Abstract
AbstractAimUnderstanding the mechanisms that allow the coexistence of species is key to preserve full ecosystem functioning. In dynamic environments, the study of ecological niches faces the complexity associated to the three dimensionality of the habitat and requires information that reflects such heterogeneity. Within this context, this study intends to identify the segregation mechanisms behind the co‐occurrence of five phylogenetically related pelagic birds by applying a functional perspective based on seabirds' vertical ranges and prey availability features such as depth and body size.LocationBay of Biscay.MethodsBased on the hypothesis that niche differentiation may occur in any of the three dimensions of the marine environment, we (a) identified the biologically meaningful vertical range affecting seabird species, (b) modelled their environmental and trophic niches, (c) estimated an environmental and trophic overlap index for each pairwise species, and (d) developed a conceptual framework with the most plausible segregation hypotheses.ResultsThe application of the conceptual framework revealed that in this particular area, pelagic birds coexist through environmental and trophic niche partitioning and potentially through vertical segregation, based on the different biologically meaningful vertical ranges we identified for each species. Indeed, some species responded to prey and oceanographic conditions on the surface (10 m), while others responded to the conditions on deeper waters (above the depth of maximum temperature gradient). These different responses could be interpreted as an additional mechanism to reduce competition, although seabirds diving records would be needed to contrast this hypothesis.Main conclusionsNiche differentiation was found to be primarily driven by trophic and environmental niche partitioning, although species were also influenced by conditions on the vertical dimension. Considering all the dimensions of the niche is essential to fully understand how diving seabirds coexist in dynamic systems and provides insights on species' 3D niches that may help advance into their management.
Highlights
The niche concept has been a major theme in ecology, mostly influenced by the definition stated by Hutchinson (1957), who described it as a “n-dimensional hypervolume of environmental states within which a species is able to survive.” even the classical definition may create a dichotomy that affects the way in which the entire concept is approached (Chase & Leibold, 2003)
To identify niche differentiation mechanisms within the pelagic bird community, we modelled separately the environmental and trophic niche of species by integrating the data at their biologically meaningful vertical range (Figure 2, step 5), estimated an environmental and trophic overlap index for each pairwise species (Figure 2, step 6) and developed a conceptual framework with the most plausible segregation hypotheses (Figure 1)
According to the test conducted to identify each species' biologically meaningful vertical range, we found that the density patterns of Cory's, great and Manx shearwaters were better explained by the explanatory variables of the surface layer (10 m), while the density patterns of sooty and Balearic shearwaters were better explained by the explanatory variables integrated over the deep layer (Table 4)
Summary
The niche concept has been a major theme in ecology, mostly influenced by the definition stated by Hutchinson (1957), who described it as a “n-dimensional hypervolume of environmental states within which a species is able to survive.” even the classical definition may create a dichotomy that affects the way in which the entire concept is approached (Chase & Leibold, 2003). The Bay of Biscay (BoB hereafter) represents such an example, as numerous seabird species stopover there during their feeding migrations attracted by a highly diverse and abundant community of small pelagic fishes (Astarloa et al, 2019) It conforms, an exceptional biogeographical area to test segregation hypothesis and provides an incomparable opportunity to understand the mechanisms that allow the coexistence of protected species. We modelled species environmental and trophic niches and developed a conceptual framework with the most plausible segregation hypotheses (Figure 1) This way, we aim to contribute to the understanding of protected and endangered species coexistence and provide insights on the 3D niches of species that may help advance into their management and conservation
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