Our current understanding of the Upper Mississippi River System floodplain forest

The silver maple-American elm floodplain forest spans throughout the floodplains of the Upper Mississippi River System (UMRS). These forests of the UMRS today are less diverse than those of pre-European expansion (ca. early 1800s). Scientists and land managers are concerned about loss of species diversity including mast species such as pin oak (Quercus palustris Muenchh.), swamp white oak (Quercus bicolor Willd.), bur oak (Quercus macrocarpa Michx. Q), pecan (Carya illinoinensis (Wangenh.) K. Koch), and other hickories. The Great Midwest Flood of 1993 maintained species diversity in the lower, unimpounded region of the Upper Mississippi River, providing an opportunity for eastern cottonwood and black willow to regenerate in this portion of the Mississippi River. However, throughout the entire region, floodplain forests of the Upper Mississippi River have become less diverse, and have become dominated by the flood-tolerant and shade-tolerant silver maple (Acer saccharinum L.). The imminent loss of green ash (Fraxinus pennsylvanica Marsh.) to the Emerald Ash Borer (Agrilus planipennis Fairmaire) follows an already changing forest structure due to a disease-related shift of American elm (Ulmus americana L.) from the overstory to the midstory strata. Another invasive, reed canary grass (Phalaris arundinaceae L.), interferes with evolved mechanisms for establishment as it outcompetes trees of the early successional floodplain forest. Further research is needed to create and maintain diverse floodplain forest communities that have been lost under current conditions. Returning flood-prone agricultural lands within the floodplain to the floodplain forest will improve the health and connectivity of the river system, increase the diversity of habitats, and provide flood relief for communities of the Upper Mississippi River.     

A spatial simulation model for forest succession in the Upper Mississippi River floodplain

A Markov-chain transition model (FORSUM) and Monte Carlo simulations were used to simulate the succession patterns and predict a long-term impact of flood on the forest structure and growth in the floodplain of the Upper Mississippi River and Illinois River. Model variables, probabilities, functions, and parameters were derived from the analysis of two comprehensive field surveys conducted in this floodplain. This modeling approach describes the establishment, growth, competition, and death of individual trees for modeled species on a 10,000-ha landscape with spatial resolution of 1 ha. The succession characteristics of each Monte Carlo simulation are summed up to describe forest development and dynamics on a landscape level. FORSUM simulated the impacts of flood intensity and frequency on species composition and dynamics in the Upper Mississippi River floodplain ecosystem. The model provides a useful tool for testing hypotheses about forest succession and enables ecologists and managers to evaluate the impacts of flood disturbances and ecosystem restoration on forest succession. The simulation results suggest that the Markov-chain Monte Carlo method is an efficient tool to help organize the existing data and knowledge of forest succession into a system of quantitative predictions for the Upper Mississippi River floodplain ecosystem.     

Cerulean Warblers in the Ozark region: habitat selection,breeding biology,survival, and space use

Cerulean Warblers (Setophaga cerulea) are a species with declining populations that exhibit regional variation in habitat selection and demographic rates. The Ozark region of the south‐central United States likely provides important habitat for Cerulean Warblers, but little is known about their breeding biology in that region. We studied Cerulean Warblers in riparian forests of the Ozarks of Arkansas from 2018 to 2020. We assessed multi‐scale habitat selection for vegetative and topographic features, documented their breeding biology, estimated within‐season and annual apparent survival, and estimated territory sizes. We found that Cerulean Warblers selected riparian habitat characterized by large‐diameter trees across all spatial scales. Contrary to the results of previous studies, males appeared to avoid white oaks (Quercus spp., Section Quercus) at the territory scale, but this avoidance may reflect an underlying preference for riparian habitat. Our logistic‐exposure estimate of nest survival (0.32; 85% confidence interval: 0.21–0.46) was similar to the median of estimates reported in previous studies. Our results indicate that maintaining riparian forests with large trees is important to provide suitable habitat for Cerulean Warblers in the Ozark region. Because of similarities in habitat selection among regions, some management practices from other populations, including retaining large trees and promoting a heterogeneous canopy structure, may be useful for managing for Cerulean Warblers in riparian areas of the Ozarks. However, selection for topography and tree species by Cerulean Warblers in our study also suggests that region‐specific management strategies will be beneficial. Finally, our demographic rate estimates for this population should prove valuable in future full‐annual‐cycle population modeling efforts.     

Effects of flood frequency and duration on the allometry of community-level stem size-density distributions in a floodplain forest

? Premise of the study: Consistent with the self-thinning law of plant population ecology, Niklas et al. in 2003 proposed that stem size-density distributions (SDDs) of multispecies forest communities should change in very predictable ways as a function of the effects of past disturbances on average tree size. To date, empirical tests of this hypothesis have not been pursued in floodplain settings. ? Methods: SDDs were constructed using tree stem-size and density data from forest plots positioned along a flood frequency and duration gradient in the Upper Mississippi River floodplain. ? Key Results: As flooding (both frequency and duration) increased, several small tree species were eliminated from forest plots and the persistent species increased in their size. Consistent with the predictions of Niklas et al., these changes corresponded with overall decreases in stem density, increases in average stem size, and reductions in both the Y-intercept and slope terms of the community-level SDDs. ? Conclusions: This study adds to a growing list of examples suggesting that theories related to forest community composition and biomass must account for both the broader effects of disturbances as well as the underlying biochemical processes that regulate plant growth. Further study is needed to fully address the role different disturbance frequencies play in determining plant density, diversity, average size, and associated size\frequency distributions.     

Historical record of an alligator gar,Atractosteus spatula (Lacépède, 1803), captured on the floodplain of the Middle Mississippi River at Columbia,Illinois, USA

Historical photographs, newspapers, and interviews can provide useful information on the abundance, distribution, and habitat use of rare fish species and can be useful in the development of conservation and management plans for target species. We report on the historical occurrence of Atractosteus spatula (alligator gar) on the Middle Mississippi River (MMR) floodplain near Columbia, Illinois (Monroe County), approximately 280.5 river kilometers above the Ohio River (River Mile 168) during the spring of 1937. Based on measurements taken from a photograph of a captured specimen and Mr. Paul Lopinot's recollection of the specimen's weight, the alligator gar was approximately 2.0 m total length and weighed 60 kg. An additional 25–30 large alligator gar were observed on the floodplain approximately 3.6 km from the river. The loss of seasonally inundated floodplain habitat due to construction of an extensive agricultural levee system on the MMR may be a contributing factor to the decline of the alligator gar in the northern portion of its range.     

Breeding bird species diversity across gradients of land use from forest to agriculture in Europe

Loss, fragmentation and decreasing quality of habitats have been proposed as major threats to biodiversity world‐wide, but relatively little is known about biodiversity responses to multiple pressures, particularly at very large spatial scales. We evaluated the relative contributions of four landscape variables (habitat cover, diversity, fragmentation and productivity) in determining different components of avian diversity across Europe. We sampled breeding birds in multiple 1‐km² landscapes, from high forest cover to intensive agricultural land, in eight countries during 2001?2002. We predicted that the total diversity would peak at intermediate levels of forest cover and fragmentation, and respond positively to increasing habitat diversity and productivity; forest and open‐habitat specialists would show threshold conditions along gradients of forest cover and fragmentation, and respond positively to increasing habitat diversity and productivity; resident species would be more strongly impacted by forest cover and fragmentation than migratory species; and generalists and urban species would show weak responses. Measures of total diversity did not peak at intermediate levels of forest cover or fragmentation. Rarefaction‐standardized species richness decreased marginally and linearly with increasing forest cover and increased non‐linearly with productivity, whereas all measures increased linearly with increasing fragmentation and landscape diversity. Forest and open‐habitat specialists responded approximately linearly to forest cover and also weakly to habitat diversity, fragmentation and productivity. Generalists and urban species responded weakly to the landscape variables, but some groups responded non‐linearly to productivity and marginally to habitat diversity. Resident species were not consistently more sensitive than migratory species to any of the landscape variables. These findings are relevant to landscapes with relatively long histories of human land‐use, and they highlight that habitat loss, fragmentation and habitat‐type diversity must all be considered in land‐use planning and landscape modeling of avian communities.     

Influence of lateral gradients of hydrologic connectivity on trophic positions of fishes in the Upper Mississippi River

1. Riverscapes consist of the main channel and lateral slackwater habitats along a gradient of hydrological connectivity from maximum connection in main channel habitats to minimum connection in backwaters. Spatiotemporal differences in water currents along this gradient produce dynamic habitat conditions that influence species diversity, population densities and trophic interactions of fishes. 2. We examined the importance of lateral connectivity gradients for food web dynamics in the Upper Mississippi River during spring (high flow, moderately low temperatures) and summer (low flow, higher temperatures). We used literature information and gut contents analyses to determine feeding guilds and stable isotope analysis to estimate mean trophic position of local fish assemblages. During June and August 2006, we collected over 1000 tissue samples from four habitats (main channel, secondary channels, tertiary channels and backwaters) distributed within four hydrologic connectivity gradients. 3. Mean trophic position differed among feeding guilds and seasons, with highest values in spring. Mean trophic position of fish assemblages, variability in trophic position and food chain length (maximum trophic position) of the two dominant piscivore species (Micropterus salmoides and M. dolomieu) in both seasons were significantly associated with habitat along the lateral connectivity gradient. Food chain length peaked in tertiary channels in both seasons, probably due to higher species diversity of prey at these habitats. We infer that food chain length and trophic position of fish assemblages were lower in backwater habitats in the summer mainly because of the use of alternative food sources in these habitats. 4. A greater number of conspecifics exhibited significant among‐habitat variation in trophic position during the summer, indicating that low river stages can constrain fish movements in the Upper Mississippi River. 5. Results of this study should provide a better understanding of the fundamental structure of large river ecosystems and an improved basis for river rehabilitation and management through knowledge of the importance of lateral complexity in rivers.     

Temporary connectivity: the relative benefits of large river floodplain inundation in the lower Mississippi River

Studies have demonstrated the importance of the synergistic relationship between large rivers and adjacent floodplain connectivity. The majority of large rivers and their associated floodplain have been isolated through a series of expansive levee systems. Thus, evaluations of the relative importance of floodplain connectivity are limited due to the aforementioned anthropogenic perturbations. However, persistent elevated river levels during spring 2011 at the confluence of the Mississippi River and Ohio River prompted the U.S. Army Corps of Engineers to create large gaps in the levee system producing an expansive floodplain (i.e. the New Madrid Floodway). Specifically, the New Madrid Floodway (approximately 475 km²) in southeast Missouri was created to divert part of the Mississippi River flow during catastrophic floods and thus alleviate flood risk on nearby population centers. Given the historic flooding of 2011, the floodway was opened and provided an unprecedented opportunity to evaluate the influence of floodplain inundation on fish species diversity, relative abundance, and growth. We sampled the floodplain and the adjacent river at three stratified random locations with replication biweekly from the commencement of inundation (late May) through early October. Overall, we found that species diversity, relative abundance, and growth were higher in the floodplain than the main river. Our data support previous examinations, including those outside North America, that suggest floodplain inundation may be important for riverine fishes. Given these apparent advantages of floodplain inundation, restoration efforts should balance benefits of floodplain inundation while safeguarding priority needs of humans.     

Feather mite abundance varies but symbiotic nature of mite‐host relationship does not differ between two ecologically dissimilar warblers

Feather mites are obligatory ectosymbionts of birds that primarily feed on the oily secretions from the uropygial gland. Feather mite abundance varies within and among host species and has various effects on host condition and fitness, but there is little consensus on factors that drive variation of this symbiotic system. We tested hypotheses regarding how within‐species and among‐species traits explain variation in both (1) mite abundance and (2) relationships between mite abundance and host body condition and components of host fitness (reproductive performance and apparent annual survival). We focused on two closely related (Parulidae), but ecologically distinct, species: Setophaga cerulea (Cerulean Warbler), a canopy dwelling open‐cup nester, and Protonotaria citrea (Prothonotary Warbler), an understory dwelling, cavity nester. We predicted that feather mites would be more abundant on and have a more parasitic relationship with P. citrea, and within P. citrea, females and older individuals would harbor greater mite abundances. We captured, took body measurements, quantified feather mite abundance on individuals’ primaries and rectrices, and monitored individuals and their nests to estimate fitness. Feather mite abundance differed by species, but in the opposite direction of our prediction. There was no relationship between mite abundance and any measure of body condition or fitness for either species or sex (also contrary to our predictions). Our results suggest that species biology and ecological context may influence mite abundance on hosts. However, this pattern does not extend to differential effects of mites on measures of host body condition or fitness.     

Theoretical habitat templets, species traits, and species richness: 548 plant and animal species in the Upper Rhône River and its floodplain

• 1 For practical reasons, conceptual developments in community ecology are usually based on studies of a restricted systematic group. The cooperation of thirty or so specialists in the synthesis of long-term ecological research on the Upper Rhône River, France, provided a unique occasion to investigate relationships among species traits, the habitat utilization by species, the relationship between species traits and habitat utilization, and trends of species traits and species richness in the framework of spatial-temporal habitat variability for 548 species of plants (Hyphomycetes, aquatic macrophytes, floodplain vegetation) and animals (Tricladida, Oligochaeta, several groups of Crustacea, Insecta and Vertebrata).
• 2 Using correspondence analysis, 100 modalities of eighteen species traits were examined; the resulting typology demonstrates that systematic groups are the most important elements for separating species traits such as size, fecundity of individuals, parental care, mobility, body form, and food type. Small species have an intermediate number of descendants per reproductive cycle and few reproductive cycles both per year and per individual; in contrast, large species have a high number of descendants per reproductive cycle and few reproductive cycles per year but many potential reproductive cycles per individual.
• 3 The analysis of habitat utilization in the Upper Rhône River and its floodplain by the 548 species demonstrated a vertical gradient separating interstitial from superficial habitats; a transverse gradient for superficial habitats from the main channel towards more terrestrial ones is also evident.
• 4 Because of a significant (P < 0.01) relationship between species traits and habitat utilization, traits such as size, fecundity of individuals, parental care, tolerance to variation in humidity, and respiration are arranged along the vertical and transverse habitat gradient. Size, the number of reproductive cycles per individual, and the tolerance to variation of humidity increases from permanent waters to temporary waters, aggrading habitats, and terrestrial habitats.
• 5 Species traits showed significant (P < 0.01) trends in the framework of spatial-temporal habitat variability and were compared with predictions based on the river habitat templet. Although each habitat showed a mixture of species traits at low temporal and spatial variability, and at high variability sites, trends corresponded to predictions for three traits (number of descendants per reproductive cycle, number of reproductive cycles per individual, attachment to soil or substrate) along a gradient of increasing temporal habitat variability.
• 6 The species richness of each habitat within the Upper Rhône River and its floodplain significantly (P = 0.03) increased as the spatial variability of habitats increased but there is no statistical correlation between spedes richness and temporal variability. An altemative hypothesis predicting that fewer spedes per resource occur in temporally stable habitats is also not supported.

     

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 F_IS 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.     

Species–topography association in a species-rich subtropical forest of China

Habitat specialization has been considered as a primary factor in determining the distribution of species. In this study, we investigated species–habitat associations while controlling for spatial neighbourhood effects in a large-scale (20 ha) stem-mapping plot in a species-rich subtropical forest of China. Habitat specialization was measured by topographic variation and its effects on species distributions were modelled at three different spatial scales (10×10, 20×20 and 25×25 m²) using log-linear regression models and randomization tests. Our results showed: (1) 83% of the species were related to at least one or more topographic variables. Among them, 66%, 60%, 65% and 70% were closely dependent on slope, aspect, elevation and convexity, respectively. (2) Topographic variables have much stronger non-linear (quadratic and cubic) effects on species distributions than linear effects. (3) The effects of topographic heterogeneity on the distribution of shrubs species are smaller than on the distribution of canopy species, and smaller effects were also found in less abundant species. (4) There was a strong neighbourhood effect on species distribution: In 85% of the species, abundance in a focal quadrat was significantly correlated with abundance in the neighbour quadrats. We conclude that habitat specialization plays an important role in maintaining the diversity of this species-rich subtropical forest.     

Understory vegetation as an indicator for floodplain forest restoration in the Mississippi River Alluvial Valley,U.S.A.

In the Mississippi River Alluvial Valley (MAV), complete alteration of river‐floodplain hydrology allowed for widespread conversion of forested bottomlands to intensive agriculture, resulting in nearly 80% forest loss. Governmental programs have attempted to restore forest habitat and functions within this altered landscape by the methods of tree planting (afforestation) and local hydrologic enhancement on reclaimed croplands. Early assessments identified factors that influenced whether planting plus tree colonization could establish an overstory community similar to natural bottomland forests. The extent to which afforested sites develop typical understory vegetation has not been evaluated, yet understory composition may be indicative of restored site conditions. As part of a broad study quantifying the ecosystem services gained from restoration efforts, understory vegetation was compared between 37 afforested sites and 26 mature forest sites. Differences in vegetation attributes for species growth forms, wetland indicator classes, and native status were tested with univariate analyses; floristic composition data were analyzed by multivariate techniques. Understory vegetation of restoration sites was generally hydrophytic, but species composition differed from that of mature bottomland forest because of young successional age and differing responses of plant growth forms. Attribute and floristic variation among restoration sites was related to variation in canopy development and local wetness conditions, which in turn reflected both intrinsic site features and outcomes of restoration practices. Thus, understory vegetation is a useful indicator of functional progress in floodplain forest restoration.     

Biodiversity of floodplain forests in Europe and eastern North America: A comparative study of the Rhine and Mississippi Valleys

In this study, we investigate the mechanisms driving biodiversity in floodplain forests with a comparison of the composition and dynamics in the warm-temperate floodplain forests of the lower Mississippi Valley and the cool-temperate floodplain forests of the lower Wisconsin and Rhine River Valleys. We employ data from original research, as well as from the literature. We compare species, genus, and family diversity across regions with respect to species richness, numbers of species per family and genus, and a similarity index. We examine these results within a historical context, as well as with respect to river-floodplain dynamics. We also compare productivity data and successional stages for each region. We find a lower species, genus, and family richness in the cool-temperate forests of the Rhine compared to the cool-temperate forests of the Wisconsin, a probable result of the lack of available refugia for Rhine species in times of glacial expansion. We find the highest richness in the lower Mississippi Valley, likely a result of climatic factors and the availability of refugia in this region. In each of the regions, floodplain forests are more diverse than their upland counterparts, demonstrating the role of river-floodplain dynamics in maintaining species diversity. Each region maintains a high and relatively similar level of productivity in the floodplain forests. They also experience similar stages of succession, although succession becomes more complex in the warm-temperate forests of the Lower Mississippi.     

Large forests enhance songbird nesting success in agricultural‐ dominated landscapes of the Midwestern US

We studied the effects of habitat composition and distance from edges on nesting success and brood parasitism of forest birds in the Kaskaskia River Bottoms, one of the largest remaining tracts of floodplain forest in the agricultural Midwestern United States. Our goal was to help the private landowners, who have maintained this region in forest cover, enhance the value of these forests for nesting birds. We measured nest predation rates and levels of brood parasitism of four species, the indigo bunting Passerina cyanea, Acadian flycatcher Empidonax virescens, northern cardinal Cardinalis cardinalis and prothonotary warbler Protonotaria citrea in relation to distances from natural and anthropogenic edges and proportion of natural and anthropogenic habitats within fixed radii around nests. We predicted that nesting success would increase with increasing distance from anthropogenic habitats and with increasing land cover in natural habitats. Our results showed no strong effect of any of these variables on avian nesting success, although parasitism levels increased slightly with increasing proportion of agricultural land around nests for two of the species. Nevertheless, nesting success for at least three of these species was much higher than in more fragmented forest tracts elsewhere in the agricultural Midwest where most forest tracts appear to be population sinks for most species. These results suggest that forest tracts in the Kaskaskia may be saturated with nest predators and brood parasites, but are not super‐saturated in a way that would cause these tracts to become ‘black hole’ population sinks. Our data further suggest that, as long as landowners maintain their private landholdings in forest cover, the details of how they manage their land may have little effect on songbird nesting success. These results also suggest that reforestation efforts in areas with many openings may still benefit forest birds.     

Predicting the effects of climate change on population connectivity and genetic diversity of an imperiled freshwater mussel,Cumberlandia monodonta (Bivalvia: Margaritiferidae), in riverine systems

In the face of global climate change, organisms may respond to temperature increases by shifting their ranges poleward or to higher altitudes. However, the direction of range shifts in riverine systems is less clear. Because rivers are dendritic networks, there is only one dispersal route from any given location to another. Thus, range shifts are only possible if branches are connected by suitable habitat, and stream‐dwelling organisms can disperse through these branches. We used Cumberlandia monodonta (Bivalvia: Unionoida: Margaritiferidae) as a model species to investigate the effects of climate change on population connectivity because a majority of contemporary populations are panmictic. We combined ecological niche models (ENMs) with population genetic simulations to investigate the effects of climate change on population connectivity and genetic diversity of C. monodonta. The ENMs were constructed using bioclimatic and landscape data to project shifts in suitable habitat under future climate scenarios. We then used forward‐time simulations to project potential changes in genetic diversity and population connectivity based on these range shifts. ENM results under current conditions indicated long stretches of highly suitable habitat in rivers where C. monodonta persists; populations in the upper Mississippi River remain connected by suitable habitat that does not impede gene flow. Future climate scenarios projected northward and headwater‐ward range contraction and drastic declines in habitat suitability for most extant populations throughout the Mississippi River Basin. Simulations indicated that climate change would greatly reduce genetic diversity and connectivity across populations. Results suggest that a single, large population of C. monodonta will become further fragmented into smaller populations, each of which will be isolated and begin to differentiate genetically. Because C. monodonta is a widely distributed species and purely aquatic, our results suggest that persistence and connectivity of stream‐dwelling organisms will be significantly altered in response to future climate change.     

The final frontier: early-stage genetic introgression and hybrid habitat use in the northwestern extent of the Golden-winged Warbler breeding range

Anthropogenic changes to the landscape and climate have resulted in secondary contact between previously allopatric species. This can result in genetic introgression and reverse speciation when closely related species are able to hybridize. The Golden-winged Warbler has declined or been extirpated across much of its range where it has come into secondary contact with the Blue-winged Warbler. Genetic screening previously showed that introgression had occurred range-wide with the exception of Manitoba, Canada. Our goal was to reassess the genetic status of the Golden-winged Warbler population in Manitoba and to examine the demographics and habitat use of phenotypic and genetic hybrids. From 2011 to 2014, we sampled and screened mtDNA from 205 Golden-winged Warblers and hybrids in southeast Manitoba. In 2012, we monitored all Golden-winged Warbler territories within those sites and measured territory- and landscape-level habitat variables. Of the birds screened, 195 had a phenotype that matched their mtDNA type, two were phenotypic hybrids, and eight showed a phenotypic-mtDNA mismatch (cryptic hybrids). We found no difference in the habitat used by Golden-winged Warblers compared with hybrids at either scale. The low proportion of hybrids found in Manitoba and the lack of a distinguishable difference in habitat use by Golden-winged Warblers and hybrids indicates that the exclusion of hybrid birds from Golden-winged Warbler habitat is unlikely to be a successful conservation strategy. The best way to manage for Golden-winged Warblers is to slow the habitat loss and fragmentation that continues within Manitoba and to actively manage early-successional deciduous forest using tools such as fire and logging.     

Documentation of lake sturgeon (Acipenser fulvescens Rafinesque, 1817) recovery and spawning success from a restored population in the Mississippi River,Missouri, USA

Lake sturgeon Acipenser fulvescens are considered rare and were nearly extirpated in the Mississippi River in Missouri by 1931 as a result of overfishing and habitat fragmentation. Propagation efforts have been implemented by the Missouri Department of Conservation since 1984 as means to restore the lake sturgeon population. Although recent population increases have been observed, a formalized evaluation to determine if lake sturgeon are self‐sustaining in the Missouri portion of the Mississippi River has not been completed. Therefore, the objectives of this study were to: (i) determine the proportion of reproductive individuals, (ii) evaluate seasonal movement patterns of adults, and (iii) validate purported spawning locations within the Mississippi River in Missouri. Lake sturgeon catch data indicated that approximately 11 percent of the population are reproductively mature. Additionally, telemetry data confirms that the greatest movement by adult lake sturgeon occurs during spring, which suggests spawning behavior. Finally, it was possible to document lake sturgeon embryos and emergent fry larvae below Melvin Price Locks and Dam 26 in the Upper Mississippi River near St. Louis, Missouri. Water velocity, depth, and substrate size were measured at this location and embryos were collected and hatched in the laboratory. River gage data suggest that spawning behavior may have been elicited by a large influx of water during a drawdown period of water above the dam. This study represents the first documented spawning of A. fulvescens in the Mississippi River and highlights the success of recovery efforts in Missouri.     

Predictive quality of macroinvertebrate — habitat associations in lower navigation pools of the Mississippi River

Macroinvertebrate community structure was compared between habitat types within a navigation pool and between navigation pools of the Upper Mississippi River. Bottom samples were taken using a grab or Wilding sampler from 40 and 14 stations on Pool 19 and 26, respectively. In both Pools, distinct communities developed based on substrate type or the presence of aquatic macrophytes rather than specific habitats as defined by river morphometry. Areas with sand substrates usually had communities of low density and diversity. Communities of the highest density, including Hexagenia or Musculium or both, occurred in habitats with silt-sand substrates. However, these areas were low in diversity. High diversity was found in both vegetated areas and habitats with coarse substrates, the latter dominated by net-spinning caddisfly larvae. Due to pool age and longitudinal distribution of species, community similarity between Pools 19 and 26 was not significant, p < 0.05, but functional feeding similarities occurred between communities from the same type of substrate.     

Isolation by distance and Pleistocene expansion of the lowland populations of the white piranha Serrasalmus rhombeus

The genetic variability and distribution of Amazonian fish species have likely been influenced by major disturbance events in recent geological times. Alternatively, the great diversity of aquatic habitat in the Amazon is likely to shape ongoing gene flow and genetic diversity. In this context, complex patterns of genetic structure originating from a joint influence of historical and contemporary gene flow are to be expected. We explored the relative influence of Pleistocene climatic fluctuations and current water chemistry on the genetic structure of a piranha, Serrasalmus rhombeus, in the Upper Amazon by the simultaneous analysis of intron length polymorphism and mitochondrial DNA sequences. The Madeira river is well suited for that purpose as it is characterized by a great diversity of water types, the presence of one of the largest floodplain of the Amazon and the potential occurrence of two Pleistocene refuges. We found evidence of genetic structure even at a small geographical scale (less than 10 km), indicating that the floodplain is not a homogenizing factor promoting interdrainage dispersal in S. rhombeus. Likewise, the hierarchical genetic structure inferred was correlated to geographical distance instead of habitat characteristic. Our results also support the hypothesis that the area underwent population expansion during the last 800 000 years. In addition, a higher level of genetic diversity was found in the samples from the putative Aripuanã refuge. The present findings suggest that Pleistocene refuges contributed significantly to the colonization of the lowlands in the Upper Amazon valley during the Pleistocene.