Michael M. Gangloff

North American beavers (Castor canadensis) are ecosystem engineers that create novel habitats in stream ecosystems. Although driven to the edge of extinction by historical over‐exploitation, beavers are recolonizing much of their former range. In the Southern Appalachian Mountains beavers alter habitats occupied by diverse fish communities across a mosaic of changing forest cover and management priorities. Fishes were sampled from nine streams with active beaver ponds and from seven streams with inactive ponds in the Southern Appalachians during summer 2019. The status of beaver ponds was among the most important factors affecting fish communities; however, both active and inactive beaver ponds affected fish community structure, α‐diversity, and local contributions to β‐diversity (LCBD). Fish α‐diversity was lower in reaches from streams with active ponds and the magnitude of this reduction was dependent on the position relative to a pond. However, both active and abandoned beaver ponds and pond tail races had higher LCBD values compared with free‐flowing reaches. Arcsin‐transformed forest cover did not improve the model fit for any dependent variables. Indicator species analysis found that two species had an association with active beaver ponds, whereas eight species were associated with inactive beaver ponds or free‐flowing reaches. The effects of beaver impoundments on fish communities in Appalachian streams are dependent on the pond activity level and spatial context. Although diversity and species richness may be reduced in individual habitats, beaver ponds contribute to higher biodiversity at a regional spatial scale. An increased understanding of beaver effects on Southern Appalachian fish communities will enable stakeholders to make informed decisions regarding the management of sensitive or economically important fishes. Mitigating conflicts between sensitive resources and these ecosystem engineers will become an increasingly important management concern as beaver populations recover in the Southern Appalachians.

Invasive species introduction is one of the major ongoing ecological global crises. Identifying factors responsible for the success of invasive species is key for the implementation of effective management actions. The invasive filter-feeding bivalve, Corbicula, is of particular interest because it has become ubiquitous in many river basins across North America and elsewhere. Here we sampled bivalve assemblages, environmental indicators, and land cover parameters in the Ouachita highlands in southeastern Oklahoma and southwestern Arkansas, and in the Gulf Coastal Plain of Alabama to test three working models (using structural equation modeling, SEM) based on a priori scientific knowledge regarding Corbicula invasions. Our models tested three competing hypotheses: (1) Native mussel declines are related to land use changes at the watershed level and subsequent Corbicula colonization is a result of an empty niche; (2) Corbicula abundance is one of the factors responsible for native mussel declines and has an interactive effect with land use change at the watershed level; (3) Native mussel declines and Corbicula success are both related to land use changes at the watershed level. We found no evidence for the first two hypotheses. However, we found that environmental indicators and land cover parameters at the watershed scale were robust predictors of Corbicula abundance. In particular, agricultural land cover was positively related with Corbicula density. These results suggest that further improvement of conventional agricultural practices including the optimization of fertilizer delivery systems may represent an opportunity to manage this species by limiting nutrient inputs to stream ecosystems. Preservation of extensive floodplain habitats may help buffer these inputs by providing key ecosystem services including sediment and nutrient retention.

Freshwater communities are threatened by the conversion of natural landscapes for urban and agricultural purposes. Changes to land use may disrupt stream nutrient and geomorphological processes and reduce water quality, increase sedimentation, and decrease habitat heterogeneity eventually leading to species loss and decreases in ecosystem productivity. Endemic species are frequently at greater risk of habitat‐mediated fragmentation and extirpation due to their constrained distributions. The Kanawha darter (Etheostoma kanawhae) is an understudied fish endemic to the New River Drainage in North Carolina and Virginia, USA. To investigate the potential effect(s) of land‐use change on Kanawha darters, naïve occupancy was modelled using instream habitat characteristics and upstream forest cover. Generalized linear models revealed that instream habitat and forest cover are reliable predictors of Kanawha darter site occupancy. Specifically, models demonstrated that occupancy increased in reaches with reduced stream width, velocity, and bedrock substrate but higher concentrations of coarse woody material. Kanawha darter occupancy was also positively associated with the extent of forest cover in upstream catchments. Although Kanawha darters are not currently considered imperilled, most populations occurred in isolated reaches separated by large sections of unoccupied habitat. Continuing ex‐urban development in riparian zones is likely to be the primary threat to Kanawha darters and other endemic species in this catchment. Resource managers and stakeholders should preserve forest cover in headwaters and occupied tributaries and protect or restore riparian zones along the main‐stem South and North Forks of the New River to preserve high‐quality habitat and enhance connectivity among isolated Kanawha darter populations. As human populations in montane regions continue to grow, there is a need to understand how land‐use change affects endemic freshwater species. This study further supports the importance of retaining forest cover as an effective strategy for protecting and restoring populations of endemic fishes in high‐gradient streams.

The Tennessee–Tombigbee Waterway is among the largest and most expensive environmental engineering projects of the 20^th century. The waterway accommodates barge navigation between the Tennessee River Drainage and Mobile River Basin through a series of locks, dams, canals, and dredged and diverted streams. These structures have altered riverine habitat and fragmented lotic habitats resulting in isolated freshwater mussel populations in patches of streams such as the East Fork Tombigbee River, where 42 species were known historically. The first post‐waterway mussel surveys in 1987 and 1988 reported 31 taxa. During 2010 and 2011 surveys, 70 sites were sampled using both timed searches and quadrats and detected 29 extant mussel species. Between 1988 and 2010–2011 the relative abundance of nine mussel taxa decreased, whereas the abundance of 11 taxa increased. The populations of three federally listed species were detected at levels below the detection limits in 1988 as well as three non‐native unionids that appear to have colonized the East Fork Tombigbee River via the Tennessee–Tombigbee Waterway River. Although mussel abundance and total species richness were relatively unchanged, assemblage composition shifted toward animals typical of smaller streams rather than large rivers. This shift suggests that present‐day East Fork Tombigbee River habitats favour smaller‐bodied, thinner shelled taxa that are laterally compressed and lack shell sculpture. These taxa are likely to be better adapted to hydrologically and hydraulically variable habitats than are thick‐shelled, large bodied, and sculptured mussels. The results suggest that mussel assemblages are dynamic and may exhibit predictable responses to changes in hydrology, physical habitat conditions, and stream connectivity. However, examinations over broad (20+ yr) temporal scales are needed to observe these shifts. The data demonstrate the value of regular monitoring of diverse mussel assemblages and the importance of stream connectivity and flow modifications to this long‐lived group of benthic invertebrates.

Conspicuous coloration coupled with secondary defensive mechanisms is known as aposematic coloration and is used in predator avoidance and defense. Classic theory argues that aposematic signals tend to be more effective in larger organisms as they are intrinsically more easily detected by predators and are also more profitable prey items. Thus, it has been hypothesized that conspicuous coloration evolves in tandem with increased body size in aposematic prey because this likely increases the visibility and efficacy of the signal. To test this hypothesis, we used a comparative phylogenetic approach to investigate associations between body size and conspicuous coloration in two North American salamander genera: Ambystoma and Plethodon, both of which secrete noxious compounds to deter predators. Our analyses showed that increased conspicuous coloration co-evolved with increased body size in Ambystoma, yet we found the opposite relationship in the Plethodon clade. We speculate this is likely because Ambystoma are generally larger than Plethodon and exhibit gregarious mating behavior. Future studies should explore the toxicity of slimy skin secretions and how this may contribute to aposematic signaling in salamanders.

Earth's aquatic habitats are some of its most important ecosystems and support populations of many of its most imperilled species. The future demands of Earth's growing human populations will increasingly stress its aquatic resources on multiple spatial and temporal scales, as highlighted by numerous authors when predicting trends in biodiversity in many key aquatic hotspots. Identifying key stressors and understanding potential linkages between these stressors are important first steps to mitigating human impacts on at‐risk aquatic resources. Here, an overview is provided of the established and emerging threats to aquatic biodiversity at local, regional and global scales, including emerging diseases, expanding influence of invasive species, new industries, and the accelerating trajectory of climate change, as well as perspectives on potential management strategies. Copyright © 2016 John Wiley & Sons, Ltd.

As part of a study of aquatic faunal community changes along riverine-lacustrine transition zones upstream of Lewis Smith Reservoir in northwest Alabama, USA, we collected crayfish from 60 sites in the Sipsey Fork, Brushy Creek, and selected tributaries (Black Warrior River system). After finding two unexpected and possibly-introduced crayfish species, we expanded our investigation of crayfish distributions to include crayfish obtained from stomachs of black bass (Micropterus spp.) caught at seven sites in the reservoir. To explore what crayfish species were in the drainage historically, we examined museum databases as well as stomach and intestinal contents of a variety of preserved fishes that were caught in the Sipsey Fork and Brushy Creek drainages upstream of the reservoir in the early 1990’s. Of the seven crayfish species collected, one, Orconectes (Procericambarus) sp. nr ronaldi, was not previously reported from Alabama, and another, O. lancifer, was not reported from the Black Warrior River system prior to the study. Three are known or possibly introduced species. Upstream of the reservoir, the native species Cambarus obstipus, C. striatus, and O. validus were common. The same three species were found in fish collected in the 1990’s. Orconectes perfectus was found only in the reservoir but may be native to the drainage. Orconectes lancifer was in the reservoir and in stream reaches influenced by the reservoir. Evidence points to O. lancifer being introduced in the drainage, but this is uncertain. Orconectes sp. nr ronaldi was found in a relatively small portion of Brushy Creek and its tributaries, in both flowing and impounded habitats, and may be introduced. Orconectes virilis is introduced in Alabama and was found only in stomachs of fish collected in the reservoir.