Technical Report NPS/NER/NRTR--2006/047
Robert P. Cook, Kelly M. Boland, and Tressa Dolbeare
Cape Cod National Seashore
U.S. Department of the Interior
Small mammals are an important component of Cape Cod National Seashores fauna. In addition to their direct contribution to species richness, they play a major role in trophic dynamics, consuming plant material and invertebrates, and in turn serving as prey items for snakes, raptorial birds, and small to mid-sized carnivorous mammals. Through these relationships, small mammals may directly influence population levels of insect pests and disease vectors such as gypsy moths and deer ticks, as well as certain regionally rare hawks and owls, and have a cascading effect up and down the food chain. Moreover, the abundance and composition of small mammal communities can affect the structure, species composition, and successional trends of plant communities (Ostfeld 2002).
At CACO, red fox (Vulpes vulpes) and other carnivores prey upon nests of colonial waterbirds and shorebirds such as the federally threatened piping plover. Since small mammals serve as a food source for these predators, variation in their abundance may affect predation pressure on these birds (Bennett 1998). Small mammal abundance and community structure at CACO is influenced by agents of change such as fire suppression, exotic species introduction, habitat succession, weather, and mast production (Wolff 1996). Some of the mechanisms by which these agents of change affect small mammal abundance include loss of herbaceous dominated habitat from suppression of fire, human caused increases in predators such as skunks and red foxes (subsidized predators), and declines in native forage material through replacement by exotic plants. In addition, small mammals also act as agents of change, influencing abundance of predators and acting to control outbreaks of pest species such as gypsy moth (Elkinton et al. 1996, Ostfeld 1996). Since small mammal species vary in their preferences for tree seedlings, their abundance and species composition also influences the rate and species composition in old field succession (Ostfeld et al. 1997).
Because of their ecological importance, and the potential for their populations to respond to numerous agents of change operating in and adjacent to CCNS (as well as become agents of change themselves) small mammals have been identified for possible monitoring as part of Cape Cod National Seashores Long Term Monitoring Program (Roman and Barrett 1999). To facilitate this, a monitoring protocol was developed (Bennett 1998), based largely on protocols from Denali National Park (Rexstad 1996). Similar protocols are employed at Channel Islands National Park (Fellers et al.1988) and at Organ Pipe Cactus National Monument (Petryszyn undated). This protocol was implemented in 2000 and 2001 for two purposes. First, to provide Cape Cod National Seashore with its first-ever quantitative inventory of small mammals and analysis of their habitat relationships. Second, to evaluate the utility of this protocol and the feasibility of its use for long term monitoring. In particular, since the protocol attempts to estimate several population parameters (e.g. abundance, survival, recruitment), and there are generally a number of methods and models for doing so, an important goal was to identify which parameters could realistically be estimated, and determine optimal field and analytical methods.
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