Dynamic Resource Partitioning in a Marine Predator Community

To avoid competition, species partition resource-use along various niche axes. However, variable resource availability, especially within dynamic environments, may influence this partitioning. Theory predicts that species will contract their ecological niche to limit competition during times of resource scarcity. We analysed blood δ¹³C and δ¹⁵N composition in four albatrosses, four penguin, two giant petrel and two fur seal species breeding on sub-Antarctic Marion Island, during two seasons (autumn and summer) over 3 years. Using the species' seasonal stable isotopic niche space as a proxy for trophic niche space, we investigated their trophic dynamics and maintenance of inter-specific resource partitioning. There were significant variations in the seasonal and inter-annual trophic niches of these predators. However, despite this high seasonal and annual variability, resource partitioning among the species was maintained over time. Between years, there was greater variability in the species' trophic niches in autumn than in summer. This might reflect species being better able to track productive dynamic oceanographic features during autumn, when most species are less spatially constrained by breeding commitments compared to during summer. Our results indicate that most of these marine predators have foraging behaviours that are either sufficiently flexible or general to cope with resources that are variable in space and time. Their foraging strategies minimise inter-specific overlap in food or foraging habitat preferences, potentially resulting from historic or present competition for resources.