Heterogeneity in demographic responses associated with the altitudinal gradient: The case of butterflies in north-eastern Iberia

Abstract

The impact of global change on biodiversity often has heterogeneous responses at a spatial scale. Citizen science programs such as the Catalan Butterfly Monitoring Scheme make it possible to study butterfly responses in the long term and over wide spatial scales, which thus helps understand the drivers of global change that are affecting them. In this work a novel methodology and the CBMS data have been used to calculate trends for a hundred species from three climatic regions: Alpine, humid Mediterranean and arid Mediterranean. A comparison between regions of the trends of a number of common species was made, as well as the relationship between these trends and species' ecological characteristics. Changes in the communities at a number of long-term monitored sites were also studied in the Alpine region using several community indices. The results show that in the three regions the percentage of species in decline exceeds that of the species that are increasing. Nevertheless, these comparisons were made using a mainly generalist fraction of the fauna and probably underestimate the declines that certain rare species are suffering. In common species, declines were more severe in the arid Mediterranean region than in the Alpine region. In this latter region there was no relationship between population trends and the ecological indices of the species. Conversely, significant changes were detected in certain community indices at local level, mainly due to the abandonment of grazing and the movement of thermophilic species towards higher altitudes.