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Mammals shown to affect prairie's entire ecosystem

By Jeff Caldwell



The presence of a number of different species of mammals on Konza Prairie Biological Station plays an important role in the maintenance of the tallgrass prairie ecosystem as a whole, according to Don Kaufman, professor of biology at Kansas State University.

Historically, the tallgrass prairie was home to smaller species, such as the deer mouse; grazers such as the bison, elk, mule deer and pronghorn; and carnivores, such as the coyote, wolf and big cats, such as the bobcat.

Kaufman said the interests of the public may differ from those of researchers. "Lots of people are fascinated by carnivores, but those are often hard animals to work on," Kaufman said. "My own research is built around the small mammals, not because they're the most important to the ecosystem, but because they are part of the system and because they are much easier to work on because there are more per unit area and you can work with greater numbers of them."

Different interests in the mammal populations of Konza Prairie are not indicative of the effects each species has on its environment. "People look at these animals for different reasons," Kaufman said. "However, you can argue that the most important mammal in the original prairie system was bison."

The bison was the principal grazer in the natural ecosystem, and, as a result, changes in its population or presence had a profound effect on both the plant and animal life with which it coexisted on the prairie.

"As a very general rule, bison graze the dominant grasses on the tallgrass prairie and, as a result, they have the potential to influence some of the less common grasses and wildflowers by removing the impact of the dominant grasses," Kaufman said. "So, bison probably influenced the species composition of the prairie the most, primarily by what they ate and didn't eat."

Hypothetically, the removal of any single mammalian species from the prairie ecosystem could affect the other species, both plant and animal. But Kaufman said it is often difficult to determine the nature, whether positive or negative, of the resulting changes on other populations.

"Many public questions about the prairie are whether an event is beneficial or detrimental, that's a question driven more by the way humans think about values and whether something's good or bad," Kaufman said.

"As researchers, we tend to ask whether the event has a positive or negative effect on the population density and behavior."

The most noted and studied behavior in all mammals on Konza Prairie, according to Kaufman, deals with periodic burning of the prairie. With bison, there is a tremendous change. "The effect of bison on the prairie undoubtedly varies with regard to whether fire has occurred recently or has not occurred for a period," Kaufman said.

The main reason for this dramatic change in the behavior of the bison is due mainly to the changes in different types of grasses. "They [bison] were undoubtedly attracted to places that burn," Kaufman said. "They would prefer to eat, if they can arrive there shortly after the fire, the small and nutritious vegetation that grows back."

Kaufman said even this can vary according to the frequency and concentration of the grazing itself. "How long some of these effects last depends in large part on the response of vegetation to grazing," he said. "If grazing happens one year, that effect may be quite small, but if the grazing is fairly heavy and it happens over many years, it makes the composition change enough that it can take years for it to return to what it was before."

In contrast, the effects of periodic burning upon the small mammal populations can be both positive and negative. On one hand, Kaufman said that some kinds of small mammals within the burned area are decreased, but not by mortality as commonly believed, since most often, they will simply leave the area in favor of an unburned region with more foliage.

"It's a pretty dramatic thing," Kaufman said. "In some cases, some rodents, such as harvest mice and prairie voles, literally leave the night after the fire."

Kaufman, along with his wife, Glennis, also a professor of biology at K-State, and a group of graduate students, conducted research on the mammal populations of Konza Prairie and looked at the effects of prairie fires.

"We are switching an unburned experimental area to one that is annually burned and vice versa, and we're going to watch the long-term dynamic as grassland rodents become less common and woodland forms become more common in the area left unburned." Kaufman said. "In the annually burned area, we expect grassland forms to increase as woody vegetation is removed by fire."

Kaufman said the movement of several species of small mammals is sensible when viewed in relation to human behavior. "It's very logical if you think about it. If the city that you live in burns down, then you're not going to continue to live there," he said. "It's primarily the same type of situation."

June 2002