How different species of animals respond to extreme weather events — which are increasing because of climate change — appears to be related to body size and habitat preference, a new study shows.
When extreme weather causes widespread flooding, smaller species and those living in low-elevation areas are most at risk. Being able to develop models that forecast the effects of natural disaster on terrestrial animals could help guide efforts to protect vulnerable species and habitats.
Department of Life and Environmental Sciences Professor Matthew Hutchinson and colleagues from Mozambique, Princeton University, the University of Idaho, British Columbia, and others analyzed data gathered during Cyclone Idai.
Idai passed over Mozambique’s Gorongosa National Park in 2019, and as one of the strongest tropical cyclones on record in the southern hemisphere, resulted in devastating flooding and vegetation destruction in the park.
The research team’s work, which appears today in the journal Nature, is some of the first real-time evidence that shows how different species respond to extreme weather events. The conclusions are consistent with previous studies that link body size and mobility to animals’ vulnerability to these events.
“The spatiotemporal unpredictability of natural disasters makes their ecological impacts inherently difficult to quantify. More than 20 years has passed since ecologists discovered how body size and dispersal ability — in lizards and spiders — influence their response to hurricanes,” Hutchinson said.
The researchers had already been studying Gorongosa National Park for close to a decade when Idai hit, and by comparing large mammals’ behavior, feeding patterns, nutrition, and population dynamics before and after the cyclone, they found that small species associated with low-lying habitats were most negatively impacted by the cyclone, Hutchinson said.
The researchers analyzed the individual and community responses of a group of animals ranging in size from small antelopes, like the bushbuck, which is about 35 inches tall, to elephants.
Cyclone Idai had a tremendous impact on the animals in Gorongosa despite their adaptation to a regular cycle of flooding and wildfires.
“In the wet season, from December through May, rains fill up Lake Urema at the park’s center and it eventually expands out to cover the entire floodplain habitat,” Hutchinson said. “Animals move away into the woodland and then return to the floodplain as the floodwaters retreat. Later in the year as the dry season progresses, vegetation dries out and provides fuel for fires, which are a natural part of African savanna ecosystems.”
But the 2019 cyclone caused much more extensive and intense flooding than in previous years.
“In the week after the cyclone, almost five-fold more of the park was flooded and the maximum flood depth increased almost three-fold,” Hutchinson said. “It took 2 1/2 months for the water levels to return to where they were in early March, just before the cyclone made landfall.”
The researchers found that many of the individual animals that survived the cyclone had moved away from the floodwaters, shifting from their home ranges to new ranges at higher elevations. The degree of displacement depended on how close their original home range was to the flooding, Hutchinson explained. After the flooding subsided, some of the animals, such as the warthog, remained in their new home ranges rather than returning to the floodplain.
The team also looked at the physiological condition of specific animals several months after the cyclone and found that smaller antelope were in worse condition than they would have been during a typical year, while the condition of larger antelope such as the kudu remained similar to previous years.
The foods of some of these herbivorous animals seemed to be more affected by the cyclone than others, and nutrition appears to be the root cause of the longer-term problems the smaller animals faced. Some were displaced quite far from their previous foraging ranges, and the lingering and wide-ranging floodwaters appeared to kill large swaths of the low-growing vegetation, keeping many of the animals from returning to those areas to find food.
Researchers also found that the cyclone shifted community composition. The smaller animals that usually live in the floodplain areas declined after the cyclone, while the larger animals that did not depend on the floodplain for food increased in population size.
The team is continuing to study how individual large mammals and their communities respond to environmental conditions, but part of the group is bringing its work closer to home.
Hutchinson and his lab conduct research in African savannas and California's grasslands to study the behavioral ecology of mammal foraging, linking animals’ eating decisions to health and fitness, population dynamics and ecosystem structure.
“One area our UC Merced team is focusing on is how climate solutions, rather than climate catastrophes, can impact large herbivores. We’re starting to study whether the vegetation growing within large-scale solar farms can provide important food resources for California’s native herbivores and support their long-term conservation,” Hutchinson said. “We’re really excited to explore this potential synergy between climate and conservation action.”