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Beyond Janzen's Hypothesis: How Amphibians That Climb Tropical Mountains Respond to Climate Variation
R P Bovo1,2, M N Simon2, D B Provete3
1Departamento de Fisiologia, IB, Universidade de São Paulo, São Paulo, SP 05508-090, Brasil.
Integrative Organismal Biology (Oxford, England)
|May 8, 2023
Summary
Tropical amphibians exhibit varied physiological responses to climate change, challenging established hypotheses. Understanding these context-dependent adaptations is crucial for predicting biodiversity impacts.
Area of Science:
- Ecology
- Physiology
- Climate Change Biology
Background:
- Janzen's hypothesis (JH) suggests low thermal variation leads to narrow physiological tolerances and restricted species ranges in the tropics.
- Existing research has not fully explained broad distributions of tropical species across altitudinal gradients or their physiological responses to climate variation.
- The climate variability hypothesis (CVH) predicts broader thermal tolerance breadth (Tbr) with increased temperature variation.
Purpose of the Study:
- To test the CVH by examining how critical thermal minimum (CTmin) and maximum (CTmax) vary along elevational gradients in Brazilian Atlantic Forest amphibians.
- To investigate the relationship between thermal tolerance and water balance traits (dehydration/rehydration rates) in these species.
- To assess the context-dependent nature of tropical amphibian responses to climate variation.
Main Methods:
- Sampling of five amphibian species across elevational gradients in two mountain ranges.
- Measurement of CTmin and CTmax to determine Tbr.
- Measurement of dehydration and rehydration rates to assess water balance.
Main Results:
- Broader temperature variation with altitude did not consistently lead to broader Tbr; changes in CTmin and CTmax were species-specific.
- Water balance traits showed no consistent altitudinal variation and low correlation with thermal traits.
- Highland populations had lower thermal stress risk but both highland and lowland populations were below their upper thermal limits.
Conclusions:
- Intraspecific variation in physiological traits and spatial climate variation create context-dependent and heterogeneous responses to climate change in tropical amphibians.
- Findings challenge predictions of both JH and CVH, indicating that tropical amphibian thermal tolerances can be comparable to temperate species.
- Overcoming geographical bias in physiological data is essential for accurate predictions of climate change impacts on biodiversity.
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