No abstract

Amphibian declines and extinction have been attributed to many causes, including disease such as chytridiomycosis. Other pathogens may also contribute to declines, with ranavirus as the most likely candidate given reoccurring die-offs observed in the wild. We were interested in whether it is possible for ranavirus to cause extinction of a local, closed population of amphibians. We used susceptibility data from experimental challenges on different life stages combined with estimates of demographic parameters from a natural population to predict the likelihood of extinction using a stage-structured population model for wood frogs (Lithobates sylvaticus). Extinction was most likely when the larval or metamorph stage was exposed under frequent intervals in smaller populations. Extinction never occurred when only the egg stage was exposed to ranavirus. Under the worst-case scenario, extinction could occur in as quickly as 5 years with exposure every year and 25-44 years with exposure every 2 years. In natural wood frog populations, die-offs typically occur in the larval stage and can reoccur in subsequent years, indicating that our simulations represent possible scenarios. Additionally, wood frog populations are particularly sensitive to changes in survival during the pre-metamorphic stages when ranavirus tends to be most pathogenic. Our results suggest that ranavirus could contribute to amphibian species declines, especially for species that are very susceptible to ranavirus with closed populations. We recommend that ranavirus be considered in risk analyses for amphibian species.

Abstract. Long-distance movements are important adaptive behaviors that contribute to population, community, and ecosystem connectivity. However, researchers have a poor understanding of the characteristics of long-distance movements for most species. Here, we examined long-distance movements for the lesser prairie-chicken (Tympanuchus pallidicinctus), a species of conservation concern. We addressed the following questions: (1) At what distances could populations be connected? (2) What are the characteristics and probability of dispersal movements? (3) Do lesser prairie-chickens display exploratory and round-trip movements? (4) Do the characteristics of long-distance movements vary by site? Movements were examined from populations using satellite GPS transmitters across the entire distribution of the species in New Mexico, Oklahoma, Kansas, and Colorado. Dispersal movements were recorded up to 71 km net displacement, much farther than hitherto recorded. These distances suggest that there may be greater potential connectivity among populations than previously thought. Dispersal movements were displayed primarily by females and had a northerly directional bias. Dispersal probabilities ranged from 0.08 to 0.43 movements per year for both sexes combined, although these movements averaged only 16 km net displacement. Lesser prairie-chickens displayed both exploratory foray loops and round-trip movements. Half of round-trip movements appeared seasonal, suggesting a partial migration in some populations. None of the long-distance movements varied by study site. Data presented here will be important in parameterizing models assessing population viability and informing conservation planning, although further work is needed to identify landscape features that may reduce connectivity among populations.

1. Previous research shows that canopy-associated shifts from an algal to a detritus-based food web can affect anuran tadpoles negatively. This may not be true of salamander larvae, however, because they are predators. 2. To investigate the influence of canopy cover on the survival and growth of salamanders, and on the subsequent export of biomass from ponds, we conducted a mesocosm experiment examining effects of shading (high or low) and litter (leaves or grass) on Ambystoma maculatum (a forest specialist) and A. texanum (a habitat generalist). Additionally, we reanalysed data from Williams, Rittenhouse & Semlitsch (2008) to examine the effects of shading and litter on biomass export of three anurans: Rana sphenocephala, Pseudacris crucifer and Hyla versicolor. 3. In contrast to previous studies, we found that salamanders performed better in mesocosms with the characteristics of closed canopy ponds (high shade and leaf litter), which resulted in a greater export of biomass. Salamanders grew larger under closed canopy conditions, probably because of differences in prey abundance among treatments. Anurans responded differently to canopy cover than caudates. The biomass export of R. sphenocephala and P. crucifer was reduced under closed canopy conditions (although differently affected by litter and shading), while the biomass of H. versicolor was not affected. 4. This and other studies suggest that changes in canopy cover may induce a shift in the amphibians emerging from ponds, from primarily anurans in open canopy ponds to primarily salamanders in closed canopy ponds. Additional multispecies studies will determine whether these trends hold true for more diverse amphibian assemblages. Further investigation into the effects of canopy cover on salamanders will be important for understanding aquatic-terrestrial linkages.