A review of niche segregation across sympatric breeding seabird assemblages

Abstract

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.

Variations in inter‐specific and sex‐related niche partitioning in pelagic boobies during their annual cycle

“…Body feathers were considered optimal given that they are easy to collect and do not impair the flight ability of the sampled birds (Bighetti et al., 2022 ; Jaeger et al., 2009 ). In contrast to whole blood, body feathers integrate information about the diet during the period when the feather was formed (from weeks to months; Grecian et al., 2015 ; Petalas et al., 2024 ), which is usually during the non‐breeding period for these boobies (Grace et al., 2020 ; Schreiber et al., 2020 ). As mentioned before, no signs of molting, such as missing primary feathers, worn feathers of feather growth were observed while manipulating the individuals, supporting that molting occurs outside the breeding season.…”

“…Nevertheless, many tropical seabird species rely on similar prey items, use other birds as information cues to detect prey, and forage in mixed‐species flocks (Ashmole, 1971 ; Ballance et al., 1997 ; Spear et al., 2007 ; Thiebault et al., 2014 ; Veit & Harrison, 2017 ), leading to questions about the degree to which tropical seabird species are able to coexist and practice niche partitioning. Little evidence for trophic segregation has been found for some species of fish (Teffer et al., 2015 ), sharks (Lear et al., 2021 ), cetaceans (Peters et al., 2022 ), and seabirds (Forero et al., 2004 ; Petalas et al., 2024 ; Weimerskirch et al., 2009 ), and this was attributed to food being sufficiently abundant to allow species to coexist, at least during specific periods of the year.…”

“…Stable isotopes are a useful tool for evaluating inter‐ and intra‐specific niche differences, because the isotopic composition of the tissues reflects the isotopic composition of their assimilated prey. Blood samples can provide information on the diet assimilated during the previous 3–4 weeks (Vander Zanden et al., 2015 ), whereas body feathers give information about the diet during the period of formation (from weeks to months; Grecian et al., 2015 ; Petalas et al., 2024 ), which usually occurs during the non‐breeding period. Nitrogen isotopes (δ 15 N) increase predictably from prey to predator and are a useful proxy for the trophic position of the organism (DeNiro & Epstein, 1981 ; Hobson & Clark, 1992 ), while carbon isotopes (δ 13 C) increase predictably from inshore to offshore food webs (Cherel & Hobson, 2007 ).…”

“…The contrasting results within species and colonies may be associated with the distribution of their prey, with the study period, or with the size of the colonies. For example, foraging segregation might be more common in heterogeneous (Castillo‐Guerrero et al., 2016 ) than in homogeneous environments (Lerma, Serratosa, et al., 2020 ), during breeding (when birds are limited to foraging close to their colonies) compared with non‐breeding periods (Phillips et al., 2017 ; Roy et al., 2021 ), and in larger colonies compared to smaller ones (Austin et al., 2021 ; Petalas et al., 2024 ; Soanes et al., 2016 ; Wakefield et al., 2017 ).…”