Survival of Western Cottonmouths (Agkistrodon Piscivorus Leucostoma) in a Pulsing Environment (Report)
Southwestern Naturalist 2010, March, 55, 1
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The western cottonmouth, Agkistrodon piscivorus leucostoma, is an iteroparous pit viper that inhabits a wide variety of habitats (Gloyd and Conant, 1990; Werler and Dixon, 2000). In Texas, the species is ubiquitous in the eastern one-half of the state and is found from coastal marshes to inland streams (Werler and Dixon, 2000). In north-central Texas, it is associated with mesic habitats, where it migrates seasonally between woodlands and river bottoms (Tennant, 1984; Ford, 2002). Because of its wide distribution and abundance, the western cottonmouth might be an important predator of fish, amphibians, birds, and small mammals (Savitzky, 1992). Furthermore, many habitats occupied by western cottonmouths, particularly the ones characterized by pulsing environments (e.g., streams and rivers) are largely influenced by activities of humans. Little is known, however, about demography of this important species, and estimates of survival based on robust statistical methods are lacking. The objective of our study was to provide estimates of survival for western cottonmouths in central Texas, based on robust approaches to statistical estimation. In the research reported herein we used results of an 11-year mark-recapture study to investigate apparent survivorship (1--mortality and permanent emigration) and probabilities of detection within a population of western cottonmouths resident in Honey Creek, a typical small, highly variable, and low-productivity stream in central Texas. Two published estimates of apparent annual survival for North American pit vipers based on robust estimators for timber rattlesnakes Crotalus horridus (Brown et al., 2007) and western rattlesnakes Crotalus viridis oreganos (Diller and Wallace, 2002) suggest high annual rates of survival (0.820-0.958) for adult terrestrial pit vipers. However, because the environment occupied by the semi-aquatic western cottonmouth at Honey Creek is extremely variable with oscillations ranging from extreme drought to flood, we hypothesized a lower apparent annual rate of survival in this population of western cottonmouths in comparison to the above estimates. We envisioned that apparent annual survivorship might be directly affected by variable stream flow via attendant effects on abundance and distribution of resources, indirectly as a consequence of flow-dependent emigration from the system, or both. We also predicted that apparent survival would be lower in male than in female western cottonmouths in this system because dispersal in snakes is hypothesized to be greater in males than females (Keogh et al., 2007) and because our own studies at Honey Creek showed that males move significantly greater distances between successive captures (unpublished data). We expected, therefore, that males would have higher probabilities of permanent emigration from the study area. Finally, we predicted that expansion of the search area would increase estimates of apparent survivorship because of higher probabilities of recapturing marked snakes that dispersed from the initial study area, or were displaced downstream during floods.
- 2,99 €
- Category: Life Sciences
- Published: 01 March 2010
- Publisher: Southwestern Association of Naturalists
- Print Length: 12 Pages
- Language: English