Thermophilization and reshuffling of montane leaf beetle communities over a two decade period

Abstract

Given the sensitivity of mountain biodiversity to human pressure, it is essential to quantify changes inmontane biological communities and contrast them with expectations based on potential drivers of change. Thisneed is particularly pressing for biological groups representing important but little‐studied fractions ofbiodiversity, such as insects. We analyze the temporal changes (between 1998 and 2015) of leaf beetlecommunities in an altitudinal gradient in the Sierra de Ancares (NW Spain). Our results show temporal changes inthe composition of local communities, with a tendency to assemblage thermophilization, as well as ahomogenization of the spatial turnover pattern, mostly driven by an increased similarity between communities atthe lower and intermediate altitudes. These temporal changes in community composition and in the spatialstructure of biodiversity were associated with upward shifts of the upper altitudinal limit of warm‐adaptedspecies and with downward shifts of the lower altitudinal limit of cold‐adapted species. While this upward shift isconsistent with expectations of climate change effects, the observed downward shift suggests a land‐use changeeffect. Our results point to the joint effect of multiple factors (climate and land‐use change) behind temporalchanges of these leaf beetle communities, which result in compositional reorganization and biotichomogenization, rather than a mere coherent displacement toward higher altitudes. More generally, we showthat understanding temporal change of biodiversity requires assessing multiple community‐level metrics (e.g.,variation in assemblage composition and/or changes in spatial turnover) for the detection of tendencies amongthe species‐specific signals (e.g., altitudinal range shifts)