Abstract
AbstractTrophic cascades and other indirect effects can significantly mediate community interactions. Movement of energy between systems has been shown to be important for trophic cascades in food webs, where coupling between habitats can be important for food web stability and species evenness. To investigate the effects of habitat coupling on the stability and dynamics of chlorophyll a (used as a proxy for phytoplankton biomass), mediated by the abundance and composition of zooplankton and macroinvertebrates, we manipulated habitat use by the predator perch. We show a greater indirect effect of predation on phytoplankton abundance when no habitat coupling occurs, indicating a stronger predation effect and a decrease in zooplankton grazing pressure leading to an increase in phytoplankton biomass. Although we found a significant effect on chlorophyll a between the treatments, this effect was not evident in the abundance of prey resources of perch (zooplankton and macroinvertebrates). Other indirect effects, not measured in this study, such as compositional changes in prey groups, could potentially explain the lack of effect in prey resources. While there is a strong theoretical argument for the stabilizing effects of habitat coupling, empirical evidence is scarce. Our study offers tentative support for these theoretical predictions in a natural system.
Highlights
Ecological models have shown that mobile consumers should have a stabilizing effect on lake food webs by foraging over a larger spatial scale than their prey, linking resources in space and potentially different habitats
Chlorophyll a The chlorophyll a concentration in the water differed significantly between treatments where the closed treatment had a higher level of chlorophyll a concentration compared to the control and the switched treatment showed a slight but non-significant higher chlorophyll a concentration compared to the control
We demonstrate a greater indirect effect of predation on the phytoplankton levels when no habitat coupling by the predator occurs
Summary
Ecological models have shown that mobile consumers (for example predatory fish) should have a stabilizing effect on lake food webs by foraging over a larger spatial scale than their prey, linking resources in space and potentially different habitats (for example littoral/benthic and pelagic habitats in lakes; McCann et al 2005, Rooney et al 2006, McCann 2012). Habitat coupling by a predator can reinforce community-wide trophic cascades by obtaining energy from several habitats and increasing predation pressure on the lower trophic levels (Polis and Strong 1996, Vadeboncoeur et al 2005). This transfer of nutrients between habitats shows that one habitat is regulated by its own resources and productivity but can be influenced by the resources and productivity of another habitat (Persson 1999)
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