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At least 253 records · Page 14Linked to original sources
USGS2005

An online operational rainfall-monitoring resource for epidemic malaria early warning systems in Africa

Periodic epidemics of malaria are a major public health problem for many sub-Saharan African countries. Populations in epidemic prone areas have a poorly developed immunity to malaria and the disease remains life threatening to all age groups. The impact of epidemics could be minimized by prediction and improved prevention through timely vector control and deployment of appropriate drugs. Malaria Early Warning Systems are advocated as a means of improving the opportunity for preparedness and timely response. Rainfall is one of the major factors triggering epidemics in warm semi-arid and desert-fringe areas. Explosive epidemics often occur in these regions after excessive rains and, where these follow periods of drought and poor food security, can be especially severe. Consequently, rainfall monitoring forms one of the essential elements for the development of integrated Malaria Early Warning Systems for sub-Saharan Africa, as outlined by the World Health Organization. The Roll Back Malaria Technical Resource Network on Prevention and Control of Epidemics recommended that a simple indicator of changes in epidemic risk in regions of marginal transmission, consisting primarily of rainfall anomaly maps, could provide immediate benefit to early warning efforts. In response to these recommendations, the Famine Early Warning Systems Network produced maps that combine information about dekadal rainfall anomalies, and epidemic malaria risk, available via their Africa Data Dissemination Service. These maps were later made available in a format that is directly compatible with HealthMapper, the mapping and surveillance software developed by the WHO's Communicable Disease Surveillance and Response Department. A new monitoring interface has recently been developed at the International Research Institute for Climate Prediction (IRI) that enables the user to gain a more contextual perspective of the current rainfall estimates by comparing them to previous seasons and climatological averages. These resources are available at no cost to the user and are updated on a routine basis.

Malaria Journal↗
USGS2024

Riverine dissolved organic matter transformations increase with watershed area, water residence time, and Damköhler numbers in nested watersheds

Quantifying the relative influence of factors and processes controlling riverine ecosystem function is essential to predicting future conditions under global change. Dissolved organic matter (DOM) is a fundamental component of riverine ecosystems that fuels microbial food webs, influences nutrient and light availability, and represents a significant carbon flux globally. The heterogeneous nature of DOM molecular composition and its propensity for interaction (i.e., functional diversity) can characterize riverine ecosystem function across spatiotemporal scales. To investigate fundamental drivers of DOM diversity, we collected seasonal water samples from 42 nested locations within five watersheds spanning multiple watershed sizes (~5 to 30,000 km2) across the United States. Patterns in DOM molecular richness, aromaticity, relative abundance of N-containing formulas, and putative biochemical transformations derived from high-resolution mass spectrometry were assessed across gradients of explanatory variables associated with watershed characteristics (e.g., watershed area, water residence time, land cover). We found that putative biochemical transformations were more strongly related to explanatory variables across watersheds than common bulk DOM parameters and that watershed area, surface water residence time and derived Damköhler numbers representing DOM reactivity timescales were strong predictors of DOM diversity. The data also indicate that catchment-specific land cover factors can significantly influence DOM diversity in diverging directions. Overall, the results highlight the importance of considering water residence time and land cover when interpreting longitudinal patterns in DOM chemistry and the continued challenge of identifying generalizable drivers that are transferable across watershed and regional scales for application in Earth system models. This work also introduces a Findable Accessible Interoperable Reusable (FAIR) dataset (>300 samples) to the community for future syntheses.

Biogeochemistry↗
USGS2025

Application of mercury stable isotopes to examine sources and hydrologic factors impacting mercury bioaccumulation and cycling in invertebrates of a model saline lake

Invertebrates, such as brine shrimp and brine flies, are key prey items for millions of resident and migratory birds that utilize saline lakes such as Great Salt Lake (GSL). Elevated methylmercury (MeHg) in invertebrate and waterfowl species of GSL has been assumed to be linked to elevated MeHg in GSL’s anoxic Deep Brine Layer (DBL) where aqueous concentrations can exceed 30 ng/L. Here, we leverage mercury (Hg) concentration and stable isotope measurements on brine flies ( Ephydra hians and Ephydra cinerea ), brine shrimp ( Artemia franciscana ), and spider (western spotted orbweaver [ Neoscona oaxacensis ]) to examine temporal changes in Hg concentrations and sources during periods of DBL presence and absence. Mercury concentrations in brine flies were inversely correlated with lake level and directly correlated with salinity, possibly resulting from factors such as enhanced Hg bioaccumulation due to osmoregulatory stress and stunted growth and/or elevated salinities impacting composition, abundance, and Hg concentrations of food sources. DBL presence did not correspond to higher invertebrate Hg concentrations, highlighting that the DBL is not the primary source of MeHg to biota. Hg stable isotope signatures (Δ 199 Hg and δ 202 Hg) in brine shrimp varied seasonally and indicated greater cumulative photochemical Hg loss from the water column in late summer and fall months. Co-located brine fly and western spotted orbweaver samples show equivalent Δ 199 Hg and δ 202 Hg signatures, supporting Hg transfer from the aquatic to terrestrial food webs. Furthermore, Hg isotope results (Δ 200 Hg) indicate that the majority of Hg accumulating in GSL invertebrates is of atmospheric origin. This study highlights temporal controls on Hg bioaccumulation within GSL, which will help assess Hg cycling within the system in response to management actions and declining lake levels.

Utah↗
USGS2000

Temporal flexibility of reproduction in temperate-breeding dabbling ducks

I compared nesting intervals during three consecutive years in five species of temperate-nesting dabbling ducks (Mallard [ Anas platyrhynchos ], Northern Pintail [ Anas acuta ], Northern Shoveler [ Anas clypeata ], Blue-winged Teal [ Anas discors ], Gadwall [ Anas strepera ]) and assessed whether differences existed in timing of refractoriness. Most nesting by females of all five species ended by the summer solstice. Nesting ended earliest for Northern Shovelers and Northern Pintails and latest for Gadwalls. Some Mallards, Blue-winged Teal, and Gadwalls continued to nest into mid- and late summer, whereas Northern Shovelers and Northern pintails did not. Mallards, Blue-winged Teal, and Gadwalls accounted for 99% (81 of 82) of flightless broods resulting from nests initiated during mid- or late summer in North Dakota and 98% (58 of 59) of flightless juveniles shot on or after 1 October by a random sample of duck hunters from across the United States. Early cessation of breeding by Northern Shovelers may have evolved in response to the species' limited flexibility in diet. Photorefractory mechanisms that limit most breeding to spring presumably evolved in response to severe constraints on reproductive success when nesting continued through summer(e.g. mortality of late-hatched young and molting females due to low temperatures). Interspecific differences in photosensitivity may account for variation in timing of cessation of nesting in late spring, but controlled experiments are needed to assess the possible role of non-photic influences. My results suggest that the refractory mechanisms controlling length of the breeding in temperate-nesting dabbling ducks are more varied and complex than previously thought, with non-photic influences (e.g. water conditions, food availability, food quality) having a larger role than indicated by earlier research.

The Auk↗
USGS2003

Pallid sturgeon in the Lower Mississippi Region: Hematology and genome information

This project (Project 1448-43270-2M-002) has been coordinated through the Natchitoches National Fish Hatchery (NNFH) and the U.S. Geological Survey’s National Wetlands Research Center (NWRC). From November 2001 to April 2002, over 280 sturgeon of the genus Scaphirhynchus (including pallid sturgeon, shovelnose, and their hybrids) were sampled from the outflow channel of the Old River Control Structure Complex (ORCC) in Concordia Parish, La. In the overall project, several datasets were collected (see Appendix), including species identification by using microsatellites and morphometric characters, food habits, physical anomalies, information on blood cells, and pathologic evidence of iridovirus – the first indication in the lower Mississippi population of pallid sturgeon. In this study, data on blood cells were obtained from the sturgeon collected monthly from approximately 20 different animals at each sampling time. This report presents preliminary information on differential blood cell identifications in sturgeon, data on comparative genomic DNA content and DNA degradation, and summaries and interpretations of data collected in light of available scientific literature addressing blood parameters of fish and sturgeon, in particular. Results obtained from collection and examination of blood and body fluids are often essential in establishing the health of fish (Blaxhall, 1972; Fange, 1992). Blood cells and sperm cells can be obtained nondestructively from fishes, even from small specimens that weigh less than 100 g (Stoskopf, 1992a). For flow cytometry assays, whereby cells are analyzed individually in a fluid stream, less than 1 :L of blood is needed. Examinations of blood by microscopy and flow cytometry were performed at NWRC in assisting in the efforts directed at recovery of the pallid sturgeon population in the Lower Mississippi River Basin.

Open-File Report↗
USGS2005

Impact of food supplementation and methionine on high densities of cotton rats: Support of the amino-acid-quality hypothesis?

Considerable research supports the tenet that quantity and quality of food limit vertebrate populations. We evaluated predictions that increased availabilities of food and the essential amino acid methionine were related to population limitation of the hispid cotton rat (Sigmodon hispidus). Effects of supplemental food and methionine on density, survival, and reproductive parameters of wild cotton rats were assessed in north-central Oklahoma in 1998-1999. Twelve enclosed groups of 16 adult cotton rats each (8 male, 8 female) were randomly assigned to either no supplementation (control), supplementation with a mixed ration that had methionine at slightly below maintenance levels (0.20%), or a methionine-enhanced mixed ration (1.20%). In general, densities of cotton rats were twice as high and were sustained longer with dietary supplementation, and methionine-supplemented populations maintained the highest densities. Treatment effects on survival depended on time of year, with higher survival in supplemented enclosures in October and November. Per capita recruitment was highest with methionine-enhanced food. Treatment effects on proportions of overall and female cotton rats in reproductive condition depended on sampling date, but males were most reproductively active with methionine supplementation. Methionine supplementation resulted in an earlier and longer reproductive season. Density-dependent and density-independent factors no doubt interplay to determine population dynamics of cotton rats, but our results suggest that methionine plays a role in the population dynamics of wild cotton rats, apparently by enhancing overall density, recruitment, and reproductive activity of males.

Journal of Mammalogy↗
USGS1993

Re-exposure of mallards to selenium after chronic exposure

Adult male mallards ( Anas platyrhynchos ) were fed a control diet or a diet containing 15 ppm selenium as seleno-D,L-methionine for 21 weeks. After this initial exposure, the mallards were fed untreated food for 12 weeks, then were re-exposed to selenium at 100 ppm for five weeks. During re-exposure to 100 ppm selenium, the birds that had previously been exposed to 15 ppm selenium and those that had not previously been exposed did not differ in percentage of mortality (14.7 and 14.3%), weight loss in survivors (39.3 and 41.2%), selenium concentrations in the livers of survivors (35 and 53 ppm, wet weight), or selenium concentrations in the livers of birds that died (35 and 40 ppm, respectively). When the data from the birds that had previously been exposed to 15 ppm selenium were combined with the data from the birds that had not previously been exposed, selenium concentrations in the livers of birds that had died on the 100-ppm selenium treatment (38 ppm) did not differ from the concentrations in the livers of birds that had survived (43 ppm).

Environmental Toxicology and Chemistry↗
USGS2017

Anticoagulant rodenticides and wildlife: Introduction

Rodents have interacted with people since the beginning of systematic food storage by humans in the early Neolithic era. Such interactions have had adverse outcomes such as threats to human health, spoiling and consumption of food sources, damage to human infrastructure and detrimental effects on indigenous island wildlife (through inadvertent anthropogenic assisted introductions). These socio/economic and environmental impacts illustrate the clear need to control populations of commensal rodents. Different methods have been applied historically but the main means of control in the last decades is through the application of rodenticides, mainly anticoagulant rodenticides (ARs) that inhibit blood clotting. The so-called First Generation Anticoagulant Rodenticides (FGARs) proved highly effective but rodents increasingly developed resistance. This led to a demand for more effective alternative compounds and paved the way to the development of Second Generation Anticoagulant Rodenticides (SGARs). These were more acutely toxic and persistent, making them more effective but also increasing the risks of exposure of non-target species and secondary poisoning of predatory species. SGARs often fail the environmental thresholds of different regulatory frameworks because of these negative side-effects, but their use is still permitted because of the overwhelming societal needs for rodent control and the lack of effective alternatives. This book provides a state-of-the-art overview of the scientific advancements in assessment of environmental exposure, effects and risks of currently used ARs. This is discussed in relation to the societal needs for rodent control, including risk mitigation and development of alternatives.

Book chapter↗
USGS2003

Population dynamics of hispid cotton rats (Sigmodon hispidus) across a nitrogen-amended landscape

We conducted a mark-recapture experiment to examine the population dynamics of hispid cotton rats (Sigmodon hispidus) in response to low-level nitrogen amendments (16.4 kg nitrogen/ha per year) and exclosure fencing in an old-field grassland. The experimental design consisted of sixteen 0.16-ha plots with 4 replicates of each treatment combination. We predicted that densities, reproductive success, movement probabilities, and survival rates of cotton rats would be greater on nitrogen-amended plots because of greater aboveground biomass and canopy cover. Population densities of cotton rats tended to be highest on fenced nitrogen plots, but densities on unfenced nitrogen plots were similar to those on control and fenced plots. We observed no distinct patterns in survival rates, reproductive success, or movement probabilities with regard to nitrogen treatments. However, survival rates and reproductive success tended to be higher for cotton rats on fenced plots than for those on unfenced plots and this was likely attributable to decreased predation on fenced plots. As low-level nitrogen amendments continue to be applied, we predict that survival, reproduction, and population-growth rates of cotton rats on control plots, especially fenced plots with no nitrogen amendment, will eventually exceed those on nitrogen-amended plots as a result of higher plant-species diversity, greater food availability, and better quality cover.

Canadian Journal of Zoology↗
USGS2021

Assessing the migratory histories, trophic positions, and conditions of lake sturgeon in the St. Croix and Mississippi Rivers using fin ray microchemistry, stable isotopes, and fatty acid profiles

Background Reproducing populations of invasive carps ( Hypophthalmichthys spp.) could alter aquatic food webs and negatively affect native fishes in the Mississippi National River and Recreation Area (MISS) and the St. Croix National Scenic Riverway (SACN). However, proposed invasive carp barriers may also threaten populations of native migratory fishes by preventing movements of fish between rivers that are necessary for life history requirements. In this study, nonlethal chemical techniques were used to provide baseline data related to the condition, trophic position, and migratory histories of lake sturgeon ( Acipenser fulvescens ) captured in the Mississippi and St. Croix Rivers. Results Fish length and weight measurements and age estimates determined from pectoral fin rays demonstrated that lake sturgeon from the Mississippi River had greater lengths-at-age compared to sturgeon from the St. Croix River. However, length–weight relations were similar for sturgeon from the Mississippi and St. Croix Rivers. Lake sturgeon captured from different locations had distinguishable fatty acid signatures, and stable isotope analyses demonstrated that lake sturgeon from the Mississippi River generally feed at a higher trophic level than those in the St. Croix River. Strontium-to-calcium ratios (Sr:Ca) from fin ray cross sections indicated that sturgeon captured from the Mississippi River had higher Sr:Ca values than sturgeon captured from the St. Croix River, and natal origins and capture locations were not significantly different among sturgeon captured within individual rivers. Most sturgeon were captured in water with a similar Sr:Ca signature as their natal waters, indicating that there is some separation between populations of lake sturgeon in the St. Croix and Mississippi Rivers. However, Sr:Ca data indicated substantial variation in movement patterns among individual lake sturgeon, indicating that populations interact through migrations of individual fish between rivers. Conclusions Study results provide baseline condition and food web structure index data for assessing changes in lake sturgeon populations should invasive carps become established in these areas of the Mississippi and St. Croix Rivers. Controlled-exposure and telemetry studies would help verify and enhance the relations between Sr:Ca signatures in water and lake sturgeon pectoral fin rays to further assess mixing of sturgeons between rivers.

Minnesota, Wisconsin↗
USGS1984

Flow-through bioassay for measuring bioaccumulation of toxic substances from sediment

Over 10 million cubic meters of sediment are dredged annually from Great Lakes waterways. Because much of this material is taken from harbors, connecting channels, and other nearshore areas that often are contaminated with toxic substances, the sediments proposed for dredging need to be evaluated for the presence of bioavailable contaminants and the potential for toxicity to the biota. Sound decisions on the appropriate disposal of the dredged material can be made only after such an evaluation. Presently, no standardized procedure exists for evaluating dredged material in freshwater systems although current criteria for discharge of dredged material into marine water have been developed (USEPA/CE 1977). In the ocean discharge guideline, it is recommended that bioassays be conducted on liquid, solid, and suspended particulate phases of dredged material. because it appears that the solid phase has the greatest potential for environmental damage and because measurement of bioaccumulation must be made to evaluate sediments for disposal (USEPA/CE 1977, Seeyle and Mac 1983), we developed a bioassay for testing the solid phase of dredged material that measures the survival of organisms and, perhaps more important, the bioaccumulation of toxic substances by aquatic organisms from naturally contaminated sediments (Peddicord et al. 1980; Rubinstein et al. 1980, 1983; Seeyle st al. 1982), several have used testing methods that result in unacceptable mortality to control organisms (Bahnick et al. 1981, Prater et al. 1983). Our bioassay is intended to estimate the potential for bioaccumlation of contaminants from sediments that are not acutely toxic to test organisms, but are suspected of containing persistent contaminants. By using test organisms that are not highly susceptible to toxic compounds, the bioaccumulation test allows estimation of the potential food-chain accumulation of contaminants that may occur in local biota from surficial sediments. In practice, bioaccumulation observed in this bioassay by organisms exposed to test sediments (sediments to be dredged) would be compared to bioaccumulation observed from sediments collected from a reference site (e.g. a disposal site or open lake), and also from control sediments (relatively clean sediment). Decisions could then be based on a comparison of results between tests and reference sediments to determine if disposal would cause dehydration to the habitat, and between reference and control sediment to determine if even the reference material is seriously contaminated. Although the test is not intended to be a toxicity test per se, use of test, reference, and control sediments enables interpretation of any mortality of organisms that may occur during the bioassays. High mortality in bioassays with test or reference sediment would indicate acute toxicity of sediments in the project area. However if high mortality occurs in all three sediments, it can be assumed that the organisms were not in a healthy state at the time of testing. We describe the results of 10-day sediment bioassays in which both mortality and bioaccumulation were measured in four aquatic organisms. We exposed two infaunal organisms and two species of fish to test and control sediments in the laboratory.

Report↗
USGS1984

Field and laboratory evaluation of the influence of copper-diquat on apple snails in southern Florida

The recent decline of apple snail ( Pomacea paludosa ) populations in canals surrounding Loxahatchee National Wildlife Refuge in southern Florida coincided with the use of copper-diquat for the control of the aquatic weed hydrilla ( Hydrilla verticillata ). Field and laboratory studies were designed to assess the effects of copper-diquat on apple snails, which are the primary food of the endangered snail kite Rostrhamus sociabilis (formerly known as the Everglade kite). Acute toxicities (96-h LC 50 values) of Cutrine-Plus and Komeen (chelated formulations of copper) to immature apple snails were 22 and 24 μg/L, respectively. Diquat was toxic at a concentration of 1,800 μg/L and did not increase the toxicity of copper when the chemicals were used in combination. Evaluation of field samples indicated that copper concentrations were higher in detritus than in water, plants and mud, and that there was a gradient of copper concentration from the canal to the interior, the highest residues being in samples from the canal. Copper associated with detritus (up to 150 μg/g) had no effect on growth or survival of apple snails in field cage and tank studies. Also, field applications of copper-diquat to hydrilla had no effect on survival of caged adult and immature snails. Copper from field applications was rapidly taken out of solution by plants and organic material in the water and subsequently incorporated into the bottom detritus. Although the effects of repeated applications of copper-diquat and high body burdens of copper (accumulated during exposure to herbicidal treatment) on survival and reproduction of apple snails are not known, the information available indicates that treatment of hydrilla with copper-diquat was probably not responsible for the decline in the apple snail population. Application at recommended rates should pose no threat to these snails in the organically rich waters of southern Florida.

Environmental Toxicology and Chemistry↗
USGS2015

Habitat, not resource availability, limits consumer production in lake ecosystems

Food web productivity in lakes can be limited by dissolved organic carbon (DOC), which reduces fish production by limiting the abundance of their zoobenthic prey. We demonstrate that in a set of 10 small, north temperate lakes spanning a wide DOC gradient, these negative effects of high DOC concentrations on zoobenthos production are driven primarily by availability of warm, well-oxygenated habitat, rather than by light limitation of benthic primary production as previously proposed. There was no significant effect of benthic primary production on zoobenthos production after controlling for oxygen, even though stable isotope analysis indicated that zoobenthos do use this resource. Mean whole-lake zoobenthos production was lower in high-DOC lakes with reduced availability of oxygenated habitat, as was fish biomass. These insights improve understanding of lake food webs and inform management in the face of spatial variability and ongoing temporal change in lake DOC concentrations.

Wisconsin and Michigan↗
USGS1981

Introduction and summary: Chlorinated hydrocarbons as a factor in the reproduction and survival of lake trout (Salvelinus namaycush) in Lake Michigan

Although lake trout ( Salvelinus namaycush ) were considered extinct in Lake Michigan by the mid 1950's, control of the parasitic sea lamprey ( Petromyzon marinus ) and extensive restocking resulted in an abundance of hatchery-produced lake trout in the lake by the early 1970's. However, no naturally produced yearling or older lake trout have been found in the lake during nearly a decade of assessment sampling. Among the numerous hypotheses proposed to account for this apparent reproductive failure of the planted lake trout, a frequently suggested cause is the well-documented contamination of the fish by toxic substances such as DDT and its metabolites, and polychlorinated biphenyls (PCB's) at concentrations reported as adversely affecting the hatching of eggs and survival of larval fish. However, manually stripped and fertilized eggs of Lake Michigan lake trout have hatched successfully and the fry have survived normally under a variety of hatchery conditions. This observation led to studies at the Great Lakes Fishery Laboratory on the performance and survival of fry hatched from eggs of Lake Michigan lake trout and exposed for 6 months to PCB's (Aroclor 1254) and DDE at concentrations similar to those present in offshore waters and zooplankton of Lake Michigan (10.0 ng/L PCB's and 1.0 ng/L DDE in water; 1.0 μg/g PCB's and 0.1 μg/g DDE in food), and at concentrations 5 and 25 times higher. Cumulative mortality of the fry exposed to simulated Lake Michigan levels of PCB's and DDE for 6 months was 40.7% — nearly twice that of unexposed (control) fry — and mortality at the highest exposure level was 46.5%. Evaluation of the growth, swimming performance, predator avoidance, temperature preference, and metabolism of the fry showed no significant effects attributable to exposure to PCB's and DDE, except for a lowering of preferred temperature at the highest (25x) exposures (the only concentration tested) to each contaminant and (additively) both contaminants combined. Although several factors have undoubtedly contributed to the lack of recruitment of naturally produced lake trout in Lake Michigan, the levels of PCB's and DDE present during the early to mid 1970's were sufficient to significantly reduce survival of any fry produced in the lake and thereby impede restoration of the lake trout population to self-sustainability. The added exposure of the fry to other toxic substances known to be present in the lake could have further reduced survival.

Book chapter↗
USGS2020

Observed and modeled mercury and dissolved organic carbon concentrations and loads at control structure S-12D, Florida Everglades, 2013–17

Mercury (Hg) has been a contaminant of concern for several decades in South Florida, particularly in the Florida Everglades. The transport and bioavailability of Hg in aquatic systems is intimately linked to dissolved organic carbon (DOC). In aquatic systems, Hg can be converted to methylmercury (MeHg), which is the form of Hg that bioaccumulates in food webs. The bioaccumulation of MeHg poses significant health risks to wildlife and humans. Fish consumption advisories triggered by elevated Hg levels first appeared in the 1980s in South Florida. Multiple structures regulate freshwater distribution to Everglades National Park, including S-12D. This report summarizes seasonal and annual concentration and load data from late September 2013 to April 2017 for the total of (1) filter-passing total mercury (FTHg), (2) filter-passing methylmercury (FMeHg), (3) particulate total mercury (PTHg), (4) particulate methylmercury (PMeHg) and, (5) DOC discharged through control structure S-12D. The loads of Hg fractions and DOC at control structure S-12D were determined by pairing discharge data with constituent concentrations estimated by empirical models based on surrogate in situ water-quality measurements. Calculated concentrations of DOC ranged from 12.8 milligrams per liter (mg/L) to 27.9 mg/L with a mean of 18.8 mg/L during the study period. Annual loads of DOC ranged from 3,950 tons in 2015 to 10,900 tons in 2016. DOC loads increased linearly with an increase in flow, and the highest monthly DOC load of 1,630 tons was observed in February 2016. Calculated concentrations of FTHg ranged from 0.35 to 1.55 nanograms per liter (ng/L) with a mean of 0.85 ng/L during the study period. Calculated concentrations of FMeHg ranged from 0.06 ng/L to 0.24 ng/L with a mean of 0.14 ng/L during the study period. Generally, FTHg and FMeHg con­centrations were lower during periods of decreased flow and higher during periods of increased flow. Calculated PTHg concentrations ranged from 0.09 ng/L to 4.19 ng/L with a mean of 0.58 ng/L during the study period. Calculated PMeHg concentrations ranged from below the limit of detection <0.01 ng/L to 0.29 ng/L with a mean of 0.03 ng/L during the study period. Loads of Hg were often zero or lowest from November to May, owing to the lack of flow or low-flow conditions. FTHg and FMeHg loads increased linearly with an increase in flow and typically were highest from June to October. During periods of increasing flow or following changes in gate operations, PTHg and PMeHg constituted a greater percentage of the total Hg load. Annual loads of total Hg (filter-passing and particulate) ranged from 254 grams in 2015 to 658 grams in 2016. FTHg was the predominant contributor to the total Hg load. Information presented herein provides the first assessment of DOC and Hg loads to Everglades National Park through control structure S-12D using continuous in situ measurements of discharge and constituent surrogates and compares the sur­rogate model approach to loads calculated from monthly sam­pling. Analysis of calculated and observed loads demonstrates the significance of flow data on calculating constituent loads.

Florida↗
USGS2009

Learning to be different: Acquired skills, social learning, frequency dependence, and environmental variation can cause behaviourally mediated foraging specializations

Question: How does the ability to improve foraging skills by learning, and to transfer that learned knowledge, affect the development of intra-population foraging specializations? Features of the model: We use both a state-dependent life-history model implemented by stochastic dynamic programming (SDPM) and an individual-based model (IBM) to capture the dynamic nature of behavioural preferences in feeding. Variables in the SDPM include energy reserves, skill levels, energy and handling time per single prey item, metabolic rate, the rates at which skills are learned and forgotten, the effect of skills on handling time, and the relationship between energy reserves and fitness. Additional variables in the IBM include the probability of successful weaning, the logistic dynamics of the prey species with stochastic recruitment, the intensity of top-down control of prey by predators, the mean and variance in skill levels of new recruits, and the extent to which learned Information can be transmitted via matrilineal social learning. Key range of variables: We explore the effects of approaching the time horizon in the SDPM, changing the extent to which skills can improve with experience, increasing the rates of learning or forgetting of skills, changing whether the learning curve is constant, accelerating (T-shaped) or decelerating ('r'-shaped), changing both mean and maximum possible energy reserves, changing metabolic costs of foraging, and changing the rate of encounter with prey. Conclusions: The model results show that the following factors increase the degree of prey specialization observed in a predator population: (1) Experience handling a prey type can substantially improve foraging skills for that prey. (2) There is limited ability to retain complex learned skills for multiple prey types. (3) The learning curve for acquiring new foraging skills is accelerating, or J-shaped. (4) The metabolic costs of foraging are high relative to available energy reserves. (5) Offspring can learn foraging skills from their mothers (matrilineal social learning). (6) Food abundance is limited, such that average individual energy reserves are low Additionally, the following factors increase the likelihood of alternative specializations co-occurring in a predator population: (1) The predator exerts effective top-down control of prey abundance, resulting in frequency-dependent dynamics. (2) There is stochastic Variation in prey population dynamics, but this Variation is neither too extreme in magnitude nor too 'slow' with respect to the time required for an individual forager to learn new foraging skills. For a given predator population, we deduce that the degree of specialization will be highest for those prey types requiring complex capture or handling skills, while prey species that are both profitable and easy to capture and handle will be included in the diet of all individuals. Frequency-dependent benefits of selecting alternative prey types, combined with the ability of foragers to improve their foraging skills by learning, and transmit learned skills to offspring, can result in behaviourally mediated foraging specialization, and also lead to the co-existence of alternative specializations. The extent of such specialization is predicted to be a variable trait, increasing in locations or years when intra-specific competition is high relative to inter-specific competition. ?? 2009 M. Tim Tinker.

Evolutionary Ecology Research↗
USGS2020

Tradeoffs with growth limit host range in complex life-cycle helminths

Parasitic worms with complex life cycles have several developmental stages, with each stage creating opportunities to infect additional host species. Using a dataset for 973 species of trophically transmitted acanthocephalans, cestodes, and nematodes, we confirmed that worms with longer life cycles (i.e. more successive hosts) infect a greater diversity of host species and taxa (after controlling for study effort). Generalism at the stage level was highest for ‘middle’ life stages, the second and third intermediate hosts of long life cycles. By simulating life cycles in real food webs, we found that middle stages had more potential host species to infect, suggesting that opportunity constrains generalism. However, parasites usually infected fewer host species than expected from simulated cycles, suggesting generalism also has costs. There was no tradeoff in generalism from one stage to the next, but worms spent less time growing and developing in stages where they infected more taxonomically diverse hosts. Our results demonstrate that life cycle complexity favors high generalism, and host use across life stages is determined by both ecological opportunity and life history tradeoffs.

The American Naturalist↗
USGS1960

The stoneroller, Campostoma anomalum (Rafinesque), in Great Smoky Mountains National Park

The stoneroller (Campostoma anomalum) is one of the more important fish in Great Smoky Mountains National Park because of its abundance and habits. Although esteemed locally as a food and a bait fish, the stoneroller is exploited but little since the fishing regulations which govern the utilization of game fishes afford it a large measure of protection. Distribution is controlled by gradient with an upper limit of 4.4 percent. Stonerollers limit reproduction of rainbow trout (Salmo gairdneri) by destroying trout redds. Artificial reduction of stoneroller populations is not considered a necessary management procedure.

North Carolina, Tennessee↗