Octavio Jiménez-Robles, Ignacio De la Riva

Current climate change-forced local extinctions of ectotherms in their warmer distribution limits have been linked to a reduction in their activity budgets by excess of heat. However, warmer distribution limits of species may be determined by biotic interactions as well. We aimed to understand the role of thermal activity budgets as drivers of the warmer distribution limit of cold-adapted mountain ectotherms, and the colder distribution limit of partially sympatric thermophilous species.
In the southern slopes of the Sierra de Guadarrama, Madrid, Spain, (1800–2200 m asl), we collected data from surveys of active individuals, thermal preferences, thermoregulation effectiveness, and activity budgets across 12 different sites exposed to different microclimates and habitats. We assessed how abundances of each species were predicted by activity budgets, restriction time, temperature deviation, habitat covers and date.
We found that Iberolacerta cyreni abundances are not predicted by heat-restricted activity time as they were absent or rare in the areas where its activity budgets are broader. Conversely, the abundances of the other lizards were positively predicted by the potential activity time. Habitat preferences and date explained also part of the occurrences of the four species.
Our results suggest that realized niches of lizards in the Sierra de Guadarrama are a consequence of niche partitioning by temperature-mediated competitive exclusion. The more thermophilous species were physiologically limited by the reduced chances of being active due to the cold, while the cold-adapted species was abundant in those areas where its potential activity is limited by cold-temperatures, but the thermophilous species cannot inhabit. We provide new insights on the ecological processes affecting the distribution of ectotherm mountain organisms, the assemblage of their communities and how climate change could affect them.