Predators are key elements in food webs because of their ability to link the fluxes of nutrients and energy between spatially separated food chains. In aquatic systems, littoral and pelagic habitats supply very different environments that can have strong influence on individual adaptations of predators and further consequences on consumer resource interactions. However, in the context of food web connectivity predator populations have been mainly treated as homogeneous units, despite of compelling evidence of individual specialization in resource use. In this study we show to which extent trophic polymorphism in a generalist freshwater predator species Eurasian perch (Perca fluviatilis) can be important for food web connectivity in lakes. If individuals of a predatory species adapt to the use of different resources associated with spatially separated food chains it is possible that this may lead to decoupling cross-habitat linkages. We tested whether intrapopulation differences in habitat use in the Eurasian perch led to long-term niche partitioning, and affected the degree of ecological habitat coupling. We evaluated trophic niche variability at successively larger time-scales by analyzing gut contents and stable isotopes (δ13C and δ15N) in liver and muscle, tissues that provide successively longer integration of trophic activity.
Results/Conclusions
We found that the use of distinct habitats in perch led to intrapopulation niche partitioning between pelagic and littoral subpopulations, consistent through the various time-scales. Pelagic fish showed narrower niche, lower individual specialization and more stable trophic behavior than littoral fish, as could be expected from inhabiting a relatively less diverse environment. The result indicated that intrapopulation niche partitioning limits the ability of individual predators to link spatially separated food chains though trophic polymorphism.
