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POPULATION DYNAMICS OF SMALL MAMMALS ACROSS A NITROGEN AMENDED LANDSCAPE
Clark, J. E., E. C. Hellgren, AND E E. Jorgensen*. POPULATION DYNAMICS OF SMALL MAMMALS ACROSS A NITROGEN AMENDED LANDSCAPE. Presented at Annual Meeting of the Wildlife Ecol. Society, Reno, NV, 9/25-29/2001.
Biogeochemical alterations of the nitrogen cycle from anthropogenic activities could have significant effects on ecological processes at the population, community and ecosystem levels. Nitrogen additions in grasslands have produced qualitative and quantitative changes in vegetation resulting in an increase in biomass and decrease in plant species diversity on nutrient-amended sites. We theorize that animal communities will decrease in species richness and become dominated by a few successful competitors that respond to increased nitrogen availability. The objective of this study was to examine how small mammal communities respond to habitat changes resulting from nitrogen additions to an old-field grassland in central Oklahoma. The experimental design consisted of 2 treatments (nitrogen addition and enclosure fencing to manipulate herbivory and predation) randomly assigned to 16, square 0.16-ha plots in a 2x2 factorial arrangement. Small mammals were sampled monthly from June 1999 to August 2001 using Sherman live-traps and mark-recapture techniques. We used a multi-strata model in Program MARK to estimate survival, capture probabilities, and transition probabilities of species in the small mammal community. Analyses based on 16 sampling periods for hispid cotton rats (Sigmodon hispidus), the dominate species of the small mammal community, indicated higher transition probabilities toward fenced or nitrogen amended plots compared to control plots (no fence or nitrogen addition). Our results will provide insights into how small mammals respond to landscapes that are altered by nitrogen additions and provide information that can be useful in assessing the functional role of small mammals in the nitrogen cycling of old-fields. The views expressed are those of the authors and do not necessarily reflect the views and policies of the U.S. Environmental Protection Agency (EPA).