Rapid changes in butterfly communities following the abandonment of grasslands: a case study

Abandonment of grasslands is a major threat for the conservation of biodiversity in Europe. The response of butterflies towards secondary succession has been studied in northern temperate grasslands, but always by comparing sites at different seral stages. Here, we present a trajectory study based on the monitoring of butterflies from a series of abandoned grasslands in northeast Spain. One additional meadow was traditionally managed for the whole 8-year sampling period and provided a useful control. Both general changes at the community level and species population trends were documented through standardised transect counts. The increase in turf height was neither accompanied by an increase in butterfly diversity nor by consistent trends in body size, dispersal ability and host-plant specialization. However, there was a significant decrease in habitat specialization, consistent with the hypothesis that richness in generalist herbivores is more dependent on biomass production than on plant richness. The number of generations decreased, in line with the hypothesis that species living in habitats subjected to greater disturbance need higher reproductive rates. Butterfly communities underwent substantial changes, as indicated by composition similarity and species population trends. Grassland specialists were forced to disperse from the abandoned meadows and search for refugial habitats, allowing the establishment of new populations in the contiguous managed meadow. Our study shows that grassland abandonment had immediate strong effects on butterflies, acting as an excellent indicator of habitat change. It also points out to the substitution of grassland specialists by common butterflies, less important for conservation purposes.