FIRE GENERATES SPATIAL GRADIENTS IN HERBIVORY: AN EXAMPLE FROM A FLORIDA SANDHILL ECOSYSTEM

Abstract

Disturbance can directly affect the interactions among species at different trophic levels. Because disturbances are typically localized, and many consumers are con- strained in their mobility, disturbances can generate spatial variability in trophic interac- tions. Here, we consider how fire alters plant-insect interactions in a longleaf pine ecosystem in central Florida, USA. We hypothesized that fire in the short term would directly depress herbivore abundance, and that the rate of re-colonization by herbivores would depend upon distance from the edge of the recently burned area. Thus, fire should generate spatially varying herbivory. Orthopterans are dominant insect consumers in our system, and many species are flightless, either as juveniles or adults; these species are particularly likely to show constrained post-fire mobility. We quantified insect abundance and herbivory levels on eight common understory plants in the edge and interior of three recently burned sites. As predicted, insect abundance at the edge of burned areas was much higher than in the interior. In addition, all plant species experienced at least twice the level of herbivory in the edge than in the interior of burned sites. This demonstrates that disturbance can create strong spatial variation in the magnitude of trophic interactions. We suggest that larger burns may aid in plant management by reducing herbivory, whereas the presence of un- burned refugia may be critical to insect conservation.