behavior? and (2) Is there evidence of interspecific competition driving the differences in foraging behaviour? We explore these questions across three foraging guilds, nectarivores (three species), insectivores (two species), and omnivores (two species), and find vertical portioning of foraging in each group. To investigate the effect of interspecific competition, we compared foraging heights of the Orange-breasted Myzomela (Myzomela jugularis) honeyeater on Viti Levu Island (where it coexists with two other honeyeater species) and Leleuvia Island (no other honeyeater species). On the main island Viti Levu, we found evidence for vertical niche partitioning within each foraging guild. On Leleuvia, with the ‘one-species only foraging guild’, Orange-breasted Myzomela occupied broader vertical foraging niche than on Viti Levu with two other competitor honeyeater species. This result supports the idea that vertical foraging height can be shaped by interspecific competition. The findings of this study support Darwin’s principle of divergence in Fiji’s forest birds for every foraging guild measured and adds to our understanding of the significance of interspecific competition and niche divergence for patterns of ecological speciation on islands.

@article{naikatini2022interspecific,
    author = "Naikatini, Alivereti N. and Keppel, Gunnar and Brodie, Gilianne and Kleindorfer, Sonia",
    title = "Interspecific Competition and Vertical Niche Partitioning in Fiji’s Forest Birds",
    year = "2022",
    journal = "Diversity",
    abstract = "Charles Darwin proposed his ‘principle of divergence’ to account for changes in traits that could promote speciation and coexistence of diverse forms through occupation of different niches to reduce interspecific competition. We explore interspecific foraging behaviour overlap in Fiji’s forest birds, and address two main questions: (1) Is there vertical stratification of foraging behavior? and (2) Is there evidence of interspecific competition driving the differences in foraging behaviour? We explore these questions across three foraging guilds, nectarivores (three species), insectivores (two species), and omnivores (two species), and find vertical portioning of foraging in each group. To investigate the effect of interspecific competition, we compared foraging heights of the Orange-breasted Myzomela (Myzomela jugularis) honeyeater on Viti Levu Island (where it coexists with two other honeyeater species) and Leleuvia Island (no other honeyeater species). On the main island Viti Levu, we found evidence for vertical niche partitioning within each foraging guild. On Leleuvia, with the ‘one-species only foraging guild’, Orange-breasted Myzomela occupied broader vertical foraging niche than on Viti Levu with two other competitor honeyeater species. This result supports the idea that vertical foraging height can be shaped by interspecific competition. The findings of this study support Darwin’s principle of divergence in Fiji’s forest birds for every foraging guild measured and adds to our understanding of the significance of interspecific competition and niche divergence for patterns of ecological speciation on islands.",
    url = "https://doi.org/10.3390/d14030223",
    doi = "10.3390/d14030223",
    number = "3",
    openalex = "W4220895314",
    pages = "223",
    volume = "14",
    references = "doi101017s0266467401001079, doi101073pnas0905137106, doi101073pnas672529, doi101073pnas7362160, doi101086284196, doi101098rstb20100034, doi101111j13652699200801892x, doi101126science1160854, doi101126science214451682, doi1023072407089"
}

Novel biotic interactions in shifting communities play a key role in determining the ability of species' ranges to track suitable habitat. To date, the impact of biotic interactions on range dynamics have predominantly been studied in the context of interactions between different trophic levels or, to a lesser extent, exploitative competition between species of the same trophic level. Yet, both theory and a growing number of empirical studies show that interspecific behavioural interference, such as interspecific territorial and mating interactions, can slow down range expansions, preclude coexistence, or drive local extinction, even in the absence of resource competition. We conducted a systematic review of the current empirical research into the consequences of interspecific behavioural interference on range dynamics. Our findings demonstrate there is abundant evidence that behavioural interference by one species can impact the spatial distribution of another. Furthermore, we identify several gaps where more empirical work is needed to test predictions from theory robustly. Finally, we outline several avenues for future research, providing suggestions for how interspecific behavioural interference could be incorporated into existing scientific frameworks for understanding how biotic interactions influence range expansions, such as species distribution models, to build a stronger understanding of the potential consequences of behavioural interference on the outcome of future range dynamics.

@article{doi101111brv12993,
    author = "Patterson, Christophe and Drury, Jonathan P.",
    title = "Interspecific behavioural interference and range dynamics: current insights and future directions",
    year = "2023",
    journal = "Biological reviews/Biological reviews of the Cambridge Philosophical Society",
    abstract = "Novel biotic interactions in shifting communities play a key role in determining the ability of species' ranges to track suitable habitat. To date, the impact of biotic interactions on range dynamics have predominantly been studied in the context of interactions between different trophic levels or, to a lesser extent, exploitative competition between species of the same trophic level. Yet, both theory and a growing number of empirical studies show that interspecific behavioural interference, such as interspecific territorial and mating interactions, can slow down range expansions, preclude coexistence, or drive local extinction, even in the absence of resource competition. We conducted a systematic review of the current empirical research into the consequences of interspecific behavioural interference on range dynamics. Our findings demonstrate there is abundant evidence that behavioural interference by one species can impact the spatial distribution of another. Furthermore, we identify several gaps where more empirical work is needed to test predictions from theory robustly. Finally, we outline several avenues for future research, providing suggestions for how interspecific behavioural interference could be incorporated into existing scientific frameworks for understanding how biotic interactions influence range expansions, such as species distribution models, to build a stronger understanding of the potential consequences of behavioural interference on the outcome of future range dynamics.",
    url = "https://doi.org/10.1111/brv.12993",
    doi = "10.1111/brv.12993",
    openalex = "W4382045811",
    references = "drury2020competition"
}

@incollection{crossref2024interspecific,
    title = "Interspecific Competition",
    year = "2024",
    booktitle = "Ecology in Action",
    url = "https://doi.org/10.1017/9781108924849.019",
    doi = "10.1017/9781108924849.019",
    openalex = "W4395105674",
    pages = "306-327",
    references = "doi101126science1245833, doi101126scienceaau1361, doi1018900702231, doi1018901307281, doi1018901312761"
}

BACKGROUND: Globally, adolescents typically display low levels of help-seeking for their mental health problems. There is limited knowledge about the help-seeking intentions and barriers among adolescents in the Caribbean. The aim of this study was to investigate help-seeking intentions, barriers and associated variables for depression and social phobia (social anxiety) among adolescents in Bermuda. METHODS: This study involved a cross-sectional survey of middle-school and high-school students aged 10–19 years in Bermuda. Online surveys conducted between November 2022 - June 2023 gathered data on age, gender and race. In response to a randomly assigned vignette describing a peer as either experiencing depression or social anxiety, the survey assessed adolescents’ mental health-related help-seeking intentions, sources of help, barriers to professional help-seeking and help-seeking preferences. RESULTS: Of 2,434 adolescents who provided valid data, less than half indicated they would seek help for the problem described in the vignette. Reporting moderate to severe depression/anxiety symptoms, older age and female gender were all associated with lower intentions to seek help. The most commonly endorsed source of help was from a parent. Stigma was the most commonly endorsed barrier to professional help-seeking. Reporting moderate to severe depression/anxiety symptoms was associated with a higher likelihood of endorsing major barriers to professional help-seeking and the help-seeking preference of trying to deal with the problem in the vignette on their own. CONCLUSIONS: This study is the first to comprehensively investigate help-seeking intentions and barriers for depression and social anxiety among adolescents in Bermuda. The low rates of help-seeking intentions among adolescents reporting moderate to severe depression/anxiety symptoms are concerning given the associated issues with delayed professional help-seeking. This study is limited in that it examined help-seeking intentions in relation to depression or social anxiety as described in a vignette. Further research is needed to understand associations with actual help-seeking behaviours for these disorders. Anti-stigma programs should be implemented for adolescents in schools to address barriers to professional help-seeking. Older adolescent females may stand the most to gain from these efforts. Early intervention and prevention programs among early adolescents are needed. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12888-025-07731-1.

@article{doi101186s12888025077311,
    author = "Cavanagh, Daniel and Hart, Laura M and Basden, Shawnee and Reavley, Nicola",
    title = "Help-seeking intentions, barriers and associated variables for depression and social anxiety among adolescents in Bermuda.",
    year = "2026",
    journal = "BMC psychiatry",
    abstract = "BACKGROUND: Globally, adolescents typically display low levels of help-seeking for their mental health problems. There is limited knowledge about the help-seeking intentions and barriers among adolescents in the Caribbean. The aim of this study was to investigate help-seeking intentions, barriers and associated variables for depression and social phobia (social anxiety) among adolescents in Bermuda. METHODS: This study involved a cross-sectional survey of middle-school and high-school students aged 10–19 years in Bermuda. Online surveys conducted between November 2022 - June 2023 gathered data on age, gender and race. In response to a randomly assigned vignette describing a peer as either experiencing depression or social anxiety, the survey assessed adolescents’ mental health-related help-seeking intentions, sources of help, barriers to professional help-seeking and help-seeking preferences. RESULTS: Of 2,434 adolescents who provided valid data, less than half indicated they would seek help for the problem described in the vignette. Reporting moderate to severe depression/anxiety symptoms, older age and female gender were all associated with lower intentions to seek help. The most commonly endorsed source of help was from a parent. Stigma was the most commonly endorsed barrier to professional help-seeking. Reporting moderate to severe depression/anxiety symptoms was associated with a higher likelihood of endorsing major barriers to professional help-seeking and the help-seeking preference of trying to deal with the problem in the vignette on their own. CONCLUSIONS: This study is the first to comprehensively investigate help-seeking intentions and barriers for depression and social anxiety among adolescents in Bermuda. The low rates of help-seeking intentions among adolescents reporting moderate to severe depression/anxiety symptoms are concerning given the associated issues with delayed professional help-seeking. This study is limited in that it examined help-seeking intentions in relation to depression or social anxiety as described in a vignette. Further research is needed to understand associations with actual help-seeking behaviours for these disorders. Anti-stigma programs should be implemented for adolescents in schools to address barriers to professional help-seeking. Older adolescent females may stand the most to gain from these efforts. Early intervention and prevention programs among early adolescents are needed. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12888-025-07731-1.",
    url = "https://pmc.ncbi.nlm.nih.gov/articles/PMC12888336/",
    doi = "10.1186/s12888-025-07731-1",
    pmcid = "PMC12888336",
    pmid = "41526894"
}

Ocean microbes contribute to biogeochemical cycles and ecosystem function, but they do so under top-down pressure imposed by viruses. While viruses are increasingly understood spatially and beginning to be incorporated into predictive modeling, high-frequency ocean virus dynamics remain understudied due to methodological challenges. Here we sampled stratified Bermuda Atlantic Time Series (BATS) waters for 112 hours at sub-daily 4- (surface) or 12- (deep chlorophyll maximum) hour intervals, purified viral particles from these samples, sequenced their metagenomes, and used the resulting data to characterize high-frequency virus community dynamics. Aggregated community diversity metrics changed with depth, but were not statistically significant temporally at a fixed location. However, finer-scale population-level analyses revealed both depth and temporal change, including physicochemical depth-driven differences and, in surface waters, thousands of viral populations that exhibited statistically significant diel rhythms. Statistical analyses revealed three main archetypes of temporal dynamics that themselves differed in abundance patterns, host predictions, viral taxonomy, and gene functions. Among these, highlights include viruses resembling an archetype with a night peaking pattern in activity that include an over-representation of viruses that putatively infect Prochlorococcus, a phototrophic cyanobacteria. Together, these efforts provide baseline community- and population-scale short-time-frame observations relevant to future climate state modeling.

@article{doi101371journalpbio3003474,
    author = "Carrillo, Alfonso and Hageman, Emily and Chittick, Lauren and Mackey, Anna I and Ndlovu, Kimberley S and Tian, Funing and Gilbert, Naomi E and Muratore, Daniel and Vik, Dean and LeCleir, Gary R and Sun, Christine and Jang, Ho B and Pavan, Ricardo R and Weitz, Joshua S and Wilhelm, Steven W and Sullivan, Matthew B",
    title = "Sub-daily virus sampling at the Bermuda Atlantic Time Series reveals diel and depth-structured population dynamics without community-level shifts.",
    year = "2026",
    journal = "PLoS biology",
    abstract = "Ocean microbes contribute to biogeochemical cycles and ecosystem function, but they do so under top-down pressure imposed by viruses. While viruses are increasingly understood spatially and beginning to be incorporated into predictive modeling, high-frequency ocean virus dynamics remain understudied due to methodological challenges. Here we sampled stratified Bermuda Atlantic Time Series (BATS) waters for 112 hours at sub-daily 4- (surface) or 12- (deep chlorophyll maximum) hour intervals, purified viral particles from these samples, sequenced their metagenomes, and used the resulting data to characterize high-frequency virus community dynamics. Aggregated community diversity metrics changed with depth, but were not statistically significant temporally at a fixed location. However, finer-scale population-level analyses revealed both depth and temporal change, including physicochemical depth-driven differences and, in surface waters, thousands of viral populations that exhibited statistically significant diel rhythms. Statistical analyses revealed three main archetypes of temporal dynamics that themselves differed in abundance patterns, host predictions, viral taxonomy, and gene functions. Among these, highlights include viruses resembling an archetype with a night peaking pattern in activity that include an over-representation of viruses that putatively infect Prochlorococcus, a phototrophic cyanobacteria. Together, these efforts provide baseline community- and population-scale short-time-frame observations relevant to future climate state modeling.",
    url = "https://pmc.ncbi.nlm.nih.gov/articles/PMC12965618/",
    doi = "10.1371/journal.pbio.3003474",
    pmcid = "PMC12965618",
    pmid = "41790828"
}

The Bermuda fireworm, Odontosyllis enopla Verrill, 1900, is a marine polychaete that displays a unique bioluminescent mating ritual. Despite the first sighting of O. enopla more than 534 years ago, molecular data have been limited. Several syllid mitogenomes are currently available; however, there are only three published genes for O. enopla: two partial mitochondrial genes (16S [508 bp] and cox1 [653 bp]; 1,161 bp total) and one partial nuclear gene (18S [1,339 bp]). This study bioinformatically mined previously published transcriptomes of O. enopla for mitochondrial reads and subsequently assembled and annotated a partial mitochondrial genome (10,172 bp). The partial mitogenome includes nine (of 13) protein-coding genes, two ribosomal RNAs, and seven (of 22) complete tRNAs. We place the Bermuda fireworm in phylogenetic context using all available syllid mitogenomes, analyze intraspecific variation among three female O. enopla partial mitogenomes, and propose a putative location for the mitochondrial origin of replication using a DNA Walker analysis.

@article{doi103897zookeys1270177446,
    author = "Wyant, Lynette D and Cruz, Brendan A and Gonzalez, Aydanni D and Kovalcik, Joshua M and Carolus, Maria A and Hutto, Lauren C and Chutjian, Hope and Roman, Jude C and Cappelmann, Anneau and Ankney, John J and Popp, Aidan and Wood, James B and Pettay, D Tye and Brugler, Mercer R",
    title = "Partial mitochondrial genome of the enigmatic Bermuda fireworm Odontosyllis enopla Verrill, 1900 (Annelida, Syllidae, Eusyllinae) and its phylogenetic implications.",
    year = "2026",
    journal = "ZooKeys",
    abstract = "The Bermuda fireworm, Odontosyllis enopla Verrill, 1900, is a marine polychaete that displays a unique bioluminescent mating ritual. Despite the first sighting of O. enopla more than 534 years ago, molecular data have been limited. Several syllid mitogenomes are currently available; however, there are only three published genes for O. enopla: two partial mitochondrial genes (16S [508 bp] and cox1 [653 bp]; 1,161 bp total) and one partial nuclear gene (18S [1,339 bp]). This study bioinformatically mined previously published transcriptomes of O. enopla for mitochondrial reads and subsequently assembled and annotated a partial mitochondrial genome (10,172 bp). The partial mitogenome includes nine (of 13) protein-coding genes, two ribosomal RNAs, and seven (of 22) complete tRNAs. We place the Bermuda fireworm in phylogenetic context using all available syllid mitogenomes, analyze intraspecific variation among three female O. enopla partial mitogenomes, and propose a putative location for the mitochondrial origin of replication using a DNA Walker analysis.",
    url = "https://pmc.ncbi.nlm.nih.gov/articles/PMC12946827/",
    doi = "10.3897/zookeys.1270.177446",
    pmcid = "PMC12946827",
    pmid = "41768310"
}