A review of niche segregation across sympatric breeding seabird assemblages

Breeding seabirds challenge the concept of niche segregation among competing species because similar competitors with comparable life histories can coexist in large multi-species colonies. This makes them an ideal model organism for studying the Hutchisonian niche model, which proposes interspecific niche segregation, across n-dimensions. Recent advances in assessment of ecological niches have improved our understanding of the mechanisms leading to at-sea segregation. We examine 152 published studies investigating one or more of three niche spaces in breeding seabirds: dietary items, stable isotopes (isotopic niche) and spatial distribution (horizontal and vertical). Most studies focused on one rather then multiple niche spaces in combination. When multiple niche spaces were combined, higher segregation than overlap was reported, compared with when niche spaces were assessed individually, as is predicted by the n-dimensional hypervolume concept. Studies investigating vertical (diving) foraging dimensions in addition to the more traditional horizontal (spatial) assessment reported more spatial segregation than overlap, compared with studies focusing only on horizontal or vertical dimensions. Segregation increased with colony size, suggesting an effect of competition. Segregation also increased during chick-rearing, when taxa were more phylogenetically distant, and when foraging ecology was more similar. To gain a comprehensive understanding of sympatric competitors' interactions and their ecological niche space, it is important to combine approaches and standardize methodologies. Embracing multidimensional approaches to assess niche segregation in seabird species can inform effective conservation and management practices in marine ecosystems.