It is hot and cold here: the role of thermotolerance in the ability of spiders to colonize tree plantations in the southern Atlantic Forest

Worldwide, with the decline of natural habitats, species with reduced niche breadth (specialists) are at greater risk of extinction as they cannot colonise or persist in disturbed habitat types. However, the role of thermal tolerance as a critical trait in understanding changes in species diversity in disturbed habitats, e.g., due to forest replacement by tree plantations, is still understudied. To examine the role of thermal tolerance on the responses of specialist and generalist species to habitat disturbances, we measured and compared local temperature throughout the year and thermotolerance traits [upper (CTmax) and lower (CTmin) thermal limits] of the most abundant species of spiders from different guilds inhabiting pine tree plantations and native Atlantic Forests in South America. Following the thermal adaptation hypothesis, we predicted that generalist species would show a wider thermal tolerance range (i.e., lower CTmin and higher CTmax) than forest specialist species. As expected, generalist species showed significantly higher CTmax and lower CTmin values than specialist species with wider thermal tolerance ranges than forest specialist species. These differences are more marked in orb weavers than in aerial hunter spiders. Our study supports the specialisation disturbance and thermal hypotheses. It highlights that habitat-specialist species are more vulnerable to environmental changes associated with vegetation structure and microclimatic conditions. Moreover, thermal tolerance is a key response trait to explain the Atlantic Forest spider's ability (or inability) to colonise and persist in human-productive land uses.