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

Background/Question/Methods
As urbanization increases across the globe, more ecologists have taken note of its consequences to stream systems. Sufficient data have been collected to document repeated patterns in urbanized streams for many abiotic parameters, aquatic insects, and fish. For example, we now know that urbanized streams experience more frequent and intense spates as a result of increased runoff form impervious surfaces in the urban watershed. The spates eventually lead to a more incised and wider stream bed. Such abiotic shifts consistently result in decreased aquatic invertebrate and fish diversity. More recently, stream-breeding salamanders have been observed to decrease in density in urban areas. We monitored the density of southern two-lined salamanders for the duration of two cohorts in 12 streams in western Georgia, USA. We then used path analysis to determine the relationships between land-use change, abiotic shifts in the stream environment, and larval salamander density. 

Results/Conclusions
We found that southern two-lined salamanders in the streams we monitored exhibited no change in reproductive output between urban and reference habitats. However, repeated sampling throughout the larval period revealed a large decline in density of larvae in urban areas prior to metamorphosis, while a similar decline was not seen in reference habitats. We evaluated several hypotheses that might explain the observed decline in urban areas, and a model in which increased impervious surface causes an increase in spate frequency and magnitude, which then leads to decreased larval density had the most support. This is the first attempt to compare multiple plausible hypotheses as to why salamander density and diversity decreases in urban habitats. By describing larval density at the beginning and end of the larval period, and by identifying a likely mechanism for the observed decline in density, species-specific and stream restoration efforts can be enhanced.
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The Rational Authority of Morality: Reason Internalism and Negative Duties

In this essay, I will argue that there are moral requirements which are requirements of practical reason that apply to all agents independent of their motives. First, I will outline the argument for the thesis of reason internalism and then briefly set up the resulting problem for the rational authority of morality. To resolve this problem, I will argue for a principle of reason transmission. From this principle, I will argue that there are cases in which agents fail to have a reason for action, regardless of their motivations. Further, I argue that these are universal requirements. Thus, I conclude that there are actions that rationality requires all agents not to do

In-stream habitat predicts salamander occupancy and abundance better than landscape-scale factors within exurban watersheds in a global diversity hotspot

The southern Appalachian Mountains have experienced rapid human population growth rates since the 1980s. Land used practices are shifting from rural to residential. The majority of development has been low density, and is often near biologically diverse areas such as National Forests and National Parks. The long-term effects of urbanization in the southeastern Appalachian Mountains are not clearly understood and even less is known with respect to stream salamander response to urbanization. In order to determine the temporal influence of exurban housing on southern Appalachian streams we sampled 27 first- and second-order streams in watersheds containing exurban developments ranging in age from 4 to 44 years, along with eight forested streams, over the course of two summers. We sought to determine if the relative age of an exurban development related to occupancy and abundance of southern Appalachian stream salamanders. Age of exurban development and other watershed scale variables were not top predictors of salamander assemblages, while local site variables such as salinity and undercut banks predicted the abundance of several species of salamander. Our results suggest local habitat improvements can be used to better conserve salamanders and stream ecosystems in an increasingly urbanized region

Urbanization and Stream Salamanders: A Review, Conservation Options, and Research Needs

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