Our results demonstrate that N. undulata
responds to predation risk by increasing its dispersal rate out of risky habits and the rate at which Notonecta
dispersed from pools containing fish was positively correlated with the number of conspecifics fish consumed. These results provide evidence for predator-induced dispersal that can introduce linkages among habitats on a discontinuous landscape. Our results also demonstrate a dose-dependent effect of risk, where dispersal propensity is adjusted to changes in perceived risk. Our findings emphasize the connections between consumptive and non-consumptive effects on metacommunity structure (Holyoak et al. 2005
; Orrock et al. 2008
It is well documented that fish can have strong effects on community structure (Wellborn et al. 1996
). These include both the direct effects of mortality within habitats, and the effects of predator-induced dispersal within continuous habitats. Our results extend these findings to predator-induced movements among disconnected habitats. Thus, fish may also influence the structure of communities in which they are not present by driving prey immigration/colonization across a metacommunity.
These results may provide an empirical example of the prey behaviour necessary for predators to exert ‘remote control’ effects on prey populations (Orrock et al. 2008
), where predators at one location affect prey dynamics in another, through their effects upon migration between locations. This in turn may have cascading effects upon competition among prey species and resource depletion in habitats where predators are not present (e.g. Holyoak et al. 2005
; Abrams 2008
; Orrock et al. 2008
). In metapopulation models that include predator-induced dispersal (e.g. Abrams 2008
; Orrock et al. 2008
), it is often assumed that the distribution and abundance of predators is independent of the distribution and abundance of prey. This assumption fits our study community because the semi-aquatic notonectid prey can move among aquatic habitats across a terrestrial matrix, whereas the fish predator cannot, thus severing a tight linkage between the two.
Our results also demonstrate that risk-sensitive dispersal by notonectids is dose-dependent, suggesting that they do not perceive habitats with and without fish as a binary state across the landscape. This aspect of predator-induced dispersal is also an assumption of metapopulation models exploring the impacts of predator-induced dispersal on prey populations. Despite this, our study is one of the few to demonstrate such dose dependence in a metapopulation context. Surprisingly, we could not detect an effect of predator density on dispersal that was independent of the number of prey consumed by predators. These data suggest that the notonectid perception of risk does not result from signals given off by the predators alone, but by their consumption of prey (cf. Crowl & Covich 1990
; Schoeppner & Relyea 2009
). Nevertheless, in general predation rate and thus perceived levels of threat will often scale with fish density and population size structure, factors that in turn may influence Notonecta
dispersal rates from these sites. Predator-induced dispersal in Notonecta
can affect the population dynamics and community structure of habitats receiving these colonists. Notonectids are predators on a broad range of prey including both aquatic vertebrates and invertebrates and N. undulata
have, for example, been demonstrated to affect zooplankton community structure (Shurin 2001
Evidence that predators have indirect effects that operate at the regional scale through prey habitat selection (Resetarits & Binckley 2009
) and by driving prey dispersal (Weisser et al. 1999
; Hakkarainen et al. 2001
; Cronin et al. 2004
; this study) is accumulating. Evidence of indirect effects operating at a metacommunity scale suggest that understanding community structure requires a broader view of species interactions that encompasses interactions operating across habitats, even when one member of the interacting pair is restricted to only one habitat. Dispersal behaviour including threat-sensitive, predator-induced dispersal provides one example of how conditions at the local level may scale up to affect species distributions and community structure at regional scales.