The landscape matrix modifies the effect of habitat fragmentation in grassland butterflies
The landscape matrix is suggested to influence the effect of habitat fragmentation on species richness, but the generality of this prediction has not been tested. Here, we used data from 10 independent studies on butterfly species richness, where the matrix surrounding grassland patches was dominated by either forest or arable land to test if matrix land use influenced the response of species richness to patch area and connectivity. To account for the possibility that some of the observed species use the matrix as their main or complementary habitat, we analysed the effects on total species richness and on the richness of grassland specialist and non-specialist (generalists and specialists on other habitat types) butterflies separately. Specialists and non-specialists were defined separately for each dataset. Total species richness and the richness of grassland specialist butterflies were positively related to patch area and forest cover in the matrix, and negatively to patch isolation. The strength of the species-area relationship was modified by matrix land use and had a slope that decreased with increasing forest cover in the matrix. Potential mechanisms for the weaker effect of grassland fragmentation in forest-dominated landscapes are (1) that the forest matrix is more heterogeneous and contains more resources, (2) that small grassland patches in a matrix dominated by arable land suffer more from negative edge effects or (3) that the arable matrix constitutes a stronger barrier to dispersal between populations. Regardless of the mechanisms, our results show that there are general effects of matrix land use across landscapes and regions, and that landscape management that increases matrix quality can be a complement to habitat restoration and re-creation in fragmented landscapes.
KeywordsBiodiversity Butterflies Connectivity Habitat loss Island biogeography Landscape matrix Metapopulation Species–area relationship
We thank Bernhard Schmid for giving us access to unpublished data and we thank three anonymous reviewers for constructive comments. This study was funded by the 6th framework EU-project “COCONUT—Understanding effects of land use changes on ecosystems to halt loss of biodiversity” (SSPI-CT-2006-044346). Additional support was given by FORMAS (The Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning) for EÖ and HGS and by the EU FP7 project 226852 “SCALES—Securing the Conservation of biodiversity across Administrative Levels and spatial, temporal and Ecological Scales” for JK, MK, JP, ISD and RB. TK was supported from IGA FZP 4290013123114 and from the Czech Department of the Environment (VaV/620/1/03) and Education (6007665801, LC06073).
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