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We examined relationships between livestock grazing and the activity of introduced rodents and population density of Jewelled Geckos, Naultinus gemmeus (Diplodactylidae) on the Otago Peninsula, South Island, New Zealand. We expected livestock grazing to prevent the proliferation of rank grass (which is often associated with high rodent densities) and thereby reduce the frequency of predation by rodents on Jewelled Geckos. Thus, we predicted activity of rodents to be lower, and density of Jewelled Geckos higher, at sites grazed by livestock. We tested this for two habitats: Coprosmaspp. shrubland and regenerating kānuka (Kunzea ericoides) forest. We quantified density of Jewelled Geckos using visual searches, photography and mark–recapture (POPAN formulation). We used tracking tunnel surveys to estimate the activity of introduced rodents. The activity of rodents (Rattusspp. and Mus musculus) was significantly higher at ungrazed compared to grazed sites in both habitats. Density of Jewelled Geckos in Coprosma was over four times higher at grazed sites and decreased with increasing rodent activity; however, in kānuka, we found a contrasting result with density being significantly higher at the ungrazed sites. We infer that in ungrazed Coprosma, rank grasses support high rodent densities and, consequently, high predation of Jewelled Geckos. Thus, grazing by introduced livestock may promote the survival of Jewelled Geckos and the persistence of high density populations in Coprosma shrubland. In contrast, grazing in regenerating kānuka may impact on Jewelled Geckos negatively, possibly by removing thermal refugia.
Lithobates catesbeianus is an invasive anuran introduced in Brazil that can affect population and community dynamics of native frogs. However, the mechanisms that allow the establishment of this species in non-native areas are not known. Considering that reproduction is a key feature in the dynamics and establishment of an invasive species in a new environment, this study investigated the reproductive biology of L. catesbeianus in a subtropical area of southern Brazil. One-hundred and four females and 79 males were collected during monthly sampling from June 2008 to May 2009 in the State of Paraná. In the laboratory, sex determination and macroscopic determination of the gonad development stage of each specimen were carried out. Subsequently, the gonads were removed and mass was determined to obtain an individual gonadosomatic index (GSI) for each specimen. We also processed a sub-sample of gonadal tissue for histological analysis. Five stages of ovarian development and four stages of testicular development were determined by microscopic analysis. The maturation curve, using the mean monthly variation of the GSI for females and males, showed that reproductive activity was more intense during spring and summer. The maturation curve of females revealed two reproductive peaks during the study period; one from August to November and another in February. There was little variation in the mean monthly GSI values obtained for males, but with greater values from August to February. The snout–vent length (SVL) of the first maturation (shortest SVL at which 50% of individuals are reproductively active [Vazzoler, 1996]) was estimated for females as 84.5 mm. The SVL of the smallest reproducing male was 76.0 mm.
Understanding the processes shaping responses of native species to environmental perturbations, such as the introduction of non-native species, will allow us to better manage such impacts. The imported Red Fire Ant, Solenopsis invicta, invaded the United States ∼70 years ago and co-occurs with Fence Lizards (Sceloporus undulatus) in portions of their range. Lizards from fire ant-invaded populations have longer hind limbs which more effectively remove ants and increase survival following fire ant attack. Prior research on this system suggests that this difference in relative hind limb length (RHL) is fixed at birth; however, RHL is a plastic trait in other lizard species and could help Fence Lizards survive. Lizards from invaded sites are more likely to climb when attacked by fire ants or when stressed (i.e., have elevated levels of corticosterone) than are lizards from uninvaded sites. We tested for climbing-induced plasticity in RHL by manipulating whether or not Fence Lizards had to climb raised platforms to bask. This testing revealed that increased climbing did not affect RHL at maturity (34 weeks of age) or hind limb growth rates. This result was unaffected by initial limb length, differential survival, source population, or ambient or body temperature of the lizards, suggesting that the amount of climbing does not plastically affect the RHL of S. undulatus.
In Puerto Rico, the number of nonnative Green Iguana, Iguana iguana, has increased and the species has proliferated throughout the island. Reports on diet in the iguana's native range indicate exclusive herbivory, but observations in their nonnative range occasionally include animal materials. The aim of our study was to determine the diet and trophic level of I. iguanain Puerto Rico using gut content and stable isotopic analysis of muscle tissue (tongue and leg). We found significant differences in the isotopic signature between leg and tongue tissue, which may be related to differing strategies for allocating nutrients during muscle formation. The isotopic analysis of δ15N and δ13C showed little enrichment of both muscle tissues from that of their diet, demonstrating that I. iguanais primarily an herbivore. However, gut contents provided evidence for a first report of I. iguanaeating crabs (Ucaspp.). The gut contents consisted primarily of black mangrove leaves (Avicennia germinans), suggesting a higher impact of herbivory on this species of mangrove. Another plant species of interest found in the gut was Brazilian pepper, Schinus terebinthifolius. We suspect that I. iguanamay be a disperser of this aggressive invasive plant in Puerto Rico. Our study indicates that I. iguanaimpacts the native flora and fauna in Puerto Rico, and that the ecological role of this species in introduced ranges warrants further investigation.
We examined the combined effects of sublethal concentrations of the pesticide diazinon and a nonnative predatory fish on the behavior and survival of amphibian prey. A 48-h experiment was performed in tubs containing predatory Western Mosquitofish and diazinon treatments (0, 0.5, 1.0 mg/L, and a solvent control). In “no-pesticide” treatments, the presence of fish reduced tadpole survival significantly. In the absence of fish, pesticide presence altered tadpole behavior (reduced refuge use) significantly but did not impact tadpole survival. In the combined presence of both fish and pesticide, tadpoles altered their behavior to become more active, and to hide less. Although these behavioral changes should expose tadpoles to an even higher predation risk, because diazinon also reduced both activity and attack rates by the predatory fish, tadpoles experienced significantly greater survival in treatments with pesticides. Despite the negative impact of diazinon on amphibian antipredator behavior, the stronger impact of diazinon on predator behavior allowed a greater survival rate for the prey. These results demonstrate the importance of studying specific species interactions in understanding the impacts of chemical contaminants on any given species.
Lantana (Lantana camara L., Verbenaceae) is an invasive species of global interest that threatens more than 300 Australian plant and animal species of conservation significance. Reptiles may be at high risk due to their ground-dwelling habit and reliance on microhabitat structure. We examined the effects of lantana, and its management, on reptile assemblages in a wet sclerophyll forest in southeast Queensland, Australia. We compared reptile assemblages across four treatments: (i) manual clearing and herbicide application; (ii) herbicide application followed by prescribed burn; (iii) untreated lantana thickets; and (iv) wet sclerophyll forest. Plots treated with herbicide and then burned were structurally more diverse than manually cleared sites and supported a greater diversity of reptiles. No species occurred exclusively in untreated lantana habitats; however, these plots supported relatively high abundances of rare species, particularly Challenger Skinks (Saproscincus rosei). Lantana also had a higher species richness compared to manually cleared and sclerophyll forest. The use of lantana as habitat by a number of species highlights the need to consider the importance of these habitats for fauna prior to implementing management options. Herbicide application followed by prescribed burning appears to be an ideal approach to manage lantana due to the increased heterogeneity and regrowth of native vegetation, an option which supported more diverse reptile communities. Our results caution against the whole scale clearing of lantana from invaded areas, as these habitats continue to support reptile communities including threatened species. Nevertheless, by treating lantana with herbicide and prescribed fire, reptile community structure might be maintained.
Amphibians are considered one of the most threatened vertebrate groups. Although numerous studies have addressed the many causes of amphibian population decline, little is known about effects of invasive plants. Chinese tallow (Triadica sebifera) is an exotic deciduous tree that has invaded the southeastern United States. Amphibian larvae in environments invaded by T. sebifera may be impacted negatively as autumn leaf litter decomposes in natal areas. We compared effects of leaf litter decomposition from T. sebifera and two native tree species on survival and development of four species of anuran larvae from eastern Texas. Larvae from Pseudacris fouquettei, Lithobates (Rana) sphenocephalus, Hyla versicolor, and Incilius (Bufo) nebulifer were introduced into mesocosms containing leaf litter from one of the three tree species. Pseudacris fouquettei and L. sphenocephalus, species that breed earlier in the year, had lower survival within the T. sebifera pools. Pseudacris fouquettei were smaller in T. sebifera mesocosms compared with native tree mesocosms, whereas L. sphenocephalus were larger in T. sebifera mesocosms. Hyla versicolor showed significant developmental and morphological differences in T. sebifera mesocosms; however, survival was not significantly different among treatments. Leaf litter treatment did not affect survival or development in I. nebulifer. Our results suggest that breeding season may determine how each species survives and develops in an environment with T. sebifera leaf litter. Triadica sebifera leaf litter breaks down faster than native species; therefore, negative effects may be short lived but pose a greater threat to species that breed soon after leaffall.
The House Gecko, Hemidactylus frenatus, is one of the world's most invasive vertebrate species and is spreading rapidly across the South Pacific, displacing other species of geckos that are native or were already resident. We studied the adhesion and locomotor capabilities of H. frenatusand the resident Lepidodactylus lugubrison the island of Moorea in French Polynesia where they are syntopic. Our goal was to determine whether H. frenatuscould stick or sprint faster than L. lugubris, two types of performance measures that could underlie superiority of H. frenatusin foraging and agonistic interactions hypothesized in other studies. The clinging ability of H. frenatusand L. lugubrisare comparable suggesting that the potential for sticking to vertical and over-hanging surfaces as geckos move through their environments does not differ between species. In contrast, H. frenatushave maximal sprint speeds that are approximately fourfold higher than L. lugubris, an advantage in speed that is even greater than that measured previously for the two species running on horizontal surfaces. Proposed superiority in foraging and agonistic interactions of H. frenatuscompared to L. lugubrisare potentially traceable to performance characteristics such as adhesion and locomotion. We demonstrate that comparatively high maximal locomotor speeds may contribute to the observed success of H. frenatusover resident geckos in French Polynesia, and possibly in other areas where they have been introduced.
Pollution and the introduction of nonnative predators, typically fish, are two frequent human-associated stressors in freshwater ecosystems. Amphibians appear to be particularly susceptible to these stressors. We conducted a mesocosm experiment to examine the independent and interactive effects of an invasive fish, the Western Mosquitofish (Gambusia affinis), and ammonium nitrate, an agricultural fertilizer, on American Toad (Anaxyrus americanus) tadpoles. Mosquitofish tended to have a negative effect on American Toad survivorship. American Toad metamorphs from mesocosms with mosquitofish were smaller than those from mesocosms without mosquitofish. Mosquitofish also delayed metamorphosis of the American Toads. Ammonium nitrate addition did not affect survivorship. However, American Toad metamorphs from ammonium nitrate addition treatments were smaller than those from treatments without ammonium nitrate addition. Mosquitofish and ammonium nitrate addition each had independent effects on American Toads, but there was no evidence for significant interactions between these two stressors.
Spatial distribution patterns of animals are shaped by their ecology and can give insights into their habitat use and behavioral interactions. Most methods used to study spatial distribution, including quadrat sampling, and nearest-neighbor distance analyses have been used primarily with sessile organisms. We used nearest-neighbor distances to look at the spatial distribution of the Zebra-tailed lizard (Callisaurus draconoides) in the Rillito Wash in Tucson, Arizona, and to determine whether these distances gave meaningful results when used with a mobile lizard. We hypothesized that spatial distributions would be random for both sexes but would differ between juveniles and adults because of differences in dominance between these groups. We recorded individuals' locations using a GPS and collected data on sex, age group, substrate, distance to nearest vegetation, and percent vegetation cover at each individual's location. Males and females were distributed randomly, whereas juveniles were distributed regularly. Juveniles were closer to one another than to adults, and females were closer to one another than they were to males, or than males were to one another. Juveniles inhabited areas with less vegetation cover than adults, which may represent marginal habitats. All individuals were distributed in a clustered manner. A lack of difference in spatial distribution between males and females may be a result of abundant resources and subordinate, nonreproducing males. The study occurred at the end of the breeding season, which may also have contributed to the lack of difference. We show that nearest-neighbor distance methods can give meaningful results when used with mobile organisms and can complement ecological studies, including more focused mark–recapture approaches.
Oudri's Fan-Footed Gecko (Ptyodactylus oudrii) is a common North African desert lizard that lives in dense colonies. Reproductive behavior shows a number of peculiarities in egg laying. Females select communal oviposition sites in rocky recesses at human-made structures. Individuals of both sexes perform communal parental care of the eggs. We performed field observations to analyze the extent of communal nesting in nature in southeast Morocco. We also carried out laboratory experiments to analyze the function of this behavior. In Experiment 1, we assessed whether the presence of previous clutches influenced whether females select a site for oviposition. In experiment 2, we tested whether parental egg-attendance influenced the hatching success of eggs. Finally, in Experiment 3, we compared hatching success of communal and solitary clutches under laboratory conditions. Communal nesting was the generally observed in the field. With a single exception, all clutches were restricted to one area. In 32% of colonies, individuals of both sexes and all ages remained in close vicinity to clutches. Females preferred oviposition sites where freshly laid eggs were present. Hatching rate significantly decreased when adult lizards were experimentally excluded from the oviposition site, and hatching success of solitary clutches was significantly lower than that of communal ones under laboratory conditions. Our results suggest that communal nesting in this species is highly adaptive, because aggregation favors parental care, defense against predators of eggs or hatchlings, and increases incubation success. These benefits are likely to be important in geckos that live in extremely dry environments.
We investigated the role of amphibian prey in the diet and distribution of the Aquatic Gartersnake (Thamnophis atratus) in the San Francisco Bay Area of California, USA. During surveys for amphibians and snakes at 185 ponds, we captured 139 T. atratus, of which 60 contained identifiable stomach contents. Native amphibians were found in 93% of the snakes containing food. Analysis of stomach contents indicated that Pacific Chorus Frogs (Pseudacris regilla) were the most important amphibian prey, followed by Western Toads (Anaxyrus [=Bufo] boreas), California Newts (Taricha torosa), and California Red-legged Frogs (Rana draytonii). The occurrence of T. atratusat a pond associated positively with the presence of all native amphibian species but negatively associated with the presence of introduced American Bullfrogs (Lithobates catesbeianus[=Rana catesbeiana]). The mean species richness of native amphibians at ponds where we detected T. atratuswas also higher than that in ponds without Gartersnakes (2.45 vs. 1.74), and the odds of finding T. atratusat ponds with native amphibians was 12 times greater than at ponds without native amphibians. Our results underscore both the importance of native amphibians in the diet and distribution of T. atratusand the potential implications of ongoing amphibian declines for animals that prey on amphibians.
The presence of Solenopsis invictain Caiman latirostris nests is suspected to be a possible cause of death in caiman hatchlings, but this has not been documented within the native distribution of this ant. In crocodilian ranching programs, wild eggs are collected from the field, and delays between collection and transportation to incubators are usually minimized in the hope of maximizing embryo survival. We analyzed nests harvested during five consecutive nesting seasons of C. latirostris to determine the phenology of S. invictacolonization of caiman nests. The percentages of colonized caiman nests for each season were calculated. Densities of S. invictamounds built on bare ground were assessed to determine potential relationships between density and the proportion of caiman nests colonized by the end of nesting season. We also evaluated whether S. invictapreferred certain habitats to establish their mounds. We found no relationship between S. invictamound densities and the percentage of C. latirostris nests with Red Fire Ants. The presence of S. invictamounds among years was similar between different habitats at the beginning of each season. We found that S. invictacan colonize C. latirostris nests during the breeding period and that colonization of nests is higher than 50% in seasons where rainfall was 200 mm at the beginning of the season (December and January). In contrast, during years in which rainfall was below 200 mm, caiman nest colonization was reduced.
New salamanders of the genus Oedipina are described from the xeric Motagua Valley in eastern Guatemala, the El Trifinio highlands near the Honduras/El Salvador borders, and the Pacific versant of south-central Guatemala. These new species have been previously associated with known species, but possess distinctive foot morphology, different numbers of teeth, and body morphology and inhabit distinctive environments.
Nuevas especies de salamandras del género Oedipina son descritas del árido Valle de la Motagua en el este de Guatemala, de las tierras altas El Trifinio cerca de la frontera de Honduras y El Salvador, y de la vertiente Pacifico de la parte sur-central de Guatemala. Estas nuevas especies han sido asociadas previamente con otras especies, pero poseen un morfología distintiva, número de dientes diferentes, y viven en ambientes distintos.
The threatened Bluetail Mole Skink (Plestiodon egregius lividus) is limited to the xeric habitats of the southern Lake Wales Ridge in central Florida. To generate important data for conserving this species, we characterized genetic variation at the mitochondrial cytochrome-b gene and seven microsatellite loci among multiple populations. We compared the Bluetail Mole Skink's pattern of genetic diversity and differentiation to those of two other lizards with similar geographic and habitat distributions—the Florida Sand Skink (Plestiodon reynoldsi) and the Florida Scrub Lizard (Sceloporus woodi). The Bluetail Mole Skink was highly variable at the genetic markers, and significant genetic differentiation occurred among scrub patches. Patches can be divided into central and southern Lake Wales Ridge groups. Our results also suggest that each sampled habitat patch should be treated as a population and reintroductions should minimize the distance between recipient and source locations to limit altering the potential long-term pattern of genetic differentiation among Bluetail Mole Skinks on the Lake Wales Ridge. The Bluetail Mole Skink and the Florida Sand Skink had similar genetic diversity, and all three lizards had comparable patterns of genetic differentiation. The concordance of genetic differentiation among these species is further evidence suggesting that similar conservation issues face the three species, namely, preserving the remaining xeric habitat. It is likely, therefore, that conservation efforts directed at the more common Florida Sand Skink and Florida Scrub Lizard would benefit the Bluetail Mole Skink.
Leptophis santamartensis, known only from Sierra Nevada de Santa Marta, Colombia, is one of the more poorly known species of the genus Leptophis. The characters used for its diagnosis largely overlap with those of other Leptophis, mainly with Leptophis ahaetulla occidentalis, the only other Leptophis known to occur in the Sierra Nevada de Santa Marta. A detailed comparison of L. a. occidentalis with the two known specimens of L. santamartensis leads to the conclusion that the latter should be relegated to the synonymy of the former.
We examined maximal and ecological performance in Ameiva ameivaon Union Island, St. Vincent and the Grenadines. Maximal sprint speed was correlated positively with lizard body size but not with hind-limb or relative hind-limb length. Lizards in the field used over 85% of maximal capacity when escaping a putative predator, and the proportion of maximal speed used was highly dependent on behavioral context. Mean and median speeds used by adults when moving undisturbed through the habitat were 15.37 ± 2.01 (SE) and 11.41% of maximal speed; and approximately 65% of undisturbed movement is at speeds <15% of maximal capacity. No individual movement exceeded 40% of maximal capacity. Mean and median values for distances moved were 7.88 ± 0.72 (SE) and 8.14 cm, with 91% of distances moved <12 cm and 69.5% <10 cm, demonstrating that undisturbed lizards move through their habitat using short individual movements at low speeds. Similar to other studies on primarily sedentary lizards, actively foraging lizards may experience stronger natural selection on locomotor speed when evading a predator rather than while foraging because these lizards use nearly 90% of their maximal capacity during the former activity.
Two intergeneric hybrid snakes (Pituophis catenifersayi × Pantherophis vulpinus) are described from the midwestern United States; one collected in south central Iowa and the other from southeastern Minnesota. Both specimens are morphologically intermediate between the putative parental species P. c. sayi and P. vulpinus. Hybrid origin was verified by comparing DNA sequence data from the hybrids to the putative parental species. Both hybrid specimens possessed P. c. sayi mitochondrial DNA haplotypes. Examination of the nuclear gene Vimentin (intron 5) showed both specimens were heterozygous at most variable sites confirming their hybrid origin. These snakes represent only the second and third confirmed instances of naturally occurring intergeneric hybridization among squamate reptile species.
Unresolved phylogenetic relationships within the subfamily Natricinae continue to exist, including the position of the genus Xenochrophis. In the present study, two mitochondrial genes (cytochrome b, 12S rRNA) and one nuclear gene (c-mos) were used to infer the phylogenetic relationships among the members of Natricinae, with a special emphasis on the position of the genus Xenochrophis. Two statistical methods, Maximum Likelihood and Bayesian Inference, were used for phylogenetic reconstruction. Both the mitochondrial and nuclear datasets produced sufficiently resolved and congruent topologies. Our findings placed the genus Xenochrophis within Natricinae consistently with strong nodal support. Findings also revealed a close association between two Indian natricid snakes, Xenochrophis piscator and Xenochrophis schnurrenbergeri. However Xenochrophis vittatus, from Indonesia, does not cluster with the remaining species of Xenochrophis, suggesting a nonmonophyly of this genus. Overall Natricinae was found to be monophyletic because the two genera, Psammodynastes pulverulentus and Amplorhinus multimaculatus, are now known to be members of the Lamprophiidae. This study also finds a close relationship between the endemic species Lycognathophis seychellensis with the African natricids.
We captured 32 Common Snapping Turtles (Chelydra serpentina) in a Canaan Valley, West Virginia lake and equipped them with radio-transmitters during 1988 through 2007 to describe their hibernation behavior and examine the relative importance of temporal and environmental effects on hibernation. We monitored entry date, exit date, and location of hibernacula. The mean date of entry into hibernation was 9 October, and the mean date of exit from hibernation was 13 April, with a mean duration of 185 days. Turtles moved a mean distance of 117 m to hibernacula and were located most often along small streams bordered by speckled alder (Alnus rugosa). Hibernation entry date was influenced by lake temperature and hibernation exit date was influenced by water temperature at hibernacula sites. We suggest that small streams are important to Common Snapping Turtles as hibernacula because they provide protection from predators and remain above freezing temperatures.