Abstract
Trophic interactions can strongly influence the structure and function of terrestrial and aquatic communities through top-down and bottom-up processes. Species with life stages in both terrestrial and aquatic systems may be particularly likely to link the effects of trophic interactions across ecosystem boundaries. Using experimental wetlands planted with purple loosestrife (Lythrum salicaria), we tested the degree to which the bottom-up effects of floral density of this invasive plant could trigger a chain of interactions, changing the behavior of terrestrial flying insect prey and predators and ultimately cascading through top-down interactions to alter lower trophic levels in the aquatic community. The results of our experiment support the linkage of terrestrial and aquatic food webs through this hypothesized pathway, with high loosestrife floral density treatments attracting high levels of visiting insect pollinators and predatory adult dragonflies. High floral densities were also associated with increased adult dragonfly oviposition and subsequently high larval dragonfly abundance in the aquatic community. Finally, high-flower treatments were coupled with changes in zooplankton species richness and shifts in the composition of zooplankton communities. Through changes in animal behavior and trophic interactions in terrestrial and aquatic systems, this work illustrates the broad and potentially cryptic effects of invasive species, and provides additional compelling motivation for ecologists to conduct investigations that cross traditional ecosystem boundaries.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-012-2357-1) contains supplementary material, which is available to authorized users.
Highlights
Communicated by Scott Peacor.Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.L
We showed the capacity of the invasive wetland plant purple loosestrife (L. salicaria) to spark a series of terrestrial-to-aquatic trophic interactions, enhancing pollinator and predatory adult dragonXy local abundance, increasing dragonXy oviposition events in our experimental wetlands, increasing predatory larval dragonXy abundance, and altering zooplankton species richness as well as community structure in the aquatic community
Previous research has demonstrated that purple loosestrife is highly attractive to pollinating insects, and usurps pollinators from native congeners (Brown et al 2002)
Summary
Increasing evidence suggests that ecological interactions can cross these habitat and ecosystem boundaries, resulting in surprisingly strong direct and indirect eVects among species in distinct environments (Wallace et al 1997; HelWeld and Naiman 2001; Baxter et al 2004). Little is known about how invasive plants might alter terrestrial and aquatic food webs simultaneously, despite the potential for strong consumer– resource interactions that could inXuence system dynamics via complex life cycle organisms. Abundant insect pollinator prey may attract a greater abundance of predatory adult dragonXies This terrestrial, bottom-up eVect resulting from increased prey resources could alter the food webs of nearby wetlands through increased dragonXy oviposition and recruitment of their aquatic larvae. By experimentally manipulating Xoral density, we addressed this gap in knowledge of trophic interactions at the terrestrial–aquatic boundary (e.g., Polis and Strong 1996; Baxter et al 2005) by focusing on dragonXies, hypothesized key players in this system
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