Ecologists have been eager to understand the eating habits of various animal species. For scientists at Brown University and the National Park Service, it was unclear how herbivores in Yellowstone National Park manage to compete for necessary food resources, such as grasses, wildflowers, and trees, to survive harsh winters.
Over a span of two years, utilizing advanced molecular biology techniques and GPS tracking data, the research team discovered not only what herbivores in Yellowstone consume but also their strategies in finding food year-round. Their findings were published in Royal Society Open Science.
Lead researcher Bethan Littleford-Colquhoun, a postdoctoral research associate at Brown, stated, “We are aware that vegetation changes with the seasons in Yellowstone, but previously, we did not understand how these seasonal variations affected animal diets or how they survived when food sources were limited. Our research shows that while different species consume similar types of food, their diets are distinct in subtle and intricate ways, and body size is a significant factor in their food-gathering strategies.”
Co-author Tyler Kartzinel, an associate professor of ecology, evolution, and organismal biology at Brown, highlighted that for many years, ecologists have contested how wildlife should handle food supply challenges.
Some researchers argue that animals should vary their diets to fulfill their preferences when food choices are abundant in the summertime, while others contend that animals should broaden their diet options during tough conditions, such as harsh winters when they must compete for limited food supplies to survive.
Kartzinel explained, “These conflicting hypotheses couldn’t both be accurate, leaving us puzzled about how the diverse herbivores of Yellowstone could consistently find enough food throughout the year despite such varied foraging methods.”
Seasonal adaptation
The research incorporated two years of GPS tracking and dietary DNA analysis to explore dietary changes during periods of low and high food availability among five well-known species in Yellowstone: bison, elk, deer, bighorn sheep, and pronghorn antelope.
Contributors at Yellowstone monitored the animals, while researchers at Brown, including several undergraduate students under Littleford-Colquhoun’s guidance, analyzed fecal samples using a sophisticated method known as metabarcoding, which identified the plants the animals had eaten.
The findings revealed that all species took advantage of the seasonal abundance of wildflowers during the summer, but each species focused its foraging on the specific types of plants it could best compete for during the winter months. Importantly, feeding behaviors varied based on the animals’ body sizes.
Smaller animals, like deer and sheep, would spread out across summer meadows and significantly diversify their diets before gathering in sheltered valleys to survive winter on the remaining plants. Conversely, larger animals, such as bison, typically did the opposite: in winter, their size allowed them to avoid competing for diminishing resources, prompting them to explore deep snow for unique food sources that were inaccessible to smaller species.
Littleford-Colquhoun remarked, “This study revealed that these species can adapt their feeding habits more flexibly than previously thought. All species adjust their food-seeking behavior, but the specific strategies that work for a bison’s migration or survival during a tough winter might only be effective due to its size, whereas smaller species may need to collaborate for protection in winter.”
So, when should animals seek out unique foods to diversify their diets — in summer or winter? Kartzinel noted that it varies by species.
“Our study showcased that the behavioral variety observed means that both theories about animal foraging could be valid, but applicable in different contexts and times,” Kartzinel stated. “Therefore, rather than arguing about which foraging strategy is superior, a more appropriate question would be, ‘When does each strategy work best for specific animal groups?'”
Kartzinel hopes these deeper insights into foraging behavior will enable scientists to adopt a more tailored approach to wildlife conservation.
“To support wildlife populations effectively,” he advised, “we need to preserve a variety of habitats and plant resources across their migration paths so that different animals, each with unique preferences, behaviors, and needs, can find the best food to sustain their journeys.”
This research received funding from the National Science Foundation (DEB-525 2046797, OIA-2033823) and the National Park Service Cooperative Research and Training Program (P22AC00332, P23AC00378).
