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Abstract The Andes, with its diverse topography and climate, is a renowned cradle for adaptive radiation, particularly for vertebrate ectotherms such as lizards. Yet, the role of temperature in promoting physiological specialization in the Andes remains unclear. Aseasonality in the tropics should favour physiological specialization across elevation in lizards, but empirical data are limited and equivocal. Determining how thermal tolerances are geographically and phylogenetically structured is therefore a priority, particularly as environments continue to change rapidly. However, there is a gap in our knowledge of thermal limits of species from the Andes, one of the planet’s most biodiverse regions. Anoles, a diverse lizard group found across thousands of metres of elevation in the Andes, can offer insights into evolutionary adaptations to temperature. This study focused on 14 anole species from two clades (Dactyloa and Draconura) that independently diversified along elevational gradients in the Andes. We measured critical thermal limits (CTmin and CTmax) and found patterns of thermal tolerance specialization across elevation, both among and within species. Patterns of thermal specialization are similar among anole clades, indicating parallel responses to similar environmental pressures. Specifically, high-elevation anoles are more cold tolerant and less heat tolerant than their low-elevation counterparts, rendering thermal tolerance breadths stable across elevation (thermal specialization). Evolutionary rates of physiological traits were similar, reflecting parallel specialization in heat and cold tolerance across elevation. The adaptive radiation of anole lizards reflects physiological specialization across elevation, and the endemism such specialization favours, probably catalysed their remarkable diversity in the tropical Andes. 

Nest predation rates critically influence avian biodiversity and evolution. In the north temperate zone, increased nest failure along edges of forest fragments is hypothesized to play a major role in the disappearance of bird species from disturbed landscapes. However, we lack comprehensive syntheses from tropical latitudes, where biodiversity is highest and increasingly threatened by habitat fragmentation and disturbance. We assembled data from five decades of field studies across the global tropics (1,112 populations of 661 species) and used phylogenetic models to evaluate proposed predictors of nest success. We found significant effects of several traits, including adult body mass and nest architecture. Contrary to results from many temperate locations, anthropogenic habitat disruption did not consistently reduce nest success; in fact, raw nest success rates were lower in large tracts of primary forest than in disturbed or fragmented landscapes. Follow-up analyses within species, using a subset of 76 species for which we had estimates of nest survival in habitats with different levels of disruption, confirmed that neither disturbance nor fragmentation significantly influenced nest success. These results suggest that nest predation alone cannot explain observed declines in avian biodiversity in tropical forest fragments, raising new questions about the demographic processes that drive extinction in the tropics. 

ABSTRACT Endotherms at high altitude face the combined challenges of cold and hypoxia. Cold increases thermoregulatory costs, and hypoxia may limit both thermogenesis and aerobic exercise capacity. Consequently, in comparisons between closely related highland and lowland taxa, we might expect to observe consistent differences in basal metabolic rate (BMR), maximal metabolic rate (MMR) and aerobic scope. Broad-scale comparative studies of birds reveal no association between BMR and native elevation, and altitude effects on MMR have not been investigated. We tested for altitude-related variation in aerobic metabolism in 10 Andean passerines representing five pairs of closely related species with contrasting elevational ranges. Mass-corrected BMR and MMR were significantly higher in most highland species relative to their lowland counterparts, but there was no uniform elevational trend across all pairs of species. Our results suggest that there is no simple explanation regarding the ecological and physiological causes of elevational variation in aerobic metabolism.