Insect communities and biotic interactions on fragmented calcareous grasslands - a mini review

We evaluate existing evidence for alternative hypotheses on the effects of fragmentation with special emphasis on insects of calcareous grasslands. Species richness of butterflies in general and the proportion of monophagous species in particular increase with fragment size. Habitat fragmentation disrupts plant-pollinator and predator-prey interactions in some cases. No evidence for changes in the outcome of competitive interactions exists for insects. Habitat connectivity increases inter-patch movement and population density and decreases extinction risk. Habitat quality changes with succession and management. Depending on life-history traits, insect species may profit from early, mid or late successional stages of calcareous grasslands. We conclude from the few well-designed and replicated studies that there is a bias towards modelling approaches and small-scale fragmentation experiments, so more large-scale studies on a community level are needed to quantify the functional roles of insects and their dependence on fragmented calcareous grasslands in the landscape mosaic. (C) 2002 Elsevier Science Ltd. All rights reserved.