Bottom-up cascades induced by fungal endophytes in multitrophic systems

CHANETON, E.J.; OMACINI, M.

Ecological communities: plant mediation in indirect interaction webs.

Cambridge University Press

Lugar: Cambridge; Año: 2007; p. 164 - 187

There is a growing concensus among ecologists that resource availability at the base of the food web and consumption pressure from upper trophic levels are both important forces structuring natural communities. However, several challenging issues still need be addressed before we fully understand the dynamics of multitrophic species assemblages. This chapter will discuss three major themes that have been largely overlooked by traditional models of community organization. We shall focus on indirect effects of fungal endophytes on herbivorous insects and their natural enemies in order to illustrate: (i) the occurrence of bottom-up trophic cascades induced by phenotypic changes in the basal food plant, (ii) the pervasive role of within-trophic level heterogeneity in species responses to trait- and density-mediated indirect interactions, and (iii) the impact of  microbial symbionts on multitrophic interaction webs. Endophytic fungi cause morphological, physiological and chemical changes in their host grass species, including synthesis of alkaloids that may confer protection against herbivores and pathogens. We first provide a brief overview of endophyte mediation of plant–insect herbivore interactions. Then we search the literature for evidence on indirect effects transmitted to natural enemies (predators and parasitoids) through shifts in the behaviour, life history or demography of herbivores feeding on endophyte-infected plants. Finally, we discuss results from our own experimental work showing how endophytes can indirectly affect the structure and diversity of  host–parasitoid interaction webs. It will become apparent from this work that plant trait-mediated indirect effects may rapidly propagate through food webs as they trigger density reactions in various consumer species at different trophic levels. Thus, current food-web dynamic models may be inadequate to predict the consequences of symbiotic interactions in ecological communities.