Vanderbilt Research Shows Tropical Mammals Shifting to Nighttime Activity in Response to Rising Temperatures
By Andy Flick, Evolutionary Studies scientific coordinator
As global temperatures climb, animals are rewriting the rules of daily life in real time. New from associate professor of Earth and Environmental Sciences Malu Jorge documents one of the clearest examples yet of a tropical mammal fundamentally restructuring its behavior in response to heat, and raises urgent questions about what that means for ecosystems across the warming tropics.
White-lipped peccaries in Brazil’s Pantanal wetlands, once creatures of daylight, are increasingly waiting for darkness to forage. The pig-like mammals, which travel in herds of 50 to 300 individuals and play a critical role in seed dispersal across Neotropical forests, are shifting their activity so dramatically that the afternoon hours have gone from peak activity to near silence. The findings, published in the journal Biotropica, come from research conducted by recent Vanderbilt Ph.D. graduate Michaela Peterson and her advisor Jorge.
Peterson spent more than a year monitoring peccary activity using camera traps and microclimate data loggers across the Pantanal. As daily maximum temperatures climbed, nocturnal activity increased in kind. The afternoon period, once the busiest window for peccary movement, became quieter.
“We have very few examples of tropical species being affected by climate change,” said Jorge. “White-lipped peccaries are just a first attempt to show that mobile organisms, who can choose where to go and find food everywhere, can still be affected by changes in temperature, even if in subtle ways. It tells us that there is much more going on than the very clear effects that we see.”
One particularly striking finding was that the peccaries showed no evidence of seeking out cooler microclimates within their habitat during hot periods. Jorge suggested the explanation is rooted in the scale of the environment itself.
“I think the variation in microclimate is not large enough to affect microhabitat choices,” Jorge explained. “I think that their habitat choices are mostly driven by food presence at small-scale and short-term. The daily and seasonal temperature range is much more effective than the small-spatial scale temperature differences.”
Because white-lipped peccaries are keystone species whose movement patterns shape forest regeneration across vast territories, their behavioral shifts carry consequences well beyond the individual animal. Jorge is candid that the research does not predict imminent collapse, but that the subtlety of these effects is itself the warning.
“I do not necessarily believe that Michaela’s study shows that peccaries will go extinct with rising temperatures, but that there are subtle effects already occurring,” Jorge said. “White-lipped peccary populations are already suffering pressure from illegal hunting, loss of forests, and roads… I would say behavioral flexibility is buying them time, but in nature, many factors work together, and sometimes the combined effect is not just the sum but can be synergistic.”
The research was conducted in collaboration with Alexine Keuroghlian of the Peccary Project in Brazil.
Funding: This study was funded by the Vanderbilt University Department of Earth and Environmental Sciences, the Vanderbilt University Center for Latin American Studies and the Vanderbilt University College of Arts and Sciences.