Spatial Ecology of Eastern Copperheads in Fragmented and Unfragmented Habitats
We quantified and compared movement and microhabitat use of Eastern Copperheads (Agkistrodon contortrix) in fragmented and unfragmented habitats to determine the effects of fragmentation on movement and habitat use. We used thread bobbins to track movement and calculate straight-line distance (SLD) moved, total distance (TDM) moved, and occupied area for individual snakes. Microhabitat use was characterized by quantifying number of trees, woody vegetation stems, herbaceous vegetation stems, percent grass coverage, and percent canopy coverage at each location a snake was observed, and at an equal number of randomly selected locations. Neither SLD nor TDM differed between fragmented and unfragmented habitats. Overall average SLD moved was 24.1 m and TDM was 39.6 m over 48 h. Although SLD and TDM did not differ between sites, mean occupied area ± standard error was significantly greater at the unfragmented (2,310.9 ± 272.7 m) compared with the fragmented site (1,025.9 ± 314.9 m). Microhabitat features were similar between the fragmented and unfragmented sites, and herbaceous vegetation and high canopy cover were associated with locations where snakes were observed at both sites. It is likely that Eastern Copperheads can persist in a variety of habitats in the southeastern United States because their preferred microhabitat features are widely distributed and common in both fragmented and unfragmented environments, demonstrating that they retain characteristics of a habitat specialist within heterogeneous environments suitable for generalists.Abstract
Scatter and box plots illustrating the relationships between the total distance moved (TDM; left column) and straight-line distance moved (SLD; right column) by Eastern Copperheads (Agkistrodon contortrix), and (A) daily air temperature (°C), (B) day of year, and (C) study site (fragmented or unfragmented site in Conway, South Carolina).
Influence of the number of snake observations on the minimum convex polygon area calculated for each Eastern Copperhead (Agkistrodon contortrix) in both fragmented and unfragmented sites in Conway, South Carolina. Both the data and the Equation 1 fit are plotted (see text for Equation 1).
Distribution of differences between Eastern Copperhead (Agkistrodon contortrix) occupied areas in the fragmented and unfragmented sites after correcting for observation bias. The histogram was generated using 1,000 independent resamplings of the original data to estimate W, the parameter representing true occupied area, for both study sites in Conway, South Carolina.
Spine plot showing the proportion of habitat type occupied by Eastern Copperheads (Agkistrodon contortrix) in the fragmented and unfragmented study sites in Conway, South Carolina. Pink shading indicates forest core, green shading box indicates forest edge, and blue shading indicates open habitat.
Movement paths of all tracked Eastern Copperheads (Agkistrodon contortrix) at (A) Coastal Carolina University Conway, South Carolina and (B) the Waccamaw National Wildlife Refuge.
An illustration of the 5m2 quadrat used to identify 24 ‘background’ microhabitats available but unchosen, and one microhabitat (#13) occupied by a copperhead. A random number generator was used to select one background microhabitat quadrat to compare against the occupied microhabitat.
