Asymmetrical habitat coupling of an aquatic predator – the importance of individual specialisation

Predators should stabilise food webs because they can move between spatially separate habitats. However, predators adapted to forage on local resources may have a reduced ability to couple habitats. Here we show clear asymmetry in the ability to couple habitats by Eurasian perch – a common polymorphic predator in European lakes. We sampled perch from two spatially separate habitats – pelagic and littoral zones – in Lake Erken, Sweden. Littoral perch showed stronger individual specialisation, but they also used resources from the pelagic zone, indicating their ability to couple habitats. In contrast, pelagic perch showed weaker individual specialisation but near complete reliance on pelagic resources, indicating their preference to one habitat. This asymmetry in the habitat coupling ability of perch challenges the expectation that, in general, predators should stabilise spatially separated food webs. Our results suggest that habitat coupling might be constrained by morphological adaptations, which in this case were not related to genetic differentiation but were more likely related to differences in individual specialisation.