Small-scale variation in herbivore abundance and grazing on Juncus roemerianus dominated salt marshes

Abstract

Herbivore-plant interactions have been shown to play central roles in determining the structure of salt marsh communities. However, relatively little is known about how marsh herbivory varies over small spatial scales (e.g., < 2 km) within a single geographic region as well as the potential driving forces for such variability. Here we quantify the small-scale spatial variablity in insect grazing on three Juncus roemerianus marshes in Grand Bay National Estuarine Research Reserve, MS, USA. Sampling covered both monthly and seasonal temporal scales (February to November) to capture the well described seasonality in insect grazing in these marshes Our results show large differences in abundance of insect herbivores and intensity of herbivory across, but not within, the three marshes. In addition, the observed spatial differences in herbivory do not appear to be related to herbivore abundance or insect species, but potentially to differences in landscape context, such as proximity to upland habitats (i.e., forestland) or habitat fragmentation. These results demonstrate that insect herbivory in marshes can also vary substantially at small spatial scales and we suggest some mechanisms responsible for such differences.