Four-dimensional niche differentiation of chick-rearing sympatric auks in the Gulf of St. Lawrence

Background/Question/Methods

Competitive interactions can shape entire community assemblages by driving patterns of evolution and modulating diversity. Ecological theory predicts that completely competitive species sharing identical overlapping niches cannot coexist in the same habitat at the same time. Coexisting breeding seabirds provide a unique opportunity to answer questions about the nature of niche partitioning because they share many similar life-history traits and often form highly competitive breeding colonies including several species foraging on similar prey. Competition may be strongest and peak during chick-rearing when energy demands and thus competition is fiercest. Partitioning may be driven by morphological variation in wing-loading, leading each species to forage in a different area around the colony, or by variation in aerobic dive limits, leading to each species foraging at a different optimum depth, or by differences in time of foraging. We tested these ideas by investigating whether niche differentiation occurs at the Mingan Archipelago National Park Reserve (Gulf of St. Lawrence, Quebec, Canada) by GPS-tracking three species of sympatrically chick-rearing auks: the Atlantic puffin (Fratercula arctica), razorbill (Alca torda), and common murre (Uria aalge).

Results/Conclusions

We found that there was high overlap in horizontal foraging characteristics and areas, centered around the colony, which was inconsistent with the wing-loading hypothesis. However, niche partitioning occurred in the depths they exploited, environmental habitat preferences (bathymetry and sea temperature), and the timing of their foraging events. Razorbills and puffins both exploited shallow depths of the water column in the same foraging areas, but puffins initiated foraging activity at different times-of-day and in warmer waters and deeper bathymetries. Unlike puffins and razorbills, murres were diving earlier in the day, diving to deep depths and in the deepest bathymetric areas with the coldest sea temperatures. These findings illustrate the extent of differences that sympatric auks implement during the most constraining time of the breeding season along a combination of four niche dimensions. This study thus provides insight into the mechanisms allowing for coexistence and increasing our understanding of colonial living, where the maintenance of these competitive interactions will determine the stability of these populations.