Abstract
Environmental temperatures are a major constraint on ectotherm abundance, influencing their distribution and natural history. Comparing thermal tolerances with environmental temperatures is a simple way to estimate thermal constraints on species distributions. We investigate the potential effects of behavioral thermal tolerance (i. e. Voluntary Thermal Maximum, VTMax) on anuran local (habitat) and regional distribution patterns and associated behavioral responses. We tested for differences in Voluntary Thermal Maximum (VTMax) of two sympatric frog species of the genus Physalaemus in the Cerrado. We mapped the difference between VTMax and maximum daily temperature (VTMax-ETMax) and compared the abundance in open and non-open habitats for both species. Physalaemus nattereri had a significantly higher VTMax than P. cuvieri. For P. nattereri, the model including only period of day was chosen as the best to explain variation in the VTMax while for P. cuvieri, the null model was the best model. At the regional scale, VTMax-ETMax values were significantly different between species, with P. nattereri mostly found in localities with maximum temperatures below its VTMax and P. cuvieri showing the reverse pattern. Regarding habitat use, P. cuvieri was in general more abundant in open than in non-open habitats, whereas P. nattereri was similarly abundant in these habitats. This difference seems to reflect their distribution patterns: P. cuvieri is more abundant in open and warmer habitats and occurs mostly in warmer areas in relation to its VTMax, whereas P. nattereri tends to be abundant in both open and non-open (and cooler) areas and occurs mostly in cooler areas regarding its VTMax. Our study indicates that differences in behavioral thermal tolerance may be important in shaping local and regional distribution patterns. Furthermore, small-scale habitat use might reveal a link between behavioral thermal tolerance and natural history strategies.
Highlights
Environmental temperatures are a major constraint on ectotherm abundance and diversity, influencing their distribution and natural history [1,2,3]
We found that Voluntary Thermal Maximum (VTMax) was significantly lower for P. cuvieri than for P. nattereri (Table 1; U = 51, p = 0.0013)
No difference in heating rate was found between species and only P. nattereri showed a significant difference on its VTMax between day and night
Summary
Environmental temperatures are a major constraint on ectotherm abundance and diversity, influencing their distribution and natural history [1,2,3]. Several studies have explored environmental constraints on ectothermic vertebrates at regional and global scales [1, 4]. Knowing species thermal tolerance and exploring how environmental temperatures might affect their physiology and restrict their distribution is of primary concern for long-term conservation, especially under current global warming crisis Thermal tolerances are rarely taken into account in studies that focus on local distribution and habitat use. High environmental temperatures and its daily variation in the microhabitats of small ectotherms (e.g. anurans and lizards) impose physiological constraints on their activity patterns and habitat use [12]. Studies that relate how thermal tolerances affect habitat use and distribution are scarce
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