Melvin L. Warren

DYNAMICS IN SPECIES COMPOSITION OF STREAM FISH ASSEMBLAGES: ENVIRONMENTAL VARIABILITY AND NESTED SUBSETS

Stream landscapes are highly variable in space and time and, like terrestrial landscapes, the resources they contain are patchily distributed. Organisms may disperse among patches to fulfill life-history requirements, but biotic and abiotic factors may limit patch or locality occupancy. Thus, the dynamics of immigration and extinction determine, in part, the local structure of assemblages. We sampled fishes and stream habitat at 12 localities for two years (96 samples) to examine the deterministic nature of immigration and extinction processes in stream fish assemblages. Mean immigration rates for assem- blages were highest at large stream localities, where the pool of potential immigrants was largest. Mean extinction rates were highest where variability in the flow regime was high, though local refugia appeared to modify the extinction process at one locality. Significant nested subset patterns in species composition occurred over time for 7 of the 12 localities. The strength of the nesting was associated with mean immigration and extinction rates. Higher extinction rates corresponded to stronger nestedness, whereas higher immigration rates were associated with weaker nestedness. Across all species, both immigration and extinction rates were strongly associated with mean abundance. Species with high local abundances had higher immigration rates and lower extinction rates than did species with low local abundances. There were no significant associations between trophic guild or body size and immigration and extinction rate. This work supports the hypothesis that immigration and extinction rates for assemblages are predictable along environmental gradients, and that species are less prone to local extinction and more prone to colonize areas when they maintain high local abundances. The extinction process in local assemblages can be a highly ordered event leading to strong nested subset patterns, but immigration appears to be more stochastic.

Genetic effects of habitat fragmentation and population isolation on Etheostoma raneyi (Percidae)

The use of genetic methods to quantify the effects of anthropogenic habitat fragmentation on population structure has become increasingly common. However, in today’s highly fragmented habitats, researchers have sometimes concluded that populations are currently genetically isolated due to habitat fragmentation without testing the possibility that populations were genetically isolated before European settlement. Etheostoma raneyi is a benthic headwater fish restricted to river drainages in northern Mississippi, USA, that has a suite of adaptive traits that correlate with poor dispersal ability. Aquatic habitat within this area has been extensively modified, primarily by flood-control projects, and populations in headwater streams have possibly become genetically isolated from one another. We used microsatellite markers to quantify genetic structure as well as contemporary and historical gene flow across the range of the species. Results indicated that genetically distinct populations exist in each headwater stream analyzed, current gene flow rates are lower than historical rates, most genetic variation is partitioned among populations, and populations in the Yocona River drainage show lower levels of genetic diversity than populations in the Tallahatchie River drainage and other Etheostoma species. All populations have negative FIS scores, of which roughly half are significant relative to Hardy–Weinberg expectations, perhaps due to small population sizes. We conclude that anthropogenic habitat alteration and fragmentation has had a profoundly negative impact on the species by isolating E. raneyi within headwater stream reaches. Further research is needed to inform conservation strategies, but populations in the Yocona River drainage are in dire need of management action. Carefully planned human-mediated dispersal and habitat restoration should be explored as management options across the range of the species.

Spatial and temporal patterns in fish assemblages of upper coastal plain streams, Mississippi, USA

We assessed spatial, seasonal, and annual variation in fish assemblages over 17xa0months in three small- to medium-sized, incised streams characteristic of northwestern Mississippi streams. We sampled 17xa0962 fish representing 52 species and compared assemblages within and among streams. Although annual and seasonal variability in assemblage structure was high, fish assemblages maintained characteristics unique to each stream. High variability in fish catch-per-unit-effort (CPUE) was exemplified in one site where total CPUE increased an order of magnitude from July 1993 to 1994. Species turnover and percent dissimilarity were often higher seasonally than annually, consistent with a period of change in spring to early summer and a return to similar species compositions between summers. Temporal variability was also high at the individual species level, and no species were classified as stable. We found little evidence for correlation between changes in fish assemblage structure and measured habitat conditions. The fish characteristics fit the profile of colonizing assemblages, which probably resulted from both natural and anthropogenic causes. Flashy hydrographs , created in part by stream channelization and incision and watershed deforestation, may play a large role in structuring these fish assemblages. Extreme interannual variability in assemblages in the absence of detectable habitat change has important implications for the statistical power of fish monitoring programs designed to detect trends in fish assemblages over time.

Troglomorphic sculpins of the Cottus carolinae species group in Perry County, Missouri: distribution, external morphology, and conservation status

The existence of cavernicolous sculpin (here allocated to Cottus carolinae, banded sculpin, and referred to as grotto sculpin), in the karst regions of Perry County, Missouri, first came to our attention in 1991. Examination of 35 caves in Missouri, 96 in Illinois, 17 in Tennessee, two in Indiana, and 11 in Arkansas revealed that banded sculpin are common in cave habitats; however, grotto sculpin are limited to two karst areas of Perry County, Missouri, where they are known from only six cave systems. These caves and their streams are extensive and apparently provide a unique habitat compared to other karst systems; this may be a critical factor in the present restricted distribution of the grotto sculpin. Grotto sculpin occupy pools and riffles of cave streams, and occur over a variety of substrates, from sediment to breakdown. Density estimates in Mystery and Running Bull caves were 0.29 and 0.63 individuals m-2, respectively. Grotto sculpin have small eyes (1–6% SL vs. 6–10% SL in epigean samples), significantly reduced pigmentation (including nearly complete loss of dorsal saddles), a reduction in pelvic fin ray number (from 4+4 elements to often 4+3 , or 3+3), and enlarged cephalic lateralis pores (e.g., mandibular pores of cavernicolous samples are 2–3 times those of epigean stream samples). Multivariate analyses of body shape revealed statistically significant separation of epigean and hypogean samples, with eye size highly variable, but smallest in the Running Bull Cave population. We interpret these results as representative of losses associated with long-term cave habitation. Caves of Perry County provide ample habitat for grotto sculpin, but because the caves are located downgradient of the city of Perryville and an intensively farmed landscape, point and non-point source pollution threaten their continued existence. Escape of farm-pond fishes through the extensive sinkhole network in Perry County has increased potential predation pressure on grotto sculpin by channel catfish, Ictalurus punctatus, and other species normally excluded from cave environments.

Spatio-temporal patterns of the decline of fresh water mussels in the Little South Fork Cumberland River,USA

The Little South Fork Cumberland River, Kentucky and Tennessee, USA, was a globally important conservation refugium for freshwater mussels (Mollusca: Unionidae) because it supported an intact example (26 species) of the unique Cumberland River mussel fauna including imperiled species. We used previous surveys and our 1997–1998 survey to reconstruct the historical fauna, to describe spatio-temporal patterns of density and number of species, and to evaluate the probable sequence and cause of observed mussel declines. We were specifically interested in better understanding how mussel assemblages respond to chronic disturbances, and how these changes manifest in persistence patterns. Density and numbers of species declined steadily from 1981 to 1998, but declines occurred first in the lower river (early 1980s), followed by declines in the upper river (late 1980s to early 1990s). Of the total species recorded from the Little South Fork, 17 (65%) are seemingly extirpated and five others appear near extirpation. Declines are associated with at least two, temporally distinct major insults. Lower river declines are associated with surface mining, whereas, oil extraction activities are implicated in upper river declines. Regardless of causal factors, species persistence was primarily a function of predecline population size with only the most numerous and widespread species surviving. At this time, the river appears lost as a conservation refugium for mussels despite its remoteness, predominantly forested watershed, and several layers of existing statutory and regulatory environmental safeguards. We suggest that the river could be restored and mussels reintroduced if an interagency task force is formed to identify and mitigate specific stressors now affecting most mussel species in the river.

Social Vulnerability and Ebola Virus Disease in Rural Liberia.

The Ebola virus disease (EVD) epidemic that has stricken thousands of people in the three West African countries of Liberia, Sierra Leone, and Guinea highlights the lack of adaptive capacity in post-conflict countries. The scarcity of health services in particular renders these populations vulnerable to multiple interacting stressors including food insecurity, climate change, and the cascading effects of disease epidemics such as EVD. However, the spatial distribution of vulnerable rural populations and the individual stressors contributing to their vulnerability are unknown. We developed a Social Vulnerability Classification using census indicators and mapped it at the district scale for Liberia. According to the Classification, we estimate that districts having the highest social vulnerability lie in the north and west of Liberia in Lofa, Bong, Grand Cape Mount, and Bomi Counties. Three of these counties together with the capital Monrovia and surrounding Montserrado and Margibi counties experienced the highest levels of EVD infections in Liberia. Vulnerability has multiple dimensions and a classification developed from multiple variables provides a more holistic view of vulnerability than single indicators such as food insecurity or scarcity of health care facilities. Few rural Liberians are food secure and many cannot reach a medical clinic in <80 minutes. Our results illustrate how census and household survey data, when displayed spatially at a sub-county level, may help highlight the location of the most vulnerable households and populations. Our results can be used to identify vulnerability hotspots where development strategies and allocation of resources to address the underlying causes of vulnerability in Liberia may be warranted. We demonstrate how social vulnerability index approaches can be applied in the context of disease outbreaks, and our methods are relevant elsewhere.

Predator density and dissolved oxygen affect body condition of Stenonema tripunctatum (Ephemeroptera, Heptageniidae) from intermittent streams

The effects of population density, fish density, and dissolved oxygen on body condition of late-instar nymphs of Stenonema tripunctatum (Ephemeroptera, Heptageniidae) were investigated using nymphs sampled from isolated, upland stream pools over summer in central Arkansas, USA. All three factors exhibited high variation among pools. Body condition was negatively related to fish density, and positively related to dissolved oxygen (when included in the model). High fish densities may be related to low body condition because they cause reduced foraging or force earlier emergence at small body sizes. These results emphasize the combined effects of biotic and abiotic factors on body condition in mayflies, and support earlier findings that population density is a less-important factor.

Microhabitat estimation of an imperiled headwater fish, the Yazoo darter (Etheostoma raneyi), in Coastal Plain streams

Headwater fishes in the southeastern United States make up much of the fish biodiversity of the region yet many are imperiled. Despite this, the specific habitat requirements of imperiled headwater fishes in lowland Coastal Plain streams have rarely been quantified. Using data collected over three years of seasonal sampling we provide estimates of the microhabitat requirements of the imperiled Yazoo darter (Etheostoma raneyi Suttkus and Bart), a small benthic insectivore. Our results indicate that the species is a microhabitat specialist and that optimum microhabitat within degraded contemporary streams consists of a narrow range of water depths (about 20–30xa0cm), current velocityxa0≥xa00.25xa0m·s−1, complex stable debris piles, rooted macrophytes, and likely coarse substrate. No pronounced or generalized seasonal shifts in microhabitat use occurs, and no evidence exists for intraspecific partitioning of microhabitat. Though stable and complex instream cover is one of the most important variables explaining variation in microhabitat use by Yazoo darters, such cover is rare in the degraded streams within the range of the species. Current conservation classifications of the Yazoo darter by governmental agencies and nongovernmental organizations as well as associated management plans that are based on the assumption that Yazoo darters are habitat generalists should be reviewed in recognition of the increased risk of decline because Yazoo darters are microhabitat specialists. These considerations should also be extended to other closely related imperiled species of snubnose darters.

Forest landscape restoration: linkages with stream fishes of the southern United States

The southern United States with over 600 native freshwater fishes supports one of the richest freshwater fish faunas on Earth, but many fishes in the region are imperiled. Historic and current land use dramatically altered the region’s landscape and its streams and rivers and consequently disrupted important linkages between forests and fishes. Impacts to the stream and river systems occurred in three overlapping developmental eras, each of which had unique and often profound effects on forests, fishes, or aquatic habitats: the era of agricultural and timber exploitation; the era of dam building and channel modification; and the era of population growth, industrialization, and urbanization. Benefits to fishes that could emerge from restoration of forest landscapes including: wood as habitat and cover for fishes, a substrate for fish food production, and a fish spawning substrate; the role of streamside forests in moderating water temperature; and use of floodplain forests by fish to forage and reproduce. Many fishes in the region derive multiple benefits from instream wood. The region faces major challenges in conserving not only native fishes but the entire richly diverse system of streams, rivers, and wetlands and the fauna they support. I believe forest landscape restoration could be an extremely positive tool in meeting these challenges and that rehabilitation of warmwater streams is possible with current knowledge but not without major shifts in stream corridor management strategies. However, implementing forest restoration in these settings is a major challenge given their past and current uses and management, regardless of the potential ecological services restoration could provide. The long-term challenge, if restoration is accomplished, will be managing riparian forests sustainably in a landscape composed of highly differing land uses overlain by a highly fragmented matrix of landownership and attitudes about the land.

Effects of Introduced Small Wood in a Degraded Stream on Fish Community and Functional Diversity

Abstract n Though the effects of introduced wood on fishes is widely studied for salmonids in upland coldwater streams, there are few studies on this topic conducted in the Coastal Plain of the southeastern US. This research gap is problematic because the introduction of wood is a critical component of efforts aimed at conserving the threatened fish diversity of the Coastal Plain, but managers lack data on the effects of installed wood on fish communities. Over a nearly 4-year study period, we contrasted the effects of introduced, small, wood bundles on the fish community in a channelized and deeply incised sand-bed Coastal Plain stream with an unmanipulated reference treatment. The central question was whether or not stream reaches with introduced wood had greater taxonomic and functional diversity than unmanipulated reference reaches within the same stream. The introduction of modest amounts of small wood had measurable and biologically significant positive impacts on fish community composition and perhaps functional diversity relative to stream reaches lacking wood. However, species-specific responses varied among treatments, suggesting the design of wood installations has an impact on whether or not managemen t goals are achieved.