Induced defenses within food webs: The role of community trade-offs, delayed responses, and defense specificity

In nature, prey and predator species are embedded in complex networks of ecological interactions. As a consequence, organism level reactions such as predator-induced prey defenses will not only influence the dynamics of both the prey exhibiting the response and its inducer predator, but also that of a wider set of populations that interact directly or indirectly with them. In this work our aim is to determine the consequences of community-level side effects, defense specificity, and timing of inducible defenses for the stability of model ecological communities. We shall consider small webs of two and three trophic levels, containing one to three species per level. The model food webs include well-known community motifs that will be studied by means of qualitative analyses of the community matrix. Our results show that side effects that suppress non-focal interactions were able to decrease community stability, particularly when defensive responses were delayed. Conversely, side effects that increase the strength of non-focal interactions stabilized communities. This work also shows that as the defensive response became more specific, it is more likely to obtain a stable community. In general terms, our results revealed that delayed responses decrease the likelihood of system stability. Our results highlight the importance of the underlying biology of species interactions for the definition of the proper topology, and consequently dynamics, of complex ecological networks. (C) 2009 Elsevier B.V. All rights reserved.