Stochastic and spatially explicit population viability analyses for an endangered freshwater turtle, Clemmys guttata

Abstract

Over two thirds of the world’s turtle species are in decline as a result of habitat destruction and harvesting. Quantitative methods for predicting the risk of extinction of turtle populations are essential for status assessments and recovery planning. Spotted turtles ( Clemmys guttata (Schneider, 1792)) are considered vulnerable internationally, and endangered in Canada. We used population viability analysis to assess the risk of extirpation of a Georgian Bay, Ontario, population that has been under study since 1977 and of nine Ontario populations for which population size is known, and to examine the effects of dispersal between breeding ponds on population persistence. A simple stochastic model for the Georgian Bay population projected a 60% probability of extirpation in 100 years. A metapopulation model for the same study area projected an 18% probability of extirpation within 100 years, suggesting that dispersal between breeding ponds is important for population persistence. Spotted turtles at this relatively pristine site have a relatively high risk of extinction despite the absence of anthropogenic additive mortality. Probability of quasi-extinction as a result of stochasticity for the model simulating nine Ontario populations was low, but the probability of six or more of the nine known Ontario populations becoming extirpated within 100 years was 26%, indicating that recovery action is necessary to prevent decline of spotted turtles within the species’ Canadian range, which is restricted to Ontario.

Conservation genetics of the endangered Spotted Turtle (Clemmys guttata) illustrate the risks of “bottleneck tests”

“…The six genetic populations also meet two of the criteria for designatable units (DUs), the subspecific categorization recognized under Canadian law (Green 2005). However, the final criterion for DUs (variation in risk of extinction among potential units) is not met, as the risk of extirpation is high for all known subpopulations of C. guttata (Enneson and Litzgus, 2009). Thus, categorization of Canadian populations of C. guttata as DUs may not be justifiable or necessary at this time, although the population of C. guttata in Hastings County is particularly vulnerable to stochastic events because it is so small (n < 50).…”

“…Assessment of a population's probability of extinction should therefore include both demographic and genetic data. Although demographic data can be used to estimate population viability (e.g., Enneson and Litzgus 2009;Shoemaker et al 2013), the implications of genetic data may be less obvious, and the two factors also interact. For example, a severe demographic bottleneck may reduce a population to a nonviable size, and the genetic diversity of the population may be simultaneously impacted by a sudden loss of alleles.…”

Landscape connectivity affects individual survival in unstable patch networks: The case of a freshwater turtle inhabiting temporary ponds

“…This is the case of freshwater turtles that often occupy wetland networks (Burke & Gibbons, 1995) and that frequently undertake overland movements between water bodies to feed or reproduce (Bowne, Bowers & Hines, 2006). However, longterm studies are still scarce (Enneson & Litzgus, 2009) and rarely incorporate connectivity and resistance to movement (Pereira, Segurado & Neves, 2011), which are crucial to improve management guidelines and get a better understanding on the overall persistence of these imperilled taxa. Freshwater turtles are long-lived organisms and hence require long-term studies to detect life-history trends.…”

“…The European pond turtle is widely distributed in Europe, occurring also in northern Africa and Central Asia. Hence, connectivity between water bodies are expected to critically affect individual survival and probability of movement, and thus the maintenance of stable populations (Enneson & Litzgus, 2009;Ficetola et al, 2004;Fortin, Blouin-Demers, & Dubois, 2012). Like other freshwater turtles (Bowne et al, 2006;Burke & Gibbons, 1995), it usually lives in patchy populations (Enneson & Litzgus, 2009), mainly occupying pond networks and marshy areas (Lebboroni & Chelazzi, 1998).…”

Modeling Agassiz's desert tortoise population response to anthropogenic stressors

“…In a comparison of spatially explicit versus spatially implicit population models, Jager et al (2005) determined that spatially explicit models were capable of detecting a greater range of population responses than could be detected with spatially implicit models. Researchers of chelonians have used spatially explicit models to examine population dynamics in a few turtle species, including relationships between habitat loss and connectivity between gopher tortoise (Gopherus polyphemus) populations (BenDor et al 2009), and extirpation probabilities for spotted turtle (Clemmys guttata) populations within isolated ponds (Enneson and Litzgus 2009). Previous threat reviews are described in USFWS recovery plans (USFWS 1994 and reviews by the United States Geological Survey (USGS; Boarman 2002) and the Desert Tortoise Recovery Plan Assessment Committee (Tracy et al 2004).…”