Print PageHabitat fragmentation associated with urban environments is unfavorable to many large mammalian carnivores including coyotes (Canis latrans) and bobcats (Felis rufus). Mesopredator release theory suggests that mesopredators (e.g. raccoon (Procyon lotor), domestic cat (Felis catus) and gray fox (Urocyon cinereoargenteus)) benefit from the absence of large predators and reduce the abundance and/or diversity of smaller mammalian species upon which they prey. In urban environments, mesopredators also benefit from anthropogenic resources. The objective of this study was to compare mammal assemblages in urban vs. rural National Park Service lands within the context of the mesopredator release theory.
Mammal communities were sampled at Petersburg National Battlefield Eastern Front Unit (urban) and Five-forks Unit (rural) in central Virginia. Multiple trap types and mark-recapture methods were used to determine the per trap-night relative abundance of small mammal species and mesopredators. Night camera photographs were taken to document the presence of mesopredators as well as larger predators. Microhabitat variables known to influence mammal assemblages were also measured within trapping plots. Replicate trapping plots were established in all available habitat types within each park unit and six trapping sessions were seasonally partitioned from June 2003 to August 2004.
Results/Conclusions
Five small mammal species (n = 86 unique individuals, 3378 trap-nights) and two mesopredator species (n = 60 captures, 297 trap-nights) were detected at the urban park. Night camera photography detected an abundance of mesopredators but no large predators. At the rural park unit, nine small prey species (n = 169 unique individuals, 3358 trap-nights) and three mesopredator species (n = 11 captures, 287 trap-nights) were detected at the rural park. Night photographs revealed the presence of bobcat and coyote. Ordination and Analysis of Similarity of trapping plots based on the abundance of small mammals revealed differences between urban and rural park units. Vector fitting indicated that percent shrub cover and raccoon abundance were significantly related to trends in the ordination.
Of the 363 National Park Service lands that reported visitation in 1985, 29.5% (107) were located in urban or suburban areas. With recent population growth, it is likely that many more are now surrounded by development. Furthermore, many of these park lands are committed to maintaining a cultural landscape which often consists of fields of monoculture grass. In such cases, the negative impacts of mesopredators on smaller prey species may be magnified by the reduction of suitable habitat.
