ENVIRONMENTAL CORRELATES OF SURVIVAL AND REPRODUCTION IN OLD-FIELD RODENTS

We used regression trees to assess seasonal relationships between vital rates (survival and reproduction) and a suite of environmental variables for hispid cotton rats (Sigmodon hispidus) and prairie voles (Microtus ochrogaster). We found only 2 relationships between vital rates and environmental variables for M. ochrogaster, whereas we found relationships in all seasons for S. hispidus. The majority of recovered regression trees contained multiple variables, indicating that the vital rates of S. hispidus were affected by interactions among environmental correlates. Vital rates of S. hispidus were affected most by precipitation, temperature, and snowfall; but the direction of effects of these environmental variables was not consistent among seasons. Our analyses indicate that populations of M. ochrogaster in northeastern Kansas are relatively insensitive to environmental variability, whereas survival and reproduction in S. hispidus are influenced by the environment throughout the year.