A meta-analysis of the effects of fragmentation on herbivorous insects.

We reviewed the evidence for the effects of fragmentation on insects and plants by conducting a meta-analysis for the effects of artificial forest edge formation on insect herbivore abundance, herbivore richness, and plant herbivory, with data pooled from 31 studies and 159 independent comparisons. Hedge's d was used as the metric to combine all studies. Edge formation exhibited strong effects on plant herbivory rates, as edge plants exhibited 70% more damage than interior plants. Edges also increased herbivore abundance by 14% and herbivore richness by almost 65%, and effects of edge formation were stronger for Lepidoptera (mainly caterpillars) and Orthoptera. Edge effects were also stronger for forested ecosystems compared with open habitats and for temperate regions. Because the studies here evaluated did not simultaneously evaluate bottom-up and top-down factors, the mechanisms responsible for the patterns found cannot be properly addressed, although variation in host plant chemistry, relaxation of pressure exerted by natural enemies, or both, can be suggested as potential factors explaining variation in herbivory between edge and interior habitats. Higher herbivory rates on edge habitats, as shown by our meta-analytical review, have the potential to alter community composition and should be studied in detail to unravel their effects on ecosystem functioning.