Meeting Abstract
Forest fragmentation is increasing in the Neotropics and has profound effects on bird communities. Certain guilds (such as understory insectivores and frugivores) are disproportionately vulnerable and experience population declines following forest fragmentation, and several hypotheses have been proposed to explain this phenomenon. The microclimate hypothesis posits that physiological sensitivity to novel microclimates in fragments is the mechanism underlying population declines of understory species. An important assumption of the microclimate hypothesis is that low climatic variation in the forest understory has selected for narrow physiological tolerances in these bird species, yet this assumption has never been tested. Describing patterns of variation in physiological tolerances among Neotropical bird guilds is thus an important first step towards establishing a link between thermal physiology and population-level responses to forest fragmentation. We measured the thermal tolerances of 83 Neotropical bird species to examine the relationship between species’ ecology, thermal tolerances and population trends. Guild was not a significant predictor of variation in thermal tolerance breadth, and the tolerances of understory insectivores/frugivores were not significantly lower than other guilds. Furthermore, variation in tolerance breadth was not associated with species’ population trends, contrary to the primary assumption of the microclimate hypothesis. Therefore, variation in thermal physiology is probably not responsible for the declines of understory species following forest fragmentation.
