Long-term change and spatial variation in butterfly communities over an elevation gradient: driven by climate, buffered by habitat

Abstract

Aim Efforts to adapt conservation to climate change are hampered by a scarcity of studies of community-level ecological responses. We examined temporal (40 years) and spatial (1700 m elevational gradient) variation in butterfly communities, aiming to test whether the composition of communities in terms of species' thermal envelopes tracked regional warming, and whether local habitat influenced community responses to climate variation.

Location Sierra de Guadarrama (central Spain).

Methods Butterfly assemblages were sampled at sites between 550 and 2250 m elevation, in 1967–1973 and 2006–2012. Changes in community composition over time and space were evaluated using the community temperature index, or CTI, which reflects for local assemblages the balance between species whose geographic ranges occupy regions of low vs. high temperatures. We used multiple regressions and an information-theoretic approach to test: (1) whether relationships of CTI with elevation or temperature remained consistent after an estimated 1.78 °C regional warming; and (2) how spatial variation in CTI was related to air temperature and land cover.

Results Community temperature index decreased consistently with increasing elevation and increased after 40 years of warming, as communities were increasingly composed by species with warmer geographic ranges. Long-term CTI change represented a c. 160 m uphill shift in community thermal composition, whereas isotherms shifted 307 m upwards. In 2006–2012, CTI was influenced positively by temperature, and negatively by forest and meadow cover.

Main conclusions Variation in community composition over space and time suggested a role of climate in structuring butterfly assemblages. Despite this, changing spatial patterns of community composition (CTI) did not appear to keep pace with climate change. In addition, lower values of CTI recorded for sites with greater forest and meadow/pasture cover suggested a role for local habitat in buffering the effects of climate change on community composition.