Determining habitat suitability for bumblebees in a mountain system: a baseline approach for testing the impact of climate change on the occurrence and abundance of species

Abstract

Aim Our aim was to determine the role of environmental variables in explaining occurrence and abundance patterns of bumblebee (Bombus) species in a mountain region. We also used a historical dataset to compare historical and recent habitat suitability predictions for forecasting variations in species' responses to regional climate warming. Location The Cantabrian Range (Iberian Peninsula, south-western Europe). Methods During 2007–09 we sampled bumblebees in 37 localities and developed generalized linear models (GLMs) to predict species' occurrence and abundance in relation to environmental variables. We extracted independent variables at different spatial scales for each locality, based on topoclimatic (slope, temperature and rainfall patterns) and land-cover (habitat configuration and composition) variables. We also used historical (1988–89) bumblebee data (23 localities) to both calibrate recent distribution models and determine the current environmental factors underlying the realized response of individual species to regional climate warming (0.8 °C) over two decades. Results Occurrence and abundance patterns of species were best predicted by models combining topoclimatic and land-cover variables. Our findings revealed three groups of species, distinguished on the basis of the realized response of individual species to regional climate warming: one comprising six species with climate-based tracking behaviour, a second with three species tracking suitable landscape composition and configuration regardless of climatic conditions, and a third comprising one species showing no apparent tracking behaviour. Main conclusions Topoclimate and land cover determined the occurrence and abundance patterns of bumblebee species in mountainous landscapes, even at fine spatial extents. Both environmental variables, however, differentially influenced bumblebees, thereby providing relevant clues for determining the current environmental factors underlying species' distributions and their susceptibility to changing environmental conditions. Our findings therefore suggest that determining habitat suitability can be used as a baseline approach for understanding species-specific responses to climate warming and for developing vulnerability assessments for conservation-focused management planning.