Establishing Reference Demography for Conservation: A Case Study of<i>Macrochelys temminckii</i>in Spring Creek, Georgia

Folt, Brian; Jensen, John B.; Teare, Amber R.; Rostal, David C.

doi:10.1655/herpmonographs-d-15-00004

Cited by 33 publications

(52 citation statements)

References 52 publications

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“…Such variation is ignored in the stage‐based matrix models traditionally applied to long‐lived reptiles, where animals are divided into a small number of size‐based stages and transition probabilities between stages assumed to be constant (Crouse, Crowder, & Caswell, ). Such models are currently being used to predict the long‐term fates of turtle populations threatened by harvesting, road mortality and pollution (Crawford, Maerz, Nibbelink, Buhlmann, & Norton, ; Folt, Jensen, Teare, & Rostal, ; Salice, Rowe, & Eisenreich, ; Zimmer‐Shaffer, Briggler, & Millspaugh, ). Although it is important to exclude unnecessary detail from population models (Caswell, ; Starfield, ), it is possible that individual variation could significantly alter the dynamics of populations, although the empirical evidence for this is currently tentative (Cressler et al., ; Kendall & Fox, ; Lindberg, Sedinger, & Lebreton, ; Vindenes, Engen, & Sæther, ).…”

Section: Discussionmentioning

confidence: 99%

“…Such models are currently being used to predict the long-term fates of turtle populations threatened by harvesting, road mortality and pollution (Crawford, Maerz, Nibbelink, Buhlmann, & Norton, 2014;Folt, Jensen, Teare, & Rostal, 2016;Salice, Rowe, & Eisenreich, 2014;Zimmer-Shaffer, Briggler, & Millspaugh, 2014). Although it is important to exclude unnecessary detail from population models (Caswell, 1988;Starfield, 1997), it is possible that individual variation could significantly alter the dynamics of populations, although the empirical evidence for this is currently tentative (Cressler et al, 2017;Kendall & Fox, 2002;Lindberg, Sedinger, & Lebreton, 2013;Vindenes, Engen, & Saether, 2008).…”

Section: Discussionmentioning

confidence: 99%

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Subtle individual variation in indeterminate growth leads to major variation in survival and lifetime reproductive output in a long‐lived reptile

et al. 2017

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The consequences of individual variation in life‐history traits have been well studied due to their importance in evolutionary ecology. However, a trait that has received little empirical attention is the rate of indeterminate growth. In long‐lived ectotherms, subtle variation in growth after maturity could have major effects over the animals’ lifetimes. These effects are difficult to measure due to the challenges involved in reliably estimating individual variation in the face of environmental stochasticity, and the need to account for trade‐offs among growth, reproduction and survival. However, modelling advances have made such analysis possible if long‐term high‐quality datasets are available. We used an integrated state‐space modelling framework to reveal relationships between indeterminate growth, reproduction and survival in a population of North American snapping turtles (Chelydra serpentina) using a 41‐year dataset for 298 adult females. A hierarchical version of the von Bertalanffy model fitted to data on carapace lengths showed substantial individual variation in growth trajectories, and hierarchical models fitted to clutch‐mass data and recapture histories showed that reproductive output and survival probability increased with size. Integration of these models revealed no detectable trade‐offs—i.e., individual growth parameters were not correlated with size‐specific survival or reproduction rates, and individual variation in reproductive output did not affect the size‐specific survival rate. Consequently, individual variation in growth parameters was estimated to result in >2‐fold variation in post‐maturity life expectancy and >4‐fold variation in expected lifetime reproductive output. These results illustrate that indeterminate growth can have major fitness consequences in long‐lived species. We suggest that the individual variation in growth rates reflects variation in environments experienced during development or later life. An understanding of this variation may be essential for predicting the population dynamics of long‐lived species under threat and identifying the most important environments to protect. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13014/suppinfo is available for this article.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Subtle individual variation in indeterminate growth leads to major variation in survival and lifetime reproductive output in a long‐lived reptile

et al. 2017

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“…Therefore, it seems possible that incidental drowning on trot lines, limb lines, and submerged hoop nets (or even ingestion of fish hooks after being cut off a fishing line) could be a major source of contemporary mortality in southwestern Louisiana. Ultimately, this could threaten the long‐term population viability of alligator snapping turtles as a result of lowered annual adult survival rates (Folt et al , Steen and Robinson ).…”

Section: Discussionmentioning

confidence: 99%

“…The distribution and scale of incidental or intentional recreational harvest is difficult to quantify in Louisiana because there are currently no requirements for commercial or recreational fishermen to report alligator snapping turtle bycatch. The current regulation in Louisiana does not stipulate a size limit or an annual bag limit to recreational take of alligator snapping turtles even though populations are sensitive to changes in adult survival (Folt et al , Louisiana Department of Wildlife and Fisheries ). Conversations with local fishermen in the field and statements from 2 respondents in the questionnaire indicate that some fishermen illegally harvest more than the stated regulation if given the opportunity, which could lead to larger effects on local populations.…”

Section: Discussionmentioning

confidence: 99%

“…Indeed, a recent field study in the region captured few individuals during field surveys, but juvenile and subadults dominated the captures (8 were 15.2–31.6 cm; 6 were 31.6–46.4 cm; Huntzinger et al ). Howey and Dinkelacker () suggested that unharvested alligator snapping turtle populations should have more adults than juveniles, an even sex ratio, and high population densities, but Folt et al () suggested that the population structure may range from either adult‐ (0.5 juveniles:1 adult) to juvenile‐skewed (1.5 juveniles:1 adult). However, one certainty is that adult apparent annual survival must be high (0.95–0.98) to maintain a relatively stable population, with population stability most sensitive to changes in adult survival (Folt et al ).…”

Section: Discussionmentioning

confidence: 99%

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Using Local Ecological Knowledge in Louisiana to Infer Distribution and Abundance of the Alligator Snapping Turtle

et al. 2019

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Local ecological knowledge (LEK) collected via formal questionnaires and informal surveys can be a useful tool to aid in species conservation, particularly with species that are rare or difficult to detect. The alligator snapping turtle (Macrochelys temminckii) is a large aquatic turtle species that was heavily harvested by the commercial fishing industry beginning in the 1960s. This led to population declines throughout its range and closure of the commercial harvest in all states. The species is of conservation concern throughout its range and currently petitioned to be listed under the Endangered Species Act. However, the species' secretive behaviors and low densities can provide difficulties for biologists trying to determine accurate population densities and demographics. In 2013, we developed a LEK questionnaire to gauge licensed recreational fishermen on their perceptions of alligator snapping turtles, and distributed 2,100 questionnaires via postal service in a 7‐parish area of southwestern Louisiana, USA. Despite a low response rate (4.7%), all parishes had ≥1 sighting of alligator snapping turtle reported by respondents within the past 5 years, suggesting that they are still relatively widespread throughout southwestern Louisiana. However, respondents' perceptions also suggested that populations are stable to declining and tighter recreational harvest regulations may be needed to ensure long‐term population viability. Responses suggesting alligator snapping turtles' widespread distribution in southwestern Louisiana have recently been corroborated by field‐trapping surveys. This concordance suggests that LEK surveys can be useful for evaluating patterns of the distribution for cryptic species such as the alligator snapping turtle, while also potentially providing inferences about species abundance in a conservation context. Therefore, we recommend that surveys like this may assist with species monitoring when population sampling is logistically difficult or cost‐prohibitive. © 2019 The Wildlife Society.

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Contrasting Patterns of Demography and Population Viability Among Gopher Tortoise Populations in Alabama

et al. 2021

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Population viability analyses are useful tools to predict abundance and extinction risk for imperiled species. In southeastern North America, the federally threatened gopher tortoise (Gopherus polyphemus) is a keystone species in the diverse and imperiled longleaf pine (Pinus palustris) ecosystem, and researchers have suggested that tortoise populations are declining and characterized by high extinction risk. We report results from a 30-year demographic study of gopher tortoises in southern Alabama , where 3 populations have been stable and 3 others have declined. To better understand the demographic vital rates associated with stable and declining tortoise populations, we used a multi-state hierarchical markrecapture model to estimate sex-and stage-specific patterns of demographic vital rates at each population. We then built a predictive population model to project population dynamics and evaluate extinction risk in a population viability context. Population structure did not change significantly in stable populations, but juveniles became less abundant in declining populations over 30 years. Apparent survival varied by age, sex, and site; adults had higher survival than juveniles, but female survival was substantially lower in declining populations than in stable ones. Using simulations, we predicted that stable populations with high female survival would persist over the next 100 years but sites with lower female survival would decline, become male-biased, and be at high risk of extirpation. Stable populations were most sensitive to changes in apparent survival of adult females. Because local populations varied greatly in vital rates, our analysis improves upon previous demographic models for northern populations of gopher tortoises by accounting for population-level variation in demographic patterns and, counter to previous model predictions, suggests that small tortoise populations can persist when habitat is managed effectively.

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Establishing Reference Demography for Conservation: A Case Study ofMacrochelys temminckiiin Spring Creek, Georgia

Cited by 33 publications

References 52 publications

Subtle individual variation in indeterminate growth leads to major variation in survival and lifetime reproductive output in a long‐lived reptile

Subtle individual variation in indeterminate growth leads to major variation in survival and lifetime reproductive output in a long‐lived reptile

Using Local Ecological Knowledge in Louisiana to Infer Distribution and Abundance of the Alligator Snapping Turtle

Contrasting Patterns of Demography and Population Viability Among Gopher Tortoise Populations in Alabama

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