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Wild animals and natural habitats are rapidly being lost because of overpopulation and global climate change. Here I recount some of my own charmed life, including adventures and experiences, and I present some preliminary new data on gender differences in 80 lizard species from 14 different families. In most of these species of desert lizards, females are larger than males but males have relatively larger heads than females. Today's lizard ecologists face impediments and a difficult future in which species and habitats are in short supply. I plan to provide access to my own data as a legacy for frustrated future lizard ecologists. These data are described here and online at A Desert Lizard Data Book for the 21st Century ( http://www.zo.utexas.edu/faculty/pianka/Proposal.html).
A comprehensive view of population declines and their underlying causes is necessary to reverse species loss. Historically, in many cases, a narrow view may have allowed species declines to continue, virtually undetected, for long periods of time (perhaps even decades). We suggest that extinction debt is likely responsible for numerous (perhaps most) amphibian declines and that this perspective should be incorporated into the structure of amphibian research and management. Extinction debt, originally proposed to explain changes in species richness following environmental disturbance, also may refer to the proportion of populations of an individual species that is expected to eventually be lost because of habitat change. A conservation framework to address extinction debt focuses research on threats at the individual, population, and metapopulation levels. This approach will help enhance, restore, and protect specific processes and habitats at the proper scale by directing management to the most vulnerable level and stage of a species. We illustrate this approach using Flatwoods Salamanders, Ambystoma cingulatum and Ambystoma bishopi, which occurred historically throughout the Coastal Plain of the southeastern United States but have experienced a greater than 85% loss of populations in recent years. Reversal of these losses is possible only if conservation and recovery efforts encompass individual, population, and metapopulation levels. We illustrate our framework by outlining actions that could be taken at each of these levels to help guide conservation and management of amphibians with complex life cycles and provide options for how to prioritize conservation actions in the face of logistical and budgetary shortfalls.
Knowledge of the distribution and abundance of crocodilian nests and threats facing them is essential in calculating recruitment and determining population trends. We studied the nesting ecology of the Nile crocodiles (Crocodylus niloticus) at Ndumo Game Reserve (NGR) in northeastern KwaZulu-Natal, South Africa from 2009 to 2012. Nesting effort in NGR was comparable to other C. niloticus populations at 18–22%. Historical data suggest that high water levels completely inundate nesting sites within the reserve once every 10 yr, whereas predation destroys on average < 20% of nests annually and can be primarily attributed to water monitor lizards (Varanus niloticus). The number of crocodile nests located in NGR remained similar from 1964–2012 despite significant increase in population size. Earlier stocking programs increased the number of C. niloticus in the greater Maputo/Phongola floodplain areas, but these numbers may not be sustainable because the majority of C. niloticus nests appear to be outside of the reserve in unprotected areas.
Graptemys is one of the least studied turtle genera in North America. Graptemys oculifera (Ringed Sawback) and Graptemys pearlensis (Pearl Map Turtle) are endemic to the Pearl River system of Mississippi and southeastern Louisiana. We studied both species near Columbia, Mississippi, on the Pearl River via a trapping and basking surveys over two years. Additionally, five sites including Columbia were trapped for 27 years to determine long-term trends in capture success and relative abundance (RA). At the Columbia site, body size distribution was bimodal for G. oculifera and atypically unimodal for G. pearlensis; G. pearlensis body lengths were smaller than museum specimens. Population estimates for G. oculifera at the Columbia site indicate a stable population over 25 years. Long-term RA trends indicated that G. pearlensis was less common than G. oculifera in all periods and at all sites from 1988 to 2013. Trends in long-term capture success for G. oculifera and G. pearlensis were negative at all sites, with significant declines at three sites for both G. oculifera and G. pearlensis. Declines occurred both upstream and downstream of a major reservoir. Therefore, a combination of factors (including altered hydrology, human disturbance, lack of recruitment, excessive sedimentation, impaired water quality, and/or the pet trade) appear to be contributing to declines. Additional conservation and protection is warranted for G. pearlensis, and current protections for G. oculifera should be extended. Future studies should continue at our long-term sites to determine whether population declines persist or whether populations stabilize.
Duvaucel's Geckos (Hoplodactylus duvaucelii) are large-bodied, long-lived, and slow-breeding geckos endemic to New Zealand. Translocation is considered an important tool for conservation of this species. The first translocation of these geckos occurred in 1998 when 40 geckos were released on a pest-free island. Despite multiple survey efforts within the decade after release, captures were too sparse to determine whether the population had successfully established. We revisited the population to investigate establishment over a longer time period (11–15 yr post release). We utilized a recently developed outcome assessment framework that assesses a translocation's success as a progression through four, time-bound ‘Stages.' We recaptured 12 founder animals and all were larger than at release (Stage 1). Recruitment was evident (Stage 2) with 91.7% of all geckos captured between 2009 and 2013 being island-born. Mark–recapture results from 144 individuals estimated that 245 geckos (95% confidence interval: 179–336) were present in the population by February 2013, an approximately 6-fold increase in number since 1998 (Stage 3). Population viability analysis indicated the population has become self-sustaining, with an average population increase rate of 6.35–10.14% per year and a negligible probability of extinction within 50 yr (Stage 4). In this case, a 10–15 yr time period appeared to be a sufficient time frame for identification of translocation success by both traditional and time-bound criteria. Fulfilment of each time-bound indicator of short-term success therefore appears to have been a reliable predictor of ultimate translocation success in this long-lived, slow-breeding lizard species.
Resource protein content and toughness strongly influence food selection and can have opposite effects on energy acquisition, growth, and fitness in many organisms. Few studies have experimentally tested the interactive effects of these parameters on food selection especially in aquatic plant feeders that are thought to have a lower protein diet. We investigated food preference in a pond dwelling tadpole (Rhacophorus arboreus) when offered the choice between foods that differ in toughness and in protein content (three levels each) in a laboratory cafeteria experiment. Food protein level and food toughness significantly interacted on food choice. The amount of food removed increased with food protein level but decreased with food toughness. In line with the pattern reported in some terrestrial herbivores, food toughness exerted larger effect (almost twice) than did resource protein content on food choice. Tadpoles discriminated foods of different protein levels, but they no longer distinguished between medium and low protein foods at high toughness. Low protein-soft food was preferred as much as the high protein hard food, but whether tadpoles gained an equivalent amount of energy remains unclear. These results suggest trade-offs between protein gain, harvestibility, and digestibility may exist. Food toughness strongly influenced tadpole food choice and may be a direct consequence of the strength of their mouthpart to penetrate the food materials. Resource toughness could be a factor used as a proximate cue for determining food quality in tadpole foraging strategies.
Call surveys offer a valuable method to monitor anuran populations attributable to their temporal breeding habits and close association with water. Many temperate locations have adopted citizen science programs to monitor local anuran populations using call surveys and road transects. These surveys, however, are not commonly conducted in the tropics. I tested use of call surveys for estimating population density of a small terrestrial poison frog, Oophaga pumilio, in six different populations in Bocas del Toro, Panama. By conducting three-minute call surveys, and searching for all individual frogs in a 10 m radius of the survey point, I directly compared the number of calling males to the observed number of frogs in a given area. I found call density to be a poor predictor of population density. Despite there being differences in population densities, the lack of a relationship between the number of calls and population density highlights the limited use for call surveys for terrestrial, territorial species. Although call surveys may be useful in some taxa for general abundance estimates, this study clearly demonstrates a startling deficiency of call surveys for anuran monitoring and highlights the need for species-specific analysis to further explore the utility of this method.
Subadult Hawksbill Turtles (Eretmochelys imbricata) reside on the coral reefs of Palm Beach County, Florida, but their movements and patterns of habitat use are poorly understood. In this study, six subadult Hawksbills were tracked with global positioning system (GPS)–linked satellite telemetry for a span of 102–429 days Total home ranges and within-range areas of “core” use were measured with minimum convex polygons (MCPs) and kernel density estimates (KDEs). Home-range estimates ranged 1.1–19.0 km2 (X = 10.1 km2) using MCP and 0.01–1.2 km2 (X = 0.49 km2) using the 95% KDE. Each turtle remained at or near the 15–25 m hard-bottom reef habitats of the area and exhibited strong site fidelity to centrally located core use areas (50% and 25% KDE >,0.03 km2); this was especially true at night, suggesting the repeated use of familiar refuges (shipwrecks/caves) for nocturnal shelter. Likely driven by predator avoidance, competition for a limited number of preferred refuges, or “roosts,” may restrict the extent of each turtle's home range and influence the abundance and distribution of the Hawksbill Turtles that occupy this site.
Bog Turtles (Glyptemys muhlenbergii) are some of the most imperiled turtles in North America, and because of threats posed by habitat loss and collection for the pet trade, the species currently is listed as threatened under the U.S. Endangered Species Act. Numerous studies have investigated home ranges and movements of this species, and reported home-range sizes have varied widely. Typically, these studies were conducted at different sites and used different home-range estimators, and these factors may influence home ranges. Few studies have assessed the impact of estimator choice on home-range size for Bog Turtles or how habitat changes have affected their movements. Our study investigated home-range sizes of female Bog Turtles at two sites in Maryland, using multiple home-range estimators. Female turtles were tracked using radiotelemetry between April and August in 2013 and 2014. Home-range sizes differed significantly between study sites but did not differ significantly between years. Choice of estimator had a significant effect on home-range size; 50% kernel and 95% minimum convex polygons were similar, but 95% kernels were significantly larger than 50% kernels or 95% polygons. A study conducted at one of our two study sites over 15 years ago reported smaller home-range sizes than were found in our study, perhaps indicating that habitat has deteriorated at that site.
Eastern Indigo Snakes (EIS, Drymarchon couperi) and Eastern Diamondbacked Rattlesnakes (EDB, Crotalus adamanteus) are species of conservation concern, in large part attributable to anthropogenic landscape changes within the southeastern Coastal Plain of North America. Both species use Gopher Tortoise (Gopherus polyphemus) burrows on xeric sandhills for winter retreat sites. Protected lands play an important role in the conservation of threatened species by offering the potential to conserve potentially limiting resources such as sandhills. We surveyed 40 randomly selected xeric sandhills containing Gopher Tortoise burrows on protected lands throughout the Lower Altamaha River Watershed in southern Georgia using visual encounter surveys over three winters (November through March). We used single-season occupancy models to relate detection and occupancy rates to survey- and site-specific covariates collected at both the sandhill- and landscape-scale. Eastern Indigo Snake occupancy was positively related to the number of Gopher Tortoise burrows and the amount of surrounding sandhill habitat. In contrast, EDB occupancy was not associated with any of the covariates we considered, perhaps because EDB/EIS use a greater diversity of winter retreat sites. Detection of EIS was higher than EDB (0.40 vs. 0.22) and most influenced by air temperature, whereas EDB detection was most influenced by survey date. Our study provides previously lacking population-level detection rates and habitat associations for EIS and corroborates the previously noted importance of Gopher Tortoise burrows as overwintering retreat sites. Our study also illustrates the potential shortcomings of monitoring multiple species using survey methodologies designed for a single species.
Long-term management of American Alligator (Alligator mississippiensis) populations necessitates a more detailed understanding of the species' ecology in human-dominated areas. We conducted a 3-yr monitoring program of American Alligators on Jekyll Island, Georgia, USA, to investigate seasonal fluctuations in abundance and the abiotic and biotic (habitat) factors influencing American Alligator abundance in human-made stormwater lagoons. We conducted monthly daytime and evening spotlight surveys from April 2011 to September 2014. Spotlight counts yielded more accurate estimates of abundance. We observed American Alligators using human-made stormwater lagoons throughout the year; however, we observed significantly fewer individuals in the winter season (November–February) than in the mating (March–June) and nesting (July–October) seasons. We collected data on lagoon salinity, lagoon area, percentage of shoreline vegetation, and distance to nearest lagoon. We used the second-order Akaike Information Criterion with a correction for finite sample sizes and subsequent model averaging techniques to examine the relationship between these factors and American Alligator abundance. We found lagoon area to be the most important predictor of abundance relative to the other three independent variables. Salinity was negatively related to American Alligator abundance. Vegetation and distance to nearest lagoon were significant and positively correlated, although ranked lower in our abundance models. Elucidation of these biological trends will allow land managers to better predict when and where human–alligator encounters may occur. In addition, these data may provide developers with valuable information on how to construct stormwater lagoons to promote or discourage lagoon colonization by American Alligators.
We used removal sampling (RS) and neutral red dye capture–mark–recapture (CMR) methods to estimate capture probabilities for larval Wood Frogs (Lithobates sylvaticus), Spring Peepers (Pseudacris crucifer), and first-year Green Frogs (Lithobates clamitans) in ponds in southern New Brunswick, Canada. We modeled capture probability as a function of environmental variables and tested whether marks were retained between surveys. We also performed simulations to understand the effect of survey effort, capture probability, and abundance on detection probabilities and the number of surveys needed to be confident of absence. Capture probabilities (P ± SD) were low and variable: Wood Frogs, P = 0.262 ± 0.128; Spring Peepers, P = 0.323 ± 0.241; and first-year Green Frogs, P = 0.159 ± 0.106. With the use of AICc, we determined a model with the proportion of non-Typha emergent vegetation to have a positive effect, whereas pond depth had a negative effort on capture probabilities in first-year Green Frog larvae. No covariate models were better than an intercept-only model for Wood Frogs or Spring Peepers. Observers missed the dye mark on 5–24% of the marked larvae. Simulations showed that at observed capture probabilities and low abundances (greater than 100 larvae) all species would be detected on average with a single survey of at least 20% of the pond, but more survey effort/repeat surveys would be required to detect smaller populations. We recommend that capture probabilities be estimated whenever abundance estimates are required.
Large gaps exist in our knowledge of the ecology of stream-breeding plethodontid salamanders in the Gulf Coastal Plain. Data describing where these salamanders are likely to occur along environmental gradients, as well as their likelihood of detection, are important for the prevention and management of amphibian declines. We used presence/absence data from leaf litter bag surveys and a hierarchical Bayesian multispecies single-season occupancy model to estimate the occurrence of five species of plethodontids across reaches in headwater streams in the Gulf Coastal Plain. Average detection probabilities were high (range = 0.432–0.942) and unaffected by sampling covariates specific to the use of litter bags (i.e., bag submergence, sampling season, in-stream cover). Estimates of occurrence probabilities differed substantially between species (range = 0.092–0.703) and were influenced by the size of the upstream drainage area and by the maximum proportion of the reach that dried. The effects of these two factors were not equivalent across species. Our results demonstrate that hierarchical multispecies models successfully estimate occurrence parameters for both rare and common stream-breeding plethodontids. The resulting models clarify how species are distributed within stream networks, and they provide baseline values that will be useful in evaluating the conservation statuses of plethodontid species within lotic systems in the Gulf Coastal Plain.
Gametogenesis studies are important to understand ecological and evolutionary processes. We report the first detailed description of spermatogenesis in amphisbaenians and describe the morphology of the male germ cells of Amphisbaena silvestrii and the organization of the germinal epithelium. We sampled the testes of 25 specimens and cut 3-μm thick sections. We then stained these sections by using 1% toluidine blue and photo-documented them. Testes are covered by the tunica albuginea that sends septa between the seminiferous tubules. The interstitial tissue is highly vascularized and consists of loose connective tissue with Leydig cells. Seminiferous tubules are coiled and coated with juxtaposed myoid cells. Sertoli cells and sperm series present a digitiform or pyramidal organization. We observed eight stages of development of the spermatids and the final maturation of spermatozoa during spermiogenesis. Further, we noted significant variation in the nuclear diameters of germ cells. This trait could be used to characterize germ cell types.
Proceratophrys dibernardoi is a newly described species belonging to the Proceratophrys cristiceps group. Herein, we describe the external morphology of tadpoles of P. dibernardoi. Although external larval morphology of P. cristiceps group members is quite similar, the tadpole of P. dibernardoi may be distinguished by a combination of morphological traits, such as body shape that is elliptical in dorsal view and depressed in lateral view; a snout that is rounded in dorsal and lateral views; small, reniform nares with a small marginal rim; and a spiracle with its centripetal wall completely fused to the body wall. The oral disc is ventrally located, with lateroventral emarginations; its tooth row formula is 2(2)/3(1).
Among anuran embryonic structures, the adhesive (cement) glands appear posterolaterally to the stomodeum and produce a mucous secretion that adheres embryos to surfaces in and out of the egg. In this paper, we study the ontogeny of the adhesive glands in five species of Phyllomedusa representing the two main clades recognized in the genus, plus embryos of Agalychnis aspera and Phasmahyla cochranae. Clutches were collected in the field, and embryos were periodically fixed to obtain complete developmental series and then studied with a stereomicroscope, scanning electron microscopy and routine histological techniques. Structural variations include glands absent (in P. cochranae and Phyllomedusa boliviana), functional club-shaped glands (morphogenetic Type C in Phyllomedusa sauvagii, Phyllomedusa iheringii, and Phyllomedusa tetraploidea), and an unusual Type C-like pattern in Phyllomedusa azurea, characterized by large, oblong glands in a horseshoe-like disposition around the oral disc. This latter gland configuration is similar to that of A. aspera. Interspecific variations also include the arrangement and regression pattern of the secretory region, which are in turn different from those of Type C glands in other clades. To interpret the origin and evolution of gland developmental patterns in the group, we still need information on gland occurrence and development in the basal genera of Phyllomedusinae (Phrynomedusa and Cruziohyla) and in the basal taxa of the two major clades of Phyllomedusa.
Understanding ecophysiological/bioenergetic responses to elevated temperatures is vital to assessing future impacts on amphibian health and demographics. There is, however, a dearth of data concerning thermal influences on the energetics of larval amphibians, including measures of respiration rates which underlie other bioenergetic processes. We therefore measured respiration rates across a range of temperatures (18.3–30°C) in wild-caught larval Cope's Gray Tree Frog (Hyla chrysoscelis), a species widespread throughout the eastern and southeastern United States. Temperature and body size significantly affected respiration rates in a linear fashion. The Q10 calculated across the range of exposure temperatures was 1.72 for absolute respiration rates (mg O2/min) and 1.76 for mass-adjusted rates (mg O2/g min), suggesting less than a doubling of respiration rates over a 10°C increase in temperature. Our data, when considered with the limited data for other amphibians, suggest there are substantial species-specific differences in respiration/bioenergetics. Such ecophysiological information is vital to future considerations of amphibian energy budgets in light of the changing global climate.
Lack of food is one of the most common natural stressors that animals face, yet the physiological response to food restriction in most nonmammalian species is poorly understood. Food restriction can elicit an elevation of plasma glucocorticoid hormones and changes in blood metabolites in several vertebrates, but this has not been shown in snakes, despite their remarkable ability to tolerate food shortages. The purpose of this study was to determine the physiological response to moderate food deprivation in Common Watersnakes (Nerodia sipedon). When food was withheld for 15 d, snakes lost body mass, had elevated baseline plasma corticosterone concentrations, lower hematocrit, and depressed levels of triglycerides and uric acid. Food deprivation had no effect on blood glucose or lactate. Elevation of corticosterone levels could help snakes mobilize stored energy to allow them to survive periods of restricted feeding. Depressed triglycerides likely indicate increased utilization of lipid stores. Because uric acid is the main excretory product of protein breakdown in reptiles, the decreased uric acid we observed suggests that snakes were not utilizing their stored protein. Protein stores may be conserved during short-term food deprivation, but could be utilized during more severe food shortages. These results help illuminate the physiological and behavioral mechanisms watersnakes employ to survive food shortages and serve as useful reference values for future studies looking at longer periods of food deprivation.
We investigated diminutive day geckos (SVL < 40 mm) of the genus Cnemaspis (Cnemaspis kandiana Group) from mainland Sumatra and islands along its western margin (Nias, Siberut, Pagai, and Enggano). The assemblage includes several species based on morphological evidence, five of which we describe as new. The new species occur in the Sumatran provinces of Aceh, North Sumatra, and West Sumatra. Finally, we provide a new key and redescriptions for three previously recognized species: Cnemaspis dezwaani, Cnemaspis modiglianii, and Cnemaspis whittenorum, based on recently collected material, and clarify contradictory information concerning their original descriptions and their key under each species account.
The Liolaemid genus Phymaturus is a clade of saxicolous lizards with 44 species recognized, grouped in the Phymaturus palluma and the Phymaturus patagonicus groups. The chromosome data about this genus are extremely scarce; however, unpublished evidence suggests a great karyotypic diversity, mainly in the P. palluma group. In this work, we describe the karyotypes of six species of the P. palluma group (one of them unnamed) and report a multiple chromosome sex determination system with heterogametic males (X1X1X2X2 / X1X2Y). This sex-system represents a putative synapomorphy for the group. In accordance with the published literature and data obtained in this study, we report a wide variability for the diploid number of the P. palluma group (2N = 26 to 36) but same autosomic fundamental number in all the species of the clade (FNa = 32). Such variation is a consequence of different numbers of telocentric macroautosome pairs among karyotypes (2 to 10), suggesting chromosomal evolution of the group, driven mainly by successive Robertsonian rearrangements.
Scarlet Snakes (Cemophora coccinea) are monotypic, poorly studied, semifossorial habitat specialists from southeastern United States that traditionally include three subspecies based on color pattern and morphology. We sequenced two mitochondrial and two nuclear loci for 62 individuals from across the species range, and analyzed data with the use of parsimony and Bayesian phylogenetic methods to test a previously proposed phylogenetic hypothesis for C. coccinea. Our results suggest two Pliocene or Pleistocene refugia for Cemophora, one in southern Texas, and the other in the region extending from southeastern Louisiana through Florida. In light of our results we elevate Cemophora coccinea lineri to a full species, C. lineri, that differs from C. coccinea sensu stricto genetically and phenotypically.