Short-term responses of plants and invertebrates to experimental small-scale grassland fragmentation

Untersuchungsgebiete: Nenzlingen, Movelier, Vicques The fragmentation of natural habitats is generally considered as a major threat to biodiversity. We investigated short-term responses of vascular plants (grasses and forbs) and four groups of invertebrates (ants, butterflies, grasshoppers and gastropods) to experimental fragmentation of calcareous grassland in the north-western Jura mountains, Switzerland. Three years after the initiation of the fragmentation -- which was created and maintained by mowing the area between the fragments -- we compared species richness, diversity and composition of the different groups and the abundance of single species in fragments of different size (area: 20.25 m², 2.25 m² and 0.25 m²) with those in corresponding control plots. The abundances of 19 (29%) of the 65 common species examined were affected by the fragmentation. However, the experimental fragmentation affected different taxonomic groups and single species to a different extent. Butterflies, the most mobile animals among the invertebrates studied, reacted most sensitively: species richness and foraging abundances of single butterfly species were lower in fragments than in control plots. Of the few other taxonomic groups or single species that were affected by the experimental fragmentation, most had a higher species richness or abundance in fragments than in control plots. This is probably so because the type of fragmentation used is beneficial to some plants through a decreased competition intensity along the edge of the fragments, and because some animals may use the fragments as retreats between their foraging bouts into the mown isolation area.