Environmental Heterogeneity Predicts Behavioural Diversity in a Widely Distributed Group of Marine Carnivores

Aim: Environmental heterogeneity shapes species diversity by creating ecological niches (habitat heterogeneity hypothesis). Yet its role in driving behavioural diversity within species remains only partially understood. Behavioural diversity enhances a population's ability to exploit ecological niches and adapt to environmental change, making it critical to understand how behaviour is shaped by environmental factors. Here we test whether spatial and temporal heterogeneity predict behavioural diversity at population and individual levels across species and environments. Location: Global. Methods: We synthesised biologging data from five species of sea lions (15 colonies, 370 individuals, ~927,000 dives) to test the relationship between population-level behavioural variation and individual specialisation/flexibility metrics with bathymetric roughness, mean chlorophyll and interannual chlorophyll variability utilising GLMMs. Results: We provide large-scale, multi-species evidence that environmental heterogeneity drives behavioural diversity. We show that populations foraging in structurally complex habitats and with greater resource variability exhibited more diverse dive and foraging behaviour, demonstrating that environmental heterogeneity, both in space and time, is associated with higher behavioural diversity. While habitat complexity fostered population-level variation, environments with low productivity favoured specialisation on the individual level, suggesting a shift from generalist to specialist strategies under resource limitation. Main Conclusions: The consistent pattern between environmental heterogeneity and population-level behavioural diversity across species and environments suggests, in combination with observations from previous studies, a fundamental principle extending beyond species and habitat borders. We therefore suggest broadening the habitat heterogeneity hypothesis from species richness to within-species variation. Our findings underscore two important conservation considerations: (1) conserving habitat complexity to help maintain behavioural diversity; and (2) prioritising protection for populations in low-heterogeneity environments, where reduced behavioural flexibility may increase vulnerability to environmental change.