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We examined diet of introduced Bullfrogs (Rana catesbeiana) and three native frog species (R. limnocharis, R. nigromaculata and Bufo bufo gargarizans) co-occurring at a group of ponds on Daishan Island, east of China, to gain insight into the nature of potential interactions between Bullfrogs and native frog species. For postmetamorphic Bullfrogs, aquatic prey items dominated volumetrically. Prey size, diet volume and volumetric percentage of native frogs in diet increased with Bullfrog body size. The number and volumetric percentage of native frogs in the diet were not different for female and male Bullfrogs, and both were higher for adults than for juveniles. Diet overlap between males and juveniles was higher than that between males and females and between females and juveniles. Diet overlap with each native frog species of male Bullfrogs was lower than that of female Bullfrogs and juvenile Bullfrogs. We did not exam effects of Bullfrogs on native frogs but our results suggest that the primary threat posed by juvenile Bullfrogs to native frogs on Daishan Island is competition for food while the primary threat posed by male Bullfrogs is direct predation. Female Bullfrogs may threaten native frogs by both competition and predation. These differences among Bullfrog groups may be attributed to differences in body size and microhabitat use.

Revisiting historical amphibian sites can provide a relatively fast assessment of amphibian status in a region. Between 2000 and 2003 we repeatedly surveyed historically documented sites for two species of concern in the northern Great Basin: the western toad (Bufo boreas), and the Columbia spotted frog (Rana luteiventris). Both of these species have experienced population declines in other parts of their ranges but their status was relatively unknown in our study area. We estimate that B. boreas occupies 49.5% (34.1% - 65.0%) of 34 historical sites and that R. luteiventris occupies 52.9% (43.5% - 62.3%) of its 30 historical sites. B. boreas was more likely to be detected at human-altered sites while R. luteiventris was more likely to be detected at sites that were deeper than other sites in our study. B. boreas was detected at three of 41 (7.3%) potential sites (located near historic sites) while R. luteiventris was detected at six of 16 (37.5%). At 187 randomly selected sites, B. boreas was detected at one and R. luteiventris at three sites. Given that the number of historical sites available for resurveys was small, these results should be interpreted with caution. Moreover, a species can shift its distribution away from historical sites due to habitat succession or metapopulation dynamics without necessarily declining. We suggest that there is sufficient evidence to conclude that B. boreas and R. luteiventris have declined in and around the northern Great Basin. However, relatively high occupancy of Potential Sites by R. luteiventris suggests they may not have declined as much as B. boreas in the region we surveyed.

We examined whether the species composition of a community influences the persistence of larval Ambystoma maculatum in assemblages composed of two larger intraguild predators (A. opacum and A. jeffersonianum) and an alternative prey species (tadpoles of Rana sylvatica). We predicted a priori that A. maculatum would have higher survival in more diverse communities containing alternative species of prey and top predators (A. opacum), the latter of which may lower the abun-dance of intermediate predators (A. jeffersonianum) via intraguild predation. In a factorial experiment, we manipulated the presence of larval A. opacum, A. jeffersonianum, and R. sylvatica in replicated artificial ponds containing larval A. maculatum. The presence of all three species significantly depressed biomass production in A. maculatum: biomass was highest in ponds lacking the other species and was zero in ponds initially containing all four species. Tadpoles severely reduced the growth of filamentous algae in the ponds. This, in turn, may have affected the abundance of some herbivorous prey of larval salamanders, although this possibility was not tested. The presence of congeneric predators severely restricted the presence in the water column of larval A. maculatum, which otherwise exhibited significant diel patterns of activity in the absence of predators. Together, the presence of tadpoles and a predator-mediated reduction in activity patterns may have limited foraging opportunities for A. maculatum, thus exacerbating the direct impact of predation on survival in this species. These results suggest that diverse assemblages consisting of these particular species may actually inhibit, rather than promote, inclusion of A. maculatum in some communities of pond-breeding amphibians.

Fundamental issues in the study of predator-prey interactions include addressing how prey coexist with their predators and, moreover, whether predators promote coexistence among competing prey. We conducted a series of laboratory experiments with a freshwater assemblage consisting of two predators that differed in their foraging modes (a crayfish, Procambarus sp., and the western mosquitofish, Gambusia affinis) and their prospective anuran prey (tadpoles of the narrow-mouthed toad, Gastrophryne carolinensis, and the squirrel treefrog, Hyla squirella). We examined whether competition occurs within and between these two prey species and, if so, whether the non-lethal presence of predators alters the outcome of competitive interactions. We also asked whether the two species of prey differ in their susceptibility to the two types of predators and whether interspecific differences in predator avoidance behavior might account for this variation. Our results indicated that Gastrophryne was a stronger competitor than Hyla; at high densities, Gastrophryne reduced the body size of both congeners and conspecifics, as well as the proportion of surviving conspecifics that metamorphosed. However, the presence of mosquitofish did not alter the outcome of this competition, nor did either type of predator affect the density-dependent responses of Gastrophryne. In laboratory foraging trials, the number of tadpoles of each prey species that was killed, but not completely consumed by mosquitofish, was similar for Gastrophryne and Hyla. Yet, significantly more individuals of Gastrophryne than of Hylawere the first prey eaten by mosquitofish; there was no difference in the number of individuals of each species eaten by crayfish. Overall, more individuals of Gastrophryne than of Hyla were killed and completely eaten by mosquitofish at the end of the experiment. The two species of prey did not differ in their spatial avoidance of either type of predator, suggesting that this behavior did not play a significant role in the differential vulnerability of the prey to predation. By reducing the abundance of G. carolinensis, the potential exists for predators, such as mosquitofish, to ameliorate this species' competitive impact on other species. In this way, predators may promote coexistence of species within some assemblages of amphibians.

Many standardized techniques are used to monitor terrestrial salamanders, but fewer protocols have been tested for inventorying stream-dwelling salamanders, especially larvae. One new method uses artificial refugia (leaf litterbags) placed in shallow streams. To test the utility of litterbags, we sampled three transects of 6 litterbags each (2 large, 2 medium, and 2 small) placed in five small, medium, and large streams in Great Smoky Mountains National Park, an area of high aquatic salamander diversity. We captured 690 larval, juvenile, and adult stream-dwelling salamanders of 11 different species from June to November 2000 in the 90 litterbags. Large and medium-sized litterbags were most effective at sampling salamanders in small streams, but all bag sizes worked equally well in medium and large streams. The number of salamanders captured varied seasonally, with most captures in June and July. The depth of bag submergence significantly influenced litterbag use by adult and larval salamanders, but had no effect on juvenile salamanders. Although the technique was effective for determining the presence of many salamander larvae, variation in the numbers of individuals captured and the inability to relate captures to overall abundance make it impossible to monitor trends without considerable additional effort. The ease of deployment and non-destructive methodology suggest that litterbags could be useful in determining salamander presence during inventory programs, especially when the time to sample a large number of sites is limited.

Ph.D. dissertation on amphibians as indicator species for Everglades restoration success and park management.

Surveys of vocalizations are a widely used method for monitoring anurans, but it can be difficult to coordinate standardized data collection across a large geographic area. Digital automated recording systems (ARS) offer a low-cost method for obtaining samples of anuran vocalizations, but the number of recordings can easily overwhelm human listeners. We tested Song Scope, an automatic vocalization recognition software program for personal computers to determine if this type of machine learning approach is currently a viable solution for anuran monitoring. For three species, Song Scope scanned more than 200 h of recordings in 3-20 h at the settings we chose. The software misidentified true calls (false positive) at rates of 2.7%-15.8% per species and failed to detect calls (false negative) in 45%-51% of recordings. There exists a tradeoff between false positive and false negative errors, which can be adjusted by setting the minimum criteria for the recognition software. Users of this approach should carefully consider their reasons for monitoring and how they intend to use the data before creating a large monitoring network.

Describes a method for automating wildlife data collection and entry by using PDAs in the field

Some studies have described a negative effect of toe clipping on return rates of marked anurans, but the return rate is limited in that it does not account for heterogeneity of capture probabilities. We used open population mark-recapture models to estimate both apparent survival (0) and the recapture probability (p) of two treefrog species individually marked by clipping 2-4 toes. We used information-theoretic model selection to examine the effect of toe clipping on survival while accounting for variation in capture probability. The model selection results indicate strong support for an effect of toe clipping on survival of Green Treefrogs (Hyla cinerea) and only limited support for an effect of toe clipping on capture probability. We estimate there was a mean absolute decrease in survival of 5.02% and 11.16% for Green Treefrogs with three and four toes removed, respectively, compared to individuals with just two toes removed. Results for Squirrel Treefrogs (Hyla squirella) indicate little support for an effect of toe clipping on survival but may indicate some support for a negative effect on capture probability. We believe that the return rate alone should not be used to examine survival of marked animals because constant capture probability must be assumed, and our examples demonstrate how capture probability may vary over time and among groups. Mark-recapture models provide a method for estimating the effect of toe clipping on anuran survival in situations where unique marks are applied.

Models currently used to estimate patterns of species co-occurrence while accounting for errors in detection of species can be difficult to fit when the effects of covariates on species occurrence probabilities are included. The source of the estimation problems is the particular parameterization used to specify species co-occurrence probability. We develop a new parameterization for estimating patterns of co-occurrence of interacting species that allows the effects of covariates to be specified quite naturally without estimation problems. In our model, the occurrence of one species is assumed to depend on the occurrence of another, but the occurrence of the second species is not assumed to depend on the presence of the first species. This pattern of co-occurrence, wherein one species is dominant and the other is subordinate, can be produced by several types of ecological interactions (predator–prey, parasitism, and so on). A simulation study demonstrated that estimates of species occurrence probabilities were unbiased in samples of 50–100 locations and three surveys per location, provided species are easily detected (probability of detection  0.5). Higher sample sizes (.200 locations) are needed to achieve unbiasedness when species are more difficult to detect. An analysis of data from treefrog surveys in southern Florida indicated that the occurrence of Cuban treefrogs, an invasive predator species, was highest near the point of its introduction and declined with distance from that location. Sites occupied by Cuban treefrogs were 9.0 times less likely to contain green treefrogs and 15.7 times less likely to contain squirrel treefrogs compared to sites without Cuban treefrogs. The detection probabilities of native treefrog species did not depend on the presence of Cuban treefrogs, suggesting that the native treefrog species are naive to the introduced species.

Documents the discovery of the Puerto Rican Coqui on St. John, USVI near Virgin Islands National Park

Documents the discovery of breeding populations of Cuban treefrogs on St. John, USVI in Virgin Islands National Park