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Data from: Sunning themselves in heaps, knots, and snarls: the extraordinary abundance and demography of island watersnakes


King, Richard B.; Stanford, Kristin M.; Jones, Peter C. (2019), Data from: Sunning themselves in heaps, knots, and snarls: the extraordinary abundance and demography of island watersnakes, Dryad, Dataset,


Snakes represent a sizable fraction of vertebrate biodiversity but until recently, data on their demography has been sparse. Consequently, generalizations regarding patterns of variation are weak and the potential for population projections are limited. We address this information gap through an analysis of spatial and temporal variation in demography (population size, annual survival, 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/km of shoreline (ca. 260 adult/ha) at our study sites (range = 160-1600 adults/km; ca. 80-800 adults/ha) and surpassing population recovery and post-delisting 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

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North America