Ecological responses of epigaeic beetle composition to a volcanic eruption across temperate mountains featuring a forest-steppe transition

Abstract

Monitoring changes in species composition near active volcanoes is important to identify environmental factors that maintain biological diversity after major disturbances. We investigated the taxonomic composition of epigaeic beetles' assemblages in five mountains in north-western Patagonia (Argentina) in the aftermath of the 2011 Puyehue Cordón-Caulle Volcanic Complex eruption. The associations of beetle composition with the thermal environment, vegetation structure and soil characteristics were analysed using 10 m × 10 m plots with nine pitfall traps each, established 100 m apart in altitude on each mountain in 2005, 2006 (pre-eruption) and 2012, 2015 and 2016 (post-eruption). We found significant differences in beetle composition between forests and high-Andean steppes before and after the eruption. The beetle composition of forests and high-Andean steppes differed due to higher plant cover and lower pH and herb richness in forests. Six months after the eruption, the herbs almost disappeared and forests showed high ash accumulation and lower temperature than the high-Andean steppes. In the medium term, plant cover, temperature and soil conditions—but not ash accumulation—remained as important correlates of beetle composition. Before the eruption, forest assemblages showed higher beetle diversity and Leiodidae indicator species, but Curculionidae predominated post-eruption. Tenebrionidae and Carabidae were high Andean steppes indicators. Post-eruption, the beetle composition in high-Andean steppes did not change significantly except for an increase in Tenebrionidae indicator species. We concluded that the conservation of landscape diversity and environmental gradients maintaining the differentiation between ecoregions is essential to protect epigaeic beetle composition and for species survival after volcanic disturbances.