Abstract
The principle of competitive exclusion postulates that ecologically-similar species are expected to partition their use of resources, leading to niche divergence. The most likely mechanisms allowing such coexistence are considered to be segregation in a horizontal, vertical or temporal dimension, or, where these overlap, a difference in trophic niche. Here, by combining information obtained from tracking devices (geolocator-immersion and time depth recorders), stable isotope analyses of blood, and conventional morphometry, we provide a detailed investigation of the ecological mechanisms that explain the coexistence of four species of abundant, zooplanktivorous seabirds in Southern Ocean ecosystems (blue petrel Halobaena caerulea, Antarctic prion Pachyptila desolata, common diving petrel Pelecanoides urinatrix and South Georgian diving petrel P. georgicus). The results revealed a combination of horizontal, vertical and temporal foraging segregation during the breeding season. The stable isotope and morphological analyses reinforced this conclusion, indicating that each species occupied a distinct trophic space, and that this appears to reflect adaptations in terms of flight performance. In conclusion, the present study indicated that although there was a degree of overlap in some measures of foraging behaviour, overall the four taxa operated in very different ecological space despite breeding in close proximity. We therefore provide important insight into the mechanisms allowing these very large populations of ecologically-similar predators to coexist.
Highlights
Analyses of ecological segregation seek to explain how species or populations differ in their use of limited resources [1]
We investigated the ecological mechanisms that may explain the coexistence of four small (120–200 g), very abundant, zooplanktivorous seabirds - blue petrel (Halobaena caerulea), Antarctic prion (Pachyptila desolata), common diving petrel (Pelecanoides urinatrix) and South Georgian diving petrel (P. georgicus) - which breed in sympatry on islands in the Southern Ocean
By combining information obtained from tracking devices, stable isotope analyses and an assessment of flight performance, we provide a very detailed investigation of ecological segregation in four species of sympatric small petrels that are major consumers in Southern Ocean ecosystems
Summary
Analyses of ecological segregation seek to explain how species or populations differ in their use of limited resources [1]. All seabirds are central-place foragers during the breeding season, with foraging ranges constrained by the distribution of prey in three-dimensional space (i.e., vertical, horizontal and temporal) [6,7,8,9,10,11] Given their patchy geographic distribution, islands that are free from terrestrial predators often hold mixed-species breeding colonies composed of thousands to millions of individuals [12,13]. Under these conditions, competition for resources is likely to be intense, and colonial seabirds provide clear examples of ecological segregation by a variety of mechanisms that are presumed to reduce inter-specific competition for food [14,15,16]. Much remains to be learnt about the role of niche partitioning among colonial seabirds
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