Article

Estimating survival rates of uncatchable animals: The myth of high juvenile mortality in reptiles

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Abstract

Survival rates of juvenile reptiles are critical population parameters but are difficult to obtain through mark-recapture programs because these small, secretive animals are rarely caught. This scarcity has encouraged speculation that survival rates of juveniles are very low, and we test this prediction by estimating juvenile survival rates indirectly. A simple mathematical model calculates the annual juvenile survival rate needed to maintain a stable population size, using published data on adult survival rates, reproductive output, and ages at maturity in 109 reptile populations encompassing 57 species. Counter to prediction, estimated juvenile survival rates were relatively high (on average, only about 13% less than those of conspecific adults) and highly correlated with adult survival rates. Overall, survival rates during both juvenile and adult life were higher in turtles than in snakes, and higher in snakes than in lizards. As predicted from life history theory, rates of juvenile survival were higher in species that produce large offspring, and higher in viviparous squamates than in oviparous species. Our analyses challenge the widely held belief that juvenile reptiles have low rates of annual survival and suggest instead that sampling problems and the elusive biology of juvenile reptiles have misled researchers in this respect.

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... Although the results of such studies may not perfectly represent free-living individuals, these estimates can be more robust than those from studies conducted in the field, which are commonly hindered by a small sample size. When empirical calculations of a vital rate are missing or not feasible to perform, but survival and fecundity rates are known for all other life stages, an estimate of the juvenile survival probability can be inferred from a population matrix by assuming a stable population growth rate Pike et al. 2008). ...
... Here, we estimate juvenile survival probabilities for three salamander species in the genus Ambystoma (A. annulatum, A. maculatum, and A. texanum) using both empirical estimation from capture-mark-recapture methods under semi-natural conditions and inference from published congeneric vital rates (following Pike et al. 2008). These species have a prototypical complex lifecycle, wherein terrestrial adults breed and lay eggs in temporary wetlands . ...
... This finding lends support to the notion that surrogate data from taxonomically and ecologically similar species can be applied to population models to yield reasonable predictions of data-deficient species' responses to both habitat change and potential management strategies (Biek et al. 2002;Schtickzell et al. 2005;Wenger 2008). Moving forward, Bayesian integrated population models can be used to harness known hierarchical data structures (e.g., spatial, temporal, and phylogenetic relationships) and extant ecological knowledge (e.g., physiological, community ecology, life history, and environmental data) from ecologically similar and phylogenetically related species to improve estimates of demographic rates by using informed vital rate prior distributions for species and populations with data gaps (Kindsvater et al. 2018 (Pike et al. 2008). ...
Thesis
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The vital rates (e.g., survival, growth, and reproduction) of distinct life stages within a species are known to influence the growth and persistence of populations. As such, studies describing stage-specific vital rates, and the factors that shape variation in these rates across species and populations, can help to improve our understanding of population dynamics and species distributions. Moreover, the insights gained from such studies can guide the prioritization of populations for conservation efforts and inform the selection of management strategies under predicted climate and land use changes. Yet life stage-specific vital rate estimates, and characterizations of the physiological responses that influence demographic rates under variable conditions, are lacking for most species. Amphibians are experiencing drastic population declines across the globe. As amphibians exhibit complex lifecycles, wherein unique life stages rely on divergent resources and habitat types, examinations of distinct life stages may be particularly critical for enhancing amphibian conservation efforts. Specifically, juveniles are known to play a critical role in amphibian population dynamics, but are relatively understudied compared with other life stages due to their small body size and often elusive life histories. The main objective of this dissertation was to elucidate survival rates, and physiological characteristics that contribute to survival, among terrestrial juveniles of multiple complex lifecycle pond-breeding salamanders in the genus Ambystoma. I first estimated juvenile survival rates among three ambystomatid species (A. annulatum, A. maculatum and A. texanum) by conducting an 11-month capture-mark-recapture study within semi-natural enclosures. I found juvenile survival rates to be constant through time and comparable among species. These similarities indicated that vital rate estimates from congeneric, ecologically similar species can serve as robust place-holder information to examine the population dynamics of the many amphibian species for which stage-specific data are lacking. Next, I reared larvae of five species (A. annulatum, A. maculatum, A. opacum, A. talpoideum, and A. texanum) from populations along an ~200 km latitudinal gradient in Missouri, USA to metamorphosis under common conditions. By performing flow-through respirometry on juveniles, I found respiratory surface area water loss (RSAWL) and standard metabolic rates (SMR) to differ between species. Though SMR showed no relationship with locality, RSAWL was weakly positively correlated with latitude. This suggested that juvenile ambystomatids exposed to warmer average conditions at more southern latitudes, and thus a higher desiccation risk, may demonstrate the locally adaptive regulation of RSAWL compared with juveniles from northern populations. Given common rearing, it is likely that differences among species and populations had a genetic basis, and were not solely the result of phenotypic plasticity. I then conducted a replicated experiment to evaluate how juvenile RSAWL, SMR, and body mass might influence individual fitness by releasing A. maculatum and A. opacum juveniles from the previous study into the semi-natural enclosures for seven months of capture-mark-recapture. Examining known survival at three time points during the study, I found juveniles with higher initial body mass and/or lower SMR to have a higher likelihood of survival, particularly under warm initial conditions. There was no effect of RSAWL on survival. Acclimation experiments with surviving salamanders revealed that thermal tolerances and SMR demonstrated plastic responses to warming. Further, a simulation of juvenile survival following high temperatures suggested that the two study species may demonstrate diverging juvenile survival rates after being thermally challenged due to distinct acclimation strategies. Collectively, the results of these studies shed light on a key vital rate for ambystomatid population dynamics in a life stage that is difficult to observe. I compiled the findings of these and other ambystomatid studies to propose management objectives and strategies to conserve A. annulatum, an endemic species of the Ozark and Ouachita Mountains. This effort demonstrated the utility of life stage-specific demographic and physiological information for guiding the conservation of biodiversity.
... We estimated the lowest survival probability of the whole study on that sampling occasion, but this model presented low support (ΔAICc = 2.11) and showed lower survival probabilities for adults than for juveniles. The shortest survival probability in adults suggest lower reproductive output and the consequent decline of the population (Pike et al., 2008). Pike et al. (2008) conducted a study using life history data from 46 lizard populations of 20 species and showed that juvenile survival was strongly related to adult survival but 13% lower on average than that of adults. ...
... The shortest survival probability in adults suggest lower reproductive output and the consequent decline of the population (Pike et al., 2008). Pike et al. (2008) conducted a study using life history data from 46 lizard populations of 20 species and showed that juvenile survival was strongly related to adult survival but 13% lower on average than that of adults. The annual apparent survival probability for adults in the conserved population (PEI) was 28% for males and 24% for females higher than that for the juveniles of the same population. ...
... This pattern may be related to higher predation rates affecting juveniles due to their smaller size (Bull, 1987), or to the fact that juveniles could present inferior escaping abilities in comparison with adults (Kacoliris et. al., 2013), or because of the difficulty in spotting them (Pike et al., 2008). Kacoliris et al. (2013) found survival to be slightly higher for adults than for juveniles of L. multimaculatus in a population located in a protected area in Argentina, indicating that this pattern might be characteristic of a stable population (Pike et al., 2008). ...
Article
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Habitat fragmentation is one of the sources of the global threat to wildlife populations. During the last four decades, urban development in Brazil’s southern coastline has seen considerable growth, fragmenting the habitat of the sand lizard Liolaemus occipitalis Boulenger, 1885, thus threatening it with extinction. In order to assess the influence of urban development on this species, we used tagging and recapture data to study two populations in Brazil’s southern coastline, one in a conserved area rarely subjected to disturbance and the other in an area undergoing different kinds of anthropogenic disturbance. We explored the consequences of this change in the natural landscape by comparing estimates of survival and abundance with Robust Design Model, and the body condition of individuals in both populations with analysis of covariance and variance. Survival of individuals were lower in the disturbed population than in the conserved population. The abundance of this lizard species was similar between populations. The body condition of females was higher in the disturbed area than in the conserved area, while males were similar among populations, but longer (SVL). This study shows how anthropic impacts can affect a population of lizards and the importance of maintaining protected areas and their interconnection to preserve Liolaemus occipitalis.
... Immature stages in particular are often poorly understood, contributing to a major gap in life-history data for most turtle species (Carr 1952, Germano 1994, Pike et al. 2008. Immature turtles are often more cryptic and secretive than adults, and ontogenetic changes in behavior, diet, or habitat associations can make immature turtles more difficult to detect even when adults can be readily found (Carr 1952, Pike et al. 2008). ...
... Immature stages in particular are often poorly understood, contributing to a major gap in life-history data for most turtle species (Carr 1952, Germano 1994, Pike et al. 2008. Immature turtles are often more cryptic and secretive than adults, and ontogenetic changes in behavior, diet, or habitat associations can make immature turtles more difficult to detect even when adults can be readily found (Carr 1952, Pike et al. 2008). In addition, trapping techniques used for adults may be less effective for capturing smaller size classes, contributing to the underrepresentation of immature individuals in turtle population surveys or mark-recapture studies (Hellgren et al. 2000). ...
... In addition, trapping techniques used for adults may be less effective for capturing smaller size classes, contributing to the underrepresentation of immature individuals in turtle population surveys or mark-recapture studies (Hellgren et al. 2000). As a result, immature turtles are often presumed to be in low abundance and to experience high levels of mortality, although these assumptions have been challenged by Pike et al. (2008). ...
Article
Population manipulations such as translocation and head‐starting are increasingly used as recovery tools for chelonians. But evaluating success of individual projects can require decades of monitoring to detect population trends in these long‐lived species. Furthermore, there are often few benchmarks from stable, unmanipulated populations against which to compare demographic rates, particularly for the immature stages. We used 8 years of mark‐recapture data to estimate apparent survival of immature gopher tortoises (Gopherus polyphemus) recruited into an introduced population of gopher tortoises first established on St. Catherines Island, Georgia, USA, in 1987. During 2006–2013, we conducted targeted trapping of immature gopher tortoises and compared survival of the hatchling, juvenile and subadult stages among treatments: individuals released shortly after hatching from eggs obtained from gravid female founders (direct releases), individuals reared in captivity for 6–9 months following hatching (head‐starts), and individuals first encountered as free‐ranging, wild‐recruited offspring (wild recruits). Among the candidate models we examined, the best fit model included additive effects of tortoise stage and treatment; however, overlapping 95% credible intervals among treatments (CrI) suggested that survival did not vary significantly among treatments. Annual apparent survival increased over the immature period, highlighting the importance of calculating separate estimates for the different immature stages. Across all treatments, the additive model estimated annual apparent survival probability to be 0.37 (CrI = 0.25–0.48) for hatchlings, 0.71 (CrI = 0.61–0.81) for juveniles, and 0.83 (CrI = 0.74–0.94) for subadults. Our study, in combination with previous monitoring efforts at St. Catherines Island, provides strong evidence that the translocation and subsequent population augmentation efforts have been successful in establishing a robust population of gopher tortoises. Additionally, our results provide estimates of demographic rates for life stages that are poorly understood but critical to understanding population dynamics of this imperiled species. © 2020 The Wildlife Society. Eight years of mark‐recapture targeting immature life stages provided survival estimates for hatchling, juvenile, and subadult gopher tortoises recruited following translocation. These results, in combination with other monitoring of the population, provide strong evidence that the translocation and subsequent population augmentation efforts have been successful in establishing a robust population of gopher tortoises.
... Although the results of such studies may not accurately represent free-living individuals, these estimates can be more robust than those from studies conducted in the field, which are commonly hindered by a small sample size. When empirical calculations of a vital rate are missing or not feasible to perform, but survival and fecundity rates are known for all other life stages, an estimate of the juvenile survival probability can be inferred from a population matrix by assuming a stable population growth rate (Harper et al. 2008, Pike et al. 2008. Alternatively, data from conspecific populations, closely related species, or ecologically similar taxa are used as surrogate information to construct population models in the absence of species-specific vital rate estimates (Etterson and Bennett 2006). ...
... Biphasic ambystomatid salamanders (Ambystoma spp.) have a prototypical complex life cycle, wherein terrestrial adults breed and lay eggs in temporary wetlands (Wilbur 1980, Petranka 1998. Aquatic larvae then hatch from inundated eggs and develop into terrestrial juveniles over several months. ...
... Though the median estimate of the ringed salamander juvenile survival probability trended lower than those of spotted or small-mouthed salamanders, species-specific posterior distributions did not differ significantly within the pens (Fig. 3). This finding indicated that juvenile survival probabilities were similar among our study species under the common pen conditions, even though each of the species likely experiences a distinct distribution of environmental conditions across their unique geographic ranges (Petranka 1998). This lends support to the notion that surrogate data from taxonomically and ecologically similar species can be applied to population models to yield reasonable predictions of data-deficient species' responses to habitat change and potential management strategies (Biek et al. 2002, Schtickzelle et al. 2005, Wenger 2008). ...
Article
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Juvenile vital rates have important effects on population dynamics for many species, but this demographic is often difficult to locate and track. As such, we frequently lack reliable estimates of juvenile survival, which are necessary for accurately assessing population stability and potential management approaches to conserve biodiversity. We estimated survival rates for elusive juveniles of 3 species, the ringed salamander (Ambystoma annulatum), spotted salamander (A. maculatum), and small‐mouthed salamander (A. texanum), using 2 approaches. First, we conducted an 11‐month (2016–2017) mark‐recapture study within semi‐natural enclosures and used Bayesian Cormack‐Jolly‐Seber models to estimate survival and recapture probabilities. Second, we inferred the expected annual juvenile survival rate given published vital rates for pre‐metamorphic and adult ambystomatids assuming stable population growth. For all 3 species, juvenile survival probabilities were constant across recapture occasions, whereas recapture probability estimates were time‐dependent. Further, survival and recapture probabilities among study species were similar. Post‐study sampling revealed that the initial study period median estimate of annual survival probability (0.39) underestimated the number of salamanders known alive at 11 months. We therefore appended approximately 1 year of opportunistic data, which produced a median annual survival probability of 0.50, encompassing salamanders that we knew to have been alive. Calculation from literature values suggested a mean annual terrestrial juvenile ambystomatid survival probability of 0.49. Similar results among our approaches indicated that juvenile survival estimates for the study species were robust and likely comparable to rates in nature. These estimates can now be confidently applied to research, monitoring, and management efforts for the study species and ecologically similar taxa. Our findings indicated that similarly robust vital rate estimates for subsets of ecologically and phylogenetically similar species can provide reasonable surrogate demographic information that can be used to reveal key factors influencing population viability for data‐deficient species. © 2020 The Wildlife Society. We empirically estimated recapture and survival probabilities for elusive juveniles of 3 complex life cycle salamander species using capture‐mark‐recapture protocols and inference from published salamander vital rates. Estimates of survival were comparable across species and estimation methods, lending support to the use of rigorously estimated vital rate data from ecologically and phylogenetically similar species as place‐holder information in demographic models used to predict population responses to management scenarios for species of conservation concern for which data are sparse.
... we might expect optimizing selection to favour an offspring size at which survival rates of progeny are similar to those of conspecific adults; and indeed, this is the observed empirical pattern -with no difference between oviparous and viviparous species in this respect (Pike, Pizzatto, Pike, & Shine, 2008). Now, we turn to the third hypothesis above: the idea that physical limits on abdominal volume of reproducing females force a tradeoff between offspring size and brood size. ...
... All else being equal, that reduction in brood size might impose strong selection against viviparity. In contrast, the acquisition of viviparity in squamate reptiles appears not to have involved major changes in physical burdening of the female (Dunham & Miles, 1985;Seigel & Fitch, 1984), nor in reproductive output (Meiri et al., 2012;current analysis) or in survival rates of offspring (Pike et al., 2008). A female that retained developing embryos in utero may have faced little 'cost' to her own survival, or to the numbers, sizes and viability of her offspring. ...
Article
Viviparity (live‐bearing) has independently evolved from oviparity (egg‐laying) in more than 100 lineages of squamates (lizards and snakes). We might expect consequent shifts in selective forces to affect per‐brood reproductive investment (RI = total mass of offspring relative to maternal mass) and in the way in which that output is partitioned (number versus size of offspring per brood). Based on the assumption that newly‐born offspring are heavier than eggs, we predicted that live‐bearing must entail either increased reproductive investment or a reduction in offspring size and/or fecundity. However, our phylogenetically‐controlled analysis of data on 1,259 squamate species revealed no significant differences in mean offspring size, clutch size or RI between oviparous and viviparous squamates. We attribute this paradoxical result to (1) strong selection on optimal offspring sizes, unaffected by parity mode, (2) the lack of a larval stage in amniotes, favouring large eggs even in the ancestral oviparous mode, and (3) the ability of viviparous females to decrease the mass of uterine embryos by reducing extra‐embryonic water stores. Our analysis shows that squamate eggs (when laid) weigh about the same as the hatchlings that emerge from them (despite a many‐fold increase in embryo mass during incubation). Most of the egg mass is due to components (such as water stores and the eggshell) not required for oviductal incubation. That repackaging enables live‐born offspring to be accommodated within the mother's body without increasing total litter mass. The consequent stasis in reproductive burden during the evolutionary transition from oviparity to viviparity may have facilitated frequent shifts in parity modes.
... In addition, potential differences in survival between life stages could affect urotomy probability. Juveniles may be less mobile and use habitats that provide more cover to predators or, conversely, have poor escaping abilities than adults, ultimately leading to different survival rates (Pike et al., 2008;Kacoliris, Berkunsky, & Velasco, 2013). We obtained the life stage of each specimen based on the known size at sexual maturity for males (176 mm SVL; Santos, 2013) and females (193 mm SVL; H.C. Costa, pers. ...
... However, tail breakage could have occurred in juveniles that survived and reached adulthood. Indeed, survival rates of juvenile reptiles seem higher than previously thought (Pike et al., 2008), making this possibility not so unlikely. Therefore, the temporal aspect of urotomy cannot be established for certain without, for example, long-term capture-mark-recapture experiments (e.g., Kuo & Irschick, 2016). ...
Article
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Predator–prey interactions are important evolutionary drivers of defensive behaviors, but they are usually difficult to record. This lack of data on natural history and ecological interactions of species can be overcome through museum specimens, at least for some reptiles. When facing aggressive interactions, reptile species may exhibit the defensive behavior of autotomy by losing the tail, which is also known as “urotomy”. The inspection of preserved specimens for scars of tail breakage can reveal possible ecological and biological correlates of urotomy. Herein, we investigated how the probability of urotomy in the worm lizard Amphisbaena vermicularis is affected by sex, body size, temperature, and precipitation. We found higher chances of urotomy for specimens with larger body size and from localities with warmer temperatures or lower precipitation. There was no difference in urotomy frequency between sexes. Older specimens likely faced – and survived – more predation attempts through their lifetime than smaller ones. Specimens from warmer regions might be more active both below‐ and aboveground, increasing the odds to encounter predators and hence urotomy. Probability of urotomy decreased with increased precipitation. Possibly, in places with heavier rainfall worm lizards come more frequently to the surface when galleries are filled with rainwater, remaining more exposed to efficient predators, which could result in less survival rates and fewer tailless specimens. This interesting defensive behavior is widespread in squamates, but yet little understood among amphisbaenians. The novel data presented here improve our understanding on the correlates of tail breakage and help us to interpret more tales of lost tails.
... The bias in males in all four species is not unusual in snake populations (Parker & Plummer, 1987) and may result from greater female mortality and the costs of reproduction (e.g., Madsen & Shine, 1993;Luiselli et al., 1996;Shine, 2003). Absence of juveniles in the sampling is typical of snake field studies (Pike et al., 2008;Sewel et al., 2016;Cayuela et al., 2019) and unfortunately this limits knowledge of juvenile sex ratios and other aspects of their biology (Pike et al., 2008). Additionally, the absence of any recaptures during 2000 in the short-term analysis at TBM illustrates the difficulties separating dispersal and mortality in MRR studies. ...
... The bias in males in all four species is not unusual in snake populations (Parker & Plummer, 1987) and may result from greater female mortality and the costs of reproduction (e.g., Madsen & Shine, 1993;Luiselli et al., 1996;Shine, 2003). Absence of juveniles in the sampling is typical of snake field studies (Pike et al., 2008;Sewel et al., 2016;Cayuela et al., 2019) and unfortunately this limits knowledge of juvenile sex ratios and other aspects of their biology (Pike et al., 2008). Additionally, the absence of any recaptures during 2000 in the short-term analysis at TBM illustrates the difficulties separating dispersal and mortality in MRR studies. ...
Article
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Reports of global declines in animal populations are now numerous and also include snakes, a group of animals now widely regarded as bio-indicators. A prerequisite for any conservation management plan to protect or restore snake population requires a data base that provides insight into population composition and changes. However snakes are well known to be particularly difficult to quantitatively sample due to their secretive and elusive nature, and hence, accumulating an adequate database for analysis requires long-term field studies that involve intensive searches. Populations of four snake species, Zamensis longissimus, Natrix helvetica, Vipera aspis and Hierophis viridiflavus living in two suburban areas of Rome, Vejo and Tor Bella Monaca, have been monitored, but with interruptions, since 1995. The results indicated that H. viridiflavus was the commonest species at both sites. Male bias was found in all four species but especially in Z. longissimus and V. aspis with detection of juveniles greatest in H. viridiflavus and N. helvetica. Snout to vent lengths (SVL) of H. viridiflavus and Z. longissimus, which were present at both sites, were greater at the less degraded habitat of the two study localities. Community metrics indicated that the degraded habitat had lower species richness, evenness, Shannon and Simpson diversity indices, but a higher dominance index. Recapture frequencies, either of snakes recaptured once or multiple times were in general greater at Vejo. The highest population densities were found in H. viridiflavus followed by V. aspis and N. helvetica, which were similar. However long term trends in densities show declines in V. aspis and N. helvetica between the 1995 and 2019. Population densities were in good agreement with density estimates found in previous studies of snakes in more natural habitats.
... Survival of subadult reptiles (hatchling and juvenile) is often understudied and underestimated through traditional markrecapture monitoring techniques because of the small size and secretive nature of individuals during early life stages (Pike et al. 2008, Ballouard et al. 2013. To date, no fieldbased estimate of hatchling survival or subadults' use of space has been documented for Texas horned lizards. ...
... survival probability is considerably lower in early life stages compared to the adult life stage (Zúñiga-Vega et al. 2008, Massot et al. 2011, Kacoliris et al. 2013, and generally for reptiles, reported juvenile survival is approximately 13% lower than for conspecific adults, with average annual survival of juvenile lizards being 0.32 (Pike et al. 2008). Higher survival rates for adult Texas horned lizards, versus our documented rates for hatchlings, have been documented at various locations throughout the species' distribution: an adult survival rate of 0.59-0.70 at TAFB ), 0.01-0.47 for translocated lizards in north-central Texas (Miller et al. 2020), 0.09-0.54 ...
Article
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Habitat fragmentation has negative consequences on threatened and endangered species by creating isolated populations. The Texas horned lizard (Phrynosoma cornutum) is experiencing population declines and localized extirpations throughout its range and has been classified as a species of greatest conservation need in Oklahoma, USA. Younger age classes have been poorly studied but may be vital to the stability of remaining populations. To address gaps in knowledge concerning subadult (hatchling and juvenile) morphometrics, survivorship, and home range sizes, we studied 2 cohorts of subadults, for 2 years each, covering their hatching and juvenile years (2016–2019). We used a combination of radio‐telemetry and novel harmonic radar methodology to study a closed population of Texas horned lizards in 15 ha of native grassland at Tinker Air Force Base, Oklahoma. Population abundance for adults and juveniles was estimated as 56.5 ± 5.5 lizards and density as 7.96 lizards/ha. Our lowest estimates of survival indicated an average survival probability for the hatchling life stage of 0.285 (95% CI = 0.15–0.44), which is lower than for adults on the site. Average home range size increased from hatchling to adult life stages. Our results will have an immediate effect on the planning and assessment of ongoing headstart and management programs for Texas horned lizards. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society. We estimated Texas horned lizard hatchling survivorship using direct, field‐based monitoring methodology, and report ontogenetic increases in morphometrics and home range area from hatchling to adult life stages. Our results can be used in the planning and assessment of future headstart and management programs for this threatened lizard.
... For example, clutch size increases with latitude but hatchling mass decreases [53]. Survival of early life stages of reptiles is very difficult to measure directly, and Pike et al. (2008) argued that juvenile survival for reptiles may be often underestimated. They used a modeling approach to estimate annual survival from egg laying to sexual maturity for 17 turtle species as 0.65, which is very similar to the value we obtained for hatchling survival (0.66) [54]. ...
... Survival of early life stages of reptiles is very difficult to measure directly, and Pike et al. (2008) argued that juvenile survival for reptiles may be often underestimated. They used a modeling approach to estimate annual survival from egg laying to sexual maturity for 17 turtle species as 0.65, which is very similar to the value we obtained for hatchling survival (0.66) [54]. ...
Article
Population models are important tools for evaluating human impacts and potential management approaches on declining species. However, often studies are limited by constraints of the specific modeling approach. In this study we considered the persistence of a diamond-backed terrapin (Malaclemys terrapin) population using two distinct modeling approaches. Two of the models were deterministic matrix models. Analysis of the discrete non-spatial models showed that female adult survival rate had the largest positive impact on population growth while delaying sexual maturity decreased population growth. The matrix models also demonstrated that an increase in crab traps skewed the sex ratio of the population in favor of females. The third model was a stochastic agent-based formulation that evaluated how increases in the number of crab traps and frequency of nest disturbances affected the long-term viability of diamond-backed terrapins. The spatial agent-based model revealed how terrapin mortality was highly sensitive to the proximity of traps to the primary terrapin habitat. Results from this project improve our understanding of threats to diamond-backed terrapins and can be used to guide conservation efforts.
... Similarly, hatchlings of many turtle species are small and secretive, and therefore are rarely encountered. For this reason, hatchling survival rates are often inferred from other life-history parameters (Wilbur 1975;Congdon et al. 1994;Pike et al. 2008). Sea turtles offer an extreme and oft-cited example of the problems of secrecy and low-detectability in assessing hatchling life history. ...
... These traits impede reliable and consistent monitoring and recapture of individuals at regular intervals, which in turn increases the difficulty of detecting hatchlings in natural environments to determine habitat preferences. It is also challenging to monitor movement and dispersal patterns, and to quantify predation and mortality rates (Morafka et al. 2000;Pike et al. 2008). Due to these challenges, most studies of hatchling turtle ecology have focused on emergence and movement away from nesting sites; predation rates during dispersal from the nest to water; and sex determination during incubation (Vogt and Bull 1984;Semlitsch and Gibbons 1989;Ewert and Nelson 1991;DeGraaf and Nein 2010;Miller and Ligon 2014). ...
Article
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Hatchling turtles are known to be cryptic and secretive; as a result, there are few species for which habitat associations and movement patterns of hatchlings and small juveniles are well understood. Such data are important because hatchlings may experience high mortality rates, making them a sensitive life stage whose success has important impacts on overall population stability. Additionally, among species in which hatchlings and adults occupy distinctly different niches, conservation of resources for both is necessary for effective management. The aim of our study was to characterize the movement patterns, habitat use, and sources of mortality of hatchling Alligator Snapping Turtles (Macrochelys temminckii) in a southeastern Oklahoma, USA, stream. Movement patterns were typically characterized by an initial move away from the site of release, followed by prolonged occupancy of an area with abundant cover and shallow water. Of the 12 turtles we released, three were preyed upon by fish and seven were confirmed to be alive in mid-November, eight weeks after the study was launched. A single hatchling turtle was washed downstream during a high flow event, and we could not confirm the fate of another turtle, either because it was removed from the study area by a predator or because its transmitter failed prematurely. Surprisingly, we observed no evidence of predation by Raccoons (Procyon lotor), a common predator of hatchling turtles.
... Complessivamente desta preoccupazione la mancata cattura di individui giovani. Sebbene sia ampiamente nota la loro minore catturabilità (Pike et al., 2008), una completa assenza dai due campionamenti fa ipotizzare l'esistenza di un problema legato al reclutamento che può essere influenzato localmente dall'elevata densità di predatori (es. ardeidi) e/o di potenziali competitori (es. ...
Conference Paper
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La presenza di Emys orbicularis all’interno della Riserva Naturale Torrile e Trecasali è nota da tempo, sebbene non siano mai stati condotti studi per approfondire la distribuzione e l'abbondanza della specie all’interno dell’area protetta. In questo lavoro preliminare sono presentati alcuni parametri di popolazione e alcuni aspetti morfometrici degli individui catturati durante due sessioni condotte nel mese di agosto 2015 e nel mese di settembre 2016. Nei due anni di campionamento sono stati catturati in totale 33 individui differenti con sex ratio prossima al rapporto 1:1. La popolazione è caratterizzata da una dominanza di testuggini (80%) con un SCL compreso tra 130 e 180 mm. La classe maggiormente rappresentata nei maschi ha un range compreso tra 141 e 150,9 mm mentre nelle femmine tra 161 e 170,9 mm. Le femmine sono più pesanti e grandi dei maschi sia in termini di lunghezza, larghezza e altezza del carapace. Particolare attenzione va rivolta all’assenza di individui giovani e sub- adulti. Sebbene sia ampiamente nota la loro minore catturabilità, una completa assenza dai due campionamenti fa ipotizzare l’esistenza di un problema legato al reclutamento che può essere influenzato localmente dall’elevata densità di predatori (es. ardeidi) e/o di potenziali competitori (es. testuggini alloctone, ittiofauna). Le testuggini ricatturate all’interno della stessa sessione di cattura sono rimaste all’interno del medesimo sito mentre tra i cinque individui marcati nel 2015 e ricatturati nel 2016, tre sono stati ritrovati nello stesso sito, mentre un maschio adulto si spostato di circa 230 m da un corpo idrico ad una altro ed una femmina di circa 400 m all’interno dello stesso corpo idrico.
... Although posthatching survival was low (37% survived to the end of the study) compared to that reported in other studies of captive hatchling lizards (Sorci et al., 1996;Warner & Lovern, 2014;Botterill-James et al., 2019; but see Elphick & Shine, 1998), this survival rate was still higher than that reported in field studies (e.g. Warner & Shine, 2007;Pike et al., 2008;Pearson & Warner, 2018). The cause of post-hatching mortality in our study is unknown, but could have been due to artificially high competition with other individuals in the cages. ...
Article
The developmental environment plays a pivotal role in shaping fitness-relevant phenotypes of all organisms. Phenotypes are highly labile during embryogenesis, and environmental factors experienced early in development can have profound effects on fitness-relevant traits throughout life. Many reptiles exhibit temperature-dependent sex determination (TSD), whereby temperature during embryonic development permanently determines offspring sex. The leading hypothesis for the adaptive significance of TSD posits that egg incubation temperature differentially affects the fitness of males vs. females so that each sex is produced at its optimal temperature. The goal of this research is to address this hypothesis by quantifying the sex-specific effects of incubation temperature on phenotypes and survival in a lizard (Agama picticauda) with TSD. By incubating eggs under constant and fluctuating temperatures, we demonstrated that incubation temperature affects fitness-relevant phenotypes in A. picticauda; but males and females had similar reaction norms. However, females produced from female-biased incubation temperatures had greater survival than those from male-biased temperatures, and male survival was lowest for individuals produced from a female-biased temperature. In addition, eggs incubated at male-biased temperatures hatched earlier than those incubated at female-biased temperatures, which may have sex-specific consequences later in life as predicted by models for the adaptive significance of TSD.
... Tradeoffs between growth and behavior may be particularly relevant to turtle headstarting programs due to the life-history attributes of most Chelonians [15]. Juvenile turtles (order Testudines) often have lower estimated survival rates than adults, with predation assumed to be the primary cause of mortality [16,17]. Older, larger animals are less vulnerable to predation, in part due to a larger and thicker shell that can be a successful deterrent for many predators [3,18]. ...
Thesis
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Translocation is the deliberate movement and release of animals and a common management technique in wildlife conservation programs. However, efforts are often unsuccessful because relocated animals have low survival, precluding population establishment. I reviewed studies using antipredator training, environmental enrichment, and soft release as pre- release behavioral conditioning in translocation programs, and I quantitatively synthesized how these approaches affect post-release success. I then conducted experiments using captive-reared juvenile eastern box turtles (Terrapene carolina) raised with or without naturalistic environmental enrichment to better understand mechanisms influencing habitat preferences in captivity. Next, I investigated if enrichment encouraged natural behaviors before turtles were released into the wild and how being raised in enriched environments affected growth over differing rearing periods (nine vs. 21 months). Finally, I examined how enrichment and captive- rearing duration affected the turtles’ post-release growth, behavior, and survival. Meta-analysis conducted on 108 effect sizes from 41 studies investigating the effects of pre-release behavioral conditioning on translocation outcomes revealed conditioned animals had higher survival, reduced movement, and greater site fidelity than unconditioned individuals. Notably, antipredator training, environmental enrichment, and soft release all resulted in improved survival. This suggests pre-conditioning is likely an important tool for improving future wildlife translocations. When I provided environmental enrichment to captive-born eastern box turtles, they preferred enriched environments, regardless of prior housing experience, suggesting this preference is innate. Thus, enrichment likely enhances welfare of captive box turtles by satisfying an instinctive desire to occupy complex habitat. However, pre-release trials revealed enriched turtles performed no better in ecologically relevant foraging tasks than unenriched turtles. In a predator recognition test, eight-month-old enriched turtles avoided raccoon (Procyon lotor) urine more than unenriched turtles of the same age, but this difference was not apparent one year later. These findings suggest any behavioral benefits conferred by enrichment were modest. Enriched turtles also attained smaller body sizes overall than unenriched turtles pre- release. Enrichment had minimal effects on post-release behavior and survival. However, turtles raised for 21 months moved farther from the release site and had higher post-release survival than those raised for only nine months, regardless of rearing environment. Although raising animals in enriched captivity can increase translocation success for several taxa, my experiments with box turtles and similar previous studies indicate enrichment might have limited utility for enhancing reptile translocations. Instead, implementing a longer rearing period to maximize body size before release appears to most benefit survival by reducing susceptibility to predation, which is commonly cited as a hindrance to post-release success.
... As observed in many species (e.g. Martin (1995) (birds), Pike et al. (2008)(reptiles), Gaillard & Yoccoz (2003) (mammals)), we considered the survival probability to be lower in juveniles than in adults. Survival was also density dependent: when current population size in a patch, N , exceeded carrying capacity K, each individual was killed with a probability 1 − N K , so that the population size did not exceed on average the carrying capacity after the survival event. ...
Thesis
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Contemporary climate change is leading to population extinction, range shift and composition changes. Dispersal shapes these two last responses by allowing colonization of new habitats and by affecting population composition through gene flow. Depending on its adaptiveness, dispersal can promote or hinder local adaptation and modify the relative influence of phenotypic plasticity and evolutionary adaptation in population phenotypic change. However, landscape fragmentation hampers dispersal, affecting both population responses to climate change, and modifying the relative influence of the different processes involved in these responses. The aim of this PhD was to understand how population responses to climate change could be influenced by landscape fragmentation and by dispersal. By monitoring lizards inhabiting experimental populations where both climatic conditions and connectivity among them were manipulated, we demonstrated that connectivity among populations buffered climate change effects on population dynamics and phenotypic composition. We found that dispersal decisions depended on multiple intrinsic and extrinsic factors allowing to reduce the influence of warmer climate on population dynamics, but decreasing population density in cooler climate. Surprisingly, we also found that dispersal could modify the strength and direction of climate-dependent selection pressures on phenotypes. As a consequence, selection and dispersal acted in synergy to counteract the plastic response of the individuals. When integrated into a model, similar adaptive dispersal behavior strongly altered predictions of species persistence under climate change. We indeed found that adaptive dispersal promoted species range shift and reduced extinction probability compared to a model where dispersal was random (i.e.independent of intrinsic and extrinsic factors). Rather than considering dispersal as a neutral process, our results highlighted the importance to consider it as a complex mechanism shaped by multiple factors and able to drive population responses to climate change. Our results further suggest that fragmentation could strongly increase the influence of climate change on populations and may therefore precipitate their extinction. We thus call for a better integration of dispersal and landscape structure when studying population responses to climate change.
... Similarly, the recapture probability of the smaller individuals was lower (Fig. 3A). Other studies have suggested that juvenile snakes tend to have a lower probability of survival than adults (Parker and Plummer 1987;Morafka et al. 2000;Brown et al. 2007), but this conclusion might be subject to bias on account of sizespecific detection rates (Pike et al. 2008). The subadult stages of many snake species have often been noted to be particularly difficult to observe because of their small size and secretive habits (Durso and Seigel 2015;Bauwens and Claus 2018). ...
Article
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Survival rate is one of the most poorly characterized components of the life history of many species of reptiles, especially snakes. Reproductive activity can increase the risk of mortality. In this study, we examined whether sex-specific reproductive costs affect the survival probability of a viviparous rattlesnake, Crotalus triseriatus, in central Mexico from 2015 to 2018. We used a multimodel inference framework to test two hypotheses: (1) female survival probability should decrease during the late-gestation and birthing period, when females are less mobile and try to achieve stable body temperatures by behavioral thermoregulation; and (2) male survival probability should decrease during the mating season, when males are more actively searching for potential mates. Our data did not support these hypotheses. Mean (±1 SE) monthly survival probability of both males and females was 0.96 ± 0.01, and recapture probability was 0.11 ± 0.01. Annual survival rate was 0.72 ± 0.12. Monthly estimated mean adult population size varied from 16 to 71 adult rattlesnakes. Survival probability was positively correlated with body size. The reproductive costs could have been obscured by the fact that females do not reproduce every year and, therefore, the demands of the mating season are not as tightly linked to survivorship as we hypothesized.
... According to some authors, the survival rate of young, immature snakes is lower than that of adults (Völkl 1989, Phelps 2004, Altwegg et al. 2005. According to others, however, the young have similar survival rate to that of adults and the low recapture rates are the results of low detectability of these snakes due to their small size, lower thermal requirements or migration to more remote areas (Pike et al. 2008, Bauwens & Claus 2018. ...
Article
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Five populations of Vipera ammodytes in Western Bulgaria located along a latitudinal gradient were studied using the Capture-Mark-Recapture method. Sex ratio among subadults and juveniles was approximately 1:1 but it was difficult to be determined in adults due to methodological biases caused by differences in catchability of males and females during the active season. The marked individuals had high survival rate, but capture probability was low. From north to south, the established numbers and densities of the species in the studied areas were as follows: Karlukovo-796 individuals, with density 5.78 ind./ha, Lakatnik-319 individuals, with density 1.59 ind./ha, Balsha-635 individuals, with density 4.12 ind./ha, Bosnek-296 individuals, with density 0.73 ind./ha, Kresna Gorge-245 individuals, with density 2.07 ind./ha. Differences in movement rate between sexes were observed, with adult males being more mobile than females. During gestation, pregnant females became very static and usually kept close to the hibernating areas. After parturition, the neonates stayed close to these areas until the beginning of hibernation.
... Obtaining the vital rate estimates necessary to populate demographic models requires investment of resources and time, which may be lacking in a critical conservation setting. The most at-risk species may be those for which information is most lacking (Beissinger & Westphal 1998;Coulson et al. 2001;González-Suárez et al. 2012), due to geographical, taxonomic, or other biases in recording (Roberts et al. 2016;Troudet et al. 2017;dos Santos et al. 2020), or logistical barriers to collecting complete demographic data (Menges 2000;Weimerskirch 2001;Pike et al. 2008;Clutton-Brock & Sheldon 2010). Consequently, complete empirical demographic data represents only a small and biased subset of species (Lebreton et al. 2012;Salguero-Gómez et al. 2015, 2016Conde et al. 2019). ...
Article
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Population responses to threats such as habitat loss, climate change and overexploitation are usually explored using demographic models parameterized with estimates of vital rates of survival, maturation and fecundity. However, the vital rate estimates required to construct such models are often unavailable, particularly for species of conservation concern. Phylogenetically informed imputation methods have rarely been applied to such demographic data but may be a powerful tool for reconstructing vital rates for vertebrates. Here, we use standardized vital rate estimates for 50 bird species to assess the use of phylogenetic imputation to fill gaps in demographic data. We calculated imputation accuracy for vital rates of focal species excluded from the dataset either singly or in combination, with and without phylogeny, body mass and life history trait data. We used imputed vital rates to calculate demographic metrics, including generation time, to validate the use of imputation in demographic analyses. Covariance among vital rates and other trait data provided a strong basis to guide imputation of missing vital rates in birds, even in the absence of phylogenetic information. Accounting for phylogenetic relationships improved imputation accuracy for vital rates with high phylogenetic signal (Pagel's λ > 0.8). Importantly, including body mass and life history trait data compensated for lack of phylogenetic information. Estimates of demographic metrics were sensitive to the accuracy of imputed vital rates. Accurate demographic data and metrics such as generation time are needed to inform conservation planning processes, for example through IUCN Red List assessments and population viability analysis. Imputed vital rates could be useful in this context but, as for any estimated model parameters, awareness of the sensitivities of demographic model outputs to the imputed vital rates is essential. Article impact statement: Exploiting covariance among vital rates, phylogeny and traits to impute missing values holds promise for bridging demographic analysis gaps. This article is protected by copyright. All rights reserved
... It is unclear whether naturally high mortality, survey bias, different habitat use, or a combination of factors best explains the low capture rates of approximately 10-40% for juveniles and hatchlings. Low captures rates for these stages are typical for freshwater turtle species (Marchand and Litvaitis 2004;Pike et al. 2008) and can represent stable levels of adult survival (Hall et al. 1999). The stable population sizes we found suggest that recruitment into the adult population is occurring. ...
Article
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Determining demographic properties for threatened and endangered species is paramount for crafting effective management strategies for at-risk populations. Collecting sufficient data to quantify population characteristics, however, is challenging for long-lived species such as chelonians. One such species in Illinois is the state-listed as Endangered Spotted Turtle (Clemmys guttata). While demographic data exist for populations from other extremes of the range of the species, no similar investigation has been published for Illinois, in which only two isolated populations remain extant. We used a long-term mark-recapture data set to analyze changes in sex and stage structure, abundance, and population growth between 1988 and 2016. Both populations exhibited a strong adult bias (76.5-90.6%) and an even adult sex ratio throughout the duration of the study. At one site the estimated population abundance increased, although there was a decreasing trend in the growth rate over time. Population size and growth rate remained relatively stable at the other site. Sex and stage distributions in the Illinois C. guttata populations were consistent with those of other populations, but the two populations are not experiencing the steep declines documented throughout the remainder of the range of the species despite threats from habitat limitations, subsidized mesopredator abundance, poaching, and traffic. We recommend increasing available habitat as the most effective strategy to reduce risks to C. guttata persistence in Illinois.
... L'étude de la biologie et de l'écologie des premiers stades de vie des reptiles est bien souvent limitée en raison de problèmes d'échantillonnage en milieux naturels, ce qui engendre des méconnaissances (Pike et al., 2008). En effet, les contraintes méthodologiques pour pouvoir révéler la présence d'individus particulièrement cryptiques pour certaines espèces sont importantes (Castellano, Behler & Ultsch, 2008). ...
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Présentée par Frédéric BEAU Soutenue le 2 décembre 2019 Ecologie de la Cistude d'Europe Emys orbicularis en Brenne : histoire de vie des nouveau-nés et influence des modes de gestion sur les populations.
... Thus, we do not see low annual hatchling production as a reason for concern. Yet, this result does suggest Komodo Dragons may exhibit very high rates of juvenile survival to allow for stable population growth in this long-lived lizard (Pike et al., 2008;Laver et al., 2012;Purwandana et al., 2014). ...
Article
We studied annual trends and characteristics of nesting activities and hatchling production by female Komodo Dragons (Varanus komodoensis) in Komodo National Park, Indonesia between 2002 and 2006. During this period, we recorded 12, 16, 15, 13, and 6 females nesting annually at 42 potential nesting sites. An average female nesting periodicity was estimated at 1.260.4 years. This result arose because most females bred annually and some biennially. Some females reused nest sites in successive years while others did not. Nesting females had significantly lower body mass compared to when they were recaptured again in a non-nesting state. All-female nesting activities were conducted within their resident valleys and suggested a strong tendency for spatial fidelity. Komodo Dragons were generally considered solitary nesters as only on one occasion were two nesting females observed to use the same nesting site. On average, 21.063.6 Komodo Dragon hatchlings emerged from each nest. We estimated that within the study area, nesting female Komodo Dragons produced between 129.0621.8 and 344.0658.16 hatchlings per annum. We discuss the ecological and evolutionary significance of these attributes. However, the main conservation management implications drawn from this study are that there are a low annual number of nesting females and associated hatchling production in Komodo National Park. Hence, a continuation of more extensive nesting surveys could provide a cost-effective and accurate way to gather important long-term demographic information for this species. Kami mempelajari tren tahunan dan karakteristik aktivitas betina bersarang serta produksi anakan biawak Komodo (Varanus komodoensis) di Taman Nasional Komodo, Indonesia antara tahun 2002 dan 2006. Selama periode tersebut, kami mencatat sejumlah 12, 16, 15, 13, dan 6 betina bersarang setiap tahun di 42 lokasi sarang potensial. Rata-rata jarak periode bersarang betina diperkirakan 1.260.4 tahun. Hal ini disebabkan karena sebagian besar betina berkembang biak setiap tahun sementara betina lainnya berkembang biak setiap dua tahun sekali. Beberapa betina menggunakan kembali lokasi sarang yang sama berturut-turut setiap tahunnya sementara yang lain tidak. Betina yang bersarang memiliki massa tubuh yang jauh lebih rendah dibandingkan ketika tidak bersarang. Semua aktivitas bersarang dilakukan di dalam lembah tempat tinggal betina hal ini menunjukkan kecenderungan yang kuat dalam kesetiaan spasial. Komodo umumnya dianggap sebagai penghuni sarang yang soliter karena hanya terdapat satu kejadian ketika dua betina teramati bersarang di lokasi sarang yang sama. Rata-rata sejumlah 21.063.6 anakan komodo menetas dari setiap sarang setiap tahunnya. Kami memperkirakan bahwa di seluruh area penelitian,Komodo-komodo betina menghasilkan antara 129.0621.8-344.0658.16 anakan setiap tahunnya. Kami membahas signifikansi ekologis dan evolusi dari atribut-atribut tersebut. Namun, implikasi utama bagi manajemen konservasi yang dapat diambil dari studi ini adalah bahwa terdapat jumlah betina bersarang dan jumlah tetasan yang cukup rendah setiap tahunnya di Taman Nasional Komodo. Oleh karena itu, survei komodo bersarang berkelanjutan yang lebih ekstensif diharapkan dapat memberikan usaha yang hemat biaya namun akurat untuk mendapatkan informasi demografis jangka panjang yang penting untuk spesies ini. In Bahasa
... In general, the capture rate of turtle hatchlings in demographic studies is very low because typical turtle capture methods, such as trapping, are not effective with small individuals [61,62]. However, in our Isla Palma study streams, the method of capture is manual and the R. nasuta population exhibits a high percentage of hatchlings [63]-they are not missing. ...
Article
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Few long-term demographic studies have been conducted on freshwater turtles of South America, despite the need for this type of inquiry to investigate natural variation and strengthen conservation efforts for these species. In this study, we examined the variation in demography of the Chocoan River Turtle (Rhinoclemmys nasuta) based on a population from an island locality in the Colombian Pacific region between 2005 and 2017. We calculated survival, recapture, and transition probabilities, and the effects of stream substrate and El Niño–Southern Oscillation (ENSO) phases (El Niño, Neutral, La Niña) on these variables using a multi-state model. We found differences in survival probabilities between ENSO phases, likely as a consequence of an increase in flood events. In addition, we found support for survival being greater in muddy streams than rocky streams, possibly because it is easier to escape or hide in mud substrates. Recapture probabilities varied by life stages; differences in the probability of recapture between size classes were associated with the high fidelity to territories by adults. The present increases in frequency and severity of El Niño and La Niña may exacerbate the consequences of climatic regimes on natural populations of turtles by increasing the mortality caused by drastic phenomena such as floods.
... Adults were found to be DATA FROM RESCUE CENTERS AND ANIMAL SANCTUARIES IN GREECE 20 more affected in a study of stranded loggerhead turtles by Komnenou et al. (2018), where 65.7% were adults and 34.3% were juveniles, although in cases of depressed turtles (25% of all cases) 52.6% of these were juveniles. Survival rates in juvenile reptiles are estimated to be higher in species with larger offspring, and higher in reptiles who give birth compared to egg laying species (Pike et al. 2008). ...
Technical Report
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To date, the welfare of wild animals living outside direct human control remains gravely understudied. This is at odds with the interest in studying the welfare of domesticated animals, despite the two groups having a similar capacity to experience poor welfare. While it is sometimes considered difficult to study, some of the factors affecting the welfare of wild animals are accessible to examination — in fact, they have often been researched because they are relevant to commonly studied issues such as the behavior or mortality of animals in the wild. Although the primary focus of such studies is not the welfare of the animals, the studies provide information that can help inform policies and programs designed for the sake of the animals themselves. The majority of studies that have investigated wild animal suffering have largely focused on anthropogenic harms, while little attention has been given to natural harms such as illness and accidents. This paper aims to identify some of the factors negatively affecting the welfare of animals in the wild by looking at the data compiled by wild animal sanctuaries and rescue centers in Greece, particularly with respect to natural harms. The types of animals admitted to these centers and the most commonly reported reasons for admission are analyzed and we discuss how accurately this data may represent wild animal suffering as a whole. This study also examines how natural factors may be an underlying cause of other reasons for admission, such as sick or starving animals being more prone to anthropogenic threats like car accidents. The possible effects of sex, age, and seasonality on wild animal injuries and mortalities are also discussed, and limitations of the current research are identified. The paper concludes with suggestions for future research regarding animal suffering in the wild.
... Interestingly, our estimate of first year survival (S h ) is very similar to the capture-recapture estimate of juvenile survival (S j ) ( Table 1). Additionally, the CRC estimate of juvenile survival may be low because of the low detectability and sample size of young individuals (Doak et al., 1994;Hailey, 2000;Tuberville et al., 2008;Pike et al., 2008), because recapture probabilities of juveniles were not modeled separately, or because some juveniles may also lose the marks when growing carapace. However, beside of methodological differences, our approach may also overestimate juvenile survival because observed juvenile population sizes stay more or less equal from age 2 to age 4 (Fig. A2, Appendix 2). ...
Article
Survival is a key parameter in species' management and conservation. Most methods for estimating survival require time series data, large sample sizes and, overall, costly monitoring efforts. Inverse modeling approaches can be less data hungry, however they are underused in conservation sciences. Here we present an inverse modeling approach for estimating relative survival rates of long-lived species that is mathematically straightforward and evaluate its performance under constraints common in conservation studies related to small sample sizes. Specifically, we (i) estimated the relative survival rates in a Testudo graeca population based on one-year monitoring, (ii) assessed the impact of sample size on the accuracy, and (iii) tested alternative hypotheses on the impact of fire on the survival rates. We then compared the results of our approach with capture-recapture (CRC) estimates based on long-term monitoring. Our approach (153 individuals within a single year) yielded estimates of survival rates overlapping those of CRC estimates (11 years of data and 1009 individuals) for adults and subadults, but not for juveniles. Simulation experiments showed that our method provides robust estimates if sample size is above 100 individuals. The best models describing the impact of fire on survival identified by our approach predicts a decrease in survival especially in hatchlings and juvenile individuals, similar to CRC estimates. Our work proves that inverse modeling can decrease the cost for estimating demographic rates, especially for long-lived species and as such, its use should be encouraged in conservation and management sciences.
... frogs and lizards) occurs within days after their natal ecdysis. Repeated success in securing prey in early life stages typically results in rapid growth in many snake taxa, which probably promotes survival and fitness [53][54][55]. The present study was limited to a single viviparous species that exhibits caudal luring, yet we anticipate the same type of tail movements we documented in late-term fetal copperheads will be present in egg-laying (oviparous) taxa that exhibit caudal luring, particularly in pitvipers (e.g. ...
Article
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With the advent of powerful imaging instruments, the prenatal behaviour of vertebrates has been discovered to be far more complex than previously believed, especially concerning humans, other mammals and birds. Surprisingly, the fetal behaviour of squamate reptiles (lizards, snakes and amphisbaenians), a group of over 11 000 extant species, are largely understudied. Using ultrasonography, 18 late-term pregnant copperhead snakes (Agkistrodon contortrix)from a single population were inspected for fecundity (number offetuses). Unexpectedly, during the ultrasound procedurethat involved 97 fetuses, we observed sinusoidal tail movements in 11 individuals from eight different copperhead mothers. These movements were indistinguishable from caudal luring, a mimetic ambush predatory strategy which is exhibited by newborn copperheads and other snakes. Caudal luring is initiated shortly after birth and is employed to attract susceptible vertebrate prey. Using the same ultrasound equipment and methods, we tested for this behaviour in two species of rattlesnakes (genus Crotalus) not known to caudal lure and none of the late-term fetuses showed any type of tail movements. Prenatal movements in humans and other vertebrates are known to be important for musculoskeletal and sensorimotor development. The fetal behaviours we describe for copperheads, and possibly other snakes, maybe similarly important and influence early survival and subsequent fitness.
... year, and complementary approaches to studying the demography of these snakes. For reptiles, early life stages are notoriously difficult to capture and recapture (Pike et al., 2008). Estimating survival rates for small, young snakes could require integrating fecundity data along with CMR into an integrated population model (Schaub & Abadi, 2011). ...
Article
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Estimates of demographic rates for animal populations and individuals have many applications for ecological and conservation research. In many animals, survival is size-dependent, but estimating the form of the size-survival relationship presents challenges. For elusive species with low recapture rates, individuals' size will be unknown at many points in time. Integrating growth and capture-mark-recapture models in a Bayesian framework empowers researchers to impute missing size data, with uncertainty, and include size as a covariate of survival, capture probability, and presence on-site. If there is no theoretical expectation for the shape of the size-survival relationship, spline functions can allow for fitting flexible, data-driven estimates. We use long-term capture-mark-recapture data from the endangered San Francisco gartersnake (Thamnophis sirtalis tetrataenia) to fit an integrated growth-survival model. Growth models showed that females reach longer asymptotic lengths than males and that the magnitude of sexual size dimorphism differed among populations. The capture probability and availability of San Francisco gartersnakes for capture increased with snout-vent length. The survival rate of female snakes exhibits a nonlinear relationship with snout-vent length (SVL), with survival flat between 300 mm and 550 mm SVL before decreasing for females between 550 mm and 700 mm SVL. For male snakes, survival decreased for adult males >550 mm SVL. The survival rates of the smallest and largest San Francisco gartersnakes were highly uncertain because recapture rates were very low for these sizes. By integrating growth and survival models and using penalized splines, we found support for size-dependent survival in San Francisco gartersnakes. Our results have applications for devising management activities for this endangered subspecies, and our methods could be applied broadly to the study of size-dependent demography among animals.
... Amiel & Shine, 2012;Elnitsky & Claussen, 2006). The average hatchling survival rate in this study (approximately 20%) was similar to that of other lizard species, reported to be approximately 30% on average from 46 populations of 20 lizard species (see details in Pike et al., 2008). Therefore, in contrast to higher survival rates observed in laboratory husbandry experiments, the survival rates in the mesocosm ecologically reflect the survival of lizards in the field (Pearson & Warner, 2018;Pruett & Warner, 2021). ...
Article
1. Warming temperatures caused by climate change are predicted to vary temporally and spatially. For mid‐ and high‐latitude reptiles, the seasonal variation in warming temperatures experienced by embryos and hatchlings may determine offspring fitness, yet this has remained largely unexplored. 2. To evaluate the independent and interactive influence of seasonal variation in warming temperatures on embryonic and hatchling development, we incubated eggs and reared hatchlings of a cold‐climate oviparous ectothermic species, the Heilongjiang grass lizard (Takydromus amurensis), following a 2 × 2 factorial design (present climate vs. warming climate for embryos × present climate vs. warming climate for hatchlings). We then evaluated embryonic and hatchling development, including hatching success, incubation period, initial hatchling body size, hatchling metabolic rate, growth rate, and survival in the mesocosms. 3. We found that warming temperatures shortened the incubation period and produced hatchlings with higher survival rates than those incubated under the present climate conditions. Similarly, hatchlings reared under a warming climate had similar growth rates and resting metabolic rates, but higher survival rates than those reared under the present climate. Hatchlings that experienced both warming incubation and warming growth conditions had the highest survival rates. 4. This study revealed that moderate warming temperatures (Representative Concentration Pathway, RCP 4.5, 1.1–2.6 °C) experienced by embryos and hatchlings interact to benefit hatchling fitness in cold‐climate oviparous ectotherms. Our study also highlighted the importance of integrating seasonal variation in warming temperatures when evaluating the responses to climate warming in multiple developmental stages in oviparous ectotherms.
... heat stress and food availability). We made that decision based on the relatively high survival rates in juvenile reptiles (close to those of conspecific adults) (Pike et al. 2008), and also the challenge of quantitatively linking stress to survival rates. Including offspring death in the model may lower (or even cancel out) the magnitude of the predicted increases in OEB under climate warming, and therefore, reduce the advantage for oviparous species at some sites. ...
Article
Squamate reptiles exhibit two reproductive modes: oviparity and viviparity. Existing large‐scale studies suggest that viviparous species are more vulnerable to climate warming based on viviparous species occupying relatively colder environments, which are predicted to decline in availability under climate warming. However, oviparous and viviparous squamates are geographically widespread and their distributions often overlap. Are oviparous or viviparous squamates more vulnerable to climate warming when they inhabit similar thermal environments? We used Sceloporus lizards in North America as a model system to predict the impact of climate warming on oviparous and viviparous species in sympatric zones. We used mechanistic models to quantify the changes in maternal energy balance (MEB) and offspring energy balance (OEB) under a climate warming scenario. We then projected the fitness impacts of future climate warming based on estimates of MEB and OEB. Under a climate warming scenario (RCP8.5), oviparous females are predicted to increase reproductive frequency more than viviparous females, which restricts time for postpartum energy accumulation before the end of the season and decreases MEB. Under climate warming, OEB of oviparous species increased more than viviparous species, but the increases were less geographically widespread. Interestingly, the developmental success and OEB of oviparous species are predicted to decline at some sites under climate warming, which is not predicted to happen for viviparous species. Our results highlight that oviparous species will respond more variably to climate warming than viviparous species. More specifically, oviparous species in hot areas with high temperature variation may be especially vulnerable under climate warming compared to sympatric viviparous species.
... Tortoise populations may not necessarily require large juvenile components because adults can reproduce over many years, but authors reporting populations with 5-56% juveniles (Judd and Rose 1983, Meek 1985, McMaster and Downs 2006 cautioned that their percentages were probably underestimates because small tortoises might have been overlooked (Pike et al. 2008). In contrast, we are confident that our estimate that 5% of the study population was juveniles was accurate because of our frequent and thorough inspections of virtually all available retreats at the core site. ...
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Inconspicuous, secretive, or sparsely distributed species receive relatively little research attention, potentially leading to uncertainty about their status and lack of efforts to conserve them. Karoo dwarf tortoises (Chersobius boulengeri) are endemic to South Africa, spend most of the time in retreats at remote arid locations, and are seldom seen. We conducted a 3‐year (2018–2020) mark‐recapture study to investigate the size and structure of the only Karoo dwarf tortoise population currently known to exist. The population in the 16‐ha core of our study site consisted primarily of adult males and females, at a density of 3.3 individuals/ha. Many individuals had severely worn shells and appeared old. Small individuals (straight carapace length <65 mm) represented just 8% of the population and were mostly recent hatchlings. Overall, tortoises had high estimated survival rates (0.77–0.95; lower 95% confidence limit for the smallest tortoises was 0.16), despite a 15‐month drought. The lack of small individuals may reflect low levels of recruitment and population decline. Predation by corvids was an obvious threat to all size classes. We estimated that the local population across the 250‐ha study area was 800–900 males and females, and recommend precautionary conservation measures focused on reducing human‐subsidized avian predation. In South Africa, the only Karoo dwarf tortoise population currently known to exist comprised mostly adults, many of which appeared old, whereas juveniles were almost absent. To improve recruitment into adult stages and counter projected population decline, removal of potential nesting sites, food and water sources that are attractions for predatory corvids is recommended.
... By assuming a specified population growth rate (ideally grounded in other data), such a model can be used to solve for the survival rate of the missing early-juvenile stage. For example, Pike et al. (2008) used this approach to correct previous underestimates of the juvenile survival rates of numerous reptile species. ...
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Wild animals experience different challenges and opportunities as they mature, and this variety of experiences can lead to different levels of welfare characterizing the day-to-day lives of individuals of different ages. At the same time, most wild animals who are born do not survive to adulthood. Individuals who die as juveniles do not simply experience a homogeneous fraction of the lifetimes of older members of their species; rather, their truncated lives may be characterized by very different levels of welfare. Here, I propose the concept of welfare expectancy as a framework for quantifying wild animal welfare at a population level, given individual-level data on average welfare with respect to age. This concept fits conveniently alongside methods of analysis already used in population ecology, such as demographic sensitivity analysis, and is applicable to evaluating the welfare consequences of human interventions and natural pressures that disproportionately affect individuals of different ages. In order to understand better and improve the state of wild animal welfare, more attention should be directed towards young animals and the particular challenges they face.
... Small mammals such as Sciurid rodents also have been implicated with depredating juveniles [11][12][13]. Juvenile turtles have lower estimated survival than adults [14], likely in part due to increased vulnerability to predators resulting from smaller body sizes and incomplete hardening of the shell [15]. Their primary anti-predator strategy appears to entail habitat selection facilitating concealment such as burrowing in substrate or seeking cover (e.g., under woody structure, leaf litter, or dense vegetation) [16]. ...
Article
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Although it is widely accepted that juvenile turtles experience high levels of predation, such events are rarely observed, providing limited evidence regarding predator identities and how juvenile habitat selection and availability of sensory cues to predators affects predation risk. We placed three‐dimensional printed models resembling juvenile box turtles (Terrapene carolina) across habitats commonly utilized by the species at three sites within their geographical range and monitored models with motion‐triggered cameras. To explore how the presence or absence of visual and olfactory cues affected predator interactions with models, we employed a factorial design where models were either exposed or concealed and either did or did not have juvenile box turtle scent applied on them. Predators interacted with 18% of models during field trials. Nearly all interactions were by mesopredators (57%) and rodents (37%). Mesopredators were more likely to attack models than rodents; most (76%) attacks occurred by raccoons (Procyon lotor). Interactions by mesopredators were more likely to occur in wetlands than edges, and greater in edges than grasslands. Mesopredators were less likely to interact with models as surrounding vegetation height increased. Rodents were more likely to interact with models that were closer to woody structure and interacted with exposed models more than concealed ones, but model exposure had no effect on interactions by mesopredators. Scent treatment appeared to have no influence on interactions by either predator group. Our results suggest raccoons can pose high predation risk for juvenile turtles (although rodents could also be important predators) and habitat features at multiple spatial scales affect predator‐specific predation risk. Factors affecting predation risk for juveniles are important to consider in management actions such as habitat alteration, translocation, or predator control.
... Proposed advantages of viviparity include increased protection from predation (Goodwin et al., 2002;Pike et al., 2008;Wourms & Lombardi, 1992) and protection from adverse environmental conditions (Ma et al., 2018;Pincheira-Donoso et al., 2017;Shine, 2004). ...
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It is of fundamental importance for the field of evolutionary biology to understand when and why major evolutionary transitions occur. Live‐bearing young (viviparity) is a major evolutionary change and has evolved from egg‐laying (oviparity) independently in many vertebrate lineages and most abundantly in lizards and snakes. While contemporary viviparous squamate species generally occupy cold climatic regions across the globe, it is not known whether viviparity evolved as a response to cold‐climate in the first place. Here, we used available published time‐calibrated squamate phylogenies and parity data on 3498 taxa. We compared the accumulation of transitions from oviparity to viviparity relative to background diversification and a simulated binary trait. Extracting the date of each transition in the phylogenies and informed by 65 my of global palaeoclimatic data, we tested the nonexclusive hypotheses that viviparity evolved under: i) cold, and ii) long‐term stable climatic conditions, and iii) with background diversification rate. We show that stable and long‐lasting cold climatic conditions are correlated with the transitions to viviparity across squamates. This correlation of parity mode and palaeoclimate is mirrored by background diversification in squamates, and simulations of a binary trait also showed a similar association with palaeoclimate, meaning that trait evolution cannot be separated from squamate lineage diversification. We suggest that these trait transitions depend on environmental and intrinsic effects, and that background diversification rate may be a factor in trait diversification more generally.
... In more recent years, there has been an increased threat of nest and hatchling predation by both Burmese pythons (Python bivittatus) and Argentine black and white tegus (Tupinambis merianae) as they have encroached on crocodile nesting sites [70]. Initially hatchling crocodiles, like young of other reptiles, exhibit high mortality rates and low survival [71]. Our estimated 25% annual survival rate for South Florida was within previous estimates from Key Largo, FL (7-43% [29]), and used in simulations [72], but is much higher than previously reported in Florida Bay (10% [73]), in ENP (estimated 10-25% [74]), at Turkey Point (9% [21], and 16% [53]), and in Panama (5% [75]). ...
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The federally threatened American crocodile ( Crocodylus acutus ) is a flagship species and ecological indicator of hydrologic restoration in the Florida Everglades. We conducted a long-term capture-recapture study on the South Florida population of American crocodiles from 1978 to 2015 to evaluate the effects of restoration efforts to more historic hydrologic conditions. The study produced 10,040 crocodile capture events of 9,865 individuals and more than 90% of captures were of hatchlings. Body condition and growth rates of crocodiles were highly age-structured with younger crocodiles presenting with the poorest body condition and highest growth rates. Mean crocodile body condition in this study was 2.14±0.35 SD across the South Florida population. Crocodiles exposed to hypersaline conditions (> 40 psu) during the dry season maintained lower body condition scores and reduced growth rate by 13% after one year, by 24% after five years, and by 29% after ten years. Estimated hatchling survival for the South Florida population was 25% increasing with ontogeny and reaching near 90% survival at year six. Hatchling survival was 34% in NE Florida Bay relative to a 69% hatchling survival at Crocodile Lake National Wildlife Refuge and 53% in Flamingo area of Everglades National Park. Hypersaline conditions negatively affected survival, growth and body condition and was most pronounced in NE Florida Bay, where the hydrologic conditions have been most disturbed. The American crocodile, a long-lived animal, with relatively slow growth rate provides an excellent model system to measure the effects of altered hydropatterns in the Everglades landscape. These results illustrate the need for continued long-term monitoring to assess system-wide restoration outcomes and inform resource managers.
... In all taxa, the most frequent age after adults were juveniles, a stage where the animals tend to disperse in search of a territory to settle [22]. The age of admission is also usually associated with the season; Orphanhood is more frequent during spring and summer [12]. ...
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Background: Human activities are permanently threatening wildlife. Wildlife Rescue and Rehabilitation Centers (WRRC) have served for the rescue, rehabilitation and reinsertion of affected and recovered animals. Methods: We reviewed the casuistry of five wildlife rescue and rehabilitation centers in Chile over 5 years, and described the main causes of admission, most affected taxonomic groups and final outcomes of the admitted individuals, shedding light into general patterns and relevant factors currently affecting wildlife in Chile. To understand the current work and status of WRRC system in Chile, we also conducted a qualitative survey to WRRC personnel and Agricultural and Livestock Service (SAG) regional offices regarding their operation. Results: A total of 3418 cases of animals admitted to WRRC were obtained; 95.3% corresponded to native species. Of native animal cases, 86.0% corresponded to birds, 12.3% were mammals and 1.7% reptiles. Trauma was the most frequently observed cause of admission in all three native fauna groups (35.8% in birds, 23.2% in mammals, 27.8% in reptiles). Conclusions: WRRC are a tool for conservation and education of wild animal species in Chile, however WRRC and SAG regional office personnel highlighted several deficiencies in the current system and suggested opportunities for improvement. The current WRRC system needs modernization and financial support from the Chilean state to fulfil their relevant mission.
... Adult chelonians' high survivorship has been attributed to agerelated increases in size, thermal and hydric homeostasis, mobility, and shell hardness (Wilson 1991;Haskell et al. 1996;Wilson et al. 2001;Nagy et al. 2011). Though the most obvious difference in survival rates in chelonians is seen when comparing adults and juveniles (Pike et al. 2008), size differences across the range of juvenile life stages presumably also lead to differential survival within this age class (Haegen et al. 2009;Nagy et al. 2015b;Arsovski et al. 2018). ...
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Captive rearing conservation programs focus primarily on maximizing post-release survival. Survival increases with size in a variety of taxa, often leading to the use of enhanced size as a means to minimize post-release losses. Head-starting is a specific captive rearing approach used to accelerate growth in captivity prior to release in the wild. We explored the effect of size at release, among other potential factors, on post-release survival in head-started Mojave desert tortoises Gopherus agassizii . Juvenile tortoises were reared for different durations of captivity (2–7 y) and under varying husbandry protocols, resulting in a wide range of juvenile sizes (68–145 mm midline carapace length) at release. We released all animals ( n = 78) in the Mojave National Preserve, California, United States, on 25 September 2018. Release size and surface activity were the only significant predictors of fate during the first year post-release. Larger head-starts had higher predicted survival rates when compared to smaller individuals. This trend was also observed in animals of the same age but reared under different protocols, suggesting that accelerating the growth of head-started tortoises may increase efficiency of head-starting programs without decreasing post-release success. Excluding five missing animals, released head-starts had 82.2% survival in their first year post-release (September 2018–September 2019), with all mortalities resulting from predation. No animals with >90 mm midline carapace length were predated by ravens. Our findings suggest the utility of head-starting may be substantially improved by incorporating indoor rearing to accelerate growth. Target release size for head-started chelonians will vary among head-start programs based on release site conditions and project-specific constraints.
... 169, 176-177). We estimated the annual survival probability of juvenile stage as 13% less than the annual survival probability of adult stage [62]. Due to lack of available nest / hatchling survival data the annual survival probability of egg stage for all turtle species was set at 0.2 [30, 31, 33]. ...
Article
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Background: Conservation strategies are urgently needed for tropical turtles that are increasingly threatened by unsustainable exploitation. Studies conducted exclusively in temperate zones have revealed that typical turtle life history traits (including delayed sexual maturity and high adult survivorship) make sustainable harvest programs an unviable strategy for turtle conservation. However, most turtles are tropical in distribution and the tropics have higher, more constant and more extended ambient temperature regimes that, in general, are more favorable for population growth. Methods: To estimate the capacity of temperate and tropical turtles to sustain harvest, we synthesized life-history traits from 165 predominantly freshwater turtle species in 12 families (Carettochelydae, Chelidae, Chelydridae, Dermatemydidae, Emydidae, Geoemydidae, Kinosternidae, Pelomedusidae, Platysternidae, Podocnemididae, Staurotypidae and Trionychidae). The influence of climate variables and latitude on turtle life-history traits (clutch size, clutch frequency, age at sexual maturity, and annual adult survival) were examined using Generalized Additive Models. The biological feasibility of sustainable harvest in temperate and tropical species was evaluated using a sensitivity analysis of population growth rates obtained from stage-structured matrix population models. Results: Turtles at low latitudes (tropical zones) exhibit smaller clutch sizes, higher clutch frequency, and earlier age at sexual maturity than those at high latitudes (temperate zones). Adult survival increased weakly with latitude and declined significantly with increasing bioclimatic temperature (mean temperature of warmest quarter). A modeling synthesis of these data indicates that the interplay of life-history traits does not create higher harvest opportunity in adults of tropical species. Yet, we found potential for sustainable exploitation of eggs in tropical species. Conclusions: Sustainable harvest as a conservation strategy for tropical turtles appears to be as biologically problematic as in temperature zones and likely only possible if the focus is on limited harvest of eggs. Further studies are urgently needed to understand how the predicted population surplus in early life stages can be most effectively incorporated into conservation programs for tropical turtles.
Article
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Obtaining robust survival estimates is critical, but sample size limitations often result in imprecise estimates or the failure to obtain estimates for population subgroups. Concurrently, data are often recorded on incidental reencounters of marked individuals, but these incidental data are often unused in survival analyses. We evaluated the utility of supplementing a traditional survival dataset with incidental data on marked individuals that were collected ad hoc. We used a continuous time‐to‐event exponential survival model to leverage the matching information contained in both datasets and assessed differences in survival among adult and juvenile and resident and translocated Mojave desert tortoises (Gopherus agassizii). Incorporation of the incidental mark‐encounter data improved precision of all annual survival point estimates, with a 3.4%–37.5% reduction in the spread of the 95% Bayesian credible intervals. We were able to estimate annual survival for three subgroup combinations that were previously inestimable. Point estimates between the radiotelemetry and combined datasets were within |0.029| percentage points of each other, suggesting minimal to no bias induced by the incidental data. Annual survival rates were high (>0.89) for resident adult and juvenile tortoises in both study sites and for translocated adults in the southern site. Annual survival rates for translocated juveniles at both sites and translocated adults in the northern site were between 0.73 and 0.76. At both sites, translocated adults and juveniles had significantly lower survival than resident adults. High mortality in the northern site was driven primarily by a single pulse in mortalities. Using exponential survival models to leverage matching information across traditional survival studies and incidental data on marked individuals may serve as a useful tool to improve the precision and estimability of survival rates. This can improve the efficacy of understanding basic population ecology and population monitoring for imperiled species. Survival estimation using radio‐telemetry datasets is often hampered by small sample size. We found that combining incidental sighting data on marked individuals with radio‐telemetry data improved survival estimation by reducing the spread of 95% credible intervals in all cases with minimal and inconsistent effects on point estimates. In three of eight sub‐groups, survival estimates were only obtainable after inclusion of the incidental encounter data.
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Background Conservation strategies are urgently needed for tropical turtles. Studies conducted exclusively in the temperate zone have revealed that the suite of life history traits that characterizes turtles and includes delayed sexual maturity and high adult survivorship makes sustainable harvest programs an unviable strategy for turtle conservation. However, most turtles are tropical in distribution and the tropics have higher, more constant and more extended ambient temperature regimes that, in general, are more favorable for population growth. Methods To estimate the capacity of freshwater turtle species from temperate and tropical regions to sustain harvest we synthesized life history traits from 165 freshwater turtle species in 12 families (Carettochelydae, Chelidae, Chelydridae, Dermatemydidae, Emydidae, Geoemydidae, Kinosternidae, Pelomedusidae, Platysternidae, Podocnemididae, Staurotypidae and Trionychidae). The influence of climate variables and latitude on freshwater turtle life history traits (clutch size, clutch frequency, age at sexual maturity, and annual adult survival) were examined using Generalized Additive Models. The biological feasibility of sustainable harvest in temperate and tropical species was evaluated using a sensitivity analysis of population growth rates obtained from stage structured matrix population models. Results Turtles at low latitudes (tropical zones) exhibit smaller clutch sizes, higher clutch frequency, and earlier age at sexual maturity than those at high latitudes (temperate zone). Adult survival increased weakly with latitude and declined significantly with increasing bioclimatic temperature (mean temperature of warmest quarter). A modeling synthesis of these data indicates that the interplay of life history traits does not create higher harvest opportunity in adults of tropical species. Yet we found potential for sustainable exploitation of eggs in tropical species. Conclusions Sustainable harvest as a conservation strategy for tropical turtles appears to be as biologically problematic as in temperature zones and likely only possible if the focus is on limited harvest of eggs. Further studies are urgently needed to understand how the predicted population surplus in early life stages can be most effectively incorporated into conservation programs for tropical turtles increasingly threatened by unsustainable exploitation, climate change and deforestation.
Article
Demographic models provide insight into which vital rates and life stages contribute most to population growth. Integral projection models (IPMs) offer flexibility in matching model structure to a species’ demography. For many rare species, data are lacking for key vital rates, and uncertainty might dissuade researchers from attempting to build a demographic model. We present work that highlights how the implications of uncertainties and unknowns can be explored by building and analyzing alternative models. We constructed IPMs for the threatened giant gartersnake (Thamnophis gigas) based on published studies to determine where management efforts could be targeted to have the greatest effect on population persistence and what unknowns remain for future research. Given uncertainty in the survival of snakes during their first year, and in the form of the size‐survival relationship, we modeled a range of scenarios and evaluated where models agree about factors influencing population growth and where discrepancies exist. For most scenarios, the survival of large adult females had the greatest influence on population growth, but the relative importance of juvenile versus adult somatic growth for population growth was dependent on the recruitment probability and the shape of the size‐survival function. More data on temporal variation and covariance among vital rates would improve stochastic models for the giant gartersnake. This paper demonstrates the effectiveness of IPMs for studying the demography of reptiles and the value of the model‐building process for formalizing what is known and unknown about the demography of rare species. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. Demographic models with continuous size–vital rate functions are well‐suited to the life history of gartersnakes and many other reptiles. The growth of threatened giant gartersnake populations is most influenced by the survival of large adult females, and the survival of snakes during their first year is a key unknown for projecting population viability.
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Detailed information on life history and ecology is essential for successful conservation and management. However, we have relatively little detailed data on the life history and ecology of most small lizard species, relative to other vertebrates, especially those that have undergone recent taxonomic changes. We studied the ecology of the elegant snake-eyed skink (Cryptoblepharus pulcher), a lizard that occurs on trees, fences, walls, and rock outcroppings in eastern Australia that spans temperate to tropical environments. In our temperate-zone study population living in natural habitat, individuals are active year-round, and gravid females were found during the months of September through December. Sexual maturity is reached in 12 months, lifespan is at least three years, and clutch size is typically two eggs. In laboratory incubation experiments, larger eggs were more likely to hatch. Low incubation temperatures (averaging 23 ± 7.5°C versus high temperatures averaging 26 ± 7.5°C) increased incubation duration significantly (range 56–72 days versus 40–51 days) and reduced the body size of hatchlings significantly (17.8 mm versus 18.7 mm snout–vent length). Skinks sheltered beneath small rocks that were not shared simultaneously with predatory snakes, and that reached average temperatures that were up to 3°C warmer during the day than unused rocks. Preferred microhabitats include substrates of rock or soil, and the largest rocks were occasionally shared by up to four individuals of all body size/sex combinations (5.8% of observations were shared, 30.2% of individual rocks were shared). Our study expands upon knowledge of the widespread genus Cryptoblepharus by providing detailed life history and ecological information on C. pulcher that can serve as a baseline for future studies.
Article
Reliable and unbiased information is needed for informing management decisions relevant to all animal life stages. Radiomarking is commonly used for adult birds, but this approach is more challenging for galliform chicks. Following preliminary experimentation of multiple attachment methods, we selected 2 radiotransmitter attachment techniques, gluing and suturing, to test on 11‐day‐old northern bobwhite (Colinus virginianus; hereafter, bobwhite) chicks in an outdoor aviary environment during 1 May 2013 through 30 Sep 2016. In addition, we field‐tested a novel, modified‐suture technique on 11‐ and 12‐day‐old wild bobwhite chicks. We found that suturing was a superior method of transmitter attachment. Glue‐on attachment of transmitters performed poorly with average retention rates <7 days. The probability of retaining a radiotransmitter for the duration of our 8‐week study was 0.76 (±0.08 SE), 0.89 (±0.09 SE), and 0.00 for normal suture, our modified suture, and glue‐on techniques, respectively. Development and growth of suture‐ and patagial‐tagged bobwhite chicks (average mass gain of 41.95 g ± 2.79 SE) was unimpeded compared with a control (patagial‐tagged only, no transmitter) group of birds (average mass gain: 40.89 g ± 2.91 SE). We observed similar tag‐retention rates (0.906 ± 0.07 SE) of transmitters affixed to wild bobwhite chicks in the field using a modified‐suture technique compared with the aviary study. Our modifications to the traditional suture methods include changing the placement of the transmitter to reduce snag rate in vegetation, using a smaller gauge syringe needle to reduce skin‐tearing, applying a surgeon's knot for increased knot‐security and reduced knot slippage while suturing, and applying insta‐set spray to rapidly dry superglue to reduce handling time of chicks. The modified‐suture technique provides improvements in tag‐retention, facilitates shorter handling time of birds in the field, and provides an effective means for tagging and tracking individuals to collect ecological data and demographic vital rates on bobwhite chicks and other birds. Future studies should investigate potential sublethal effects that suture tags may impose on individuals to identify and account for estimable biases of vital rates. © 2020 The Wildlife Society. Limited data exist on game birds with precocial young because of the difficulty of capturing and tagging small, rapidly growing chicks with miniature tracking devices. The modified suture technique we have developed provides a technique for quickly and reliably affixing miniature radiotags to bobwhite chicks, affording a new window of opportunity into their ecology.
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Multiple hypotheses have been proposed to explain the variation of dorsal patterns observed in snakes, but no studies yet have tested them over broad taxonomic and geographical scales. The Viperidae offer a powerful model group to test eco-evolutionary processes that lead to disruptive and cryptic ornaments. We developed a database reporting dorsal ornamentation, ecological habitus, habitat features and climatic parameters for 257 out of 341 recognized species. Three patterns of dorsal ornamentation were considered: “zig-zag”, “blotchy” and “uniform” patterns. Phylogenetic comparative analyses were based on 11 mitochondrial and nuclear genes. Forty-eight species presented a zig-zag pattern type, 224 a blotchy pattern type and 32 a uniform pattern type. All the patterns showed a strong phylogenetic signal. Character phylogenetic reconstruction analyses suggested an ancestral state for blotchy ornamentation, with multiple independent evolutions of the other patterns. The blotchy pattern was more frequent in terrestrial species living in warm climates and sandy habitats, supporting the hypothesis of a disruptive function. The zig-zag pattern evolved independently in several isolated taxa, particularly in species living in cold climates and in dense vegetation or water-related habitats, supporting the hypothesis of disruptive and aposematic functions. Uniform coloration was particularly frequent in arboreal species, supporting the hypothesis of a cryptic function.
Article
Blanding's Turtles (International Union for Conservation of Nature [IUCN] Endangered) are long-lived reptiles with delayed sexual maturity. Anthropogenic landscape changes have increased threats to juvenile turtles, resulting in unnaturally low recruitment. Head-starting has become a popular conservation strategy that aims to increase juvenile recruitment by avoiding the increased predation of the vulnerable nest and hatchling age class. However, there is still debate about whether or not it is an effective management tool. Assessments of head-starting are becoming more prevalent, but long-term studies are needed to critically evaluate the success of such interventions. In particular, information is needed on how head-starts fare compared to wild-hatched turtles. The Lake County Forest Preserve District (LCFPD) in northeastern Illinois initiated a long-term capturemarkrecapture project in 2004. As of 2018, 127 wild-hatched juvenile turtles had been captured (59 of which had been captured in multiple years) and 148 adult turtles had been captured (116 of which had been recaptured in multiple years). Since 2010, LCFPD has released 491 headstarted turtles during the year following hatching, 138 of which have been recaptured during successive years. We used von Bertalanffy growth analysis to compare growth trajectories and Cormack-Jolly-Seber modeling techniques to compare survival rates of wild-hatched and head-started turtles. At release, head-started turtles were about the size of two-year-old wild-hatched turtles and grew in parallel to their wild-hatched counterparts. The top-ranked survival models demonstrated that survival increased with age for both wild-hatched (7198%) and head-started turtles (6390%), with overlapping confidence intervals. These results suggest that head-started juveniles perform similarly to like-aged wild-hatched juveniles despite head-starts having attained greater body size. We estimated adult survival to be 95% with an environmental variance of 0.0011 and stable or positive population growth (k). Although the success of head-starting cannot be fully assessed until turtles are recruited into the adult population and successfully reproduce, patterns of head-start growth and survival provide positive intermediate measures of success. Our estimation of juvenile and adult survival, along with other demographic information from this population, will provide for more accurate population projections that will aid in evaluating conservation strategies for this population and potentially for Blanding's Turtles elsewhere.
Article
Conservation biologists need to effectively monitor species given resource limitations and the inherent challenges of assessing long‐term demographic processes. We assessed gopher tortoise (Gopherus polyphemus) abundance at a landscape scale and at the scale of 3 local populations within the Conecuh National Forest (CNF), Alabama, USA, between 1991 and 2017. We collected landscape‐level data from line transect distance sampling arranged uniformly across the CNF during a single season (2011); we obtained data for local populations from long‐term mark‐recapture of individuals at 3 sites selected based on prior knowledge of high density at each. At a landscape scale, we estimated 5,242 (95% CI = 3,538–7,768) tortoises occurred across the approximately 34,000‐ha forest, yielding a density of 0.14–0.32 tortoises/ha. These low densities across the landscape suggest that, on average, management activities across the property have not allowed tortoise populations to retain the social structure needed for long‐term persistence. The 3 local populations, however, contained 25–60 individuals and densities of 1.9–6.9 tortoises/ha. Over the study period, populations at 2 sites were stable and the third experienced significant population growth. Mean annual survival of individuals was 0.89 and invariant across size classes. Overall, line transect distance sampling is important for assessing landscape‐scale abundance of tortoises but may fail to detect local clusters of high‐density sites important for population persistence. Our mark‐recapture efforts at the local scale revealed that small populations on these high‐density sites can exhibit long‐term stability or growth even though they do not meet current established criteria for viability. Improved models that incorporate immigration and emigration and better reflect the dynamics of peripheral populations would assist in determining how such populations best contribute to species recovery and regional conservation targets. © 2020 The Wildlife Society. We studied gopher tortoise population demographics over 25 years and compared estimates of density and abundance using 2 separate methods. Resulting conservation implications were highly variable; landscape density estimates revealed a nonviable population density, whereas local population estimates revealed dense viable gopher tortoise populations.
Article
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Community-based conservation and resource management (CBCRM) programs often incorporate the dual goals of poverty alleviation and conservation. However, robust assessments of CBCRM program outcomes are relatively scarce. This study uses a multidisciplinary, systems approach to assess the ecological and social dimensions of success of an internationally acclaimed CBCRM program. This program, located in one of the largest protected areas in the Peruvian Amazon (Pacaya-Samiria National Reserve), strives for the sustainable harvest and trade of a turtle species (Podocnemis unifilis). We used mixed methods analysis, including interviews and population viability modeling, to understand three elements: how local perceptions of changes in the managed population compare to changes inferred by ecological analyses, the indicators stakeholders use to measure success, and the barriers to long-term program success and social–ecological system sustainability. We find that stakeholders perceive a growth trend in the managed turtle population, but this perception may diverge from our ecological understanding of the system under current management. Population viability analyses with a 1:1 sex ratio suggested population size will decline under two of three management scenarios (different degrees of harvest). Yet this and similar studies are plagued by a lack of species- and site-specific population parameters that could improve understanding of the system. Significant vulnerabilities exist for system sustainability, notably the recent decrease in foreign demand for the traded resource. Identifying a sustainable species-specific harvest rate, developing locally-grounded ecological and social indicators, and focusing on data-driven adaptive management will facilitate the identification of key leverage points for future management interventions.
Article
Species differ widely in their strategies of resource allocation to offspring mass and number, ranging from teleost fishes and amphibians that produce many tiny offspring to reptiles and mammals that produce relatively few large offspring. Tradeoffs between offspring survivorship and fecundity are thought to limit the success of any particular reproductive strategy, but these tradeoffs have not been evaluated quantitatively across the full range of variability in offspring size and number. Here we examine the relationship of offspring size to reproductive success (i.e. fitness) within and across teleost fishes, amphibians, reptiles and mammals. To do so, we evaluate the relationships of offspring mass to survivorship (proportion of offspring surviving to maturity) and to fecundity (no. offspring/time). We show that survivorship tends to increase in proportion with relative offspring mass (offspring mass/adult mass), whereas fecundity, normalized to offspring biomass production rate, tends to decrease in proportion with offspring mass. Consequently, the product of survivorship and fecundity – reproductive success – is generally independent of offspring mass. Thus, our results show quantitatively how survivorship and fecundity tradeoff across diverse taxa to limit reproductive success.
Technical Report
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Recovery plan for Phelsuma borbonica and Phelsuma inexpectata
Article
Demographic models are useful for projecting population trends, identifying life stages, most important to population dynamics, and investigating the demographic effects of potential management scenarios. We incorporated site‐specific population parameters into stage‐based matrix models to estimate population growth and to assess potential management scenarios for five intensively sampled (>15 years) populations of federally threatened bog turtles (Glyptemys muhlenbergii) in North Carolina, USA. Only two of the five populations modeled were stable or growing under estimated vital rates. Long‐term sampling of bog turtle populations in NC suggests the declining populations in this study share several demographic characteristics with other populations in the region. Elasticity analysis revealed small changes in adult survival rates have the largest effect on population growth rate. These models also highlight that increased survival of egg and juvenile stages can sometimes buffer higher adult mortality and emigration, and reduced survival at multiple life stages can induce population‐level decline. Our results indicate that management scenarios targeting increased recruitment (especially a head‐start scenario) provide increased population growth among all populations, and allowed two of three declining populations to reach stability under current estimated vital rates. Population growth rates will be higher when population augmentation coincides with habitat restoration efforts that increase survival and site fidelity at all life stages. These models emphasize the importance of considering site‐specific dynamics when evaluating conservation interventions for an imperiled long‐lived species. We incorporated site‐specific population parameters into stage‐based matrix models to estimate population growth and to assess potential management scenarios for five intensively‐sampled populations of bog turtles (Glyptemys muhlenbergii) in North Carolina, USA. Only two of the five populations modeled were stable or growing under estimated vital rates. These models highlight that increased survival of the egg and juvenile stages can sometimes buffer higher adult mortality and emigration, and reduced survival at multiple life‐stages can induce population level decline.
Article
Wildlife translocations have the potential to assist conservation efforts by mitigating mortality caused by site‐specific human activities. Despite the potential, the effectiveness of snake translocations for conservation purposes is not yet clear. Eastern diamondback rattlesnakes (Crotalus adamanteus, EDB) have limited ability to adapt to habitat loss and fragmentation due to the species' slow life history, high habitat specificity, and minimal dispersal ability. We translocated a cohort of EDBs to investigate the potential of using translocations as a conservation tool for this species. In July 2018, we translocated 12 adult eastern diamondback rattlesnakes from Parris Island Marine Corps Recruit Depot to an inland wildlife management area. We used radio‐telemetry data to examine the effects of translocation on home‐range size and average daily movement. We used known‐fate survival models to examine adult survival post‐translocation. Post‐translocation home ranges were larger than the pre‐translocation home ranges and EDBs moved more, on average, per day post‐translocation. We failed to detect an effect of translocation on 2‐year survival probability. We suspect that large post‐translocation home ranges and average daily movements reflected the need to find suitable ambush and hibernacula sites and differences between coastal and inland habitats. More research is needed to determine the long‐term viability of translocated rattlesnake populations. Our results suggest that translocations may be a viable conservation and mitigation strategy for eastern diamondback rattlesnakes. Translocation of eastern diamondback rattlesnakes did not affect 2‐year survival probability but did cause greater home‐range size and average daily movement. Our results suggest that translocations may be a viable conservation and mitigation strategy for large viperids, but habitat characteristics of both the donor and release sites should be taken into consideration. Mean average daily movement (m) for translocated and non‐translocated (control) eastern diamondback rattlesnakes (Crotalus adamanteus) during 2018 and 2019 in Jasper County, SC, USA. Error bars show standard error and the letters designate significance at α = 0.05 based on the differences of the least square means from the 2‐way, repeated measures ANOVA.
Preprint
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Law enforcement is widely regarded as a cornerstone to effective natural resource management. Practical guidelines for the optimal use of enforcement measures are lacking particularly in areas protected under sustainable and/or mixed use management regimes and where legal institution are weak. Focusing on the yellow-spotted river turtles ( Podocnemis unifilis ) along 33 km of river that runs between two sustainable–use reserves in the Brazilian Amazon as an illustrative example, we show that two years of patrols to enforce lawful protection regulations had no effect on nest harvesting. In contrast, during one year when community-based management approaches were enacted harvest levels dropped nearly threefold to a rate (26%) that is likely sufficient for river turtle population recovery. Our findings support previous studies that show how community participation, if appropriately implemented, can facilitate effective natural resource management where law enforcement is limited or ineffective.
Article
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The relationship between the spatial distribution of turtle nest sites and nest predation was investigated in a landscape encompassing a 12-ha freshwater wetland in west-central South Carolina, USA. The goals of the study were to determine if nest predation is a function of nest density, and if two other spatial factors, habitat type and distance of nests from the wetland, influence survival rate. Gravid females of three turtle species (Kinosternon subrubrum, Pseudemys concinna floridana, and Trachemys scripta) inhabiting the wetland were monitored from the time they exited the wetland to nest until they returned from their nesting forays. A total of 145 nests were located during three nesting seasons (1992-1994). Nests were monitored from the day of oviposition until they were deemed to have successfully produced hatchlings or depredation was documented. The three-year mean predation rate was 84.2% (80%, 88%, and 81% for 1992, 1993 and 1994, respectively). Modeling of the point pattern of nest locations suggests that nests were distributed at varying densities and that density changed with habitat type and distance to the wetland. Logistic regressions of predation rates against two crowding indices demonstrate no significant evidence for density-dependent nest predation. Furthermore, autologistic regression provided no evidence indicating that nest survival is dependent on the survivorship of neighboring nests. Logistic regressions of predation rates against habitat type and distance from the marsh of origin suggest that predation rate is not a function of these two spatial characteristics. In summary, no evidence was found that linked predation rate to any of the spatial characteristics of nest distribution that were examined. The lack of density dependent nest predation is contrary to findings from some previous avian and chelonian studies, but supports the findings of other researchers. It is suggested that predation during the current study was either density independent or that any local density effects were masked by an ideal free distribution of turtle nests. Our data support the findings of several researchers that suggest density, as a single factor, is not a generalizable predictor of nest predation probability.
Article
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Using field data on fecundity, age at first reproduction and adult life expectancy, we reconsider the so-called r-K gradient by analyzing relationships between these three demographic parameters in 80 mammal species and 114 bird species. After the allometric effect of adult body weight is removed, the three variables remain correlated. The existence of demographic tactics which are independent of adult body weight is demonstrated by multivariate analyses of these variables. These analyses confirm the importance of ecological and phylogenetic constraints. The main structure is a time-scale gradient ranking species according to turn-over, both in birds and mammals. A second gradient ranking species according to iteroparity level appears significantly both in birds and mammals. In mammals, this pattern is related to patterns of parental investment.
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A mark-recapture study of a population of painted turtles, Chrysemys picta, started by O. J. Sexton between 1953 and 1957 was continued between 1968 and 1973. Life tables are constructed and a demographic history of the population is suggested. Males mature during their 4th yr and first breed at age five. Females mature at age seven and lay two clutches of about 6 to 7 eggs each year. Mortality is about 92% between laying and the arrival of the hatchlings at the pond. Juvenile and adult mortality is at a constant exponential rate of about 0.15 for males and 0.18 for females each year. Raccoons, Procyon lotor, are an important predator during spring migrations. There is no indication of senescence; females over 30 yr old are still reproductive. Between 1954 and 1972 the population's size has been reduced from an estimated 981 to about 186 animals. This has been accompanied by a decrease in mean generation time from 12.35 to 10.70 yr. Survivorship from laying to arrival at the pond has more than doubled, but adult survivorship has decreased. These changes are attributed to an increased predation rate resulting from a reduction in the number of safe basking sites. A hypothetical population was simulated by recurrent use of a population projection matrix, derived from the 1954 life table, to demonstrate the stability characteristics of this long-lived, iteroparous species. The evolution of this life history is interpreted as an adaptation to a highly uncertain probability of nest success and an effective predator defense in the adult stage.
Article
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Most turtle species suffer high mortality in their first year, have a long juvenile period, and can live for decades once they reach adulthood. Conservationists have implemented a number of recovery plans for threatened turtle populations, including experimental ''headstart'' programs. Headstarting involves the captive rearing of hatchlings from eggs collected in the wild. The hatchlings are held for several months to help them avoid high mortality in their first year. It is hoped that these turtles survive and grow like wild turtles after release. The purpose of our study was to evaluate headstarting as a management tool for threatened turtle populations. We critically examined the population-level effects of headstarting with a series of deterministic matrix models for yellow mud turtles (Kinosternon flavescens), a ''non-threatened,'' well-studied species, and endangered Kemp's ridley sea turtles (Lepidochelys kempi). We show that management efforts focused exclusively on improving survival in the first year of life are unlikely to be effective for long-lived species such as turtles. Population projections for both turtles predict that headstarting can augment increasing populations when adult survival is returned to or maintained at high levels, provided that headstarted juveniles are as vigorous as wild turtles. However, when subadult and adult survival is reduced, headstarting cannot compensate for losses in later stages. Proportional sensitivity (elasticity) analyses of stage-based matrix models indicated that annual survival rates for subadult and adult turtles are most critical; small decreases in the survival of older turtles can quickly overcome any potential benefits of headstarting. In general, the biological benefits of headstarting programs may be overestimated for turtles, and a careful examination of stage-specific mortality sources, demography, and life history can guide us toward more effective management strategies.
Article
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Nesting ecology and reproduction of painted turtles (Chrysemys picta) in southeast Michigan were intensively studied from 1975 to 1978. The average clutch size of Michigan painted turtles was 7.55, with body size accounting for only 9-13% of the variance. Data on nesting frequency indicate that from 30 to 50% of the females possibly do not reproduce every year and that approx. =6% reproduce twice in a given year. Predation within 48 h of egg-laying is responsible for the failure of 20% of the nests. An additional 12% nest failure is due to various other causes. These data substantially alter the life table previously reported in this population of painted turtles.
Article
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We present evidence of an opportunity to measure the strength of natural selection on body size through size-specific winter mortality of freshwater turtles. Data were collected from three overwintering sites along the Missouri River floodplain in central Missouri. Carcasses and live captures of four species indicated that mortality was nonrandomly distributed among species and may be explained by differences in overwintering behaviors. Analyses of mean body size within age classes for two species demonstrated standardized selection differentials ranging from 0.23–0.98 (standard deviation units) against small-sized (juvenile) individuals. Our study provides evidence of winterkill as a selective force on body size and of a possible adaptive mechanism for Bergmann's Rule.
Article
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A study of Blanding's turtles conducted during 27 of the last 37 years provided demographic data sufficient to examine how life-history characteristics may constrain population responses of long-lived organisms. Eight independent estimates of annual adult survivorship exceeded 93%. Nest survival was variable and ranged from 0.0 to 63% annually, with a mean of 44% from 1976 to 1984 and 3.3% from 1985 to 1991. Recruitment of juveniles and adults was sufficient to replace individuals estimated to have died during the study. A life table for the population resulted in a cohort generation time of 37 years and required a 72% annual survivorship of juveniles between 1 and 13 years of age to maintain a stable population. Population stability was most sensitive to changes in adult or juvenile survival and less sensitive to changes in age at sexual maturity, nest survival, or fecundity. The results from the present study indicate that life-history traits of long-lived organisms consist of co-evolved traits that result in severe constraints on the ability of populations to respond to chronic disturbances. Successful management and conservation programs for long-lived organisms will be those that recognize that protection of all life stages is necessary. Programs such as headstarting or protection only of nesting sites, in the absence of programs to reduce mortality of older juveniles and adults, appear to be less than adequate to save long-lived organisms such as sea turtles and some tortoises. The concept of sustainable harvest of already-reduced populations of long-lived organisms appears to be an oxymoron.
Article
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Clutch size declines with advancing laying date in many birds. This relationship is thought to represent a reaction norm of individual optimization in response to local environmental conditions. This implies that: (1) individuals should vary in the properties of their clutch size-laying date trends; (2) these differences should be reflected in their fitness; and (3) parts of this variation should be heritable. Here, we show that 44 Ural owl females of known lifespan, with a statistically sufficient number (greater than or equal to5) of clutch size-laying date observations each, differed individually both in the slope and the elevation of their clutch size-laying date relationships. As an estimate of individual fitness, we used the lifetime production of fledglings, which is a known correlate of recruitment in this population. Females with a higher elevation had a higher lifetime reproductive success. However, plasticity - that is, the slope of the clutch size-laying date relationship - did not have app
Article
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MARK provides parameter estimates from marked animals when they are re-encountered at a later time as dead recoveries, or live recaptures or re-sightings. The time intervals between re-encounters do not have to be equal. More than one attribute group of animals can be modelled. The basic input to MARK is the encounter history for each animal. MARK can also estimate the size of closed populations. Parameters can be constrained to be the same across re-encounter occasions, or by age, or group, using the parameter index matrix. A set of common models for initial screening of data are provided. Time effects, group effects, time x group effects and a null model of none of the above, are provided for each parameter. Besides the logit function to link the design matrix to the parameters of the model, other link functions include the log—log, complimentary log—log, sine, log, and identity. The estimates of model parameters are computed via numerical maximum likelihood techniques. The number of parameters that are estimable in the model are determined numerically and used to compute the quasi-likelihood AIC value for the model. Both the input data, and outputs for various models that the user has built, are stored in the Results database which contains a complete description of the model building process. It is viewed and manipulated in a Results Browser window. Summaries available from this window include viewing and printing model output, deviance residuals from the model, likelihood ratio and analysis of deviance between models, and adjustments for over dispersion. Models can also be retrieved and modified to create additional models. These capabilities are implemented in a Microsoft Windows 95 interface. The online help system has been developed to provide all necessary program documentation.
Article
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In long-lived birds, pre-breeders are often difficult or impossible to observe, and even though a proportion of marked adults may be of known age, the estimation of age-specific survival is complicated by the absence of observations during the first years of life. New developments in MARK now allow use of an updated individual covariate. We used this powerful approach to model age-dependence in survival of Black-legged Kittiwakes (Rissa tridactyla) at a North Sea colony. Although only 69 marked breeders were of known age, there was strong evidence for a quadratic relationship between true age and survival. We believe that this simple but powerful approach could be implemented for many species and could provide improved estimates of how survival changes with age, a central theme in life history theory.
Article
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Squamate reptiles (snakes, lizards, and amphisbaenians) serve as model systems for evolutionary studies of a variety of morphological and behavioral traits, and phylogeny is crucial to many generalizations derived from such studies. Specifically, the traditional dichotomy between Iguania (anoles, iguanas, chameleons, etc.) and Scleroglossa (skinks, geckos, snakes, etc.) has been correlated with major evolutionary shifts within Squamata. We present a molecular phylogenetic study of 69 squamate species using approximately 4600 (2876 parsimony-informative) base pairs (bp) of DNA sequence data from the nuclear genes RAG-1(approximately 2750 bp) and c-mos(approximately 360 bp) and the mitochondrial ND2 region (approximately 1500 bp), sampling all major clades and most major subclades. Under our hypothesis, species previously placed in Iguania, Anguimorpha, and almost all recognized squamate families form strongly supported monophyletic groups. However, species previously placed in Scleroglossa, Varanoidea, and several other higher taxa do not form monophyletic groups. Iguania, the traditional sister group of Scleroglossa, is actually highly nested within Scleroglossa. This unconventional rooting does not seem to be due to long-branch attraction, base composition biases among taxa, or convergence caused by similar selective forces acting on nonsister taxa. Studies of functional tongue morphology and feeding mode have contrasted the similar states found in Sphenodon(the nearest outgroup to squamates) and Iguania with those of Scleroglossa, but our findings suggest that similar states in Sphenodonand Iguania result from homoplasy. Snakes, amphisbaenians, and dibamid lizards, limbless forms whose phylogenetic positions historically have been impossible to place with confidence, are not grouped together and appear to have evolved this condition independently. Amphisbaenians are the sister group of lacertids, and dibamid lizards diverged early in squamate evolutionary history. Snakes are grouped with iguanians, lacertiforms, and anguimorphs, but are not nested within anguimorphs.
Article
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Squamate reptiles number approximately 8000 living species and are a major component of the world's terrestrial vertebrate diversity. However, the established relationships of the higher-level groups have been questioned in recent molecular analyses. Here we expand the molecular data to include DNA sequences, totaling 6192 base pairs (bp), from nine nuclear protein-coding genes (C-mos, RAG1, RAG2, R35, HOXA13, JUN, alpha-enolase, amelogenin and MAFB) for 19 taxa representing all major lineages. Our phylogenetic analyses yield a largely resolved phylogeny that challenges previous morphological analyses and requires a new classification. The limbless dibamids are the most basal squamates. Of the remaining taxa (Bifurcata), the gekkonids form a basal lineage. The Unidentata, squamates that are neither dibamids nor gekkonids, are divided into the Scinciformata (scincids, xantusiids, and cordylids) and the Episquamata (remaining taxa). Episquamata includes Laterata (Teiformata, Lacertiformata, and Amphisbaenia, with the latter two joined in Lacertibaenia) and Toxicofera (iguanians, anguimorphs and snakes). Our results reject several previous hypotheses that identified either the varanids, or a burrowing lineage such as amphisbaenians or dibamids, as the closest relative of snakes. Our study also rejects the monophyly of both Scleroglossa and Autarchoglossa, because Iguania, a species-rich lineage (ca. 1440 sp.), is in a highly nested position rather than being basal among Squamata. Thus iguanians should not be viewed as representing a primitive state of squamate evolution but rather a specialized and successful clade combining lingual prehension, dependence on visual cues, and ambush foraging mode, and which feeds mainly on prey avoided by other squamates. Molecular time estimates show that the Triassic and Jurassic (from 250 to 150 Myr) were important times for squamate evolution and diversification.
Article
In the E.S. George Reserve, SE Michigan, younger and smaller snapping turtle and painted turtle were more likely than older and larger juveniles to be captured in shallow portions of the marsh. A relationship of increased water depth with turtle size and age continued through to sexual maturity. By restricting their activity to shallow water near shore, younger and smaller turtles may increase their foraging success and reduce the probability of encountering large fish or adult turtle predators. -from Authors
Article
Population ecology, requires reliable population samples. We assessed sampling reliability, for black rat snakes (Elaphe obsoleta) using 1724 captures obtained by two different methods: trapping at communal hibernacula and opportunistic capture of snakes at large. Recapture intervals indicated that opportunistic captures were biased by size (larger snakes were over-represented) but not by sex. Furthermore, opportunistic captures of snakes seen on roads (while observers were driving) had a stronger size bias than other opportunistic captures. Trapping at hibernacula sampled the respective hibernacula populations reliably, but the hibernacula populations themselves were not representative samples of the local population. Among 13 hibernacula, sex ratios ranged from 31-65% females and age structure from 42-86% sexually mature individuals. Because rat snakes can take many years before they join communal hibernacula, young snakes were under-represented in all hibernacula samples. We found highly significant differences in the size and sex composition of our samples from the Ontario population and from samples from a population in Maryland (from published data). Those differences seem more likely to be a consequence of biases associated with how snakes were sampled at each location than a reflection of real population differences. We recommend that future sampling of rat snakes include opportunistic sampling of snakes at large combined with sampling at several hibernacula. Also, researchers sampling snakes should assess biases in their samples, because biases that are not recognized will be more problematic than those of which researchers are aware.
Article
A 5-yr field study examined the ways in which prey abundance can influence the reproductive rates of predators. Water pythons (Liasis fuscus) on the Adelaide River floodplain in tropical Australia prey almost exclusively on dusky rats (Rattus colletti). Rat numbers varied dramatically among years of the study. Feeding rates of pythons were highest when rats were abundant, and the snakes were in good condition (mass relative to body length) at these times. The proportion of adult female pythons that reproduced in a given year was also tightly linked to rat abundances. However, reproductive output per litter (offspring size, and fecundity relative to maternal body size) was unaffected by prey availability, perhaps because of high fecundity-independent costs of reproduction. Instead, female pythons reproducing in ''good'' years were in better condition after oviposition. These data support an energy-limitation model for snake reproduction, whereby prey availability determines predator reproductive output, but the relationship between the two variables is complex. The degree to which prey availability influences feeding rates of pythons and the degree to which feeding rates influence body condition depend crucially on snake body size (due to size-related shifts in foraging abilities and metabolic costs). Thus, a given prey abundance translates into different energy reserves for different-sized predators. Also, females delay reproduction until they can gain enough energy for a large clutch of eggs, and reproductive output per litter does not then increase with additional energy availability. Such nonlinearities in predator responses to prey availability may be widespread.
Article
Neonatal reptiles are here defined as an age class of young eureptilian amniotes (excluding birds) that express attributes most influenced by the pre-paritive development environment (oviduct, egg, and egg nest) and by the demands of parition and first dispersal. Neonatal character states are typically transformed, reduced, or eliminated during the first 10% of their pre-reproductive development. Traditionally, neonates have not been distinguished from juvenile reptiles. As a result the neonatology of reptiles has rarely been addressed in past literature. Recent studies reveal a complex array of developmental scenarios involving character state transformations, heterochrony, unique character states in morphology, behavior, physiology, nutrition, dispersion and health. Unique morphological features (such as egg teeth) and limited skeletal ossification characterize many neonates. Distinguishing behaviors include "reversal" movements, utilization of bright color patterns, and startling movements with both serving as anti-predation mechanisms. Prolonged association with protective parents, group migration, unique agonistic behavior, and tendencies toward rapid dispersion characterize the neonates of individual species. Neonatal physiological attributes include: a special availability to inoculation by symbiont fermenting anaerobes in herbivores, rapid conforming responses to their external environments in thermal and hydric exchanges, and in the case of some turtles, extraordinary capacities for supercooling (8.9 C). Post-paritive lecithotrophy (nutrition from residual yolk) sustain both the overwintering of nestlings and the dispersion of non-feeding young for as long as several months. Resistance to infections (such as mycoplasmas) from their maternal parents, combine with nutritive reserves of residual yolk and a common tendency for rapid dispersion to make neonates attractive candidates for augmentation and translocation programs. Coupled with the practical advantages of maintaining and manipulating small animals in a laboratory environment, these qualities distinguish neonates as particularly useful models for experimentally evaluating the relative apportionment of reproductive resources into greater numbers of offspring or into improved quality/survivorship of individual offspring.
Article
I investigated diamondback terrapin (Malaclemys terrapin Schoepff) in 1973 and 1974 in a sand dune colony at Brigantine National Wildlife Refuge, New Jersey, to study the factors determining hatching success. Nesting occurs from early June through mid-July, and nests were observed until early October when the fate of all nests was known. Eighty-four percent (n = 32) of the nests had eggs hatch in 1973, but only 25% (n = 200) had eggs hatch in 1974. Nests that were not successful were preyed upon by fox, raccoon, gull and crow. Fox and raccoon predation occurred at night throughout the developmental period, whereas gulls and crows were only successful at the time of egg laying. Mammalian predation was highest in the protected dune areas surrounded by trees and shrubs, and avian predation was highest in the open sand areas nearer the cove. The rate of predation is highest during the egg-laying and hatching period. Forty-five percent of the nests having hatchlings were preyed upon in this 4 - 10 day period. Early nests, initiated from 1 - 29 June, had a lower predation rate (58%) than those initiated in July (80%). I estimated 1546 nests in the study area by comparing predation rates on known nests with those previously undetected nests preyed upon in the area. The developmental period for eggs was 61 - 104 days. Within individual nests, eggs hatched in 1 - 4 days. This spread was positively correlated with the number of eggs and nest depth. Individual hatchlings emerged 1 - 9 days (x̄= 2.5) after hatching. Emergence ranged from 1 - 11 days in an individual nest. Early emergence after hatching reduces the individual's chance of predation while in the nest.
Article
A natural population of painted turtles [Chrysemys picta (Schneider)] was studied in University Bay of Lake Mendota, Dane County, Wisconsin, from September 1960 to October 1962. Five methods were used to capture turtles for marking, measurement, and release. Each of the methods yielded a different size-class distribution and a sex ratio which, in four out of five cases, was significantly different from that of the total population estimate. Baited hoop nets yielded predominantly males and relatively few juveniles; basking traps tended to yield higher percentages of females than did nets, and large turtles were an important component of the sample. Hand capture resulted in a sample heavily weighted by juveniles and a 1 : 1 sex ratio for adults. The influence of trapping method in the estimation of population structure in turtles must not be overlooked. This study indicates that even within a species, trapping method introduces considerable bias in the estimation of sex ratio and size-class distribution.
Article
The population structure and survivorship were determined for the painted turtle, Chrysemys picta, in a southwestern Michigan marsh. More than 1000 turtles were marked and released during the study. Age of older individuals was estimated on the basis of age-length relationships. Slightly more than half of the population was estimated to be comprised of immature individuals. The adult sex ratio was not significantly different from 1: 1. The survivorship curve for the study population is a combination of Slobodkin's Types IV and III, with egg mortality being close to 100%, juvenile mortality being close to 0, and adult mortality being constant and independent of age. Contrary to popular belief, juvenile Chrysemys recruited into the population have an extremely high survival rate and will usually live to reach maturity.
Article
What are supertrees and what is all the fuss about?
Article
Limited evidence in the literature suggests that the assumption of equal catchability in mark-recapture studies of turtles may be invalid. These papers suggest that turtles may alter their behavior to avoid recapture following initial handling. If turtles are less likely to be recaptured following initial capture and handling, then population models estimating demographic characteristics and population sizes from mark-recapture data may be invalid (e.g., overestimating population size). Because conservation and management decisions are largely based on population sizes and trends, it is essential to investigate whether marking animals has any effect on behavior. We tested the effects of handling and permanently marking gopher tortoises (Gopherus polyphemus) at the Kennedy Space Center, Florida from 20-22 July 2003 to determine if short-term activity and recapture rates were affected. We used two distinct groups of tortoises: one group was handled (captured, measured, marked) and the other was not handled, but was marked with paint from a distance of 2.2 m. Although the behavior of handled and non-handled animals was distinct, we found no differences in recapture rates or time to recapture between the groups. We suggest that handled gopher tortoises are as likely to be recaptured as tortoises that have not been handled, although more subtle or long-term effects cannot be ruled out.
Article
Population size is a major determinant of extinction risk. However, controversy remains as to how large populations need to be to ensure persistence. It is generally believed that minimum viable population sizes (MVPs) would be highly specific, depending on the environmental and life history characteristics of the species. We used population viability analysis to estimate MVPs for 102 species. We define a minimum viable population size as one with a 99% probability of persistence for 40 generations. The models are comprehensive and include age-structure, catastrophes, demographic stochasticity, environmental stochasticity, and inbreeding depression. The mean and median estimates of MVP were 7316 and 5816 adults, respectively. This is slightly larger than, but in general agreement with, previous estimates of MVP. MVPs did not differ significantly among major taxa, or with latitude or trophic level, but were negatively correlated with population growth rate and positively correlated with the length of the study used to parameterize the model. A doubling of study duration increased the estimated MVP by approximately 67%. The increase in extinction risk is associated with greater temporal variation in population size for models built from longer data sets. Short-term studies consistently underestimate the true variances for demographic parameters in populations. Thus, the lack of long-term studies for endangered species leads to widespread underestimation of extinction risk. The results of our simulations suggest that conservation programs, for wild populations, need to be designed to conserve habitat capable of supporting approximately 7000 adult vertebrates in order to ensure long-term persistence.
Article
Comparative studies of the relationship between 2 phenotypes, or between a phenotype and an environment, are frequently carried out by invalid statistical methods. Most regression, correlation, and contingency table methods, including nonparametric methods, assume that the points are drawn independently from a common distribution. When species are taken from a branching phylogeny, they are manifestly nonindependent. Use of a statistical method that assumes independence will cause overstatement of the significance in hypothesis tests. Some illustrative examples of these phenomena are given, and limitations of previous proposals of ways to correct for the nonindependence discussed. A method of correcting for the phylogeny is proposed. It requires that we know both the tree topology and the branch lengths, and that we be willing to allow the characters to be modeled by Brownian motion on a linear scale. Given these conditions, the phylogeny specifies a set of contrasts among species, contrasts that are statistically independent and can be used in regression or correlation studies. -from Author
Article
A sample of 261 Ctenotus taeniolatus revealed that this species of skink is principally insectivorous, the most common foods being lepidopteran and coleopteran larvae, orthopterans and formicids. The occurrence of these foods in the diet followed seasonal patterns. The prey of adults and juveniles did not differ qualitatively, although adults were capable of eating a greater diversity of prey sizes than juveniles. Lizards used both sit-and-wait and active foraging strategies, with adults and juveniles exhibiting these behaviours in different ratios.
Book
From Darwin onward, it has been second nature for evolutionary biologists to think comparatively because comparisons establish the generality of evolutionary phenomena. Do large genomes slow down development? What lifestyles select for large brains? Are extinction rates related to body size? These are all questions for the comparative method, and this book is about how such questions can be answered. The first chapter elaborates on suitable questions for the comparative approach and shows how it complements other approaches to problem-solving in evolution. The second chapter identifies the biological causes of similarity among closely related species for almost any observed character. The third chapter discusses methods for reconstructing phylogenetic trees and ancestral character states. The fourth chapter sets out to develop statistical tests that will determine whether different characters that exist in discrete states show evidence for correlated evolution. Chapter 5 turns to comparative analyses of continuously varying characters. Chapter 6 looks at allometry to exemplify the themes and methods discussed earlier, while the last chapter looks to future development of the comparative approach in both molecular and organismic biology. Japanese translation (1997) The Comparative Method in Evolutionary Biology. Hokkaido University Press in cooperation with Oxford University Press.
Article
We discuss and clarify several aspects of applying Felsenstein's (1985, Am. Nat. 125: 1–15) procedures to test for correlated evolution of continuous traits. This is one of several available comparative methods that maps data for phenotypic traits onto an existing phylogenetic tree (derived from independent information). Application of Felsenstein's method does not require an entirely dichotomous topology. It also does not require an assumption of gradual, clocklike character evolution, as might be modeled by Brownian motion. Almost any available information can be used to estimate branch lengths (e.g., genetic distances, divergence times estimated from the fossil record or from molecular clocks, numbers of character changes from a cladistic analysis). However, the adequacy for statistical purposes of any proposed branch lengths must be verified empirically for each phytogeny and for each character. We suggest a simple way of doing this, based on graphical analysis of plots of standardized independent contrasts versus their standard deviations (i.e., the square roots of the sums of their branch lengths). In some cases, the branch lengths and/or the values of traits being studied will require transformation. An example involving the scaling of mammalian home range area is presented. Once ad