Introduction

Current views on ecological communities have been shaped by conceptual and empirical progress in two related themes. First, the last two decades have seen a shift from the traditional emphasis on pair-wise species interactions towards a broader, multispecies approach, which highlights the impact of indirect interactions on community dynamics (Wootton 1994, Abrams et al. 1996, Gange and Brown 1997, Schmitz 1998, Werner and Peacor 2003). Second, there is increasing recognition that resources and productivity at the base of the food web (bottom–up forces) as well as predation from higher-level consumers (top–down forces) are both important in community structuring (Oksanen et al. 1981, Hunter and Price 1992, Leibold et al. 1997, Polis 1999, Meserve et al. 2003). Nevertheless, some issues remain to be addressed before a comprehensive understanding of community regulation can be achieved. One aspect that needs attention is the role of microbial symbionts in trophic dynamics (Hunter and Price 1992, Polis and Strong 1996). Ecosystems would probably look very different without such “hidden players,” yet we are only beginning to uncover the influence of plant and animal symbionts in multitrophic systems (Omacini et al. 2001, Gange et al. 2003, Oliver et al. 2003).

In this chapter, we focus on fungal endophytes as potential elicitors of bottom–up indirect effects transmitted to upper trophic levels through a modification of host plant traits. Endophytic fungi grow systemically within the aerial tissues of many grass species (Clay 1990, Clay and Schardl 2002).