Abandonment and restoration of Mediterranean meadows: long-term effects on a butterfly-plant network

Abstract

Both the intensification and abandonment of traditional agricultural practices are known to be major threats to biodiversity worldwide, above all in industrialized countries. Although land abandonment in particular has a negative effect on the diversity of both plant and insect communities, few studies have ever analysed these two groups together and none has yet examined the effect on plant-insect interactions using a network approach. In view of the notable decline of pollinator insects reported in past decades, it is essential to understand how the structure of a plant-pollinator network changes during the ecological succession that occurs as traditionally managed habitats are abandoned, and to what extent this network is re-established when habitats are restored. We monitored a butterfly-plant network for 22 years in habitats where land abandonment and restoration have taken place and were able to compare restoration by grazing with restoration combining mowing and grazing. Abandonment leads to significant reductions in the cover of typical grasslands plants and, in turn, rapidly provokes changes in butterfly assemblages and plant interactions. Specifically, it caused a replacement of multivoltine by monovoltine species, increasing network specialization due to the great specificity in the interactions that monovoltine species established with plants. Changes in butterfly communities were also recorded in a nearby unaltered habitat due to the metapopulation structure of some species. A highly dynamic source-sink system was established between managed and unmanaged habitat patches, which ultimately allowed the metapopulations to persist. Restoration combining mowing and grazing promoted a quick return to the pre-abandonment situation in the butterfly community, and also increased generality and nestedness, two network descriptors that are known to enhance community stability.