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Understanding rates and patterns of change in physiological and climatic-niche variables is of urgent importance as many species are increasingly threatened by rising global temperatures. Here, we broadly test several fundamental hypotheses about physiological and niche evolution for the first time (with appropriate phylogenetic methods), using published data from 2059 vertebrate species. Our main results show that: (i) physiological tolerances to heat evolve more slowly than those to cold, (ii) the hottest climatic-niche temperatures change more slowly than the coldest climatic-niche temperatures, and (iii) physiological tolerances to heat and cold evolve more slowly than the corresponding climatic-niche variables. Physiological tolerances are significantly and positively related to the corresponding climatic-niche variables, but species often occur in climates outside the range of these tolerances. However, mismatches between climate and physiology do not necessarily mean that the climatic-niche data are misleading. Instead, some standard physiological variables used in vertebrates (i.e. critical thermal maxima and minima) may reflect when species are active (daily, seasonally) and their local-scale microhabitats (sun versus shade), rather than their large-scale climatic distributions.
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Effects of climate on bill morphology within and across Toxostoma thrashers
Bird bills possess an important thermoregulatory function as they are a site for environmental heat exchange. Previous studies have demonstrated that birds in warmer climates have larger bills than those living in colder climates, as larger bills can dissipate more heat. Because this dry heat transfer does not incur water loss, it may be additionally advantageous in water‐restricted habitats. Here, we examine the influence of climate on bill morphology inToxostomathrashers, a group of 10 North American species that varied in bill morphology and occupied climate niche, with several species inhabiting arid climates. Past examinations of thrasher bill morphology have only considered foraging, leaving unanswered the role of climate in morphological divergence within this group. We photographed 476Toxostomamuseum specimens encompassing all 10 species and calculated bill measurements from the photos using a MATLAB‐based program. For each species, we calculated occupied climate niche using data from WorldClim describing temperature and precipitation. We found no reliable significant relationships between climate variables and bill morphology across species, suggesting that other factors such as foraging behavior may be more important in shaping bill morphology in this genus. Within species, we found threeToxostomaspecies have significant relationships between bill morphology and climate that follow Allen's rule. However, we also found the relationships between climate and bill morphology varied in strength and direction across species. Notably, we found a negative relationship between maximum temperature of the hottest month and bill surface area in LeConte's thrasher, which occupies the hottest and most arid climates of the thrashers. This adds to the evidence that Allen's rule may reverse in extremely hot climates when the bill may become a heat sink instead of a heat radiator. These results demonstrate the importance of considering the generality of ecogeographical rules across lineages that occupy extreme climates.
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- Award ID(s):
- 1916850
- PAR ID:
- 10468473
- Editor(s):
- Nord, Andreas; Nilsson, Janake
- Publisher / Repository:
- Nordic Society Oikos
- Date Published:
- Journal Name:
- Journal of Avian Biology
- Edition / Version:
- 1
- Volume:
- 2022
- Issue:
- 1
- ISSN:
- 0908-8857
- Page Range / eLocation ID:
- 1-12
- Subject(s) / Keyword(s):
- Allen’s rule, climate niche, desert birds, foraging ecology, image analysis, thermoregulation
- Format(s):
- Medium: X Size: 2MB Other: pdf
- Size(s):
- 2MB
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1111/jav.02871
