The daily activity patterns of mammals (or diel phenotypes) are highly sensitive to environmental factors, such as human-induced climate changes; a global analysis based on camera observations of 445 mammal species reveals this. The work also indicates that the previous literature documenting mammalian diel phenotypes may be outdated.
“Recognizing the consequences of the diurnal phenotype plasticity of species and the lack thereof is an important step toward understanding the impacts of environmental changes and can help guide conservation actions,” Kadambari Devarajan and colleagues write.
All animals have circadian rhythms that regulate their diel (daily) cycles. Collectively, these rhythms can lead to generalized, species-wide behaviors. However, climate changes threaten to alter these established patterns with unexpected consequences.
Devarajan et al. studied 14,587 diurnal activity patterns for 67 mammal families, covering 445 species. They analyzed the data collected by the Global Animal Diel Activity Project, which includes 217 collaborators, from 20,080 camera locations in 38 countries.
First, the team examined whether the current diurnal activity matched the literature. Only 39% of the species’ diurnal activity phenotypes aligned with the prior documentation—and many species exhibited multiple diurnal phenotypes at the same time. They then checked whether circadian activity was reactive to or resistant to environmental changes.
Species demonstrated high plasticity in their diel patterns. Finally, the scientists selected 126 species and investigated how geography affected diurnal plasticity. The distance from the equator, daily hours of daylight, and exposure to human activity influenced the diel phenotypes of 74% of these species.
“The increasing anthropogenic pressure has led some mammals, particularly those in North America, to switch to a nocturnal phenotype,” the authors write.
