Demography of the San Francisco Gartersnake in Coastal San Mateo County, California

Halstead, Brian J.; Wylie, Glenn D.; Amarello, Melissa; Smith, Jeffrey J.; Thompson, Michelle E.; Routman, Eric J.; Casazza, Michael L.

doi:10.3996/012011-jfwm-009

Cited by 13 publications

(22 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Neonates were not included in the analysis, therefore births did not affect our population sample. Further, Halstead et al (2011) re ported high annual survival rates for this subspecies (≥0.74, with 95% CL ranging from 0.49 to 0.95), indicating that mortality during our shorter sampling occasions could be assumed minimal. Therefore, Huggins' closed capture models (Huggins 1989(Huggins , 1991 were used to derive estimates of population abundance (N ) and capture (p) and recapture probabilities (c).…”

Section: Discussionmentioning

confidence: 99%

“…In our sample, we found that young-of-year snakes ranged in size from 152 to ~200 mm, which is in agreement with measurements reported for newborns by Barry (1994) and Larsen (1994). It should be noted that our survey periods did not encompass the expected peak of activity for young-of-year T. s. tetrataenia (based on Halstead et al 2011), and therefore we do not present a reliable maximum size attained for snakes born within the year.…”

Section: Discussionmentioning

confidence: 99%

“…Wharton's (1989) study spanned 2.5 yr, using trapping and visual surveys, while Larsen's (1994) spanned approximately 20 mo, with variable trapping effort over time. In Halstead et al (2011), 95% confidence limits from Bayesian analysis of bi nomial proportions indicated that their population's sex ratio fell anywhere between 0.85 and1.62. Sex ratios calculated from abundance estimates (obtained by our best supported mark−recapture models) showed that females outnumbered males in both 2007 and 2013 with sex ratios (M:F) of 0.77 and 0.76, respectively.…”

Section: Discussionmentioning

confidence: 99%

“…Previous studies found T. s. tetrataenia to occur at 2.1 ind. ha −1 at a coastal site (Halstead et al 2011), and 7.6 ind. ha −1 (Barry 1994) and 6.8 ind.…”

Section: Discussionmentioning

confidence: 99%

“…Advancements in statistical modeling of mark−recapture data over the past 20 yr now allow much more rigorous and in-depth analyses of population biology, in particular through incorporation of detection probabilities (and variability within) into demographic models (Williams et al 2002). Halstead et al (2011) were the first to publish such an analysis of one T. s. tetrataenia population, estimating 443 ind. on a large (213 ha), protected, coastal site contiguous with an even larger area of undeveloped habitat.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

An endangered snake thrives in a highly urbanized environment

Reeder¹,

Byrnes²,

Stoelting³

et al. 2015

Endang. Species. Res.

View full text Add to dashboard Cite

The endangered San Francisco garter snake Thamnophis sirtalis tetrataenia occurs in only 2 counties on the densely populated San Francisco Peninsula, California, USA. Due to its limited geographic range and destruction of populations by the rapid pace of urban development in the 1950s and 1960s, T. s. tetrataenia was the only snake included in the inaugural US Endangered Species Act. Several large areas preserved as public parks, utility lands, or private trusts support remnant populations that are the focus of recovery and conservation efforts. To assist in assessment of status and trend for this subspecies, we fit Huggins' closed capture models in RMark to mark−recapture data collected in 2007 and 2013 to estimate population size of an isolated population on a small (72.8 ha) property surrounded by residential development and transportation infrastructure. Our best supported models indicate a population of 1763 individuals (95% CI: 1302−2446) in 2007 and 1761 (95% CI: 1211−2639) in 2013. In addition, total captures of an important prey species increased 2 orders of magnitude from 829 in 2007 to 17 180 in 2013. These findings highlight the potential for well-managed but small habitat units ('the good'), to compliment vast natural areas ('the ideal') in recovery and conservation strategies for threatened and endangered species that can be supported by a small home range.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…Previous studies found T. s. tetrataenia to occur at 2.1 ind. ha −1 at a coastal site (Halstead et al 2011), and 7.6 ind. ha −1 (Barry 1994) and 6.8 ind.…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

An endangered snake thrives in a highly urbanized environment

Reeder¹,

Byrnes²,

Stoelting³

et al. 2015

Endang. Species. Res.

View full text Add to dashboard Cite

show abstract

Estimating relationships between size and fecundity in the threatened giant garter snake in seminatural and agricultural wetlands

et al. 2019

View full text Add to dashboard Cite

Increasing numbers of populations of threatened and endangered plants and animals occur in environments altered by human activity. Life history traits may vary among populations in natural and human‐dominated environments, and therefore, management strategies may need to be tailored to different environments to promote persistence. The primary objectives of this project were to estimate the probability of being pregnant for females of the threatened giant garter snake (Thamnophis gigas) and test for differences in these demographic parameters between populations in seminatural wetlands and wetlands in areas dominated by rice agriculture. We also hypothesized that the probability of breeding and the number of fetuses would increase with increasing body size, a commonly reported relationship for snakes. We analysed data on T. gigas fecundity from 9 years using a Bayesian hurdle model and found no evidence of variation in the probability of being pregnant or in the number of fetuses given pregnancy for T. gigas in the two environments. The probability of being pregnant in a year was higher for females of larger size and ranged from <0.10 for snakes smaller than 631 mm snout‐to‐vent length (SVL) to >0.96 for the largest females. Similarly, given that a female was pregnant, the number of fetuses produced was higher for larger females. Pregnant females of average SVL were expected to produce 14 fetuses, and the largest females were expected to produce 34 fetuses. The inferences from our analyses are needed for subsequent population modeling, which will guide planning and decision‐making for T. gigas.

show abstract

Sunning themselves in heaps, knots, and snarls: The extraordinary abundance and demography of island watersnakes

King

Stanford²,

Jones

2018

Ecology and Evolution

View full text Add to dashboard Cite

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.

show abstract

Demography of the San Francisco Gartersnake in Coastal San Mateo County, California

Cited by 13 publications

References 16 publications

An endangered snake thrives in a highly urbanized environment

An endangered snake thrives in a highly urbanized environment

Estimating relationships between size and fecundity in the threatened giant garter snake in seminatural and agricultural wetlands

Sunning themselves in heaps, knots, and snarls: The extraordinary abundance and demography of island watersnakes

Contact Info

Product

Resources

About