Thermal physiology and habitat constraints in the microendemic, viviparous Nimba toad (Nimbaphrynoides occidentalis)

Climate change and habitat destruction threaten species by disrupting their ecological balance. For range-restricted or highly specialized species understanding their thermal physiology and capabilities is crucial for informing conservation efforts. The Nimba toad, Nimbaphrynoides occidentalis (Angel, 1943), is an especially unique species, being small (~0.5 g), microendemic to the Nimba Mountains and truly viviparous. We measured the resting metabolic rate of adult Nimba toads to different temperatures via closed system respirometry and investigated whether the realized niche of this species aligns with its physiological constraints. As expected for an ectotherm, the resting metabolic rate of Nimba toads increased with temperature, with the steepest increase between 25°C and 30°C. Despite their unique biology, the thermal response observed in the toads was comparable to that of other anuran species. This may suggest that metabolic rates are evolutionarily conserved across amphibians despite a variety of lifestyles and habitats. Nimba toads effectively used the thermal landscape of their habitat and primarily occupied cooler, shaded microhabitats where metabolic rates remained comparatively low. However, as the toads did not select the coldest available microclimates, it is to be hoped that moderate further warming would still allow them some scope for behavioral thermoregulation through the use of cooler microhabitats.