Steven J. Price

Quantitative evidence for the effects of multiple drivers on continental-scale amphibian declines

Since amphibian declines were first proposed as a global phenomenon over a quarter century ago, the conservation community has made little progress in halting or reversing these trends. The early search for a “smoking gun” was replaced with the expectation that declines are caused by multiple drivers. While field observations and experiments have identified factors leading to increased local extinction risk, evidence for effects of these drivers is lacking at large spatial scales. Here, we use observations of 389 time-series of 83 species and complexes from 61 study areas across North America to test the effects of 4 of the major hypothesized drivers of declines. While we find that local amphibian populations are being lost from metapopulations at an average rate of 3.79% per year, these declines are not related to any particular threat at the continental scale; likewise the effect of each stressor is variable at regional scales. This result - that exposure to threats varies spatially, and populations vary in their response - provides little generality in the development of conservation strategies. Greater emphasis on local solutions to this globally shared phenomenon is needed.

Effects of Urbanization on Occupancy of Stream Salamanders

Urban development is the most common form of land conversion in the United States. Using a before-after control-impact study design, we investigated the effects of urbanization on larval and adult stages of southern two-lined salamanders (Eurycea cirrigera) and northern dusky salamanders (Desmognathus fuscus). Over 5 years, we estimated changes in occupancy and probabilities of colonization and survival in 13 stream catchments after urbanization and in 17 catchments that were not urbanized. We also examined effects of proportion of urbanized area in a catchment and distance of the salamander population to the nearest stream on probabilities of colonization and survival. Before urbanization, adult and larval stages of the two salamander species occupied nearly all surveyed streams, with occupancy estimates ranging from 1.0 to 0.78. Four years after urbanization mean occupancy of larval and adult two-lined salamanders had decreased from 0.87 and 0.78 to 0.57 and 0.39, respectively. Estimates of mean occupancy of larval northern dusky salamanders decreased from 1.0 to 0.57 in urban streams 4 years after urbanization; however, adult northern dusky salamander occupancy remained close to 1.0 in urban streams over 5 years. Occupancy estimates in control streams were similar for each species and stage over 5 years. Urbanization was associated with decreases in survival probabilities of adult and larval two-lined salamanders and decreases in colonization probabilities of larval dusky salamanders. Nevertheless, proportion of impervious surface and distance to nearest stream had little effect on probabilities of survival and colonization. Our results imply that in the evaluation of the effects of urbanization on species, such as amphibians, with complex life cycles, consideration of the effects of urbanization on both adult and larval stages is required.

Effects of Relocation on Movements and Home Ranges of Eastern Box Turtles

Abstract To examine effects of relocation on eastern box turtles (Terrapene carolina), we compared home ranges and movement patterns of 10 resident and 10 relocated box turtles in Davidson, North Carolina, USA. Home ranges of relocated turtles were approximately 3 times larger than those of resident turtles when measured by minimum convex polygons, 6 times larger than resident turtles when measured with 95% kernels and 7.5 times larger than resident turtles when measured by 50% kernels. Relocated turtles also moved a greater average distance per day than resident turtles. Additionally, 5 relocated turtles experienced mortality or disappearance compared to no mortality or disappearance of resident turtles. Our results raise questions about the success of relocation as a management strategy for eastern box turtles.

Pond age and riparian zone proximity influence anuran occupancy of urban retention ponds

Urbanization is widespread throughout the United States and negatively affects many wildlife populations. However, certain urban features, such as retention ponds, may provide habitat for some species, such as amphibians. This study examines the influence of riparian zone proximity and pond age on retention pond occupancy by anurans. We identified and estimated the age of 25 retention ponds near Charlotte, North Carolina, USA and used a geographic information system to determine the distance to the nearest riparian zone. Occupancy modeling indicated that anuran presence decreased with increasing distance to riparian zone. Pond age also appeared to be an important factor, but the effect varied among species. Although the results of this study demonstrate the potential value of retention ponds to anurans, it is important to be conservative in estimating the ability of these ponds to sustain amphibian populations in urbanized regions.

Natural History of Terrapene carolina (Box Turtles) in an Urbanized Landscape

Abstract Urbanization and other anthropogenic factors are often implicated in turtle population declines, yet limited research on the natural history of turtles in urban areas has been conducted. To assess the effects of urbanization and to help develop proper conservation strategies for Terrapene c. carolina (Eastern Box Turtles), we conducted a mark-recapture study in the vicinity of Davidson, NC, from 1999 to 2004. We made 354 turtle captures, 42 of which were recapture events. We evaluated meristic characters, body condition, activity patterns, population structure, and growth rates, and then examined relationships among these variables and the amount of anthropogenically-modified habitat within 100 m of each turtles collection location. Males and females had different patterns of seasonal activity and body condition indices. Growth rates decreased with turtle age and varied between developed and forested habitats. More turtles over the age of 20 were found in areas with extensive forest cover than in areas that were developed. Although box turtles may persist in urbanized landscapes and may grow more quickly there, they suffer higher mortality in these habitats compared to forested landscapes.

Terrestrial Activity and Habitat Selection of Eastern Mud Turtles (Kinosternon subrubrum) in a Fragmented Landscape: Implications for Habitat Management of Golf Courses and Other Suburban Environments

Abstract In urbanized landscapes, golf course ponds may provide the only remaining habitat for semi-aquatic animals. Eastern Mud Turtles (Kinosternon subrubrum), which rely heavily on both aquatic and terrestrial habitats, may face challenges on golf courses, which typically have significantly modified and fragmented landscapes. We conducted a radio-telemetric study of 11 mud turtles inhabiting a golf course pond in the western Piedmont of North Carolina to investigate their terrestrial activity and habitat selection in a fragmented landscape. Most turtles moved to terrestrial habitats in late summer and emigrated a mean distance (± SE) of 187.2 ± 67.4 m and moved a mean straight line distance (± SE) of 119.3 ± 47.4 m from the pond. We determined habitat selection using logistic regression to compare turtle locations with random locations and found that mud turtles selected forested habitats with moderate canopy cover and no grass. Mud turtles also selected habitat containing herbaceous vegetation and woody debris as overwintering locations. Mud turtles did not select heavily disturbed habitats with limited canopy cover and pavement or cut grass associated with fairways, roughs, and residential lawns. Overall, our study suggests that maintaining relatively undisturbed forested habitat within fragmented urban landscapes, such as those found on golf courses, may allow for the persistence of these semi-aquatic turtles. Information from this study can be used to better understand critical upland habitat requirements of other semi-aquatic species inhabiting fragmented landscapes and aid in the implementation of habitat management plans.

Snake fungal disease: an emerging threat to wild snakes

Since 2006, there has been a marked increase in the number of reports of severe and often fatal fungal skin infections in wild snakes in the eastern USA. The emerging condition, referred to as snake fungal disease (SFD), was initially documented in rattlesnakes, where the infections were believed to pose a risk to the viability of affected populations. The disease is caused by Ophidiomyces ophiodiicola, a fungus recently split from a complex of fungi long referred to as the Chrysosporium anamorph of Nannizziopsis vriesii (CANV). Here we review the current state of knowledge about O. ophiodiicola and SFD. In addition, we provide original findings which demonstrate that O. ophiodiicola is widely distributed in eastern North America, has a broad host range, is the predominant cause of fungal skin infections in wild snakes and often causes mild infections in snakes emerging from hibernation. This new information, together with what is already available in the scientific literature, advances our knowledge of the cause, pathogenesis and ecology of SFD. However, additional research is necessary to elucidate the factors driving the emergence of this disease and develop strategies to mitigate its impacts. This article is part of the themed issue ‘Tackling emerging fungal threats to animal health, food security and ecosystem resilience’.

An Assessment of Leech Parasitism on Semi-aquatic Turtles in the Western Piedmont of North Carolina

Abstract In 2005, we assessed the occurrence of leeches on semi-aquatic turtles in nine ponds in the North Carolina Piedmont. Placobdella parasitica (smooth turtle leech) was the only parasitic leech found on turtles and was present on turtles from all ponds. Female Chrysemys picta (Painted Turtles) were more frequently parasitized than males (females 54.7%, males 40.9%; p = 0.039), possibly because they are larger and provide more surface for leech attachment. Chelydra serpentina (Snapping Turtles) had the highest leech load of any species (mean = 32.3/turtle), which we attributed to its large size and bottom-dwelling habits. Most leeches were found attached to the underside of marginal scutes or between the plastron and inguinal region. These sites likely offer protection from the environment when a turtle emerges from the water.

Are Anurans of Great Lakes Coastal Wetlands Reliable Indicators of Ecological Condition

ABSTRACT Frogs and toads (anurans) are sensitive to a variety of anthropogenic stressors and are widely suggested as indicators of ecological condition. We surveyed 220 coastal wetlands along the U.S. shores of the Laurentian Great Lakes and quantified relationships between presence of anuran species and degree of anthropogenic disturbance. Results were used to derive explicit, functional relationships between environmental condition and anuran occurrences. These functions were subsequently used to calculate a multi-species indicator of ecological condition at other (novel) wetlands. Of 14 anuran species observed, spring peeper (Pseudacris crucifer) exhibited the strongest and most consistent relationship with environmental condition across the entire study area. Other species exhibited significant relationships with the environmental gradient, but the direction of association varied geographically or the overall species abundance was very low (e.g., mink frog, Rana septentrionalis). Even if applied to separate ecological provinces (Laurentian Mixed Forest or Eastern Deciduous Forest), multi-species estimates of wetland condition based on anurans are not much better indicators of environmental condition based on human disturbance than are indices based solely on occurrence of spring peeper. Nevertheless, indicators grounded in explicit relationships with environmental stress are superior to traditional measures (e.g., species richness) that combine species with different responses to the stress gradient. At least one anuran species (spring peeper) can contribute meaningfully to the assessment of ecological condition in Great Lakes coastal wetlands; its value as an indicator will be improved if it can be combined with information from other wetland species such as birds, fishes, and vascular plants.

Survivorship and Population Densities of Painted Turtles (Chrysemys picta) in Recently Modified Suburban Landscapes

Abstract Populations of long-lived animals, such as semi-aquatic turtles, that depend on high survivorship of reproductive adults, are particularly susceptible to the negative effects associated with habitat modification in suburban areas. Survivorship of semi-aquatic turtles in suburban landscapes may be reduced as a result of a number of factors, including the elimination of appropriate nesting habitat and the introduction of human-subsidized predators. Unfortunately, few studies on turtle populations in anthropogenically modified habitats estimate vital rates, and researchers are rarely able to study populations both before and after development. We studied painted turtle (Chrysemys picta) vital rates at 5 ponds in the Charlotte Metropolitan area of North Carolina; 2 ponds and their surrounding habitat underwent development after the first year of study, 1 pond was on a golf course, and 2 were farm ponds. We used Program MARK to generate open population models examining the effects of location and sex on turtle survivorship. Our results showed relatively stable population densities over 4 years across all ponds, with the largest density (approximately 100 turtles/ha) occurring at a recently developed site. Among ponds, turtles had variable annual adult survivorship (ca. 60%–95%), and males generally had lower survivorship than females. Our results emphasize the importance of site-specific habitat factors that influence turtle population demography and indicate that for long-lived species, whose population densities may not respond immediately to habitat change, long-term monitoring efforts examining population vital rates are needed to more fully evaluate the effects of anthropogenic modification.