Testing the thermal physiology, habitat, and competition hypotheses for elevational range limits in four tropical songbirds

Journal article

Restricted elevational ranges are common across tropical montane species, but the mechanisms generating and maintaining these patterns remain poorly resolved. A longstanding hypothesis is that specialised thermal physiology explains these distributions. However, biotic factors such as habitat and interspecific competition have also been proposed to limit tropical species' elevational ranges. We combined point-level abundances, respirometry-based measurements of metabolic rate, habitat surveys, and playback experiments to simultaneously test these three hypotheses for four species of Central American cloud forest songbirds. Contrary to the physiological hypothesis, we found no evidence that thermoregulatory costs constrain species distributions. Instead, thermal conditions across each species' elevational range remained well within sustainable limits, staying ≤65% of hypothesised thresholds for tropical birds, even at the highest elevations. By contrast, we found some support for a combined role of habitat and competition in shaping elevational ranges. In one related species pair, the dominant lower-elevation species appears restricted by microhabitat, while the higher-elevation species is likely prevented from expanding downslope by the presence of this congener. Taken together, we conclude that thermoregulatory costs are an inadequate explanation for elevational range limits of tropical birds at our site, and suggest that biotic factors can be key in shaping these distributions.

Authors: Jones, S; Freeman, B; Tobias, J; Portugal, S

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Royal Society
• Journal: Proceedings of the Royal Society B: Biological Sciences
• Volume: 292
• Issue: 2058
• Article number: 20251953
• Publication date: 2025-11-12
• Acceptance date: 2025-09-24
• DOI: 10.1098/rspb.2025.1953
• EISSN: 1471-2954
• ISSN: 0962-8452
• Language: English
• Keywords: physiological niche; range determinants; tropical mountains; interspecific competition