Response of a Small Mammal Community to Water and Nitrogen Treatments in a Shortgrass Prairie Ecosystem

Abstract

The response of small mammal communities to continuous water and nitrogen treatments on 1 hectare (ha) plots of shortgrass prairie was monitored over a 4 year period. Small mammals were live-trapped 18 times on each of eight plots representing water, nitrogen, water plus nitrogen, and control treatments. Four species ( Microtus ochrogaster , Onychomys leucogaster, Peromyscus maniculatus , and Spermophilus tridecemlineatus ) were captured. Analysis of variance with the variability in population densities (individuals/ha) partitioned between treatments and sample dates indicates significant treatment effects for all four species. Population densities of Microtus and Peromyscus were significantly higher (P < .001 and F < .02, respectively) on the water plus nitrogen treatment than on other treatments; Onychomys populations were significantly higher ( P < .05) on the nitrogen and control treatments than on the water and water plus nitrogen treatments; Spermophilus populations were significantly higher ( P < .05) on the nitrogen and control treatments than on the water plus nitrogen treatment. Analysis of variability in total small mammal biomass (grams, g, live weight/ha) also indicates significant treatment effects. Total biomass on the water plus nitrogen treatment was significantly higher ( P < .001) than on other treatments. Proportional species composition of the small mammal communities differed, with Microtus occurring primarily on the two “wet” treatments, Onychomys occurring primarily on the two “dry” treatments, and Peromyscus and Spermophilus occurring on all treatments. The ratio of community respiration to community consumption on the water plus nitrogen treatment, and to a lesser extent on the water treatment, is lower than on the nitrogen and control treatments as a result of the higher proportion of grazing herbivores (that is, Microtus ) on these treatments. Small mammal utilization of food resources never exceeded 4 percent of the available plants or 34 percent of the available arthropods on any of the treatments. Results tentatively support the hypothesis that changes in the small mammal communities were tightly coupled to changes in vegetation structure.