Chelonian Conservation and Biology最新文献

With the exception of the savanna side-necked turtle (Podocnemis vogli) and the red-headed river turtle (Podocnemis erythrocephala), the species within the pleurodire genus Podocnemis have been relatively well-characterized in terms of their temperature-dependent sex determination (TSD) parameters. In this study, we incubated 4 nests of P. vogli (46 eggs) under controlled laboratory incubation conditions to determine whether this species also presents a TSD Ia pattern where males are produced at lower temperatures, characterize the constant temperature producing a 1:1 sex ratio (T_piv), and document the transitional range of temperatures (TRT) that produces both sexes. The incubation temperatures employed were 29°, 31°, and 33°C (± 0.15°C). Our results were consistent with the conclusion that P. vogli exhibits a TSD Ia pattern, but it was not possible to document the T_piv or the superior TRT, because the 29° and 31°C conditions produced all males and even the 33°C condition produced male-biased sex ratios, suggesting a high pivotal temperature for this species. We also documented maternal effects in initial size of the hatchlings, with the female that laid larger eggs producing hatchlings that were larger. Incubation periods of P. vogli were notably longer than those of its congeners incubated under comparable constant temperature and soil moisture conditions. In species of this genus, the TSD Ia pattern suggests that besides the threats these species face from overexploitation and habitat degradation, they also are highly vulnerable to the effects of global warming.

Burrowing organisms augment the availability of important resources for other species. The gopher tortoise (Gopherus polyphemus) is a keystone excavator in open canopy pine-forest ecosystems in the southeastern United States because its burrows are utilized by over 360 species. Across its range, the gopher tortoise is declining, which is thought to negatively affect burrow-associated species and ecosystem functionality. The nine-banded armadillo (Dasypus novemcinctus) is another burrower of similar size that has become syntopically distributed with the gopher tortoise as a result of range expansion. Recent studies have documented vertebrates utilizing armadillo burrows, linking armadillo burrowing to support of local biodiversity similar to the gopher tortoise. We sought to determine the potential for ecological redundancy between gopher tortoises and armadillos and test quantitatively for differences in associate events at their burrows in a mixed-pine–hardwood forest where they co-occur. Using motion activated game cameras to monitor burrows, we compared metrics of vertebrate occurrence between armadillo and tortoise burrows and examined the effects of environmental variables using a series of regression models. A total of 40 vertebrate taxa were observed visiting burrows between October 2019 and December 2020. Richness, diversity, and community composition were not significantly different between the two burrow types. However, associate event counts were significantly greater at tortoise burrows. Burrow and microhabitat variables had varying effects on associate event counts, with consistently positive effects for tortoise burrows, active burrows, and increased richness of tree species, while negative effects were detected for increased canopy cover as well as increased proportions of hardwood trees. Our study provides a framework for testing redundancy of function between syntopic ecosystem engineers, adds to the growing body of work on the ecological significance of armadillo range expansion, and identifies aspects of the habitat that cause fluctuations in the importance of burrows for associate species.

Effective management of a species requires that resource managers know critical aspects of its ecology, including information on home range and habitat use. We conducted the first telemetry study on the Suwannee alligator snapping turtle (Macrochelys suwanniensis), and we examined movements at an upper river (UR) site and a lower river (LR) site in the Suwannee River in Florida, USA. We estimated home range size with kernel density estimates (KDE) using the FishTracker GIS toolbox, and we examined potential differences in KDEs with Generalized Linear Models (GLMs). We also used GLMs (family = binomial) to examine habitat selection for M. suwanniensis. We used an information-theoretic approach to rank and select the most parsimonious models. Overall, our models revealed that M. suwanniensis possessed larger 90% KDEs in the LR site than the UR site, and in both sites, turtles moved into the floodplain during flooded conditions. Remarkably, these movements continued even after water levels receded and the aquatic links were severed. Interestingly, M. suwanniensis selected shallow water with some type of subsurface cover, especially large woody debris (LWD). Instream LWD is likely extremely important, especially during low water levels when undercut banks and other bank habitats are unavailable, so the removal of LWD, including deadhead logs, could negatively affect the species. Minimum flows have been established in the drainage, but river water levels have declined an estimated 40% since human settlement, partly because of groundwater withdrawal outside the drainage, potentially imperiling this state Threatened species.

Variation in sand composition at the individual beach level is an important factor for hatching success and hatchling phenotype that does not appear to have been previously investigated. We studied variation in intrabeach substrate composition in an important loggerhead turtle (Caretta caretta) nesting colony on the island of Maio, Cabo Verde, and examined its relationship with embryonic development success, hatchling phenotype, and hatchling vitality. Thirty-two nests from different females were studied under experimental conditions, controlling for beach position, depth, humidity, and temperature in a randomized block design. Two sand treatments corresponding to 2 types of sand from the same beach were used. While nesting females selected nesting sites indiscriminately between substrate types, their nests differed significantly in all variables measured for reproductive success (hatching success, hatchling size, and hatchling agility) between the 2 sand types. Therefore, the intrabeach observations of substrate phenotype of progeny found here could differentially affect offspring survival. The effects of choosing different nesting sites will generally act to spread the probability of selective pressures on embryos. Variation in reproductive success was due to differences between substrate types within the beach rather than the location of nests within the beach. The importance of determining sand types with the highest hatching success, even within the same beach, should be greatest in colonies or populations highly threatened with extinction, where the hatching success of each nest becomes of utmost importance.