Community-level patterns of insect herbivory in a fragmented Atlantic forest landscape

Insect herbivores largely affect plant population structure, community organization, and ecosystem functioning, but little is known on how insect herbivory is altered in human-modified landscapes. Here we assessed 3,566 woody seedlings inhabiting 20 Atlantic forest fragments (3-91 ha) in northeast Brazil to examine the extent to which standing levels of herbivory on woody seedlings correlated with forest fragment metrics (fragment area and distance to forest edge) and resource availability (pioneer plants). Overall, 78% of all seedlings and 36% of the 23,003 recorded leaves experienced injuries caused by folivorous insects, the bulk of them promoted by chewing insects (85.9% of damaged leaves). This insect guild removed 9.2 ± 1.9 cm(2) of foliar tissue per leaf, which represented 10.2 ± 1.8% of the standing leaf area. Contrary to our expectations, frequency and magnitude of foliar damage by insects were statistically uncorrelated to either basic forest fragment metrics (fragment area, edge proximity) or resource abundance (percentage of pioneer seedlings). Our findings indicate that insect herbivory is a pervasive ecological process in fragmented landscapes. However, rather than being a function of simple fragment metrics or resource availability, its variation seems to be caused by a range of drivers, such as dispersal ability of folivorous insects and vulnerability of their parasitoids and predators to human disturbance.