PARENT SESSION

THE INFLUENCE OF TRAP DENSITY ON ESTIMATES OF SMALL MAMMAL ABUNDANCE, DIVERSITY, AND SPECIES RICHNESS. Jeremy A. Baumgardt, Jonathan M. Conard and Philip S. Gipson. Division of Biology, Kansas State University, Manhattan, KS.

ABSTRACT- Small mammals were trapped at Fort Riley Military Installation, Kansas during 2002 and 2003. Trap station densities of 9, 16, 25, and 36 per ha were used during winter, spring, summer, and fall 2002. Trap station densities of 9, 36, 64, 100, and 144 per ha were used during spring and fall of 2003. Two traps were placed at each trap station. During 2002, traps were checked for four consecutive mornings, during 2003, we increased our effort to eight consecutive mornings. Species richness, small mammal abundance, and Shannon diversity were compared among the various trap densities. During 2002, the detection of small mammal species richness increased with trap density and showed no indication of a plateau. Differences between the plots with the highest density of traps compared to the plots with the lowest density of traps were significant during the summer (P = .02) and fall seasons (P = .02). During 2003, the detection of species richness appeared to plateau at 100 trap stations/ha, with a steady increase up to that point. Shannon diversity values increased steadily as trap density increased during 2002, although no detectable differences between trap densities were found. During 2003, Shannon diversity values increased from plots with 9 trap stations/ha to plots with 36 trap station/ha, but did not appear to increase at higher trap densities. During the 2002 trapping seasons, relative abundance of small mammals was estimated by using the number of new captures. Small mammal abundance estimates were positively related to the density of traps. The plots with 36 trap stations/ha had more new captures than the plots with 9 trap stations/ha during the spring (P = .04), summer (P = .001), and fall (P < .001). During 2003, relative abundance was estimated using a removal by mark method that allowed for heterogeneous capture probabilities (Model Mbh, Program CAPTURE). Estimates of relative abundance for Microtus ochrogaster and Peromyscus maniculatus tended to increase with trap density. We noted estimates of small mammal abundance, species richness, and Shannon diversity to be influenced by trap density. It is important to consider relationships between sampling effort, species diversity, and estimates of abundance when planning an ecological investigation.

KEY WORDS: small mammals, richness, trap density, abundance