FLEXIBLE FORAGERS IN FOOD WEBS Consequences of adaptive foraging in diverse communities Nicolas Loeuille* Laboratoire Ecologie et Evolution, Universite Paris VI 7 quai St Bernard, 75005 Paris, France Summary 1. Selective pressures acting on foraging activities constrain the strength of interaction, hence the stability and energetic availability in food webs. 2. Because such selective pressures are usually measured at the individual level and because most experimental and theoretical works focus on simple settings, linking adaptive foraging with com- munity scale patterns is still a far stretch. 3. Some recent models incorporate foraging adaptation in diverse communities. The models vary in the way they incorporate adaptation, via evolutionary or behavioural changes, and define individual fitness in various ways. 4. In spite of these differences, some general results linking adaptation to community structure and functioning emerge. In the present article, I introduce these different models and highlight their common results. 5. Adaptive foraging provides stability to large food web models and predicts successfully inter- action patterns within food webs as well as other topological features such as food chain length. 6. The relationships between adaptive foraging and other structuring factors particularly depend on how well connected the local community is with surrounding communities (metacommunity aspect). Key-words: adaptative foraging, complex adaptive systems, diffuse co-evolution, food web structure, metacommunity, optimal foraging Introduction Incorporating adaptive foraging —or any influence of adap- tation on species interaction— in a community context is not a simple matter. Communities are defined as a collec- tion of species selected by local abiotic and biotic condi- tions, but niches are most often expressed using abiotic components. Interactions with other species of the commu- nity are usually simplified. Adaptation to the physical envi- ronment is most often studied while species adaptation in response to interactions and co-evolution are usually sepa- rated from community structure. As an illustrative example of the focus on abiotic condi- tions, consider the recent development of climate change effects on natural communities. Most predictions are based on climate-envelop models (e.g. Pearson et al. 2002; Peterson et al. 2002; Pyke & Fischer 2005), in which it is assumed that species react as independent entities and according to their own climate tolerances and dispersal abilities exclusively. The role of species interactions and their plasticity has only just begun to be incorporated in such models (Sutherst, Maywald & Bourne 2007) though their relevance to climate change has been shown in many instances (Davis et al. 1998; Suttle, Thomsen & Power 2007, Tylianakis et al. 2008). Similarly, models used to reproduce food web structures have long focused on equilibria situations and did not incorporate any dynamical or adaptive components (Cohen 1989; Williams & Martinez 2000; Cattin et al. 2004). That adaptation takes a secondary place in food web ecol- ogy seems paradoxical given the multiple ways in which we know it affects trophic interactions. Adaptive foraging behav- iour is known to be common and it is supported by many empirical observations. From a behavioural point of view, choices of prey species depend on the energy they bring and how the prey might constrain the predator diet breadth (McArthur & Pianka 1966; Charnov 1976; Parker & Stuart 1976). Switching from one prey species to another or their handling is also dependent on the predator behaviour. Han- dling and switching are commonly included in functional responses (Holling 1959; Beddington 1975; Oaten & Mur- doch 1975). Their effects on stability and equilibrium densi- ties are well-known in small models. From the prey point of *Correspondence author. E-mail: nicolas.loeuille@snv.jussieu.fr Ó 2010 The Author. Journal compilation Ó 2010 British Ecological Society Functional Ecology 2010, 24,18–27 doi: 10.1111/j.1365-2435.2009.01617.x