A stable foraging polymorphism buffers Galápagos sea lions against environmental change

Understanding the ability of animals to cope with a changing environment is critical in a world affected by anthropogenic disturbance.¹ Individual foraging strategies may influence the coping ability of entire populations, as these strategies can be adapted to contrasting conditions, allowing populations with foraging polymorphisms to be more resilient toward environmental change.^2,3 However, environmentally dependent fitness consequences of individual foraging strategies and their effects on population dynamics have not been conclusively documented.^4,5 Here, we use biologging data from endangered Galápagos sea lion females (Zalophus wollebaeki) to show that benthically foraging individuals dig after sand-dwelling prey species while pelagic foragers hunt in more open waters. These specialized foraging behaviors result in distinct and temporally stable patterns of vibrissae abrasion. Using vibrissae length as a visual marker for the benthic versus pelagic foraging strategies, we furthermore uncovered an environment-dependent fitness trade-off between benthic and pelagic foragers, suggesting that the foraging polymorphism could help to buffer the population against the negative effects of climate change. However, demographic projections suggest that this buffering effect is unlikely to be sufficient to reverse the ongoing population decline of the past four decades.⁶ Our study shows how crucial a deeper understanding of behavioral polymorphisms can be for predicting how populations cope within a rapidly changing world.