COS 248-2 - Using isotopic niche characteristics to investigate how ecological traits drive resource segregation in global seabird colonies: A test of niche theory.

Background/Question/Methods

Ecological niche theory predicts that closely related, or morphologically similar, organisms cannot coexist in the same space at the same time. Thus, the competitive exclusion principal predicts that coexistence of multiple organisms occupying similar niche space will avoid dietary niche overlap by partitioning resources through species-specific habitat or dietary characteristics. However, how habitat and foraging characteristics shape resource segregation among communities is not widely known. Seabirds are a group of organisms which show colonial breeding on many remote oceanic islands, constraining the foraging distance seabirds can make (i.e., central place foraging). Seabirds have evolved a diversity of foraging behaviours to avoid overlapping with community members in shared local resources. Since resource limitation is a prominent reproductive constraint for seabirds, and many species within colonies overlap in space and time, we investigate how habitat and foraging characteristics shape resource partitioning amongst seabird colonies. We conducted a metanalysis of stable isotope values (δ¹³C & δ¹⁵N) of seabirds and used isotopic values to estimate resource overlap among members of 12 seabird communities across the globe. We then characterized both habitat and foraging characteristics for each species and tested for relationships with our intra-community inter-species isotopic niche overlap matrix.

Results/Conclusions

Isotopic values were transformed into z-scores to account for baseline isotopic variation and test for intra-community overlap and relationships with foraging and habitat characteristics. We found that latitude significantly positively predicts species overlap in isotopic space, with northern communities overlapping more in isotopic space than southern communities. Further, communities which host a higher proportion of omnivorous seabirds had a greater proportion of isotopic overlap. Finally, we detected a significant relationship between community overlap and species-standard ellipse area, where species with larger isotopic niches overlapped more. Resource segregation between community members is driven by both latitudinal and species-specific niche size. With the current rate of environmental change, understanding the dynamics of resource segregation This provides the first estimate of resource partitioning using isotopic niche characteristics across a global scale of seabird communities.