Evidence for limited adaptive responsiveness to large-scale spatial variation of habitat quality

The ability of organisms to adapt their foraging behaviour to spatial variations in food availability and habitat quality is crucial to maximize energy intake and hence fitness. Under ideal conditions, habitat selection should result in a spatial distribution of individuals such that their fitness (energy reserves or condition) is roughly equal across habitats of varying quality. Using 11 yr of field data on Atlantic cod Gadus morhua distribution along the Greenland shelf, we investigated the foraging behaviour and life history of cod in heterogeneous environments. We combined information on energy reserves of cod with spatially resolved diet composition data to derive a measure of habitat quality and heterogeneity. Energy reserves in individual fish were best explained by the particular area they inhabited, whereas growth, population density, food quantity and interannual effects were of minor importance. Condition differed on relatively small spatial scales, at which cod would be capable of redistributing in favour of high-quality habitats. Our results indicate that particular areas may persistently allow higher fitness by sustaining highconditioned individuals but suggest that replenishment of well-conditioned individuals in these high-quality habitats may take longer than expected. We conclude that cod exhibited limited scope in its behavioural response to spatial variation of habitat quality, leading to persistent spatio-temporal differences in energy reserves. Current climate change and fishing activities alter ecosystems and affect habitat heterogeneity, and the adaptive responsiveness of species to such changes in habitat quality is important in natural resource management.