USGS Science⌕ Search

SEARCH · USGS Science

Results for “One Ecosystem”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
USGS2000

Managers' summary - Ecological studies of the Pryor Mountain Wild Horse Range, 1992-1997

Ecological Studies of the Pryor Mountain Wild Horse Range, 1992-1997 provides a synthesis of key findings of landscape-scale, interdisciplinary studies of the effects of wild horses and native ungulates on a rugged, mountain ecosystem. This is perhaps the most comprehensive study of a wild horse herd conducted. This was a complex study and one involving a truly interagency approach. Six agencies either provided input to research priority setting, funding, or both. The agencies included the Bureau of Land Management, National Park Service, U.S. Geological Survey, Montana Department of Fish, Wildlife and Parks, Wyoming Game and Fish Department, and U.S. Forest Service. The major research direction and effort came from the U.S. Geological Survey and Natural Resources Ecology Lab, Colorado State University with Montana State University and the University of Kentucky also participating. Ungulate monitoring was conducted by the U.S. Geological Survey, Biological Resources Division, Bureau of Land Management, Billings Field Office and the Montana Fish and Wildlife Parks, with funding by Bighorn Canyon National Recreation Area. Many other individuals and groups were involved and deserve credit. The report printing was made possible with funds from the Bureau of Land Management, Wild Horse and Burro Program, Washington Office. This report was prepared by the Information Management Project, Midcontinent Ecological Science Center, U.S. Geological Survey.

Montana, Wyoming↗
USGS2014

A multiscale, hierarchical model of pulse dynamics in arid-land ecosystems

Ecological processes in arid lands are often described by the pulse-reserve paradigm, in which rain events drive biological activity until moisture is depleted, leaving a reserve. This paradigm is frequently applied to processes stimulated by one or a few precipitation events within a growing season. Here we expand the original framework in time and space and include other pulses that interact with rainfall. This new hierarchical pulse-dynamics framework integrates space and time through pulse-driven exchanges, interactions, transitions, and transfers that occur across individual to multiple pulses extending from micro to watershed scales. Climate change will likely alter the size, frequency, and intensity of precipitation pulses in the future, and arid-land ecosystems are known to be highly sensitive to climate variability. Thus, a more comprehensive understanding of arid-land pulse dynamics is needed to determine how these ecosystems will respond to, and be shaped by, increased climate variability.

Annual Review of Ecology, Evolution, and Systemati↗
USGS2021

Science needs of southeastern grassland species of conservation concern: A framework for species status assessments

The unglaciated southeastern United States is a biodiversity hotspot, with a disproportionate amount of this biodiversity concentrated in grasslands. Like most hotspots, the Southeast is also threatened by human activities, with the total reduction of southeastern grasslands estimated as 90 percent (upwards to 100 percent for some types) and with many threats escalating today. This report summarizes the results of a multistakeholder workshop organized by the Southeastern Grasslands Initiative and the U.S. Geological Survey, held in January 2020 to provide a scientific needs assessment to help inform the Species Status Assessment (SSA) process under the U.S. Endangered Species Act, with a focus on grassland species and communities of conservation concern in the southeastern United States. This report reviews the ecology of southeastern grasslands, including influences on their origin, maintenance, and high species richness and endemism; presents findings from the workshop; and discusses science questions, hypotheses, and possibilities for future research projects to help fill key knowledge gaps. Participants in the January 2020 workshop, representing diverse expertise in various topics in southeastern grassland ecology, were tasked with identifying major threats to grassland species in the Southeast as well as potential ways to make the SSA process more efficient and effective. An underlying assumption and starting place for workshop discussion was that an ecosystem-based approach to the SSA process is more cost-efficient than a species-by-species approach, in large part because many species with similar biological requirements can be addressed by the same actions. Nevertheless, one partner in this effort, the U.S. Fish and Wildlife Service, does require specific attention be given to taxa that have been petitioned for Federal listing, though as often as possible these taxa are considered alongside a larger group of priority taxa with an ecosystem approach. For group discussions, workshop participants followed a modified “World Café” method, a structured conversational approach for knowledge sharing. Group discussions focused on five categories of threats to grassland communities and species: (1) habitat loss, fragmentation, and disruption of functional population connectivity; (2) climate change, especially changes in temperature and precipitation, including intensity and seasonality, and impacts on soil moisture, groundwater levels, and other ecosystem parameters; (3) changes to disturbance regimes, as influenced by climate and land-use change, extinctions, and human attitudes and behaviors; (4) invasive species (not limited to nonnative species); and (5) localized or subregional impacts such as sea-level rise. In addition to group discussions, workshop participants—as well as other grassland experts who were unable to attend the workshop—completed a preworkshop survey concerning challenges and opportunities for grassland conservation. Findings reported here under each of these topics represent ideas, problems, hypotheses, and questions identified by a diverse community of grassland managers and researchers which may be addressed by future research and monitoring in southeastern grassland ecosystems to help guide science-based conservation of grassland-dependent species.

Alabama, Arkansas, Florida, Georgia, Kentucky, Lou↗
USGS2012

Ecosystem services from converted land: the importance of tree cover in Amazonian pastures

Deforestation is responsible for a substantial fraction of global carbon emissions and changes in surface energy budgets that affect climate. Deforestation losses include wildlife and human habitat, and myriad forest products on which rural and urban societies depend for food, fiber, fuel, fresh water, medicine, and recreation. Ecosystem services gained in the transition from forests to pasture and croplands, however, are often ignored in assessments of the impact of land cover change. The role of converted lands in tropical areas in terms of carbon uptake and storage is largely unknown. Pastures represent the fastest-growing form of converted land use in the tropics, even in some areas of rapid urban expansion. Tree biomass stored in these areas spans a broad range, depending on tree cover. Trees in pasture increase carbon storage, provide shade for cattle, and increase productivity of forage material. As a result, increasing fractional tree cover can provide benefits land managers as well as important ecosystem services such as reducing conversion pressure on forests adjacent to pastures. This study presents an estimation of fractional tree cover in pasture in a dynamic region on the verge of large-scale land use change. An appropriate sampling interval is established for similar studies, one that balances the need for independent samples of sufficient number to characterize a pasture in terms of fractional tree cover. This information represents a useful policy tool for government organizations and NGOs interested in encouraging ecosystem services on converted lands. Using high spatial resolution remotely sensed imagery, fractional tree cover in pasture is quantified for the municipality of Rio Branco, Brazil. A semivariogram and devolving spatial resolution are employed to determine the coarsest sampling interval that may be used, minimizing effects of spatial autocorrelation. The coarsest sampling interval that minimizes spatial dependence was about 22 m. The area-weighted fractional tree cover for the study area was 1.85 %, corrected for a slight bias associated with the coarser sampling resolution. The pastures sampled for fractional tree cover were divided between ‘high’ and ‘low’ tree cover, which may be the result of intentional incorporation of arboreal species in pasture. Further research involving those ranchers that have a higher fractional tree cover may indicate ways to promote the practice on a broader scale in the region.

Urban Ecosystems↗
USGS2024

Effects of temporal hydrologic shifts on the population biology of an endangered freshwater fish in a dryland river ecosystem

Species occupying dryland river ecosystems often experience “boom-and-bust” demographic cycles that coincide with shifts in habitat availability. Knowing whether declines are within natural thresholds versus those caused by acute human disturbance is critical for managing protected species. We investigated temporal shifts in abundance and habitat use of an endangered population of the threespine stickleback Gasterosteus aculeatus in southern California, where a Mediterranean climate leads to ephemeral habitat in one of the regions' least hydrologically modified rivers, the Santa Clara River. We conducted population surveys over a period of below-average rainfall in the upper watershed in Soledad Canyon, with predefined reaches surveyed multiple times per year to capture different hydrologic conditions. Abundances were stable across years but varied significantly depending on location, with some reaches remaining dry and others drying seasonally to varying degrees. Occupancy models showed that the presence of stable perennial reaches, drying regime, and other site-specific factors were important predictors of habitat use, and that certain reaches may be key to ensuring source-sink dynamics as flow dissipates over the dry season. Low occupancy in two sections was driven by different predominant mechanisms, one by diel cycles of evapotranspiration and the other by cattails ( Typha spp.), with both having greater effects during the hotter, drier parts of the year. As dryland river ecosystems are vulnerable to the effects of anthropogenic-induced climate change, this study demonstrates how temporal monitoring can delimit dry-state benchmarks for improving management interventions (i.e., translocation and habitat restoration) for protected species under conditions that are predicted to worsen in the coming years.

California↗
USGS2017

Environmental conditions and prey-switching by a seabird predator impact juvenile salmon survival

Due to spatio-temporal variability of lower trophic-level productivity along the California Current Ecosystem (CCE), predators must be capable of switching prey or foraging areas in response to changes in environmental conditions and available forage. The Gulf of the Farallones in central California represents a biodiversity hotspot and contains the largest common murre ( Uria aalge ) colonies along the CCE. During spring, one of the West Coast's most important Chinook salmon ( Oncorhynchus tshawytscha ) populations out-migrates into the Gulf of the Farallones. We quantify the effect of predation on juvenile Chinook salmon associated with ecosystem-level variability by integrating long-term time series of environmental conditions (upwelling, river discharge), forage species abundance within central CCE, and population size, at-sea distribution, and diet of the common murre. Our results demonstrate common murres typically forage in the vicinity of their offshore breeding sites, but in years in which their primary prey, pelagic young-of-year rockfish ( Sebastes spp.), are less available they forage for adult northern anchovies ( Engraulis mordax ) nearshore . Incidentally, while foraging inshore, common murre consumption of out-migrating juvenile Chinook salmon, which are collocated with northern anchovy, increases and population survival of the salmon is significantly reduced. Results support earlier findings that show timing and strength of upwelling , and the resultant forage fish assemblage, is related to Chinook salmon recruitment variability in the CCE, but we extend those results by demonstrating the significance of top-down impacts associated with these bottom-up dynamics. Our results demonstrate the complexity of ecosystem interactions and impacts between higher trophic-level predators and their prey, complexities necessary to quantify in order to parameterize ecosystem models and evaluate likely outcomes of ecosystem management options.

California↗
USGS2011

Conservation Effects Assessment Project-Wetlands assessment in California's Central Valley and Upper Klamath River Basin

Executive Summary-Ecosystem Services Derived from Wetlands Reserve Program Conservation Practices in California's Central Valley and Oregon's Upper Klamath River Basin. The Wetlands Reserve Program (WRP) is one of several programs implemented by the U.S. Department of Agriculture (USDA). Since the WRP's inception in 1990, it has resulted in the restoration of approximately 29,000 hectares in California's Central Valley (CCV) and roughly 12,300 hectares in Oregon's Upper Klamath River Basin (UKRB). Both the CCV and UKRB are agricultural dominated landscapes that have experienced extensive wetland losses and hydrological alteration. Restored habitats in the CCV and UKRB are thought to provide a variety of ecosystem services, but little is known about the actual benefits afforded. The U.S. Geological Survey (USGS) California Cooperative Fish and Wildlife Unit in collaboration with the USDA Natural Resources Conservation Service surveyed 70 WRP sites and 12 National Wildlife Refuge sites in the CCV, and 11 sites in the UKRB to estimate ecosystem services provided. In the CCV, sites were selected along three primary gradients; (1) restoration age, (2) management intensity, and (3) latitude (climate). Sites in the UKRB were assessed along restoration age and management intensity gradients where possible. The management intensity gradient included information about the type and frequency of conservation practices applied at each site, which was then ranked into three categories that differentiated sites primarily along a hydrological gradient. Information collected was used to estimate the following ecosystem services: Soil and vegetation nutrient content, soil loss reduction, floodwater storage as well as avian, amphibian, fish, and pollinator use and habitat availability. Prior to this study, very little was known about WRP habitat morphology in the CCV and UKRB. Therefore in this study, we described these habitats and related them to ecosystem services provided. Our results indicate that although WRP in the CCV and UKRB provide a number of benefits, there may be management mediated trade-offs among ecosystem services. In this report, we considered ecosystem services at the site-specific scale; however, future work will extend to include effects of WRP relative to surrounding cropland.

California, Oregon↗
USGS2007

Climate correlates of 20 years of trophic changes in a high-elevation riparian system

The consequences of climate change for ecosystem structure and function remain largely unknown. Here, I examine the ability of climate variation to explain long-term changes in bird and plant populations, as well as trophic interactions in a high-elevation riparian system in central Arizona, USA, based on 20 years of study. Abundances of dominant deciduous trees have declined dramatically over the 20 years, correlated with a decline in overwinter snowfall. Snowfall can affect overwinter presence of elk, whose browsing can significantly impact deciduous tree abundance. Thus, climate may affect the plant community indirectly through effects on herbivores, but may also act directly by influencing water availability for plants. Seven species of birds were found to initiate earlier breeding associated with an increase in spring temperature across years. The advance in breeding time did not affect starvation of young or clutch size. Earlier breeding also did not increase the length of the breeding season for single-brooded species, but did for multi-brooded species. Yet, none of these phenology-related changes was associated with bird population trends. Climate had much larger consequences for these seven bird species by affecting trophic levels below (plants) and above (predators) the birds. In particular, the climate-related declines in deciduous vegetation led to decreased abundance of preferred bird habitat and increased nest predation rates. In addition, summer precipitation declined over time, and drier summers also were further associated with greater nest predation in all species. The net result was local extinction and severe population declines in some previously common bird species, whereas one species increased strongly in abundance, and two species did not show clear population changes. These data indicate that climate can alter ecosystem structure and function through complex pathways that include direct and indirect effects on abundances and interactions of multiple trophic components. ?? 2007 by the Ecological Society of America.

Ecology↗
USGS2011

Long-term change in perennial vegetation along the Colorado river in Grand Canyon national park (1889-2010)

Long-term monitoring data are difficult to obtain for high-value resource areas, particularly in remote parts of national parks. One long-used method for evaluating change uses ground-based repeat photography to match historical images of landscapes. River expeditions that documented a proposed railroad route through Grand Canyon with large-format photographs occurred in 1889 and 1890. A total of 452 images from those expeditions are still in existence, and these were matched as closely as possible from December 1989 through March 1992. In 2010 and 2011, we are repeating these matches 120 years after the originals and 20 years after the first matches. This repeat photography provides visual information that can be interpreted for changes in terrestrial and riparian ecosystems along the river corridor, including change in the desert plant assemblages related to increasing winter low temperatures and severe drought. The riparian ecosystem, which originally consisted of native species established along the stage of frequent floods, has increased in area, density, and biomass as both nonnative and native species have become established following flow regulation by Glen Canyon Dam. The original and matched images provide the basis for one element of a robust monitoring program for the effects of climate change on ecosystem resources.

Grand Canyon National Park↗
USGS2009

Projected climate-induced faunal change in the Western Hemisphere

Climate change is predicted to be one of the greatest drivers of ecological change in the coming century. Increases in temperature over the last century have clearly been linked to shifts in species distributions. Given the magnitude of projected future climatic changes, we can expect even larger range shifts in the coming century. These changes will, in turn, alter ecological communities and the functioning of ecosystems. Despite the seriousness of predicted climate change, the uncertainty in climate-change projections makes it difficult for conservation managers and planners to proactively respond to climate stresses. To address one aspect of this uncertainty, we identified predictions of faunal change for which a high level of consensus was exhibited by different climate models. Specifically, we assessed the potential effects of 30 coupled atmosphere-ocean general circulation model (AOGCM) future-climate simulations on the geographic ranges of 2954 species of birds, mammals, and amphibians in the Western Hemisphere. Eighty percent of the climate projections based on a relatively low greenhouse-gas emissions scenario result in the local loss of at least 10% of the vertebrate fauna over much of North and South America. The largest changes in fauna are predicted for the tundra, Central America, and the Andes Mountains where, assuming no dispersal constraints, specific areas are likely to experience over 90% turnover, so that faunal distributions in the future will bear little resemblance to those of today. ?? 2009 by the Ecological Society of America.

Ecology↗
USGS2017

Lichens and microfungi in biocrusts: Structure and function now and in the future

Biological soil crusts (biocrusts) are formed by soil-surface communities of biota that live within, or immediately on top of, the uppermost millimeters of soil. They consist of cyanobacteria, algae, mosses, microfungi, and lichenized fungi (hereafter, lichens). Cyanobacterial and microfungal filaments, rhizinae and rhizomorphs of lichens, and rhizinae and protonemata of bryophytes weave throughout the top few millimeters of soil, gluing loose soil particles together (Fig. 1). The intimate association between soil particles and organisms forms a coherent crust. A quantitative estimate of global biological crust cover is difficult to obtain and not yet available, but the worldwide coverage of the terrestrial surface by biocrusts is very high. In arid and semiarid areas, biocrusts may constitute up to or more than 70% of the living cover and dryland (hyper-arid, arid, semi-arid, and polar deserts) ecosystems, where they often dominate, cover ~40% of the terrestrial land mass (Pointing and Belnap 2014). Lichens and microfungi are an essential and often dominant part of biocrusts. About one fifth (19 %) of all known species of fungi are lichenized; that is, they form a stable symbiotic association with green algal or/and cyanobacterial photobionts that provide nutrients for the mycobiont (fungi). The vast majority of lichenized fungi belong to the Ascomycota, with 42% of all fungi in this group forming lichens (Kirk et al., 2001). About 85% of lichen-forming fungi are symbiotic with Chlorophyta (green algae, creating "chlorolichens), approximately 10% with Cyanophyta, (creating "cyanolichens"), and the remainder are associated simultaneously with both groups. About 40 genera of photobionts have been identified in lichens: 25 are green algae and 15 are cyanobacteria. The autotrophic lifestyle of lichens requires an exposure of the green thallus to light. Most lichens are long-lived organisms with high habitat specificity. They are especially ecologically successful in dryland areas where competition with phanerogamous vegetation is reduced. It is estimated that approximately 8% of the earth's terrestrial surface has lichens as its most dominant life-form (Ahmadjian 1995). One of their most important habitats are biocrusts, which lichens often dominate. In the present Chapter we concentrate on those widely distributed biocrusts in which free-living and lichenized fungi play a dominating role. We describe their community structure, analyze the special properties and functions of these organisms as key members of biocrusts, and then discuss the function of the fungi-rich biocrusts as components of larger ecosystems and landscapes (for details and specific literature, see Belnap and Lange 2003).

Book chapter↗
USGS1999

U.S. Geological Survey Program on the South Florida Ecosystem; proceedings of South Florida Restoration Science Forum, May 17-19, 1999, Boca Raton, Florida

The purpose of the forum is to highlight the powerful connection between science and management decisions in restoration efforts. The public's investment in science is paying off in support of better management decisions and restoration of imperiled south Florida Ecosystems, including the internationally recognized, globally significant Everglades. The forum affords a unique opportunity for elected officials and other policy- and decision makers, along with the general public, to see--under one roof--highlights of the most significant restoration science and management efforts underway. The forum promotes the link between science and management. Scientists and decisionmakers will come together to discuss the needs of each in order to ensure that plans for restoration are based in science and are the most cost effective and highest quality possible. Continued vigilance over south Florida ecosystems is essential to prevent further harm and to restore them. Representatives from numerous federal, state, local, and nongovernmental entities are organizing the forum for the Science Coordination Team of the South Florida Ecosystem Working Group. The U.S. Geological Survey and the South Florida Water Management District are the primary hosts of the forum.

Florida↗
USGS2014

Nutrient concentrations in coarse and fine woody debris of Populus tremuloides Michx.-dominated forests, northern Minnesota, USA

Contemporary forest harvesting practices, specifically harvesting woody biomass as a source of bioenergy feedstock, may remove more woody debris from a site than conventional harvesting. Woody debris, particularly smaller diameter woody debris, plays a key role in maintaining ecosystem nutrient stores following disturbance. Understanding nutrient concentrations within woody debris is necessary for assessing the long-term nutrient balance consequences of altered woody debris retention, particularly in forests slated for use as bioenergy feedstocks. Nutrient concentrations in downed woody debris of various sizes, decay classes, and species were characterized within one such forest type, Populus tremuloides Michx.-dominated forests of northern Minnesota, USA. Nutrient concentrations differed significantly between size and decay classes and generally increased as decay progressed. Fine woody debris (≤ 7.5 cm diameter) had higher nutrient concentrations than coarse woody debris (> 7.5 cm diameter) for all nutrients examined except Na and Mn, and nutrient concentrations varied among species. Concentrations of N, Mn, Al, Fe, and Zn in coarse woody debris increased between one and three orders of magnitude, while K decreased by an order of magnitude with progressing decay. The variations in nutrient concentrations observed here underscore the complexity of woody debris nutrient stores in forested ecosystems and suggest that retaining fine woody debris at harvest may provide a potentially important source of nutrients following intensive removals of bioenergy feedstocks.

Minnesota↗
USGS2026

Bird breeding success in restored grasslands compared to croplands and natural grasslands: A meta-analysis

Reproductive success is central to long-term population persistence, yet it is rarely assessed in ecosystem restoration. We performed a multilevel meta-analysis to assess whether bird breeding success increases from croplands to restored grasslands or from restored grasslands to natural grasslands. We quantified five comparisons of two breeding success variables between croplands and restored grasslands in three species, and 228 comparisons of nine variables between natural and restored grasslands in 22 species using 14 datasets from North America and Europe. For the few grassland birds that nest in croplands, clutch size was higher in restored fields than in croplands. Most importantly, breeding success did not differ between restored and natural grasslands in nine species and for all species combined. In 13 species, breeding success differed between restored and natural grasslands, and it was often higher in restored grasslands during early breeding stages, but higher in natural grasslands during later stages. Eight species did better in restored grasslands (Clay-colored Sparrow, Dickcissel, Eastern Meadowlark, Lesser Prairie-chicken, Mourning Dove, Red-winged Blackbird, Sprague's Pipit, Western Meadowlark), whereas four species did better in natural grasslands (Baird's Sparrow, Common Nighthawk, Lark Bunting, Savannah Sparrow). Our results suggest that bird breeding success can be as high in restored grasslands as in natural ones, and certainly higher than in croplands. While restored grasslands differ widely by geography, climate, method and management, our results offer hope for ecosystem restoration. However, the differences found also imply that species requirements should be considered in grassland ecosystem restoration and management.

Biological Conservation↗
USGS2013

Measuring the relative resilience of subarctic lakes to global change: redundancies of functions within and across temporal scales

1. Ecosystems at high altitudes and latitudes are expected to be particularly vulnerable to the effects of global change. We assessed the responses of littoral invertebrate communities to changing abiotic conditions in subarctic Swedish lakes with long-term data (1988–2010) and compared the responses of subarctic lakes with those of more southern, hemiboreal lakes. 2. We used a complex systems approach, based on multivariate time-series modelling, and identified dominant and distinct temporal frequencies in the data; that is, we tracked community change at distinct temporal scales. We determined the distribution of functional feeding groups of invertebrates within and across temporal scales. Within and cross-scale distributions of functions have been considered to confer resilience to ecosystems, despite changing environmental conditions. 3. Two patterns of temporal change within the invertebrate communities were identified that were consistent across the lakes. The first pattern was one of monotonic change associated with changing abiotic lake conditions. The second was one of showing fluctuation patterns largely unrelated to gradual environmental change. Thus, two dominant and distinct temporal frequencies (temporal scales) were present in all lakes analysed. 4. Although the contribution of individual feeding groups varied between subarctic and hemiboreal lakes, they shared overall similar functional attributes (richness, evenness, diversity) and redundancies of functions within and between the observed temporal scales. This highlights similar resilience characteristics in subarctic and hemiboreal lakes. 5. Synthesis and applications. The effects of global change can be particularly strong at a single scale in ecosystems. Over time, this can cause monotonic change in communities and eventually lead to a loss of important ecosystem services upon reaching a critical threshold. Dynamics at other spatial or temporal scales can be unrelated to environmental change. The relative ‘intactness’ of these scales that are unaffected by global change and the persistence of functions at those scales may safeguard the whole system from the potential loss of functions at the scale at which global change impacts can be substantial. Thus, an understanding of scale-specific processes provides managers with a realistic assessment of vulnerabilities and the relative resilience of ecosystems to environmental change. Explicit consideration of ‘intact’ and ‘affected’ scales in analyses of global change impacts provides opportunities to tailor more specific management plans.

Journal of Applied Ecology↗
USGS2012

Concentration, distribution, and translocation of mercury and methylmercury in mine-waste, sediment, soil, water, and fish collected near the Abbadia San Salvatore mercury mine, Monte Amiata district, Italy

The distribution and translocation of mercury (Hg) was studied in the Paglia River ecosystem, located downstream from the inactive Abbadia San Salvatore mine (ASSM). The ASSM is part of the Monte Amiata Hg district, Southern Tuscany, Italy, which was one of the world’s largest Hg districts. Concentrations of Hg and methyl-Hg were determined in mine-waste calcine (retorted ore), sediment, water, soil, and freshwater fish collected from the ASSM and the downstream Paglia River. Concentrations of Hg in calcine samples ranged from 25 to 1500 μg/g, all of which exceeded the industrial soil contamination level for Hg of 5 μg/g used in Italy. Stream and lake sediment samples collected downstream from the ASSM ranged in Hg concentration from 0.26 to 15 μg/g, of which more than 50% exceeded the probable effect concentration for Hg of 1.06 μg/g, the concentration above which harmful effects are likely to be observed in sediment-dwelling organisms. Stream and lake sediment methyl-Hg concentrations showed a significant correlation with TOC indicating considerable methylation and potential bioavailability of Hg. Stream water contained Hg as high as 1400 ng/L, but only one water sample exceeded the 1000 ng/L drinking water Hg standard used in Italy. Concentrations of Hg were elevated in freshwater fish muscle samples and ranged from 0.16 to 1.2 μg/g (wet weight), averaged 0.84 μg/g, and 96% of these exceeded the 0.3 μg/g (methyl-Hg, wet weight) USEPA fish muscle standard recommended to protect human health. Analysis of fish muscle for methyl-Hg confirmed that > 90% of the Hg in these fish is methyl-Hg. Such highly elevated Hg concentrations in fish indicated active methylation, significant bioavailability, and uptake of Hg by fish in the Paglia River ecosystem. Methyl-Hg is highly toxic and the high Hg concentrations in these fish represent a potential pathway of Hg to the human food chain.

Monte Amiata↗
USGS2013

Community food webs

Community food webs describe the feeding relationships, or trophic interactions, between the species of an ecological community. Both the structure and dynamics of such webs are the focus of food web research. The topological structures of empirical food webs from many ecosystems have been published on the basis of field studies and they form the foundation for theory concerning the mean number of trophic levels, the mean number of trophic connections versus number of species, and other food web measures, which show consistency across different ecosystems. The dynamics of food webs are influenced by indirect interactions, in which changes in the level of a population in one part of the food web may have indirect effects throughout the web. The mechanisms of these interactions are typically studied microcosm experiments, or sometimes in-field experiments. The use of mathematical models is also a major approach to understanding the effects of indirect interactions. Both empirical and mathematical studies have revealed important properties of food webs, such as keystone predators and trophic cascades.

Book chapter↗
USGS2009

Land crabs as key drivers in tropical coastal forest recruitment

Plant populations are regulated by a diverse assortment of abiotic and biotic factors that influence seed dispersal and viability, and seedling establishment and growth at the microsite. Rarely does one animal guild exert as significant an influence on different plant assemblages as land crabs. We review three tropical coastal ecosystems-mangroves, island maritime forests, and mainland coastal terrestrial forests-where land crabs directly influence forest composition by limiting tree establishment and recruitment. Land crabs differentially prey on seeds, propagules and seedlings along nutrient, chemical and physical environmental gradients. In all of these ecosystems, but especially mangroves, abiotic gradients are well studied, strong and influence plant species distributions. However, we suggest that crab predation has primacy over many of these environmental factors by acting as the first limiting factor of tropical tree recruitment to drive the potential structural and compositional organisation of coastal forests. We show that the influence of crabs varies relative to tidal gradient, shoreline distance, canopy position, time, season, tree species and fruiting periodicity. Crabs also facilitate forest growth and development through such activities as excavation of burrows, creation of soil mounds, aeration of soils, removal of leaf litter into burrows and creation of carbon-rich soil microhabitats. For all three systems, land crabs influence the distribution, density and size-class structure of tree populations. Indeed, crabs are among the major drivers of tree recruitment in tropical coastal forest ecosystems, and their conservation should be included in management plans of these forests. ?? 2009 Cambridge Philosophical Society.

Biological Reviews↗