Butterflies of fragmented wet grassland in Western European lowland forests: Effects of vegetation, connectivity and plot size
2021
Schlegel, Jürg | Hofstetter, Andreas
Habitat fragmentation, as a result of habitat loss and degradation, is widely considered to be a major threat to biodiversity. Our study focused on the distribution, diversity and abundance of butterflies on 22 isolated plots, mainly consisting of wet grassland. The plots were surrounded by deciduous mixed forests and located in an agglomeration area close to Lake Zurich, Switzerland. In addition to vegetation parameters, we assessed structural connectivity, adapted to least cost distances, using digital surface and terrain models. The resulting mixed-effects models revealed on plot level that (1) Molinia meadows had a significantly positive effect on rarefied Simpson butterfly diversity, (2) structural connectivity had a highly significant negative impact on rarefied Simpson butterfly diversity, whereas (3) plot size showed a significant positive impact, and (4) higher butterfly abundance was strongly related to blossom density. Across plot level, Molinia meadows had a higher rarefied butterfly species richness and rarefied Simpson butterfly diversity than any of the other habitat types evaluated. Among the endangered target species, the preferences of the Alcon Blue Phengaris alcon alcon were consistent with (1) to (3), while those of the Marsh Fritillary's E. aurinia aurinia were not. (2) is discussed with regards to the predominant influence of habitat type, vegetation and plot size, relativizing the effect of structural connectivity on butterfly communities in presumably resilient metapopulations. Ongoing targeted maintenance measures in the study area provide a promising basis for the sustainable conservation of local butterfly communities in isolated wet grassland plots.
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