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At least 541 records · Page 30Linked to original sources
USGS2021

Disease or drought: Environmental fluctuations release zebra from a potential pathogen-triggered ecological trap

When a transmission hotspot for an environmentally persistent pathogen establishes in otherwise high-quality habitat, the disease may exert a strong impact on a host population. However, fluctuating environmental conditions lead to heterogeneity in habitat quality and animal habitat preference, which may interrupt the overlap between selected and risky habitats. We evaluated spatio-temporal patterns in anthrax mortalities in a plains zebra ( Equus quagga ) population in Etosha National Park, Namibia, incorporating remote-sensing and host telemetry data. A higher proportion of anthrax mortalities of herbivores was detected in open habitats than in other habitat types. Resource selection functions showed that the zebra population shifted habitat selection in response to changes in rainfall and vegetation productivity. Average to high rainfall years supported larger anthrax outbreaks, with animals congregating in preferred open habitats, while a severe drought forced animals into otherwise less preferred habitats, leading to few anthrax mortalities. Thus, the timing of anthrax outbreaks was congruent with preference for open plains habitats and a corresponding increase in pathogen exposure. Given shifts in habitat preference, the overlap in high-quality habitat and high-risk habitat is intermittent, reducing the adverse consequences for the population.

Etosha National Park↗
USGS2017

Anticoagulant rodenticides and wildlife: Concluding remarks

Rodents are known to affect human society globally in various adverse ways, resulting in a widespread demand for their continuous control. Anticoagulant rodenticides (ARs) have been, and currently remain, the cornerstone of rodent control throughout the world. Although alternative control methods exist, they are generally less effective. ARs work by affecting vitamin K metabolism, thereby preventing the activation of blood clotting factors and eventual coagulopathy. Since ARs are non-selective, their undoubted benefits for rodent control have to be balanced against the environmental risks that these compounds pose. Although they have been used for decades, pharmacokinetic and toxicokinetic data are mainly available for laboratory mammals and have concentrated on acute effects. Limited information is available on chronic exposure scenarios and for wildlife species. Important gaps exist in our understanding of the large inter- and intra-species differences in sensitivity to ARs, especially for non-target species, and in our knowledge about the occurrence and importance of sub-lethal effects in wildlife. It is clear that mere presence of AR residues in the body tissues may not indicate the occurrence of effects, although unequivocal assessment of effects under field conditions is difficult. Ante-mortem symptoms, like lethargy, subdued behaviour and unresponsiveness are generally not very specific as is true for more generic post-mortem observations (e.g. pallor of the mucous membranes or occurrence of haemorrhages). It is only by combining ante or post-mortem data with information on exposure that effects in the field may be confirmed. We do know however that a wide variety of non-target species are directly exposed to ARs. Secondary exposure in predators is also widespread although there is limited information on whether this exposure causes actual effects. Exposure is driven by ecological factors and is context specific with respect to spatial habitat configuration and bait placement. Another key factor that affects the interaction between ARs and wildlife is the development of resistance in target species. The development of resistance has resulted in higher use of SGARs, thereby increasing the potential of non-target and secondary exposure. AR use has increasingly become more strictly regulated, increasing the need for alternatives. Alternatives are available, including non-anticoagulant rodenticides, but these may also pose significant risk to environmental organisms, humans and pets. There are also various mitigation measures that can be implemented when using ARs, including bait protection, pulsed baiting at the onset of infestation, restricting use by non-professionals, and avoiding use in areas of high non-target density. Reduction in secondary exposure may result from e.g. non-chemical control, habitat management, and, in agricultural habitats, the use of lure crops and supplemental feeding. Such Integrated Pest Management (IPM) may not only reduce non-target exposure but also benefit resistance management. Barriers to adopt IPM approaches however, include the perception that they do not work or too slowly and are more laborious, expensive and time consuming. It is therefore important that the expectations of stakeholders are considered and managed. Nevertheless, further development of alternatives and IPM measures is essential, so the key research priority related to rodent control may ultimately be to address the lack of scientific assessment of the effectiveness of both specific AR mitigation measures and of IPM approaches to rodent control.

Book chapter↗
USGS2006

Myxobolus cerebralis in native cutthroat trout of the Yellowstone Lake ecosystem

The exotic parasite Myxobolus cerebralis was first detected in native adult Yellowstone cutthroat trout Oncorhynchus clarkii bouvierii from Yellowstone Lake in 1998, seriously threatening the ecological integrity of this pristine, naturally functioning ecosystem. We immediately began to assess the prevalence and spatial extent of M. cerebralis infection in Yellowstone cutthroat trout within Yellowstone Lake and to determine the infection risk of age-0 Yellowstone cutthroat trout, the relative abundance and actinospore production of lubificid worms, and the basic environmental characteristics of tributaries. During 1999-2001, juvenile and adult Yellowstone cutthroat trout were infected throughout Yellowstone Lake; the highest prevalence (15.3-16.4%) occurred in the northern and central regions. Exposure studies in 13 streams indicated that Pelican and Clear creeks and the Yellowstone River were positive for M. cerebralis; the highest prevalence (100%) and severity was found in Pelican Creek during mid-July. Sexually mature individuals of the oligochaete Tubifex tubifex were most abundant in early summer, were genetically homogenous, and were members of a lineage known to produce moderate to high levels of M. cerebralis triactinomyxons. Only 20 of the 3,037 sampled tubificids produced actinospores after 7 d in culture, and none of the actinospores were M. cerebralis. However, one non-actinospore-producing T. tubifex from Pelican Creek tested positive for M. cerebralis by polymerase chain reaction. Stream temperatures at Pelican Creek, a fourth-order, low-gradient stream, were over 20??C during the first exposure period, suggesting that T. tubifex were capable of producing triactinomyxons at elevated temperatures in the wild. Although the infection of otherwise healthy adult Yellowstone cutthroat trout within Yellowstone Lake suggests some resistance, our sentinel cage exposures indicated that this subspecies may be more susceptible to whirling disease than previous laboratory challenges have indicated, and M. cerebralis may be contributing to a significant recent decline in this population. ?? Copyright by the American Fisheries Society 2006.

Wyoming↗
USGS2017

Field study suggests that sex determination in sea lamprey is directly influenced by larval growth rate

Sex determination mechanisms in fishes lie along a genetic-environmental continuum and thereby offer opportunities to understand how physiology and environment interact to determine sex. Mechanisms and ecological consequences of sex determination in fishes are primarily garnered from teleosts, with little investigation into basal fishes. We tagged and released larval sea lamprey ( Petromyzon marinus ) into unproductive lake and productive stream environments. Sex ratios produced from these environments were quantified by recapturing tagged individuals as adults. Sex ratios from unproductive and productive environments were initially similar. However, sex ratios soon diverged, with unproductive environments becoming increasingly male-skewed and productive environments becoming less male-skewed with time. We hypothesize that slower growth in unproductive environments contributed to the sex ratio differences by directly influencing sex determination. To the best of our knowledge, this is the first study suggesting that growth rate in a fish species directly influences sex determination; other studies have suggested that the environmental variables to which sex determination is sensitive (e.g. density, temperature) act as cues for favourable or unfavourable growth conditions. Understanding mechanisms of sex determination in lampreys may provide unique insight into the underlying principles of sex determination in other vertebrates and provide innovative approaches for their management where valued and invasive.

Proceedings of the Royal Society B: Biological Sci↗
USGS2006

The Amphibian Research and Monitoring Initiative (ARMI): 5-year report

The Amphibian Research and Monitoring Initiative (ARMI) is an innovative, multidisciplinary program that began in 2000 in response to a congressional directive for the Department of the Interior to address the issue of amphibian declines in the United States. ARMI’s formulation was cross-disciplinary, integrating U.S. Geological Survey scientists from Biology, Water, and Geography to develop a course of action (Corn and others, 2005a). The result has been an effective program with diverse, yet complementary, expertise. ARMI’s approach to research and monitoring is multiscale. Detailed investigations focus on a few species at selected local sites throughout the country; monitoring addresses a larger number of species over broader areas (typically, National Parks and National Wildlife Refuges); and inventories to document species occurrence are conducted more extensively across the landscape. Where monitoring is conducted, the emphasis is on an ability to draw statistically defensible conclusions about the status of amphibians. To achieve this objective, ARMI has instituted a monitoring response variable that has nationwide applicability. At research sites, ARMI focuses on studying species/environment interactions, determining causes of observed declines, and developing new techniques to sample populations and analyze data. Results from activities at all scales are provided to scientists, land managers, and policymakers, as appropriate. The ARMI program and the scientists involved contribute significantly to understanding amphibian declines at local, regional, national, and international levels. Within National Parks and National Wildlife Refuges, findings help land managers make decisions applicable to amphibian conservation. For example, the National Park Service (NPS) selected amphibians as a vital sign for several of their monitoring networks, and ARMI scientists provide information and assistance in developing monitoring methods for this NPS effort. At the national level, ARMI has had major exposure at a variety of meetings, including a dedicated symposium at the 2004 joint meetings of the Herpetologists’ League, the American Society of Ichthyologists and Herpetologists, and the Society for the Study of Amphibians and Reptiles. Several principal investigators have brought international exposure to ARMI through venues such as the World Congress of Herpetology in South Africa in 2005 (invited presentation by Dr. Gary Fellers), the Global Amphibian Summit, sponsored by the International Union for Conservation of Nature (IUCN) and Wildlife Conservation International, in Washington, D.C., 2005 (invited participation by Dr. P.S. Corn), and a special issue of the international herpetological journal Alytes focused on ARMI in 2004 (edited by Dr. C.K. Dodd, Jr.). ARMI research and monitoring efforts have addressed at least 7 of the 21 Threatened and Endangered Species listed by the U.S. Fish and Wildlife Service (California red-legged frog [Rana draytonii], Chiricahua leopard frog [R. chiricahuensis], arroyo toad [Bufo californicus], dusky gopher frog [Rana sevosa], mountain yellow-legged frog [R. muscosa], flatwoods salamander [Ambystoma cingulatum], and the golden coqui [Eleutherodactylus jasperi]), and 9 additional species of concern recognized by the IUCN. ARMI investigations have addressed time-sensitive research, such as emerging infectious diseases and effects on amphibians related to natural disasters like wildfire, hurricanes, and debris flows, and the effects of more constant, environmental change, like urban expansion, road development, and the use of pesticides. Over the last 5 years, ARMI has partnered with an extensive list of government, academic, and private entities. These partnerships have been fruitful and have assisted ARMI in developing new field protocols and analytic tools, in using and refining emerging technologies to improve accuracy and efficiency of data handling, in conducting amphibian disease, malformation, and environmental effects research, and in implementing a network of monitoring and research sites. Accomplishments from these endeavors include more than 40 publications on amphibian status and trends, nearly 100 publications on amphibian ecology and causes of declines, and over 30 methodological publications. Several databases have emerged as a result of ARMI and its partnerships; one, a digital atlas of ranges for all U.S. amphibian species, was used by the IUCN to display amphibian distribution maps in the Global Amphibian Assessment Project. Given the scope of ARMI and the panoply of projects, findings have had implications for policy. Investigations that demonstrate amphibian declines or illuminate causes of declines provide valuable information about habitat management, environmental effects, mechanisms for the spread of disease, and human/amphibian interfaces. This information has been made available to land managers, scientists, educators, Congress and other policymakers, and the public. The support afforded ARMI by Congress has been influential in the program’s development and success. The value of ARMI’s efforts will continue to increase as we are able to extend our studies spatially and temporally to answer critical questions with more confidence. We are using ARMI’s resources efficiently and continuing to develop innovative mechanisms for leveraging resources for maximum effectiveness during challenging financial times. This report is a 5-year retrospective of the structure, methodology, progress, and contributions to the broader scientific community that have resulted from this national USGS program. We evaluate ARMI’s success to date, with regard to the challenges faced by the program and the strengths that have emerged. We chart objectives for the next 5 years that build on current accomplishments, highlight areas meriting further research, and direct efforts to overcome existing weaknesses.

Scientific Investigations Report↗
USGS2010

Global positioning system and associated technologies in animal behaviour and ecological research

Biologists can equip animals with global positioning system (GPS) technology to obtain accurate (less than or equal to 30 m) locations that can be combined with sensor data to study animal behaviour and ecology. We provide the background of GPS techniques that have been used to gather data for wildlife studies. We review how GPS has been integrated into functional systems with data storage, data transfer, power supplies, packaging and sensor technologies to collect temperature, activity, proximity and mortality data from terrestrial species and birds. GPS 'rapid fixing' technologies combined with sensors provide location, dive frequency and duration profiles, and underwater acoustic information for the study of marine species. We examine how these rapid fixing technologies may be applied to terrestrial and avian applications. We discuss positional data quality and the capability for high-frequency sampling associated with GPS locations. We present alternatives for storing and retrieving data by using dataloggers (biologging), radio-frequency download systems (e.g. very high frequency, spread spectrum), integration of GPS with other satellite systems (e.g. Argos, Globalstar) and potential new data recovery technologies (e.g. network nodes). GPS is one component among many rapidly evolving technologies. Therefore, we recommend that users and suppliers interact to ensure the availability of appropriate equipment to meet animal research objectives.

Philosophical Transactions of the Royal Society B:↗
USGS2017

Lyme disease ecology in a changing world: Consensus, uncertainty and critical gaps for improving control

Lyme disease is the most common tick-borne disease in temperate regions of North America, Europe and Asia, and the number of reported cases has increased in many regions as landscapes have been altered. Although there has been extensive work on the ecology and epidemiology of this disease in both Europe and North America, substantial uncertainty exists about fundamental aspects that determine spatial and temporal variation in both disease risk and human incidence, which hamper effective and efficient prevention and control. Here we describe areas of consensus that can be built on, identify areas of uncertainty and outline research needed to fill these gaps to facilitate predictive models of disease risk and the development of novel disease control strategies. Key areas of uncertainty include: (i) the precise influence of deer abundance on tick abundance, (ii) how tick populations are regulated, (iii) assembly of host communities and tick-feeding patterns across different habitats, (iv) reservoir competence of host species, and (v) pathogenicity for humans of different genotypes of Borrelia burgdorferi . Filling these knowledge gaps will improve Lyme disease prevention and control and provide general insights into the drivers and dynamics of this emblematic multi-host–vector-borne zoonotic disease.

Philosophical Transactions of the Royal Society B:↗
USGS2023

Declines in body size of sockeye salmon associated with increased competition in the ocean

Declining body sizes have been documented for several species of Pacific salmon; however, whether size declines are caused mainly by ocean warming or other ecological factors, and whether they result primarily from trends in age at maturation or changing growth rates remain poorly understood. We quantified changes in mean body size and contributions from shifting size-at-age and age structure of mature sockeye salmon returning to Bristol Bay, Alaska, over the past 60 years. Mean length declined by 3%, corresponding to a 10% decline in mean body mass, since the early 1960s, though much of this decline occurred since the early 2000s. Changes in size-at-age were the dominant cause of body size declines and were more consistent than trends in age structure among the major rivers that flow into Bristol Bay. Annual variation in size-at-age was largely explained by competition among Bristol Bay sockeye salmon and interspecific competition with other salmon in the North Pacific Ocean. Warm winters were associated with better growth of sockeye salmon, whereas warm summers were associated with reduced growth. Our findings point to competition at sea as the main driver of sockeye salmon size declines, and emphasize the trade-off between fish abundance and body size.

Alaska↗
USGS2007

Winter behavior and ecology of the Alder Flycatcher (Empidonax alnorum) in Peru

The winter ecology and behavior of Alder Flycatchers (Empidonax alnorum) were studied along the Manu, a white-water meander river in Manu National Park, Madre de Dios, Peru?? during October and November, 1993 to 1997. The birds occupied territories in primary-succession habitats on growing point bars. They were most common in mixed stands of Tessaria integrifolia (Asteraceae) and Gynerium sagittatum (Gramineaceae) interspersed with bare sand areas. The uneven height of the Tessaria canopy, which resulted in openings in the vegetation large enough for the birds to flycatch, was an important habitat feature. Birds obtained insects, which formed about 96% of the diet, by aerial hawking (91%), perch gleaning (6%), and hover gleaning (3%). They also fed on fruit. Territory sizes ranged from 0.04 to 0.25 ha. Of nine territories that we observed closely, six were occupied by two birds each, two by one bird each, and one by three birds. Every territory had one dominant individual who was primarily responsible for territory defense; the other birds were associates. Vocalizations given included the fee-bee-o song, a two-syllable song, nd the pit note, which are also given on the breeding grounds. A series of pits given increasingly rapidly signaled a territorial interaction. In aggressive encounters, the birds (1) interacted vocally, remaining on their territories and counter calling or exchanging agitated calls; (2) moved toward a common territorial boundary and engaged in a vocal duel; or (3) the dominant chased intruders out of the territory. Chases were most common when a wave of new birds entered the area. Dominant birds, which sang the full song, were probably adult males. Immature males do not sing a full song, and females are not known to sing in nature. Associate individuals were likely females or young males. ?? The Neotropical Ornithological Society.

Ornitologia Neotropical↗
USGS2023

Network analysis of a northern long-eared bat (Myotis septentrionalis) maternity colony in a suburban forest patch

Many bat species are highly social, forming groups of conspecifics, particularly during the maternity season. In temperate North America, these social groups are typically comprised of closely related individuals or individuals that share some common trait (i.e. reproductive state or shared hibernacula from the previous winter). In the summer, when bats use forests for day-roosts, these social groups often demonstrate nonrandom patterns of periodically associating in common roosts and disassociating using different roosts as a ‘fission–fusion society’. As cave hibernating bat species in North America continue to decline due to the impacts of White-nose Syndrome, opportunities to describe these dynamics are becoming rare. Unfortunately, these patterns often are still poorly documented, yet understanding these behaviors is critical for species-specific habitat conservation and management. In our study, we tracked female northern long-eared bats ( Myotis septentrionalis ) to their day-roosts in a small, suburban forest fragment in coastal New York, USA, in the summers of 2018 and 2019. We confirmed that the bats shared roost sites and, using network analyses, analyzed social dynamics and space use. In contrast to previous research on this imperiled species in large, unfragmented core forests, we found a more dense, connected roost network that concentrated around forest patch edges. Unusual for this species, primary roosts were anthropogenic structures. Our findings suggest that northern long-eared bats can utilize small forest patches and that incorporation of specific types of anthropogenic roosts might be an effective strategy for long-term conservation in more urbanized landscapes where forest management actions to enhance day-roosting conditions a

New York↗
USGS2014

Predicting connectivity of green turtles at Palmyra Atoll, central Pacific: a focus on mtDNA and dispersal modelling

Population connectivity and spatial distribution are fundamentally related to ecology, evolution and behaviour. Here, we combined powerful genetic analysis with simulations of particle dispersal in a high-resolution ocean circulation model to investigate the distribution of green turtles foraging at the remote Palmyra Atoll National Wildlife Refuge, central Pacific. We analysed mitochondrial sequences from turtles ( n = 349) collected there over 5 years (2008–2012). Genetic analysis assigned natal origins almost exclusively (approx. 97%) to the West Central and South Central Pacific combined Regional Management Units. Further, our modelling results indicated that turtles could potentially drift from rookeries to Palmyra Atoll via surface currents along a near-Equatorial swathe traversing the Pacific. Comparing findings from genetics and modelling highlighted the complex impacts of ocean currents and behaviour on natal origins. Although the Palmyra feeding ground was highly differentiated genetically from others in the Indo-Pacific, there was no significant differentiation among years, sexes or stage-classes at the Refuge. Understanding the distribution of this foraging population advances knowledge of green turtles and contributes to effective conservation planning for this threatened species.

Journal of the Royal Society Interface↗
USGS2002

Spatio-temporal dynamics of species richness in coastal fish communities

Determining patterns of change in species richness and the processes underlying the dynamics of biodiversity are of key interest within the field of ecology, but few studies have investigated the dynamics of vertebrate communities at a decadal temporal scale. Here, we report findings on the spado-temporal variability in the richness and composition of fish communities along the Norwegian Skagerrak coast having been surveyed for more than half a century. Using statistical models incorporating non-detection and associated sampling variance, we estimate local species richness and changes in species composition allowing us to compute temporal variability in species richness. We tested whether temporal variation could be related to distance to the open sea and to local levels of pollution. Clear differences in mean species richness and temporal variability are observed between fjords that were and were not exposed to the effects of pollution. Altogether this indicates that the fjord is an appropriate scale for studying changes in coastal fish communities in space and time. The year-to-year rates of local extinction and turnover were found to be smaller than spatial differences in community composition. At the regional level, exposure to the open sea plays a homogenizing role, possibly due to coastal currents and advection.

Proceedings of the Royal Society B: Biological Sci↗
USGS2003

Nest-site selection and success of mottled ducks on agricultural lands in southwest Louisiana

Listing of the mottled duck (Anas fulvigula maculosa) as a priority species in the Gulf Coast Joint Venture of the North American Waterfowl Management Plan, coupled with recent declines of rice (Oryza sativa) acreage, led us to investigate the nesting ecology of this species on agricultural lands in southwest Louisiana. We examined nest-site selection at macro- and microhabitat levels, nest success, causes of nest failures, and habitat features influencing nest success. We found that female mottled ducks preferred to nest in permanent pastures with knolls (53% of nests) and idle fields (22% of nests). Vegetation height was greater at nests than at random points within the same macrohabitat patch. Successful nests were associated with greater numbers of plant species, located farther from water, and associated with higher vegetation density values than were unsuccessful nests. We determined that mammalian predators caused most nest failures (77% of 52 unsuccessful nests). Our results suggest that nest success of mottled ducks on agricultural lands in southwest Louisiana could be improved by 1) locating large permanent pastures and idle fields near rice fields and other available wetlands, 2) managing plant communities in these upland areas to favor dense stands of perennial bunch grasses, tall composites, dewberry (Rubus trivialis), and other native grasses and forbs, and 3) managing cattle-stocking rates and the duration and timing of grazing to promote tall, dense stands of these plant taxa during the nesting season (March-June).

Wildlife Society Bulletin↗
USGS2017

Response of fish population dynamics to mitigation activities in a large regulated river

Extensive water development in large rivers has precipitated many negative ecological effects on native fish populations. Mitigation for such development often focuses on restoring biological integrity through remediation of the physical and chemical properties of regulated rivers. However, evaluating and defining the success of those programs can be difficult. We modeled the influence of mitigation-related environmental factors on growth and recruitment of two ecologically important native fish species (Largescale Sucker Catostomus macrocheilus and Mountain Whitefish Prosopium williamsoni ) in the Kootenai River, Idaho. Artificial nutrient (phosphorus) addition best predicted the variability in annual growth of both species. Nutrient addition was positively related to Largescale Sucker growth but negatively related to Mountain Whitefish growth. The best model explained 82% of the annual variability in incremental growth for Largescale Suckers and 61% of the annual variability for Mountain Whitefish. Year-class strength of Largescale Suckers was not closely related to any of the environmental variables evaluated; however, year-class strength of Mountain Whitefish was closely associated with nutrient addition, discharge, and temperature. Most research has focused on biotic assemblages to evaluate the effects of mitigation activities on fishes, but there is an increased need to identify the influence of rehabilitation activities on fish population dynamics within those assemblages. Here, we demonstrate how fish growth can serve as an indicator of rehabilitation success in a highly regulated large river. Future fish restoration projects can likely benefit from a change in scope and from consideration of an evaluation framework involving the response of population rate functions to mitigation.

Idaho↗
USGS2023

Incorporating environmental heterogeneity and observation effort to predict host distribution and viral spillover from a bat reservoir

Predicting the spatial occurrence of wildlife is a major challenge for ecology and management. In Latin America, limited knowledge of the number and locations of vampire bat roosts precludes informed allocation of measures intended to prevent rabies spillover to humans and livestock. We inferred the spatial distribution of vampire bat roosts while accounting for observation effort and environmental effects by fitting a log Gaussian Cox process model to the locations of 563 roosts in three regions of Peru. Our model explained 45% of the variance in the observed roost distribution and identified environmental drivers of roost establishment. When correcting for uneven observation effort, our model estimated a total of 2340 roosts, indicating that undetected roosts (76%) exceed known roosts (24%) by threefold. Predicted hotspots of undetected roosts in rabies-free areas revealed high-risk areas for future viral incursions. Using the predicted roost distribution to inform a spatial model of rabies spillover to livestock identified areas with disproportionate underreporting and indicated a higher rabies burden than previously recognized. We provide a transferrable approach to infer the distribution of a mostly unobserved bat reservoir that can inform strategies to prevent the re-emergence of an important zoonosis.

Proceedings of the Royal Society B: Biological Sci↗
USGS2024

Age, growth, and trophic ecology of the Redeye Bass, an introduced invader of California rivers

Objective The Redeye Bass Micropterus coosae is a piscivore introduced into California, which has become a threat to the state's endemic freshwater fishes. It has eliminated native fishes from the middle reaches of the Cosumnes River, our study stream, which is the largest stream without a major dam on its main stem in the Sacramento–San Joaquin River drainage, central California, USA. We thoroughly documented its novel life history and ecology in California to shed light on why it has been such a successful invader despite its relatively small native range. Methods Over 4000 stable carbon and nitrogen isotope samples were utilized to refine our understanding of fish trophic position within the river food web, along with a stable isotope mixing model that accounts for uncertainty in trophic enrichment data. Result Growth was slow, with an adult size range of 9–25 cm standard length (SL), although few were larger than 15-cm SL (5–6 years old). Stable isotope analyses showed that Redeye Bass dominate the river ecosystem to the exclusion of most native fishes, occupying multiple trophic levels and microhabitats. Adults largely consumed non-native crayfish and large aquatic insects, while juveniles consumed aquatic insects, the size of prey increasing with Redeye Bass length. There was no evidence of cannibalism. Redeye Bass have effectively occupied the diverse trophic positions of at least four native fish species and have altered the trophic position of Rainbow Trout Oncorhynchus mykiss in sites where they co-occur with bass. Conclusion The introduction of Redeye Bass poses a continuing threat to native stream fishes in California and elsewhere.

Transactions of the American Fisheries Society↗
USGS2001

Control of ungulate numbers in a protected area

Successful long-term control of ungulate numbers within a protected area requires continuous review and refinement of management practices. Insights gained may have application to other sites. We evaluated management objectives and actions to control populations of exotic axis deer (Axis axis) and fallow deer (Dama dama) at Point Reyes National Seashore, California. Using records of numbers of each species culled from 1968 to 1996 and demographic data, we modeled each population's potential response to management actions and to the cessation of control in 1996. These simulations indicated that control measures hold numbers of both populations below ecological carrying capacity (K) and that populations of fallow and axis deer may have reached K within 5 to 13 years of ceasing control, respectively. We also simulated each population's response to removal of actual numbers of males killed but no females and actual numbers of females killed but no males from 1968 to 1996. Removing males only resulted in both populations reaching K. Removing females only led to the extirpation of both populations. Cessation of control activities prior to removal of all females resulted in recovery of both populations. A team of personnel expended an average of 1.75 work-hours/deer to remove 1,182 exotic deer of both species from 1984 to 1994. The work effort to kill each deer increased 2-fold from 1984 to 1994. The work effort required to remove s2 deer/day reached as great as 20 hours/deer. Elimination of the axis deer population is feasible and likely a more cost-effective management alternative than continued population control. Elimination of fallow deer is potentially more difficult but may be more costeffective than continuing control actions indefinitely. We recommend similar assessments of management alternatives to those charged with controlling ungulate numbers in protected areas.

California↗
USGS2000

Drainage-basis-scale geomorphic analysis to determine refernce conditions for ecologic restoration-Kissimmee River, Florida

Major controls on the retention, distribution, and discharge of surface water in the historic (precanal) Kissimmee drainage basin and river were investigated to determine reference conditions for ecosystem restoration. Precanal Kissimmee drainage-basin hydrology was largely controlled by landforms derived from relict, coastal ridge, lagoon, and shallow-shelf features; widespread carbonate solution depressions; and a poorly developed fluvial drainage network. Prior to channelization for flood control, the Kissimmee River was a very low gradient, moderately meandering river that flowed from Lake Kissimmee to Lake Okeechobee through the lower drainage basin. We infer that during normal wet seasons, river discharge rapidly exceeded Lake Okeechobee outflow capacity, and excess surface water backed up into the low-gradient Kissimmee River. This backwater effect induced bankfull and peak discharge early in the flood cycle and transformed the flood plain into a shallow aquatic system with both lacustrine and riverine characteristics. The large volumes of surface water retained in the lakes and wetlands of the upper basin maintained overbank flow conditions for several months after peak discharge. Analysis indicates that most of the geomorphic work on the channel and flood plain occurred during the frequently recurring extended periods of overbank discharge and that discharge volume may have been significant in determining channel dimensions. Comparison of hydrogeomorphic relationships with other river systems identified links between geomorphology and hydrology of the precanal Kissimmee River. However, drainage-basin and hydraulic geometry models derived solely from general populations of river systems may produce spurious reference conditions for restoration design criteria.

Florida↗