Stage-dependent niche segregation: insights from a multi-dimensional approach of two sympatric sibling seabirds

Abstract

Niche theory predicts that to reduce competition for the same resource, sympatric ecologically similar species should exploit divergent niches and segregate in one or more dimensions. Seasonal variations in environmental conditions and energy requirements can influence the mechanisms and the degree of niche segregation. However, studies have overlooked the multi-dimensional aspect of niche segregation over the whole annual cycle, and key facets of species co-existence still remain ambiguous. The present study provides insights into the niche use and partitioning of two morphologically and ecologically similar seabirds, the common (CDP, Pelecanoides urinatrix) and the South Georgian diving petrel (SGDP, Pelecanoides georgicus). Using phenology, at-sea distribution, diving behavior and isotopic data (during the incubation, chick-rearing and non-breeding periods), we show that the degree of partitioning was highly stage-dependent. During the breeding season, the greater niche segregation during chick-rearing than incubation supported the hypothesis that resource partitioning increases during energetically demanding periods. During the post breeding period, while species-specific latitudinal differences were expected (species specific water mass preference), CDP and SGDP also migrated in divergent directions. This segregation in migration area may not be only a response to the selective pressure arising from competition avoidance between sympatric species, but instead, could reflect past evolutionary divergence. Such stage-dependent and context-dependent niche segregation demonstrates the importance of integrative approaches combining techniques from different fields, throughout the entire annual cycle, to better understand the co-existence of ecologically similar species. This is particularly relevant in order to fully understand the short and long-term effects of ongoing environmental changes on species distributions and communities.This work demonstrates the need of integrative multi-dimensional approaches combining concepts and techniques from different fields to understand the mechanism and causal factors of niche segregation.

Consistent seasonal foraging niche segregation between critically endangered Whenua Hou Diving Petrels and abundant Common Diving Petrels

“…During this time, Common Diving Petrels switched from an apparent specialist foraging strategy during the breeding period to a more generalist strategy during the non-breeding period. Fine-scale spatial segregation between Whenua Hou Diving Petrels and Common Diving Petrels in non-breeding areas in the Southern Ocean may still limit competition during this period (Fromant et al 2020(Fromant et al , 2022. The nonbreeding ranges of Common Diving Petrels of the chathamensis subspecies remain unknown and further tracking is required to confirm fine-scale spatial segregation.…”

“…2013, Fromant et al . 2022). During the non‐breeding period, the foraging niche segregation was reduced, and isotopic niches of both species increased and overlapped considerably (Peterson & Fry 1987, Cherel & Hobson 2007, Jaeger et al .…”

“…2010, Fromant et al . 2022). These patterns match attendance rates observed at the breeding colony, as Whenua Hou Diving Petrels change incubation shifts every 2–4 days (Fischer et al .…”

“…2020, Fromant et al . 2020, 2022), the foraging areas of the subspecies in Southern Aotearoa ( P. u. chathamensis ) during both breeding (September–February; Richdale 1945) and non‐breeding periods remain unknown. Prey composition of both species in Aotearoa also remains largely unknown, but anecdotal evidence suggests that Whenua Hou Diving Petrels feed on euphausiids, small fish and small cephalopods during the breeding period (Imber & Nilsen 1980).…”

“…2013, 2015, Fromant et al . 2020, 2022). However, no study has investigated the foraging niches of diving petrels on Whenua Hou or the vulnerability of the critically endangered Whenua Hou Diving Petrel to at‐sea competition with congenerics and future environmental change.…”