MICROHABITAT USE BY GOLDEN MICE (OCHROTOMYS NUTTALLI) AND WHITE-FOOTED MICE (PEROMYSCUS LEUCOPUS) IN SOUTHERN ILLINOIS

Similarities between golden mice (Ochrotomys nuttalli) and white-footed mice (Peromyscus leucopus) have been well-studied in both field and laboratory settings. Often sympatric, these species share similar habitat, as well as other resources, yet previous researchers have found little evidence for interspecific competition. Niche partitioning may reduce direct competition through specialization of resource use. Although the golden mouse is considered a resource specialist, it is likely that the degree of habitat specialization differs by locality, and thus, the degree of interspecific competition with similar species is variable. To determine the extent to which microhabitat use differs between golden mice and white-footed mice, I measured 16 and 15 microhabitat variables during the leaf-on and leaf-off seasons, respectively, in Jackson County, Illinois. Trapping took place on 3 grids from March 2010 to September 2011. The ratio of individual golden mice (n = 74) to white-footed mice (n = 85) was unusually high during this study. Microhabitat use models were constructed for both species during both seasons using logistic regression by comparing microhabitat at trapping stations where each species was captured vs. stations without captures. Few variables described habitat occupied by golden mice. Overall, dense vegetation up to 2.0 m was most important for golden mice and ground-level structures such as logs were most important for white-footed mice. Captures and noncaptures were predicted with a high degree of accuracy by logistic regression (81.5-90.3%). Discriminant function analysis was used to identify which microhabitat variables optimally discriminated between habitat used by golden mice, white-footed mice, and neither species. More variables discriminated between species during the leaf-on season than the leaf-off season although discriminating variables during leaf-off were more important overall. Habitat where either species was captured was combined and compared against habitat where no mice were captured; microhabitat used by mice was statistically distinct within the study area. Captures and noncaptures were classified correctly more than would be expected by chance by discriminant function analysis but moderate classification success values indicated microhabitat differences between species were subtle. Microhabitat and elevated trap use varied between seasons for both species, but neither species used ground or elevated traps more than expected during the leaf-on season. Spatial segregation was more apparent during the leaf-off season when golden mice used elevated traps more than expected and white-footed mice used ground traps more than expected. Overall results suggest that golden mice exhibited a great deal of plasticity in microhabitat use seasonally, and are more habitat generalists than previous literature would suggest. Although some spatial segregation was apparent between golden mice and white-footed mice, there was no evidence for avoidance between species, which implies a lack of interference competition. It is likely that other life-history factors (such as metabolic rate, nest building, or sociality) in combination with microhabitat and vertical partitioning allow coexistence between these species rather than microhabitat segregation alone