Abstract
Although adult cane toads (Rhinella marina) are generally active only at night, a recent study reported that individuals of this species switched to diurnal activity in response to encountering a novel habitat type (deeply shaded gorges) in the course of their Australian invasion. Our sampling over a broader geographic scale challenges the idea that this behaviour is novel; we documented diurnal behaviour both in the species’ native range and in several sites within the invaded range, in multiple habitat types. Diurnal activity was most common in the tropics and in areas where toads attain high population densities and are in poor body condition, suggesting that the expansion of activity times may be induced by intraspecific competition for food.
Highlights
All animals are active for only a limited period of the diel cycle, and that timing is so consistent that we commonly define species as nocturnal, diurnal or crepuscular
In the course of our own fieldwork, we have sampled over a greater geographic range and find that diurnal activity occurs in multiple populations of cane toads, in widely separated areas, and in several habitat types
The first two of these hypotheses predict that diurnal behaviour should be most common in cooler and moister parts of the toads’ geographic range, whereas the third hypothesis predicts the opposite pattern and predicts that diurnality will occur in areas where toads are abundant and are in poor body condition
Summary
All animals are active for only a limited period of the diel cycle, and that timing is so consistent that we commonly define species as nocturnal (e.g., owls), diurnal (e.g., bearded dragons) or crepuscular (twilight hours; e.g., microbats). The first two of these hypotheses predict that diurnal behaviour should be most common in cooler and moister parts of the toads’ geographic range, whereas the third hypothesis predicts the opposite pattern (i.e., we expect more diurnality in hotter regions, because high temperatures increase metabolic rates and maintenance requirements) and predicts that diurnality will occur in areas where toads are abundant (increasing intraspecific competition for limited prey resources) and are in poor body condition. To test these competing predictions, we regressed the incidence of diurnal behaviour against other site-specific parameters
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