Movement and Spatial Dispersion of Sistrurus catenatus and Heterodon platirhinos: Implications for Interactions with Roads
The ability to predict the effects that new or modified roads will have on species or populations of conservation interest is critically important to protection efforts. We documented patterns of movement and spatial dispersion of two sympatric snake populations by radiotracking 34 Eastern Massasaugas (Sistrurus catenatus) and 13 Eastern Hog-Nosed Snakes (Heterodon platirhinos) over four years. The two species differed substantially in their movements (frequency, rate, tortuosity, distance) and ensuing spatial dispersion. Regardless of species, males were more vagile than female conspecifics during the mating season. The primary factors hypothesized to have generated the interspecific differences in movement and spatial dispersion were foraging mode, mating system, and reproductive mode. By combining our understanding of how these snakes used space with knowledge of their natural history and ecology, we examined which attributes of their spatial ecology might render S. catenatus and H. platirhinos most susceptible to road effects. For S. catenatus, our observations suggest that spatial fidelity and space use relative to hibernacula are the primary factors influencing the species' susceptibility to road effects. For H. platirhinos, tortuous and extensive movements, space use relative to hibernacula, and large spatial dispersion distances from hibernacula are likely the most important factors.Abstract
Monthly plots of (A) movement frequency (MF), (B) movement rate (MR), (C) distance-weighted strength of angular tendency (Rw), and (D) total distance moved (TDM) for Sistrurus catenatus and Heterodon platirhinos. Means of each month are connected with smoothed lines for visual trend purposes only.
Seasonal plots of (A) movement frequency (MF), (B) movement rate (MR), (C) distance-weighted strength of angular tendency (Rw), and (D) total distance moved (TDM) for Sistrurus catenatus. See text for description of season demarcation. Means and 95% confidence intervals are presented with sample sizes beneath each group. Different lowercase letters below groups within a season denote significant intersexual differences. Different uppercase letters above groups denote significant differences between seasons within sex.
Relationship between total distance moved (TDM) and tracking duration for Sistrurus catenatus and Heterodon platirhinos. Sample sizes are shown in parentheses next to each group. Confidence intervals (95%) are presented with associated regression lines for each group. Note: tracking durations span multiple active seasons (max = 4); a tracking duration for a full active season was on average 162 days for S. catenatus (n = 15) and 159 days for H. platirhinos (n = 4).
Annual measures of spatial dispersion: (A) maximum distance from hibernacula (MDH); (B) maximum linear dispersion (MLD); (C) MDH∶MLD; (D) DW (dispersion width)∶MLD (see Table 1 for descriptions of metrics). Means and 95% confidence intervals are presented with sample sizes beneath each group. Different uppercase letters centered within each species denote significant differences between species, whereas different uppercase letters situated above groups denote significant intergroup differences.
Pictorial summary of the ecological attributes hypothesized to affect the interaction of Sistrurus catenatus and Heterodon platirhinos with modified roads (newly constructed or those experiencing changes in traffic flow: see text). MDH = maximum distance from hibernacula; MLD = maximum linear dispersion; Hibernacula = ▪.
Contributor Notes
Associate Editor: S. E. Wise.