Top-down control of an acrtiid moth varies spatially

Background/Question/Methods

It is well established that trophic factors can influence herbivore abundance and distribution. What is less understood is how trophic forces vary across space and time and how non-trophic factors such as habitat complexity mediate species interactions. In this study, we quantified pupal predation of an arctiid moth by vertebrate and invertebrate predators across two spatial scales: host plant and habitat.  In addition, we conducted surveys to obtain predator abundances and plot-level environmental data. This information was used to construct models to test hypotheses explaining pupal survival.  

Results/Conclusions

Ants and rodents are the predominant pupal predators in this system and consumed more than 70% of pupae in some trials. The strength of pupal predation depended on habitat type and host plant species. At the habitat level, pupal predation depends on both natural enemy abundance and non-trophic factors such as vegetation cover. At the host plant level, we found that pupae experimentally affixed to physically defended host plants (thistle spp.) were more likely to survive than those in non-physically defended host plants (Lupinus arboreus and Achillea millefolium). This result was consistent with the natural distribution of cocoons across host plants within the study system.  These findings suggest that natural enemies and non-trophic factors interact to influence pupal survival and the strength of these interactions varies spatially.