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At least 433 records · Page 24Linked to original sources

USGS2021

Stable oxygen isotopes in shallow marine ostracodes from the northern Bering and Chukchi Seas

Stable oxygen isotope measurements on calcitic valves of benthic ostracodes (δ18Oost) from the northern Bering and Chukchi Seas were used to examine ecological and hydrographic processes governing ostracode and associated seawater δ18O values. Five cryophilic taxa were analyzed for δ18Oost values: Sarsicytheridea bradii; Paracyprideis pseudopunctillata; Heterocyprideis sorbyana; Heterocyprideis fascis; and the subarctic species Normanicythere leioderma. Controls on the stable oxygen isotope composition of ostracode calcite were investigated by first establishing species' vital effects and then comparing δ18Oost to seawater δ18O values (that ranged from −2.7 to −0.5‰), CTD temperature (−1.7 to 8.7 °C) and salinity (30–34) measured at sampling stations in the Bering and Chukchi Seas during the six summers of 2013–2018. Results from 297 δ18Oost measurements from 53 sites on the Bering and Chukchi Sea continental shelves are consistent with the temporal and spatial variation in δ18O values of continental shelf bottom water, as impacted by seasonality, regional hydrography, and physical processes (i.e., sea-ice melt and extent, vertical mixing, precipitation/evaporation). Regression statistics for δ18Oost values of two species, N. leioderma and P. pseudopunctillata, showed correlations to temperature and salinity that may facilitate prediction of water-mass characteristics when applied to sediment core records. Specifically, a significant linear regression relationship was found between δ18Oost values of N. leioderma and P. pseudopunctillata and temperature (R2 = 0.67 and 0.52, respectively). A principal component analysis confirmed temperature as the main controlling factor in the δ18Oost values of all species except S. bradii, with samples of distinct water masses grouping together. The δ18Oost values of S. bradii exhibited a narrow range of values (~3 to 4.5‰) across a temperature range of 10 °C. Due to strong vital effects and possibly other undetermined factors, the incorporation of δ18Oost in S. bradii was not driven by any obvious predominant environmental factors.

Marine Micropaleontology↗

USGS2017

Seventy-five years of vegetation treatments on public rangelands in the Great Basin of North America

On the Ground Land treatments occurring over millions of hectares of public rangelands in the Great Basin over the last 75 years represent one of the largest vegetation manipulation and restoration efforts in the world. The ability to use legacy data from land treatments in adaptive management and ecological research has improved with the creation of the Land Treatment Digital Library (LTDL), a spatially explicit database of land treatments conducted by the U.S. Bureau of Land Management. The LTDL contains information on over 9,000 confirmed land treatments in the Great Basin, composed of seedings (58%), vegetation control treatments (24%), and other types of vegetation or soil manipulations (18%). The potential application of land treatment legacy data for adaptive management or as natural experiments for retrospective analyses of effects of land management actions on physical, hydrologic, and ecologic patterns and processes is considerable and just beginning to be realized.

California, Idaho, Nevada, Oregon, Utah↗

USGS2023

Understanding ecological response to physical characteristics in side channels of a large floodplain-river ecosystem

Side channels in large floodplain rivers serve a variety of important ecological roles, particularly in reaches where habitat conditions have been degraded or diminished. We developed hypotheses regarding side channel ecological structure whereby we expected species richness of young-of-year fishes to generally be higher in shallower, more physically heterogeneous side channels with lower velocities, with differences based on reproductive guild. We also hypothesized species richness of adult fishes to be higher in side channels with greater heterogeneity that could support diverse foraging resources and provide refugia during extreme flow conditions. To test these hypotheses, we used a 28-year fish community dataset from the Upper Mississippi and Illinois Rivers. Across six study reaches, we assessed metrics of side channel physical size, heterogeneity, and connectivity that were hypothesized to explain variance of fish community response, while accounting for site-level factors across 52 side channels using multilevel models. We then used these side channel-level characteristics in a K-means cluster analysis to classify 1126 side channels across 32 reaches of the river system. Our results indicated that the relative explanatory contributions of physical metrics varied by response variable, providing varying evidence in support of our hypotheses, and indicating that different forms of heterogeneity matter in different ways. Side channel-level factors were more explanatory of fish community responses in side channels of upstream reaches compared to downstream reaches and percent wet forest was the most explanatory side channel-level factor of fish community responses across all models. Our classification of side channels indicated strong spatial contrasts in the abundance and diversity of side channels across reaches. Scaling up to understand how the diversity and abundance of different types of side channels contributes to landscape-scale ecological functions and processes would be useful for establishing targets for reach-scale physical heterogeneity.

Upper Mississippi River and Illinois River↗

USGS2017

Spatial dependence of reduced sulfur in Everglades dissolved organic matter controlled by sulfate enrichment

Sulfate inputs to the Florida Everglades stimulate sulfidic conditions in freshwater wetland sediments that affect ecological and biogeochemical processes. An unexplored implication of sulfate enrichment is alteration of the content and speciation of sulfur in dissolved organic matter (DOM), which influences the reactivity of DOM with trace metals. Here, we describe the vertical and lateral spatial dependence of sulfur chemistry in the hydrophobic organic acid fraction of DOM from unimpacted and sulfate-impacted Everglades wetlands using X-ray absorption spectroscopy and ultrahigh-resolution mass spectrometry. Spatial variation in DOM sulfur content and speciation reflects the degree of sulfate enrichment and resulting sulfide concentrations in sediment pore waters. Sulfur is incorporated into DOM predominantly as highly reduced species in sulfidic pore waters. Sulfur-enriched DOM in sediment pore waters exchanges with overlying surface waters and the sulfur likely undergoes oxidative transformations in the water column. Across all wetland sites and depths, the total sulfur content of DOM correlated with the relative abundance of highly reduced sulfur functionality. The results identify sulfate input as a primary determinant on DOM sulfur chemistry to be considered in the context of wetland restoration and sulfur and trace metal cycling.

Florida↗

USGS2022

Classifying mixing regimes in ponds and shallow lakes

Lakes are classified by thermal mixing regimes, with shallow waterbodies historically categorized as continuously mixing systems. Yet, recent studies demonstrate extended summertime stratification in ponds, underscoring the need to reassess thermal classifications for shallow waterbodies. In this study, we examined the summertime thermal dynamics of 34 ponds and shallow lakes across temperate North America and Europe to categorize and identify the drivers of different mixing regimes. We identified three mixing regimes: rarely ( n = 18), intermittently ( n = 10), and often ( n = 6) mixed, where waterbodies mixed an average of 2%, 26%, and 75% of the study period, respectively. Waterbodies in the often mixed category were larger (≥4.17 ha) and stratification weakened with increased wind shear stress, characteristic of “shallow lakes.” In contrast, smaller waterbodies, or “ponds,” mixed less frequently, and stratification strengthened with increased shortwave radiation. Shallow ponds (<0.74 m) mixed intermittently, with daytime stratification often breaking down overnight due to convective cooling. Ponds ≥0.74 m deep were rarely or never mixed, likely due to limited wind energy relative to the larger density gradients associated with slightly deeper water columns. Precipitation events weakened stratification, even causing short-term mixing (hours to days) in some sites. By examining a broad set of shallow waterbodies, we show that mixing regimes are highly sensitive to very small differences in size and depth, with potential implications for ecological and biogeochemical processes. Ultimately, we propose a new framework to characterize the variable mixing regimes of ponds and shallow lakes.

Water Resource Research↗

USGS2026

More water, more of the time: Spatial changes in flooding over 83 years in the upper Mississippi River floodplain and relationships with streamgage-derived proxies

The hydrologic regime of the upper Mississippi River (UMR) has become wetter, with greater discharges, longer-lasting high-flow conditions, and seasonal shifts in these patterns over the past several decades. How these changes are expressed spatially as floodplain inundation area, frequency, depth, duration, and timing is not well understood. It is also unclear to what degree spatial patterns of submergence are represented by examining discharge data alone. We assessed changes in floodplain inundation characteristics from 1940 to 2022 in navigation pools 3–10 of the UMR using a geospatial model to simulate daily inundation depths. Inundation characteristics shifted significantly across pools, but the direction and magnitude of change varied by pool and metric. Characteristics summarized at the pool scale correlated with streamgage-derived proxies but the strength of the relationship varied. Within pools, variability in inundation trends highlighted the importance of spatially explicit modeling. Our study demonstrates that changes in discharge over 83 years have manifested across the UMR floodplain in ways that may have consequences for ecological patterns and processes. By mapping hydrologically sensitive areas, we can anticipate which areas may be susceptible to additional shifts in river discharge in a climatically uncertain future.

Iowa, Minnesota, Wiscosnin↗

USGS2005

Host population persistence in the face of introduced vector-borne diseases: Hawaii amakihi and avian malaria

The past quarter century has seen an unprecedented increase in the number of new and emerging infectious diseases throughout the world, with serious implications for human and wildlife populations. We examined host persistence in the face of introduced vector-borne diseases in Hawaii, where introduced avian malaria and introduced vectors have had a negative impact on most populations of Hawaiian forest birds for nearly a century. We studied birds, parasites, and vectors in nine study areas from 0 to 1,800 m on Mauna Loa Volcano, Hawaii from January to October, 2002. Contrary to predictions of prior work, we found that Hawaii amakihi (Hemignathus virens), a native species susceptible to malaria, comprised from 24.5% to 51.9% of the avian community at three low-elevation forests (55-270 m). Amakihi were more abundant at low elevations than at disease-free high elevations, and were resident and breeding there. Infection rates were 24-40% by microscopy and 55-83% by serology, with most infected individuals experiencing low-intensity, chronic infections. Mosquito trapping and diagnostics provided strong evidence for year-round local transmission. Moreover, we present evidence that Hawaii amakihi have increased in low elevation habitats on south-eastern Hawaii Island over the past decade. The recent emergent phenomenon of recovering amakihi populations at low elevations, despite extremely high prevalence of avian malaria, suggests that ecological or evolutionary processes acting on hosts or parasites have allowed this species to recolonize low-elevation habitats. A better understanding of the mechanisms allowing coexistence of hosts and parasites may ultimately lead to tools for mitigating disease impacts on wildlife and human populations.

Proceedings of the National Academy of Sciences of↗

USGS2015

Spatial structure of morphological and neutral genetic variation in Brook Trout

Brook Trout Salvelinus fontinalis exhibit exceptional levels of life history variation, remarkable genetic variability, and fine-scale population structure. In many cases, neighboring populations may be highly differentiated from one another to an extent that is comparable with species-level distinctions in other taxa. Although genetic samples have been collected from hundreds of populations and tens of thousands of individuals, little is known about whether differentiation at neutral markers reflects phenotypic differences among Brook Trout populations. We compared differentiation in morphology and neutral molecular markers among populations from four geographically proximate locations (all within 24 km) to examine how genetic diversity covaries with morphology. We found significant differences among and/or within streams for all three morphological axes examined and identified the source stream of many individuals based on morphology (52.3% classification efficiency). Although molecular and morphological differentiation among streams ranged considerably (mean pairwise F ST : 0.023–0.264; pairwise P ST : 0.000–0.339), the two measures were not significantly correlated. While in some cases morphological characters appear to have diverged to a greater extent than expected by neutral genetic drift, many traits were conserved to a greater extent than were neutral genetic markers. Thus, while Brook Trout exhibit fine-scale spatial patterns in both morphology and neutral genetic diversity, these types of biological variabilities are being structured by different ecological and evolutionary processes. The relative influences of genetic drift versus selection and phenotypic plasticity in shaping morphology appear to vary among populations occupying nearby streams.

Maryland↗

USGS2016

Demographic mechanisms underpinning genetic assimilation of remnant groups of a large carnivore

Current range expansions of large terrestrial carnivores are occurring following human-induced range contraction. Contractions are often incomplete, leaving small remnant groups in refugia throughout the former range. Little is known about the underlying ecological and evolutionary processes that influence how remnant groups are affected during range expansion. We used data from a spatially explicit, long-term genetic sampling effort of grizzly bears ( Ursus arctos ) in the Northern Continental Divide Ecosystem (NCDE), USA, to identify the demographic processes underlying spatial and temporal patterns of genetic diversity. We conducted parentage analysis to evaluate how reproductive success and dispersal contribute to spatio-temporal patterns of genetic diversity in remnant groups of grizzly bears existing in the southwestern (SW), southeastern (SE) and east-central (EC) regions of the NCDE. A few reproductively dominant individuals and local inbreeding caused low genetic diversity in peripheral regions that may have persisted for multiple generations before eroding rapidly (approx. one generation) during population expansion. Our results highlight that individual-level genetic and reproductive dynamics play critical roles during genetic assimilation, and show that spatial patterns of genetic diversity on the leading edge of an expansion may result from historical demographic patterns that are highly ephemeral.

Northern Continental Divide Ecosystem↗

USGS2015

Genetic diversity is related to climatic variation and vulnerability in threatened bull trout

Understanding how climatic variation influences ecological and evolutionary processes is crucial for informed conservation decision-making. Nevertheless, few studies have measured how climatic variation influences genetic diversity within populations or how genetic diversity is distributed across space relative to future climatic stress. Here, we tested whether patterns of genetic diversity (allelic richness) were related to climatic variation and habitat features in 130 bull trout ( Salvelinus confluentus ) populations from 24 watersheds (i.e., ~4–7th order river subbasins) across the Columbia River Basin, USA. We then determined whether bull trout genetic diversity was related to climate vulnerability at the watershed scale, which we quantified on the basis of exposure to future climatic conditions (projected scenarios for the 2040s) and existing habitat complexity. We found a strong gradient in genetic diversity in bull trout populations across the Columbia River Basin, where populations located in the most upstream headwater areas had the greatest genetic diversity. After accounting for spatial patterns with linear mixed models, allelic richness in bull trout populations was positively related to habitat patch size and complexity, and negatively related to maximum summer temperature and the frequency of winter flooding. These relationships strongly suggest that climatic variation influences evolutionary processes in this threatened species and that genetic diversity will likely decrease due to future climate change. Vulnerability at a watershed scale was negatively correlated with average genetic diversity ( r = −0.77; P < 0.001); watersheds containing populations with lower average genetic diversity generally had the lowest habitat complexity, warmest stream temperatures, and greatest frequency of winter flooding. Together, these findings have important conservation implications for bull trout and other imperiled species. Genetic diversity is already depressed where climatic vulnerability is highest; it will likely erode further in the very places where diversity may be most needed for future persistence.

Global Change Biology↗

USGS2011

Productivity is a poor predictor of plant species richness

For more than 30 years, the relationship between net primary productivity and species richness has generated intense debate in ecology about the processes regulating local diversity. The original view, which is still widely accepted, holds that the relationship is hump-shaped, with richness first rising and then declining with increasing productivity. Although recent meta-analyses questioned the generality of hump-shaped patterns, these syntheses have been criticized for failing to account for methodological differences among studies. We addressed such concerns by conducting standardized sampling in 48 herbaceous-dominated plant communities on five continents. We found no clear relationship between productivity and fine-scale (meters −2 ) richness within sites, within regions, or across the globe. Ecologists should focus on fresh, mechanistic approaches to understanding the multivariate links between productivity and richness.

Science↗

USGS2024

Rayleigh step-selection functions and connections to continuous-time mechanistic movement models

Background The process known as ecological diffusion emerges from a first principles view of animal movement, but ecological diffusion and other partial differential equation models can be difficult to fit to data. Step-selection functions (SSFs), on the other hand, have emerged as powerful practical tools for ecologists studying the movement and habitat selection of animals. Methods SSFs typically involve comparing resources between a set of used and available points at each step in a sequence of observed positions. We use change of variables to show that ecological diffusion implies certain distributions for available steps that are more flexible than others commonly used. We then demonstrate advantages of these distributions with SSF models fit to data collected for a mountain lion in Colorado, USA. Results We show that connections between ecological diffusion and SSFs imply a Rayleigh step-length distribution and uniform turning angle distribution, which can accommodate data collected at irregular time intervals. The results of fitting an SSF model with these distributions compared to a set of commonly used distributions revealed how precision and inference can vary between the two approaches. Conclusions Our new continuous-time step-length distribution can be integrated into various forms of SSFs, making them applicable to data sets with irregular time intervals between successive animal locations.

Movement Ecology↗

USGS2013

Bayes and empirical Bayes estimators of abundance and density from spatial capture-recapture data

In capture-recapture and mark-resight surveys, movements of individuals both within and between sampling periods can alter the susceptibility of individuals to detection over the region of sampling. In these circumstances spatially explicit capture-recapture (SECR) models, which incorporate the observed locations of individuals, allow population density and abundance to be estimated while accounting for differences in detectability of individuals. In this paper I propose two Bayesian SECR models, one for the analysis of recaptures observed in trapping arrays and another for the analysis of recaptures observed in area searches. In formulating these models I used distinct submodels to specify the distribution of individual home-range centers and the observable recaptures associated with these individuals. This separation of ecological and observational processes allowed me to derive a formal connection between Bayes and empirical Bayes estimators of population abundance that has not been established previously. I showed that this connection applies to every Poisson point-process model of SECR data and provides theoretical support for a previously proposed estimator of abundance based on recaptures in trapping arrays. To illustrate results of both classical and Bayesian methods of analysis, I compared Bayes and empirical Bayes esimates of abundance and density using recaptures from simulated and real populations of animals. Real populations included two iconic datasets: recaptures of tigers detected in camera-trap surveys and recaptures of lizards detected in area-search surveys. In the datasets I analyzed, classical and Bayesian methods provided similar – and often identical – inferences, which is not surprising given the sample sizes and the noninformative priors used in the analyses.

PLoS ONE↗

USGS2013

Introduction to the special issue on “Understanding and predicting change in the coastal ecosystems of the northern Gulf of Mexico”

The coastal region of the northern Gulf of Mexico owes its current landscape structure to an array of tectonic, erosional and depositional, climatic, geochemical, hydrological, ecological, and human processes that have resulted in some of the world's most complex, dynamic, productive, and threatened ecosystems. Catastrophic hurricane landfalls, ongoing subsidence and erosion exacerbated by sea-level rise, disintegration of barrier island chains, and high rates of wetland loss have called attention to the vulnerability of northern Gulf coast ecosystems, habitats, built infrastructure, and economy to natural and anthropogenic threats. The devastating hurricanes of 2005 (Katrina and Rita) motivated the U.S. Geological Survey Coastal and Marine Geology Program and partnering researchers to pursue studies aimed at understanding and predicting landscape change and the associated storm hazard vulnerability of northern Gulf coast region ecosystems and human communities. Attaining this science goal requires increased knowledge of landscape evolution on geologic, historical, and human time scales, and analysis of the implications of such changes in the natural and built components of the landscape for hurricane impact susceptibility. This Special Issue of the Journal of Coastal Research communicates northern Gulf of Mexico research results that (1) improve knowledge of prior climates and depositional environments, (2) assess broad regional ecosystem structure and change over Holocene to human time scales, (3) undertake process studies and change analyses of dynamic landscape components, and (4) integrate framework, climate, variable time and spatial scale mapping, monitoring, and discipline-specific process investigations within interdisciplinary studies.

Journal of Coastal Research↗

USGS2020

Consequences of ignoring group association in spatial capture-recapture analysis

Many models in population ecology, including spatial capture–recapture (SCR) models, assume that individuals are distributed and detected independently of one another. In reality, this is rarely the case – both antagonistic and gregarious relationships lead to non-independent spatial configurations, with territorial exclusion at one end of the spectrum and group-living at the other. Previous simulation studies suggest that grouping has limited impact on the outcome of SCR analyses. However, group associations entail not only spatial clustering of activity centers but also coordinated space use by group members, potentially impacting both ecological and observation processes underlying SCR analysis. We simulated SCR scenarios with different strengths of aggregation (clustering of individuals into groups with shared activity centers) and cohesion (synchronization of detection patterns of members of a group). We then fit SCR models to the simulated data sets and evaluated the effect of aggregation and cohesion on parameter estimates. Low to moderate aggregation and cohesion did not impact the bias and precision of estimates of density and the scale parameter of the detection function. However, non-independence between individuals led to high levels of overdispersion. Overdispersion strongly decreased the coverage of confidence intervals around parameter estimates, thereby increasing the probability of erroneous predictions. Our results indicate that SCR models are robust to moderate levels of aggregation and cohesion. Nonetheless, spatial dependence between individuals can lead to false inference. We recommend that practitioners 1) test for the presence of overdispersion in SCR data caused by aggregation and cohesion, and, if necessary, 2) correct their variance estimates using the overdispersion factor ĉ . Approaches for doing both are described in this paper. We also urge the development of SCR models that incorporate spatial associations between individuals not only to account for overdispersion but also to obtain quantitative information about social aspects of study populations.

Wildlife Biology↗

USGS2021

New faunal records from a World Heritage Site in danger: Rennell Island, Solomon Islands

Remote oceanic islands have high potential to harbor unique fauna and flora, but opportunities to conduct in-depth biotic surveys are often limited. Furthermore, underrepresentation of existing biodiversity in the literature has the potential to detract from conservation planning and action. Between 18 and 29 October 2018, we surveyed the terrestrial vertebrates of East Rennell, a UNESCO World Heritage Site in Solomon Islands. We documented 56 species, including 15 squamates, 13 mammals, and 38 birds, and present four new vertebrate records for the island: Stephan's emerald dove ( Chalcophaps stephani ), Maluku myotis ( Myotis moluccarum ), littoral skink ( Emoia atrocostata ) and brahminy blindsnake ( Indotyphlops braminus ). East Rennell was designated a World Heritage site for its significant on-going ecological and biological processes, and importance for the study of island biogeography. The new records presented here provide evidence that continued field studies combined with DNA analysis will continue to uncover even greater endemic biodiversity. Rennell is currently experiencing major habitat destruction in parts of the island that are not under World Heritage protection, and we anticipate collateral damage will likely extend into protected areas. Our survey also underscores the incredible vertebrate biodiversity that stands to be lost unless conservation actions and local community needs are intertwined to promote beneficial outcomes on both fronts.

Pacific Science↗

USGS2011

USGS research on Florida's isolated freshwater wetlands

The U.S. Geological Survey (USGS) has studied wetland hydrology and its effects on wetland health and ecology in Florida since the 1990s. USGS wetland studies in Florida and other parts of the Nation provide resource managers with tools to assess current conditions and regional trends in wetland resources. Wetland hydrologists in the USGS Florida Water Science Center (FLWSC) have completed a number of interdisciplinary studies assessing the hydrology, ecology, and water quality of wetlands. These studies have expanded the understanding of wetland hydrology, ecology, and related processes including: (1) the effects of cyclical changes in rainfall and the influence of evapotranspiration; (2) surface-water flow, infiltration, groundwater movement, and groundwater and surfacewater interactions; (3) the effects of water quality and soil type; (4) the unique biogeochemical components of wetlands required to maintain ecosystem functions; (5) the effects of land use and other human activities; (6) the influences of algae, plants, and invertebrates on environmental processes; and (7) the effects of seasonal variations in animal communities that inhabit or visit Florida wetlands and how wetland function responds to changes in the plant community.

Florida↗

USGS2016

Mangrove postcard

Mangrove ecosystems protect vulnerable coastlines from storm effects, recycle nutrients, stabilize shorelines, improve water quality, and provide habitat for commercial and recreational fish species as well as for threatened and endangered wildlife. U.S. Geological Survey scientists conduct research on mangrove ecosystems to provide reliable scientific information about their ecology, productivity, hydrological processes, carbon storage stress response, and restoration success. The Mangrove Science Network is a collaboration of USGS scientists focused on working with natural resource managers to develop and conduct research to inform decisions on mangrove management and restoration. Information about the Mangrove Science Network can be found at: http://www.usgs.gov/ecosystems/environments/mangroves.html .

General Information Product↗