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At least 1,423 records · Page 79Linked to original sources
USGS2021

Feather corticosterone reveals developmental challenges in a long-term study of juvenile northern spotted owls

Corticosterone is a steroid hormone integral to a variety of physiological pathways and is strongly associated with the vertebrate stress response. In avian species, circulating corticosterone is sequestered into developing feathers and is used as an indicator of energy allocation during feather growth and widely applied in conservation physiology. The northern spotted owl Strix occidentalis caurina is a federally threatened old-growth forest obligate of conservation concern endemic to the Pacific Northwest of the United States and Canada. The effects of landscape characteristics and individual variation on early development in spotted owls remain unstudied despite long recognition of this knowledge gap and its potential importance to species conservation. We quantified corticosterone concentrations in 4,720 feathers from 1,056 juvenile spotted owls across seven study areas between 2001 and 2017. We used an information-theoretic approach to examine the environmental and individual factors related to feather corticosterone in juvenile spotted owls as an indicator of challenges during early development. Feather corticosterone was positively related to temperature and precipitation, and negatively related to juvenile mass at banding. We found strong support for an interaction between mass and precipitation, with greater amounts of precipitation being associated with higher levels of feather corticosterone in lighter juveniles. The temperature and precipitation metric with the strongest relationship with feather corticosterone occurred during the fledging period, suggesting that this period presents an energetic challenge for juvenile spotted owls. Greater juvenile mass decreased the effect of precipitation, suggesting that greater mass was important for juveniles to maintain homeostasis during fledgling. Feather corticosterone in juvenile spotted owls provided insights to the challenges faced during early development, adding to our understanding of spotted owl life history and potential for population recovery.

Oregon, Washington↗
USGS2020

AMMonitor: Remote monitoring of biodiversity in an adaptive framework with R

Ecological research and management programs are increasingly using autonomous monitoring units (AMUs) to collect large volumes of acoustic and/or photo data to address pressing management objectives or research goals. The data management requirements of an AMU-based monitoring effort are often overwhelming, with a considerable amount of processing to translate raw data into models and analyses that have research and management utility. We created the r package AMMonitor to simplify the process of moving from remotely collected data to analysis and results, using a comprehensive SQLite database for data management that tracks all components of a remote monitoring program. This framework enables the tracking of analyses and research/management objectives through time. We illustrate the AMMonitor approach with the example of evaluating an occurrence-based management objective for a target species. First, we provide an overview of the database and data management approach. Next, we illustrate a few available workflows: temporally adaptive sampling, automated detection of species sounds from acoustic recordings and aggregation of automated detections into an encounter history for use in an occupancy analysis, the outcome of which can be analysed with respect to the motivating management objective. Without a comprehensive framework for efficiently moving from raw remote monitoring data collection to results and analysis, monitoring programs are limited in their capacity to systematically characterize ecological processes and inform management decisions through time. AMMonitor provides an option for such a framework. Code, comprehensive documentation, and step-by-step examples are available online at https://code.usgs.gov/vtcfwru/AMMonitor

Methods in Ecology and Evolution↗
USGS2014

Effectiveness of eugenol sedation to reduce the metabolic rates of cool and warm water fish at high loading densities

Effects of eugenol (AQUI-S ® 20E, 10% active eugenol) sedation on cool water, yellow perch Perca flavescens (Mitchill), and warm water, Nile tilapia Oreochromis niloticus L. fish metabolic rates were assessed. Both species were exposed to 0, 10, 20 and 30 mg L −1 eugenol using static respirometry. In 17°C water and loading densities of 60, 120 and 240 g L −1 , yellow perch controls (0 mg L −1 eugenol) had metabolic rates of 329.6–400.0 mg O 2 kg −1 h −1 , while yellow perch exposed to 20 and 30 mg L −1 eugenol had significantly reduced metabolic rates of 258.4–325.6 and 189.1–271.0 mg O 2 kg −1 h −1 respectively. Nile tilapia exposed to 30 mg L −1 eugenol had a significantly reduced metabolic rate (424.5 ± 42.3 mg O 2 kg −1 h −1 ) relative to the 0 mg L −1 eugenol control (546.6 ± 53.5 mg O 2 kg −1 h −1 ) at a loading density of 120 g L −1 in 22°C water. No significant differences in metabolic rates for Nile tilapia were found at 240 or 360 g L −1 loading densities when exposed to eugenol. Results suggest that eugenol sedation may benefit yellow perch welfare at high densities (e.g. live transport) due to a reduction in metabolic rates, while further research is needed to assess the benefits of eugenol sedation on Nile tilapia at high loading densities.

Aquaculture Research↗
USGS2024

The underlying causes of differential migration: Assumptions, hypotheses, and predictions

Mechanisms governing the migratory decisions of birds have long fascinated ecologists and sparked considerable debate. Identifying factors responsible for variation in migration distance, also known as differential migration, has been a popular approach to understanding the mechanisms underlying migratory behaviour more generally. However, research progress has been slowed by the continued testing of overlapping, non-mechanistic, and circular predictions among a small set of historically entrenched hypotheses. We highlight the body size hypothesis and suggest that the predictions commonly tested have impeded progress because body size relationships with migration distance are predictions made by several distinct hypotheses with contrasting mechanisms. The cost of migration itself has not been adequately accounted for in most hypotheses, and we propose two flight efficiency hypotheses with time- and energy-minimizing mechanisms that allow individuals to mitigate the risks inherent to longer migrations. We also advance two conceptual versions of the social dominance hypothesis based on two distinct underlying mechanisms related to distance minimization and food maximization that will help clarify the role of competition in driving migratory decisions. Overall, we describe and refine 12 mechanistic hypotheses proposed to explain differential migration (along with several other special-case hypotheses), seven of which have underlying mechanisms related to food limitation as past research has identified this to be an important driver of differential migration. We also thoroughly reviewed 145 publications to assess the amount of support for 10 critical assumptions underlying alternative hypotheses for differential migration in birds. Our review reveals that surprisingly few studies explicitly evaluate assumptions within a differential migration context. Generating and testing strong predictions and critical assumptions underlying mechanisms of alternative hypotheses will improve our ability to differentiate among these explanations of differential migration. Additionally, future intraspecific progress will be greatest if investigators continue to focus on mechanisms underlying variation in migration distance within rather than among demographic classes, as previous research has found differing mechanisms to be responsible for differential migration among demographic classes. Interspecifically, a thorough comparative analysis that seeks to explain variation in migration distance among species would broaden both our understanding of the mechanisms regulating current differential migration patterns and those that led to the evolution of migration more generally. Collectively, we provide a framework that, together with advances in animal-borne tracking and other technology, can be used to advance our understanding of the causes of differential migration distance, and migratory decisions more generally.

Biological Reviews↗
USGS2021

Mechanistic invasive species management models and their application in conservation

Management strategies to address the challenges associated with invasive species are critical for effective conservation. An increasing variety of mathematical models offer insight into invasive populations, and can help managers identify cost effective prevention, control, and eradication actions. Despite this, as model complexity grows, so does the inaccessibility of these tools to conservation practitioners making decisions about management. Here, we seek to narrow the science-practice gap by reviewing invasive species management models (ISMMs). We define ISMMs as mechanistic models used to explore invasive species management strategies, and include reaction-advection–diffusion models, integrodifference equations, gravity models, particle transport models, nonspatial and spatial discrete-time population growth models, cellular automata, and individual-based models. For each approach, we describe the model framework and its implementation, discuss strengths and weaknesses, and give examples of conservation applications. We conclude by discussing how ISMMs can be used in concert with adaptive management to address scientific uncertainties impeding action and with multiple objective decision processes to evaluate tradeoffs among management objectives. We undertook this review to support more effective decision-making involving invasive species by providing conservation practitioners with the information they need to identify tools most useful for their applications.

Conservation Science and Practice↗
USGS2022

Mismatch between temperature and discharge disrupts spawning cues in a fluvial specialist, blue sucker Cycleptus elongatus

Seasonal movements cued by environmental variables are a critical component of riverine fish life history. Life-history events for species such as blue sucker Cycleptus elongatus are likely cued by discharge and temperature and may be disrupted if those life-history events and environmental regimes are mismatched. However, this effect may be dependent upon the habitat occupied when environmental cues are received by individuals. We tracked telemetered blue sucker in the Colorado River, Texas, USA, from 2015 to 2017 and modelled the relative effects of discharge, temperature and habitat structure on seasonal movement patterns. Tagged fish varied in their propensity to move, although most returned to their original tagging locations. Decreasing temperatures and increasing discharge resulted in increased seasonal movements. Temperature and discharge had the largest effect on movement behaviour, but the magnitude of movements was largely dependent on the year. Temperatures between 12 and 19°C and discharges between 10 and 240 m 3 s −1 resulted in greater probabilities of spawning movements. Spawning was most probable in 2015 and reduced or halted in 2016 and 2017. Future climate scenarios suggest North America will experience increased drought, warmer temperatures and more variable weather patterns. These future scenarios could negatively impact blue sucker by disrupting environmental cues and habitat availability for seasonal life-history events. Our results suggest temperature and discharge are critical cues for the species, but that their combined effect is largely dependent on the occupied habitat.

Texas↗
USGS2012

Optimal temperature for malaria transmission is dramaticallylower than previously predicted

The ecology of mosquito vectors and malaria parasites affect the incidence, seasonal transmission and geographical range of malaria. Most malaria models to date assume constant or linear responses of mosquito and parasite life-history traits to temperature, predicting optimal transmission at 31 °C. These models are at odds with field observations of transmission dating back nearly a century. We build a model with more realistic ecological assumptions about the thermal physiology of insects. Our model, which includes empirically derived nonlinear thermal responses, predicts optimal malaria transmission at 25 °C (6 °C lower than previous models). Moreover, the model predicts that transmission decreases dramatically at temperatures > 28 °C, altering predictions about how climate change will affect malaria. A large data set on malaria transmission risk in Africa validates both the 25 °C optimum and the decline above 28 °C. Using these more accurate nonlinear thermal-response models will aid in understanding the effects of current and future temperature regimes on disease transmission.

Ecology Letters↗
USGS2004

Spatial-temporal population dynamics across species range: From centre to margin

Understanding the boundaries of species' ranges and the variations in population dynamics from the centre to margin of a species' range is critical. This study simulated spatial-temporal patterns of birth and death rates and migration across a species' range in different seasons. Our results demonstrated the importance of dispersal and migration in altering birth and death rates, balancing source and sink habitats, and governing expansion or contraction of species' ranges in changing environments. We also showed that the multiple equilibria of metapopulations across a species' range could be easily broken following climatic changes or physical disturbances either local or regional. Although we refer to our models as describing the population dynamics across whole species' range, they should also apply to small-scale habitats (metapopulations) in which species abundance follows a humped pattern or to any ecosystem or landscape where strong central-marginal (C-M) environmental gradients exist. Conservation of both central and marginal populations would therefore be equally important considerations in making management decisions.

Oikos↗
USGS2010

Long-term increases in young-of-the-year growth of Arctic cisco Coregonus autumnalis and environmental influences

Arctic cisco Coregonus autumnalis young-of-year (YOY) growth was used as a proxy to examine the long-term response of a high-latitude fish population to changing climate from 1978 to 2004. YOY growth increased over time (r2 = 0·29) and was correlated with monthly averages of the Arctic oscillation index, air temperature, east wind speed, sea-ice concentration and river discharge with and without time lags. Overall, the most prevalent correlates to YOY growth were sea-ice concentration lagged 1 year (significant correlations in 7 months; r 2 = 0·14-0·31) and Mackenzie River discharge lagged 2 years (significant correlations in 8 months; r 2 = 0·13-0·50). The results suggest that decreased sea-ice concentrations and increased river discharge fuel primary production and that life cycles of prey species linking increased primary production to fish growth are responsible for the time lag. Oceanographic studies also suggest that sea ice concentration and fluvial inputs from the Mackenzie River are key factors influencing productivity in the Beaufort Sea. Future research should assess the possible mechanism relating sea ice concentration and river discharge to productivity at upper trophic levels.

Journal of Fish Biology↗
USGS1993

Monitoring of the in-river migration of smolts from two groups of spring chinook salmon, Oncorhynchus tshawytscha (Walbaum), with different profiles of Renibacterium salmoninarum infection

Broodstock segregation based on the measurement of maternal Renibacterium salmoninarum infection levels by the enzyme-linked immunosorbent assay (ELISA) and the membrane filtration-fluorescent antibody technique (MF-FAT) was previously shown to affect the prevalence and levels of bacterial kidney disease (BKD) in progeny of chinook salmon, Oncorhynchus tshawytscha (Walbaum), during hatchery rearing. Subgroups of fish from that study were marked with passive integrated transponder (PIT) tags, and monitored by PIT-tag detectors during the first 342km of their migration to the Pacific Ocean. Differences in the recovery of tagged fish were significant ( P ≤ 0·01) at each detection point and became more pronounced as the fish moved downstream. Cumulative recoveries of fish from the low-BKD group and the high-BKD group, respectively, were 31% and 28% after 116km, 44% and 37% after 176km, and 51% and 42% after 342km. There were no apparent differences in the migration timing of the two groups to the first detection point. The data suggested that in-river survival was higher in the progeny group from parents that had low R. salmoninarum infection levels or tested negative for R. salmoninarum (low-BKD group) than in the group female parents with high infection levels (high-BKD group).

Aquaculture Research↗
USGS2010

Identification and evaluation of shark bycatch in Georgia’s commercial shrimp trawl fishery with implications for management

Many US states have recreational and commercial fisheries that occur in nursery areas occupied by subadult sharks and can potentially affect their survival. Georgia is one of few US states without a directed commercial shark fishery, but the state has a large, nearshore penaeid shrimp trawl fishery in which small sharks occur as bycatch. During our 1995-1998 investigation of bycatch in fishery-dependent sampling events, 34% of 127 trawls contained sharks. This bycatch totalled 217 individuals from six species, with Atlantic sharpnose shark, Rhizoprionodon terraenovae (Richardson), the most common and finetooth shark, Carcharhinus isodon (Müller & Henle) and spinner shark, Carcharhinus brevipinna (Müller & Henle), the least common. The highest catch rates for sharks occurred during June and July and coincided with the peak months of the pupping season for many species. Trawl tow speed and tow time did not significantly influence catch rates for shark species. Gear configurations [net type, turtle excluder device (TED), bycatch reduction device] affected catch rates for shark species. Results of this study indicate gear restrictions, a delayed season opening, or reduced bar spacing on TEDs may reduce shark bycatch in this fishery.

Fisheries Management and Ecology↗
USGS2011

Patterns in young-of-year smallmouth bass microhabitat use in multiple stream segments with contrasting land uses

Young-of-the-year (YOY) smallmouth bass, Micropterus dolomieu Lacepede, were evaluated in streams from eight catchments with two contrasting land uses to determine their use of microhabitats under a variety of stream conditions. Step-wise discriminant function analyses revealed patterns of habitat use by discriminating used from available microhabitat conditions. Velocity was significant in 88% of streams sampled, whereas depth was significant in only the smallest stream in the forest-dominated catchments and 75% of stream segments located in pasture-dominated catchments. Mean velocities used by YOY bass were lower than available velocities, and mean depths used were greater than mean availability in all cases. Substrata varied significantly with availability in different stream segments. Error rates associated with classification ranged from 5 to 39%. Results indicate that YOY smallmouth bass are somewhat opportunistic, but use low-velocity habitats in most cases and deeper water when streams are impacted by pasture land use and associated physical changes.

Fisheries Management and Ecology↗
USGS2006

The importance of fluvial hydraulics to fish-habitat restoration in low-gradient alluvial streams

1. A major cause of degradation and loss of stream fish is alteration of physical habitat within and adjacent to the channel. We describe a potentially efficient approach to fish restoration based upon the relationship between fluvial hydraulics, geomorphology, and those habitats important to fish. 2. The aquatic habitat in a low-gradient, alluvial stream in the Ozark Plateaus physiographical province was classified according to location in the channel, patterns of water flow, and structures that control flow. The resulting habitat types were ranked in terms of their temporal stability and ability to be manipulated. 3. Delineation and quantification of discrete physical spaces in a stream, termed hydraulic habitat units, are shown to be useful in stream restoration programmes if the ecological importance of each habitat unit is known, and if habitats are defined by fluvial dynamics so that restoration is aided by natural forces. 4. Examples, using different taxa, are given to illustrate management options.

Missouri↗
USGS2011

A trans-dimensional Bayesian Markov chain Monte Carlo algorithm for model assessment using frequency-domain electromagnetic data

A meaningful interpretation of geophysical measurements requires an assessment of the space of models that are consistent with the data, rather than just a single, ‘best’ model which does not convey information about parameter uncertainty. For this purpose, a trans-dimensional Bayesian Markov chain Monte Carlo (MCMC) algorithm is developed for assessing frequencydomain electromagnetic (FDEM) data acquired from airborne or ground-based systems. By sampling the distribution of models that are consistent with measured data and any prior knowledge, valuable inferences can be made about parameter values such as the likely depth to an interface, the distribution of possible resistivity values as a function of depth and non-unique relationships between parameters. The trans-dimensional aspect of the algorithm allows the number of layers to be a free parameter that is controlled by the data, where models with fewer layers are inherently favoured, which provides a natural measure of parsimony and a significant degree of flexibility in parametrization. The MCMC algorithm is used with synthetic examples to illustrate how the distribution of acceptable models is affected by the choice of prior information, the system geometry and configuration and the uncertainty in the measured system elevation. An airborne FDEM data set that was acquired for the purpose of hydrogeological characterization is also studied. The results compare favorably with traditional least-squares analysis, borehole resistivity and lithology logs from the site, and also provide new information about parameter uncertainty necessary for model assessment.

Geophysical Journal International↗
USGS2011

High-frequency Born synthetic seismograms based on coupled normal modes

High-frequency and full waveform synthetic seismograms on a 3-D laterally heterogeneous earth model are simulated using the theory of coupled normal modes. The set of coupled integral equations that describe the 3-D response are simplified into a set of uncoupled integral equations by using the Born approximation to calculate scattered wavefields and the pure-path approximation to modulate the phase of incident and scattered wavefields. This depends upon a decomposition of the aspherical structure into smooth and rough components. The uncoupled integral equations are discretized and solved in the frequency domain, and time domain results are obtained by inverse Fourier transform. Examples show the utility of the normal mode approach to synthesize the seismic wavefields resulting from interaction with a combination of rough and smooth structural heterogeneities. This approach is applied to an ∼4 Hz shallow crustal wave propagation around the site of the San Andreas Fault Observatory at Depth (SAFOD).

Geophysical Journal International↗
USGS2011

Quantifying the hydrological responses to climate change in an intact forested small watershed in southern China

Responses of hydrological processes to climate change are key components in the Intergovernmental Panel for Climate Change (IPCC) assessment. Understanding these responses is critical for developing appropriate mitigation and adaptation strategies for sustainable water resources management and protection of public safety. However, these responses are not well understood and little long-term evidence exists. Herein, we show how climate change, specifically increased air temperature and storm intensity, can affect soil moisture dynamics and hydrological variables based on both long-term observation and model simulations using the Soil and Water Assessment Tool (SWAT) in an intact forested watershed (the Dinghushan Biosphere Reserve) in Southern China. Our results show that, although total annual precipitation changed little from 1950 to 2009, soil moisture decreased significantly. A significant decline was also found in the monthly 7-day low flow from 2000 to 2009. However, the maximum daily streamflow in the wet season and unconfined groundwater tables have significantly increased during the same 10-year period. The significant decreasing trends on soil moisture and low flow variables suggest that the study watershed is moving towards drought-like condition. Our analysis indicates that the intensification of rainfall storms and the increasing number of annual no-rain days were responsible for the increasing chance of both droughts and floods. We conclude that climate change has indeed induced more extreme hydrological events (e.g. droughts and floods) in this watershed and perhaps other areas of Southern China. This study also demonstrated usefulness of our research methodology and its possible applications on quantifying the impacts of climate change on hydrology in any other watersheds where long-term data are available and human disturbance is negligible.

Guangdong Province↗
USGS2005

The accuracy of matrix population model projections for coniferous trees in the Sierra Nevada, California

1 We assess the use of simple, size-based matrix population models for projecting population trends for six coniferous tree species in the Sierra Nevada, California. We used demographic data from 16 673 trees in 15 permanent plots to create 17 separate time-invariant, density-independent population projection models, and determined differences between trends projected from initial surveys with a 5-year interval and observed data during two subsequent 5-year time steps. 2 We detected departures from the assumptions of the matrix modelling approach in terms of strong growth autocorrelations. We also found evidence of observation errors for measurements of tree growth and, to a more limited degree, recruitment. Loglinear analysis provided evidence of significant temporal variation in demographic rates for only two of the 17 populations. 3 Total population sizes were strongly predicted by model projections, although population dynamics were dominated by carryover from the previous 5-year time step (i.e. there were few cases of recruitment or death). Fractional changes to overall population sizes were less well predicted. Compared with a null model and a simple demographic model lacking size structure, matrix model projections were better able to predict total population sizes, although the differences were not statistically significant. Matrix model projections were also able to predict short-term rates of survival, growth and recruitment. Mortality frequencies were not well predicted. 4 Our results suggest that simple size-structured models can accurately project future short-term changes for some tree populations. However, not all populations were well predicted and these simple models would probably become more inaccurate over longer projection intervals. The predictive ability of these models would also be limited by disturbance or other events that destabilize demographic rates. ?? 2005 British Ecological Society.

Journal of Ecology↗
USGS2008

Elevated CO 2 enhances biological contributions to elevation change in coastal wetlands by offsetting stressors associated with sea-level rise

1. Sea-level rise, one indirect consequence of increasing atmospheric CO 2 , poses a major challenge to long-term stability of coastal wetlands. An important question is whether direct effects of elevated CO 2 on the capacity of marsh plants to accrete organic material and to maintain surface elevations outweigh indirect negative effects of stressors associated with sea-level rise (salinity and flooding). 2. In this study, we used a mesocosm approach to examine potential direct and indirect effects of atmospheric CO 2 concentration, salinity and flooding on elevation change in a brackish marsh community dominated by a C 3 species, Schoenoplectus americanus, and a C 4 grass, Spartina patens. This experimental design permitted identification of mechanisms and their role in controlling elevation change, and the development of models that can be tested in the field. 3. To test hypotheses related to CO 2 and sea-level rise, we used conventional anova procedures in conjunction with structural equation modelling (SEM). SEM explained 78% of the variability in elevation change and showed the direct, positive effect of S. americanus production on elevation. The SEM indicated that C 3 plant response was influenced by interactive effects between CO 2 and salinity on plant growth, not a direct CO 2 fertilization effect. Elevated CO 2 ameliorated negative effects of salinity on S. americanus and enhanced biomass contribution to elevation. 4. The positive relationship between S. americanus production and elevation change can be explained by shoot-base expansion under elevated CO 2 conditions, which led to vertical soil displacement. While the response of this species may differ under other environmental conditions, shoot-base expansion and the general contribution of C 3 plant production to elevation change may be an important mechanism contributing to soil expansion and elevation gain in other coastal wetlands. 5. Synthesis. Our results revealed previously unrecognized interactions and mechanisms contributing to marsh elevation change, including amelioration of salt stress by elevated CO 2 and the importance of plant production and shoot-base expansion for elevation gain. Identification of biological processes contributing to elevation change is an important first step in developing comprehensive models that permit more accurate predictions of whether coastal marshes will persist with continued sea-level rise or become submerged. ?? 2008 The Authors.

Journal of Ecology↗