Thermal tolerances in rodents: species that evolved in cold climates exhibit a wider thermoneutral zone
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Date
2014
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Abstract
Background: Thermal constraints are often invoked to explain animal distributions. Maximum temperatures are less variable in different biomes around the globe than are minimum temperatures. Considerable information is available for mammals about basal metabolic rate and thermal conductance.
Aims: Evaluate the correlation of lower critical temperature (T-LC), upper critical temperature (T-UC) or TNZ breadth (T-UC - T-LC = TNZ(b)) with three ambient temperatures in rodent species.
Hypotheses: T-LC, T-UC and TNZ(b) should be adjusted by selective processes to the ambient temperature that is most usually experienced by mammal species. TNZ(b) should be greater in species inhabiting colder habitats.
Methods: We used T-LC, T-UC data from published studies of 85 species of rodents. We determined the average annual mean, minimum and maximum temperatures across the distribution of each species. Then, using standard least squares regression with body mass as a covariate, we determined the statistical relationships between the physiological variables and the temperatures. We evaluated the effect of phylogeny using a Bayesian Phylogenetic Mixed Model in addition to Bayesian Model Averaging.
Results: Ambient temperatures correlate positively with T-LC and T-UC, and negatively with TNZ(b). Species that evolved in cold climates exhibited a greater mass-independent TNZ(b) than species from warmer climates. Species that evolved in cold climates exhibited lower T-LC and T-UC than species from warmer climates. Phylogenetic as well as conventional statistics indicated that there are thermoregulatory constraints across geographic gradients.
Aims: Evaluate the correlation of lower critical temperature (T-LC), upper critical temperature (T-UC) or TNZ breadth (T-UC - T-LC = TNZ(b)) with three ambient temperatures in rodent species.
Hypotheses: T-LC, T-UC and TNZ(b) should be adjusted by selective processes to the ambient temperature that is most usually experienced by mammal species. TNZ(b) should be greater in species inhabiting colder habitats.
Methods: We used T-LC, T-UC data from published studies of 85 species of rodents. We determined the average annual mean, minimum and maximum temperatures across the distribution of each species. Then, using standard least squares regression with body mass as a covariate, we determined the statistical relationships between the physiological variables and the temperatures. We evaluated the effect of phylogeny using a Bayesian Phylogenetic Mixed Model in addition to Bayesian Model Averaging.
Results: Ambient temperatures correlate positively with T-LC and T-UC, and negatively with TNZ(b). Species that evolved in cold climates exhibited a greater mass-independent TNZ(b) than species from warmer climates. Species that evolved in cold climates exhibited lower T-LC and T-UC than species from warmer climates. Phylogenetic as well as conventional statistics indicated that there are thermoregulatory constraints across geographic gradients.
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Keywords
macrophysiology, energetics, environmental temperature, global ecology, climate change, small mammals