Effects of Amazonian forest fragmentation on the interaction between plants, insect herbivores, and their natural enemies

We evaluated the effects of forest fragmentation on herbivory on central Amazonian trees. Levels of herbivory were measured on leaves from a total of 1200 saplings from 3 3 7 species. There was a positive and significant effect of forest fragment area on herbivore damage, with plants from continuous forest having twice as much damage as plants in the smallest fragments studied (I ha). Measurements of herbivory rates on two species, however, indicate that the effect can be species-specific. Forest area had a positive and linear effect on rates of herbivory in Henriettella caudata (Melastomataceae), whereas in Protium hebetataum (Burseraceae), rates of herbivory were greater in the 10-ha fragments than in the I-ha fragments and in continuous forest. There is no evidence that the nutritional and defensive characteristics of the leaves of the species we studied changed as a result of forest fragmentation, at least not in a manner consistent with the observed herbivory patterns. Herbivore predation levels, measured with artificial caterpillars, also showed no significant relationship with forest area. Therefore, neither of these top-down and bottom-up forces could explain the observed patterns of herbivory. It is suggested, instead, that forest fragmentation may affect the dispersal of insect herbivores, and reduce their abundances on small forest isolates. Altered patterns of herbivory on tree saplings may have important consequences for forest structure and dynamics.