Sunning themselves in heaps, knots, and snarls: The extraordinary abundance and demography of island watersnakes. Issue 15 (4th July 2018)

• Record Type: Journal Article
• Authors: King, Richard B.; Stanford, Kristin M.; Jones, Peter C.
• Is Part Of: Ecology and evolution. Volume 8:Issue 15(2018)
• Page Start: 7500
• Page End: 7521
• Publication Date: 2018-07-04
• Subjects: body size -- capture–mark–recapture -- life history -- population estimation -- process variance -- realized population growth -- survival -- vital rates; Ecology -- Periodicals; Evolution -- Periodicals; 577.05
• DOI: 10.1002/ece3.4191
• Languages: English
• ISSNs: 2045-7758

Abstract

Abstract: Snakes represent a sizable fraction of vertebrate biodiversity, but until recently, data on their demography have been sparse. Consequently, generalizations regarding patterns of variation are weak and the potential for population projections is limited. We address this information gap through an analysis of spatial and temporal variation in demography (population size, annual survival, and realized population growth) of the Lake Erie Watersnake, Nerodia sipedon insularum, and a review of snake survival more generally. Our study spans a period during which the Lake Erie Watersnake was listed as threatened under the U.S. Endangered Species Act, recovered, and was delisted. We collected capture–mark–recapture data at 14 study sites over 20 years, accruing 20, 000 captures of 13, 800 individually marked adults. Lake Erie Watersnakes achieve extraordinary abundance, averaging 520 adults per km of shoreline (ca. 260 adult per ha) at our study sites (range = 160–1, 600 adults per km; ca. 80–800 adults per ha) and surpassing population recovery and postdelisting monitoring criteria. Annual survival averages 0.68 among adult females and 0.76 among adult males, varies among sites, and is positively correlated with body size among study sites. Temporal process variance in annual survival is low, averaging 0.0011 or less than 4% of total variance; thus, stochasticity in annual survival may be of minor significance to snake extinction risk. Estimates of realized population growth indicate that population size has been stable or increasing over the course of our study. More generally, snake annual survival overlaps broadly across continents, climate zones, families, subfamilies, reproductive modes, body size categories, maturation categories, and parity categories. Differences in survival in relation to size, parity, and maturation are in the directions predicted by life history theory but are of small magnitude with much variation around median values. Overall, annual survival appears to be quite plastic, varying with food availability, habitat quality, and other ecological variables. Abstract : We make use of an extensive capture–mark–recapture data set on the Lake Erie Watersnake (perhaps the largest such data set for any snake) and a compilation of 65 studies of snake demography to characterize variation in annual survival within and among species. Our Lake Erie Watersnake study demonstrates (a) the extraordinary abundance that this snake achieves, (b) an association between body size and survival among study sites, and (c) exceedingly low process variance in survival, a rarely estimated demographic parameter. Our review of snake survival suggests that differences in adult annual survival across continents, climate zones, families, subfamilies, reproductive modes, body size categories, maturation categories, and parity categories are generally lacking; rather, annual survival is quite plastic, varying with food availability, habitat quality, and other ecological variables.