Kyle Barrett

Urbanization and stream salamanders: a review, conservation options, and research needs

Abstract: Urban areas are increasing in size and human population density. The implications of widespread urbanization are apparent for a wide variety of stream organisms, but the responses of stream-dwelling salamanders to urbanization have been understudied historically. Studies on this assemblage have increased sufficiently over the last decade to warrant a review and synthesis of current knowledge. Our survey of the literature indicates a research bias toward species within the Piedmont ecoregion of the USA and a strong emphasis on changes in species richness, relative abundance, and occupancy along an urbanization gradient. Very few investigators have examined vital rates for specific life stages, population dynamics over extended periods, or mechanistic explanations for the specific aspects of urbanization that drive species loss and decline. We reviewed a broad array of literature on stream salamanders to identify the key abiotic and biotic drivers that explain species responses in urban watersheds. Based on these findings and the applied ecological literature, we identified conservation options for urban areas where decision makers and stakeholders wish to preserve stream salamanders and their habitats. We have listed 7 future research priorities that will further efforts to conserve stream salamanders in rapidly urbanizing regions.

Evolution of sexual dimorphism in the forelimb muscles of Andrew's toad (Bufo andrewsi) in response to putative sexual selection

Sexual differences in morphological traits are widespread among animals. Theory predicts that dimorphism in secondary sexual characters evolves as a consequence of sexual selection. We investigated the intersexual difference in mass of forelimb muscles of the Andrews toad, Bufo andrewsi, an elongated species inhabiting montane regions in western China. Our results showed that average body size of females was significantly larger than males. However, when the influence of body size was removed, the forelimb muscle mass of males significantly exceeded that of females, and total mass of forelimb muscles of amplectant males was significantly larger than that of non-amplectant males. These results suggest that the robustness of the forelimbs can allow amplectant males to retain a firm grip on the female in amplexus, which may aid resistance to inference by conspecific males. Our findings are consistent with the prediction that sexual selection favors large forelimb muscle mass in males.

Water from Urban Streams Slows Growth and Speeds Metamorphosis in Fowler's Toad (Bufo fowleri) Larvae

Abstract We evaluated the effect of a potentially stressful urban aquatic environment on growth and development of Fowlers Toad (Bufo fowleri) larvae. We reared larvae to metamorphosis in water from urban and forested streams in a laboratory setting. We found no evidence of oral disc anomalies associated with urban environments, but we did find that tadpoles in these environments were smaller at 26 days of age (but not at metamorphosis) and metamorphosed faster than tadpoles reared in water from forested streams. The observed results were partially consistent with the predictions of H. M. Wilbur and J. P. Collins, who suggested in 1973 that stressful aquatic environments should result in an earlier date of metamorphosis for larvae attempting to escape that environment. We suggest further work to pinpoint factor(s) responsible for the results we observed, and we relate our findings to previous findings of declines in amphibian species richness in the study area.

Southern Two-Lined Salamander Diets in Urban and Forested Streams in Western Georgia

Abstract Streams are heavily affected by watershed urbanization as increased stormwater runoff changes their physical and chemical composition. Benthic macroinvertebrate species richness has been consistently shown to decline with urbanization. Conversely, biomass of macroinvertebrates can increase with urban development. We examined the effect of such shifts in macroinvertebrate assemblages on the diet of larval Eurycea cirrigera (Southern Two-lined Salamanders). Salamanders have been documented to decrease in diversity in urban habitats; however, Southern Two-lined Salamander larvae which persist in urban streams (at lower densities) tend to grow larger than larvae in forested streams. Diet may play a role in these diversity and growth trends. We examined prey consumed by larval salamanders during spring, summer, and winter seasons across urban and forested watersheds. Prey diversity in salamander digestive tracts peaked during summer. We found Chironomidae (Diptera) larvae to be the most common prey item, followed by Ostracoda. Gastropoda were a common prey item during summer, which may be indicative of nutrient requirements of premetamorphic larvae. Overall, we observed minor differences in larval diet between urban and forested watersheds. A previous study within these same watersheds found that larvae in urban watersheds grew larger than those in forested watersheds, and the authors suggested prey availability may have contributed to that finding. The diet data we present here do not support such a hypothesis.

Long-Term Bird Assemblage Trends in Areas of High and Low Human Population Density

Urban areas are expanding globally, and the impact of high human population density (HHPD) on bird species richness remains unresolved. Studies primarily focus on species richness along an urban-to-rural gradient; however, some studies have analyzed larger-scale patterns and found results that contrast with those obtained at smaller scales. To move the discussion beyond static species richness patterns, we analyzed the effect of HHPD on bird assemblage dynamics (year-to-year extinction probability, turnover, changes in species richness) across the United States over a 25-year period. We found that bird assemblages in both high and low human population density areas changed significantly over the period of record. Specifically, bird assemblages increased in species richness on average. Assemblage change in areas of HHPD was not significantly different from assemblage change in areas with LHPD. These results suggest that human population density alone does not alter the persistence of avian assemblage patterns.

Detritus Quality and Locality Determines Survival and Mass, but Not Export, of Wood Frogs at Metamorphosis

Single-site experiments have demonstrated detritus quality in wetlands can have strongly negative, neutral, and even positive influences on wildlife. However, an examination of the influence of detritus quality across several regions is lacking and can provide information on whether impacts from variation in detritus quality are consistent across species with wide ranges. To address this gap in regional studies we examined effects of emergent and allochthonous detritus of different nutrient qualities on amphibians and assessed a mechanism that may contribute to potential impacts. We used aquatic mesocosms to raise wood frogs (Rana sylvatica) from two regions of the United States with whole plants from purple loosestrife (Lythrum salicaria), leaf litter from native hardwood trees, and a mixture of both. We examined several metrics of amphibian fitness and life history, including survival, number of days to metamorphosis, and size at metamorphosis. Further, we quantified whether the effects of detritus type could translate to variation in anuran biomass or standing stock of nitrogen or phosphorus export. Our results show detritus with high nutrient quality (purple loosestrife) negatively influenced survival of wood frogs, but increased size of metamorphic individuals in two different regions of the United States. Despite the decrease in survival, the increase in size of post-metamorphic anurans raised with high quality detritus resulted in anuran biomass and standing stock of N and P export being similar across treatments at both locations. These results further demonstrate the role of plant quality in shaping wetland ecosystem dynamics, and represent the first demonstration that effects are consistent within species across ecoregional boundaries.

Stream and Riparian Habitat Use by Anurans along a Forested Gradient in Western Georgia, USA

Urban development is known to alter the structure, chemistry, and biota associated with stream systems; however, little is known about the dynamics of anurans that breed in and around streams. We used automated devices to record breeding anurans for one year across a forested gradient in an effort to identify species-specific sensitivities to urbanization. Six of 13 total species found during the study were present in surveyed streams that were representative of a gradient ranging from heavily urbanized to largely forested, and maximum species richness occurred in watersheds with rapid urban development but low values of impervious surfaces such as pavement and roof tops. The best landscape-scale predictor of assemblage metrics such as species richness, total species activity, and species diversity was generally percent forest cover at the watershed scale (or in very large buffers around the sample point). We used Bayesian inference to estimate detection probability and occupancy for 11 species. While detection probability varied across sampling occasions, there was no evidence that occupancy was a function of forest loss for any species. Urban streams and riparian areas are often severely altered when compared to similar habitats in forested areas. Anuran richness and diversity from urban areas was not altered to the same extent as caudates, which have been sampled from these same streams in previous studies. Increased vagility of anurans, coupled with different breeding strategies, may help to explain this discrepancy.

Detritus Quality Produces Species-Specific Tadpole Growth and Survivorship Responses in Experimental Wetlands

Abstract Although many non-native species negatively influence amphibian populations, non-native aquatic vegetation has been documented to have positive, negative, and neutral effects on anuran larvae. To evaluate the response of anurans to non-native plants, we exposed two frog species, Gray Treefrog (Hyla versicolor-chrysoscelis) and Southern Leopard Frog (Lithobates sphenocephalus), to detritus from either native hardwood trees, non-native purple loosestrife (Lythrum salicaria), or a mixture of both. Experiments were conducted in artificial ponds, and we recorded the survival, growth, and metamorphic size of larvae. Gray Treefrog survival was highest in tanks with native leaf litter. Developmental time did not differ among treatments, but tadpoles in tanks with purple loosestrife were significantly larger than those in tanks with native leaf litter. Southern Leopard Frog survival was lowest in the mixed vegetation treatment. As with Gray Treefrogs, developmental time was not influenced by treatment, but larvae from tanks with purple loosestrife were significantly larger than those from other treatments. Lower survival in the presence of purple loosestrife has been linked to secondary compounds in the plant, and the higher growth rates we observed are consistent with recent findings on response of anuran larvae to other non-native plants. Our results suggest the negative effects of purple loosestrife detritus on the species examined are manifest at the individual and (perhaps) population level. Because the fewer animals that did survive in tanks with purple loosestrife grew larger, overall ecosystem-level effects may not be present; however, larger scale experiments are needed to evaluate this hypothesis.

Stable isotopes reveal an invasive plant contributes more than native sources to anuran larvae diets

ABSTRACT Foraging theory suggests organisms increase their fitness through dietary and energetic choices. In nature, organisms choose to consume balanced optimal diets but as exotic plants invade ecosystems, new foraging options become available. Often these plants have different traits and can negatively affect fitness of foragers by lowering survival or growth due to toxicity. Wetland habitats are highly susceptible to plant invasions which can have negative effects on nutrient cycling. The purpose of this study was to examine whether invasion of purple loosestrife (Lythrum salicaria) alters tadpole foraging preference thus potentially impacting their survivorship and fitness. We designed a common garden experiment and utilized stable isotopic signatures to investigate the contribution of purple loosestrife and native hardwood detritus to larval wood frog (Rana sylvatica) and southern leopard frog (Rana sphenocephala) diets. Tadpoles derived a higher percentage of resources from purple loosestrife compared to native hardwood detritus when presented with both options, despite its high concentration of toxic secondary compounds. It is unknown if tadpoles can detect competing fitness signals that may be associated with higher nutrient and toxicity levels in purple loosestrife. Discovering the presence or absence of such signals will promote a greater understanding of selective foraging in changing environments.

Increased flood frequency and magnitude decreases density of a stream-breeding salamander in urbanized watersheds

• Path analysis was used to evaluate individual models and AIC was used to compare among models. Fig. 2. Path diagram representing a model describing how land cover change impacts salamanders in urban streams. Spate frequency was the top model among those compared by AIC (see Bonus Table). Boldface numbers represent multiple correlation coefficients (analogous to r2) • density decreases because larvae are washed from streams. Experiment supported the conclusions from field data described above. Salamander density .