Paul A. Stone

Estimating Lizard Home Range: The Rose Model Revisited

Abstract In 1982, B. Rose pointed out that home-range area could easily be underestimated unless sufficient numbers of sightings were obtained for each individual, and recommended a population-specific test to determine the minimum sample size at which home-range area can be accurately measured. This recommendation has been generally ignored. We explore how sample size affects interpretation of space use data in male lava lizards, Microlophus albemarlensis, and male eastern collared lizards Crotaphytus collaris. Using the criteria established by Rose, the minimum sample sizes for collared lizards and lava lizards were 45 and 84 sightings, respectively. These are much larger samples than we anticipated and reinforce the need for empirical determination of minimum sample size. Our data suggest that lizard movement rate is a better predictor of minimum sample size than home-range area. Collared lizard home ranges were over 10 times larger than lava lizard home ranges, yet the higher movement rates of collared lizards resulted in a minimum sample size that was about one-half that of lava lizards. Restricting data collection to any one-quarter of the total study period would have markedly underestimated home-range area and home-range overlap in both species. Every lizard of both species had a core area within their home range, suggesting the absence of major temporal shifts during the study. On average, lava lizard core areas occupied 21.7 ± 2.8% of total home-range area, yet core areas included 78.8 ± 3.1% of all lizard sightings. Collared lizard core areas averaged 25.4 ± 2.4%, with a lower percentage of collared lizard sightings occurring within core areas (66.3 ± 3.0%). There was only one incidence of core overlap in either species. Lava lizards may be defending core areas but in an unusual manner, what amounts to “sit-and-wait territoriality.” This unusual mode of space use would not be detectable from a smaller number of sightings per individual.

Cutaneous surface area and bimodal respiration in soft-shelled (Trionyx spiniferus), stinkpot (Sternotherus odoratus), and mud turtles (Kinosternon subrubrum)

Total mass-specific cutaneous surface area was determined for three species of freshwater turtles: Trionyx spiniferus, Sternotherus odoratus, and Kinosternon subrubrum. Similarly sized individuals of the three species exhibited high, intermediate, and low values of cutaneous surface area, respectively. Respiratory gas exchange in both air and water was measured in unrestrained individuals of each species. Because the T. spiniferus used in these experiments were on the average over an order of magnitude heavier than the S. odoratus, these two species had similar mass-specific cutaneous surface areas, whereas both had considerably higher values than K. subrubrum. All species were bimodal breathers, exchanging gases with both air and water. The percent aquatic V̇o2 and V̇co2 were highest in soft-shells (38% and 85%, respectively), intermediate in stinkpots (26% and 56%), and lowest in mud turtles (14% and 46%). The inverse pattern was observed for aerial gas exchange. Regression analysis (cutaneous surface area vs. percent aquatic V̇o2) with ANOVA on the residuals indicated that T. spiniferus was more reliant on aquatic gas exchange than could be explained by cutaneous surface area alone. A similar analysis using V̇o2 as the dependent variable indicated that cutaneous surface area explained most of the differences in V̇o2. The interpretation of these results was not substantially altered when differences in proportional skeletal mass between the species were taken into account. The results show that aquatic gas exchange is important even in species with few adaptations that facilitate such exchange and that the degree of aquatic gas exchange is directly related to the mass-specific cutaneous surface area across which gases can diffuse.

Factors Affecting Range Expansion in the Introduced Mediterranean Gecko, Hemidactylus turcicus

Abstract Exotic species colonize new areas through the processes of jump dispersal, population establishment, and diffusion dispersal. From 1962 to 1997, Mediterranean Geckos, Hemidactylus turcicus, were intentionally introduced multiple times into a science building on the campus of the University of Central Oklahoma, Edmond, Oklahoma. In 2005, we recorded 365 captures of 305 individuals. The population size was estimated to be 1005 individuals with a density of 478 geckos/ha. The population has dispersed a maximum distance of 200 m from the point of introduction which translates to a maximum rate of diffusion dispersal of 20 m/yr. These results support the hypothesis that range expansion of introduced Mediterranean Geckos has occurred because of multiple jump dispersal events, despite slow diffusion dispersal.

The Effect of Aquatic O₂ Levels on Diving and Ventilatory Behavior in Soft-Shelled (Trionyx spiniferus), Stinkpot (Sternotherus odoratus), and Mud Turtles (Kinosternon subrubrum)

Diving and ventilatory behavior were observed in three species of bimodally breathing turtles: Trionyx spiniferus, Sternotherus odoratus, and Kinosternon subrubrum. These turtles have high, intermediate, and low reliances on aquatic gas exchange, respectively. Turtles with access to normoxic air were filmed in normoxic, hypoxic, and hyperoxic water. Ninety percent of all dives were shorter than 20 min. Despite differences in the partitioning of respiratory gas exchange, dive duration in normoxia did not differ among species. Dive duration was directly proportional to aquatic PO₂ in soft-shells and independent of aquatic PO₂ in mud turtles. Stinkpots had consistently but not significantly shorter dives in normoxia. Aquatic PO₂ had no effect on the ventilation patterns of soft-shells. Regardless of PO₂, soft-shells typically engaged in one breathing bout, during which one breath was taken, per emersion period. Stinkpots and mud turtles underwent more bouts ofbreathingper emersion period and took more breaths per breathing bout than did soft-shells. Stinkpots in normoxia took more breaths than in hypoxia or hyperoxia, while mud turtles showed no response to aquatic PO₂. These results agree with previous research that found soft-shells to be the least reliant of the three species on aerial respiration. These results also indicate that aquatic PO₂ is an important factor in the regulation of diving and ventilatory behavior in at least some bimodally breathing turtles.

Temporal changes in two turtle assemblages

Turtle assemblages at two adjacent farm ponds in east-central Alabama were monitored during 1972-1974 and 1988-1990. At pond 1 a drift fence with pitfall traps was constructed during both study periods. Aquatic trapping was conducted in both ponds during both study periods. Pond 1 had been fertilized for 15 consecutive years prior to 1972-1974 but subsequently received no fertilizer. Aquatic vegetation was absent in pond 1 during 1972-1974 but was dense by 1988. Pond 2 had almost no fertilization history and underwent little vegetational change over time. In both study periods pond 1 had a higher density of Kinosternon subrubrum, and both ponds held more K. subrubrum during 1972-1974 than during 1988-1990

Radiotelemetry Reveals Terrestrial Estivation in Sonoran Mud Turtles (Kinosternon sonoriense)

Abstract Drought-related survival strategies were examined in a population of Sonoran Mud Turtles (Kinosternon sonoriense) inhabiting an ephemeral stream in the Peloncillo Mountains, New Mexico. Behavioral responses to seasonal drying of the habitat were investigated via radiotelemetry and repeated sampling of the resident population. All transmittered turtles were observed engaging in terrestrial dormancy for periods of 11–34 days. Two nontransmittered turtles remained in a small puddle through the drought, and no turtles were observed migrating to permanent bodies of water. Our results indicate that estivation is the dominant drought-survival strategy employed by K. sonoriense in our study population.

A survey of the coccidian parasites of reptiles from islands of the Galápagos Archipelago: 1990-1994.

From 1990 through 1994, fecal samples were collected and examined for coccidian parasites from 26 giant land tortoises Geochelone nigra, from 715 lava lizards Tropidurus spp., from 139 land iguanas Conolophus subcristatus, and from 128 marine iguanas Amblyrhynchus cristatus, all of which inhabit various islands in the Galápagos Archipelago. None of the samples from A. cristatus or from C. subcristatus was infected with coccidia. Only 1 of 26 (4%) G. nigra was infected with a single Eimeria species that we describe here as new. A total of 262 of 715 (37%) individuals representing 3 species of Tropidurus discharged oocysts of 1-3 different coccidian species; these included 2 previously described species Eimeria tropidura and Isospora insularius, and an eimerian that we describe here as new. Additionally, 104 fecal samples from Tropidurus spp. were from 51 animals recaptured in either 2 or 3 yr; 21 had no infections in any year, 15 were infected at least once, 14 were infected in 2 yr, and only 1 was infected during 3 yr. No animal was recaptured and sampled during each of the 4 yr of this study. Of the 262 infected individuals, 30 (12%) had multiple coccidial infections at the time of collection (eimerian and isosporan, or 2 eimerians). Where determination of the sexes was possible in the lava lizards, there was no difference in prevalence rates between males (39%) and females (41%). Sporulated oocysts of the new eimerian from Tropidurus are ellipsoidal, 27.1 x 15.6 (25-31 x 14-18) microns, with a polar body, but without a micropyle or oocyst residuum; they contain ellipsoidal sporocysts, 11.8 x 6.7 (10-14 x 6-8) microns, without Stieda, sub-, or parastieda bodies, but with a sporocyst residuum. Sporulated oocysts of the new eimerian from G. nigra are ellipsoidal to ovoidal, 21.6 x 18.1 (18-25 x 16-20) microns, with a large polar body, but without a micropyle or oocyst residuum; they contain ellipsoidal sporocysts 10.7 x 7.0 (8-12 x 5-8) microns, with Stieda body but no sub- or parastieda bodies. Also present is a sporocyst residuum of medium to large granules randomly distributed among the sporocysts.

FRESHWATER TURTLE ASSEMBLAGES IN CENTRAL OKLAHOMA FARM PONDS

Abstract Turtle assemblages in Oklahoma are potentially interesting because the species pool is a mixture of eastern and western species, several of which are approaching their longitudinal geographic range boundaries in Oklahoma. From 1996 to 2002, we captured 1,940 turtles in 12 assemblages in central Oklahoma. Pond area ranged from 0.04 to 26.1 ha. Species composition was a mixture of 2 ubiquitous and 3 rare species. Trachemys scripta and Chelydra serpentina occurred in 11 and 10 assemblages, respectively. The rare species included Pseudemys concinna (4 assemblages), Kinosternon flavescens (3), and Apalone spinifera (1). In ponds with multiple species, T. scripta was always the most abundant species (mean ± SD percentage of individuals captured = 80.0 ± 27.4%) and C. serpentina was always the second most abundant (18.5 ± 27.7%). Population density and biomass of T. scripta and C. serpentina varied an order of magnitude and approached maximum published values.

Ontogenetic Factors Affecting Diffusion Dispersal in the Introduced Mediterranean Gecko, Hemidactylus turcicus

Abstract Dispersal occurs when an individual leaves its natal area or home range, travels through adjacent areas, and then establishes a new home range where it will attempt to reproduce. Previous studies have suggested that subadults (i.e., hatchlings and juveniles) are the main agents of dispersal among introduced populations of Mediterranean Geckos, Hemidactylus turcicus. We derived a testable hypothesis for subadult dispersal in Mediterranean Geckos. In September 2006, we conducted tethering experiments to test the prediction that adults act aggressively toward subadults. From June to October 2006, we conducted 18 mark-recapture samples to test predictions of perch height occupancy and relative presence of adults and subadults at buildings and areas between buildings (i.e., transient habitats). As predicted, subadults occupied lower regions of buildings than adults, and subadults were disproportionately abundant in transient habitats. Apparently because of small sample size, there was no difference in the relative presence of adults and subadults at recently occupied buildings (i.e., arrival habitats). Our results supported the hypothesis that hatchlings were the main agents of diffusion dispersal within our study population and suggested that hatchling dispersal may be motivated by hostile encounters with adults. It was also clear that Mediterranean Geckos attempt to disperse from buildings more frequently than previously suggested.

Terrestrial Flight Response: A New Context for Terrestrial Activity in Sonoran Mud Turtles

Abstract The risk allocation hypothesis predicts that animals should be most averse to risk during brief and infrequent high risk situations. For animals in shallow aquatic habitats, encounters with terrestrial predators may represent such a situation. Terrestrial flight responses, acute movements from water onto land following a disturbance, may be a viable escape strategy during encounters with terrestrial predators foraging in shallow aquatic habitats. Sonoran mud turtles (Kinosternon sonoriense) occur in intermittent aquatic habitats in the Peloncillo Mountains, New Mexico. When Sonoran mud turtles were captured by hand in shallow pools or shallow stock tanks they frequently underwent terrestrial flight responses. In five of six trials in shallow stock tanks, and three of seven trials in shallow pools, turtles left the water within 20 min of being released, often climbing out of sight up relatively steep slopes. This behavior was not observed in four trials in which turtles were captured with hoop nets in deep stock tanks. Turtles that underwent terrestrial flight responses were significantly larger than non-responders. Terrestrial flight responses appear to be a risk aversion strategy in Sonoran mud turtles occupying shallow aquatic habitats. This unusual behavior may be widespread among animals that inhabit shallow aquatic habitats.