SEARCH · PubMed Health

Results for “Ecosystem”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 217 records · Page 12Linked to original sources

PubMed2005

Investigating the evolutionary history of the Pacific Northwest mesic forest ecosystem: hypothesis testing within a comparative phylogeographic framework.

We examine the evolution of mesic forest ecosystems in the Pacific Northwest of North America using a statistical phylogeography approach in four animal and two plant lineages. Three a priori hypotheses, which explain the disjunction in the mesic forest ecosystem with either recent dispersal or ancient vicariance, are tested with phylogenetic and coalescent methods. We find strong support in three amphibian lineages (Ascaphus spp., and Dicampton spp., and Plethodon vandykei and P. idahoensis) for deep divergence between coastal and inland populations, as predicted by the ancient vicariance hypothesis. Unlike the amphibians, the disjunction in other Pacific Northwest lineages is likely due to recent dispersal along a northern route. Topological and population divergence tests support the northern dispersal hypothesis in the water vole (Microtus richardsoni) and northern dispersal has some support in both the dusky willow (Salix melanopsis) and whitebark pine (Pinus albicaulis). These analyses demonstrate that genetic data sampled from across an ecosystem can provide insight into the evolution of ecological communities and suggest that the advantages of a statistical phylogeographic approach are most pronounced in comparisons across multiple taxa in a particular ecosystem. Genetic patterns in organisms as diverse as willows and salamanders can be used to test general regional hypotheses, providing a consistent metric for comparison among members of an ecosystem with disparate life-history traits.

Amphibians↗

PubMed2006

[Respiration rate of broadleaved Korean pine forest ecosystem in Changbai Mountains].

In this paper, the respiration rates of soil, foliage, and stem and branch in the broadleaved Korean pine forest ecosystem of Changbai Mountains were measured by Li-6400 CO2 analysis system in 2003, with the microclimate factors determined synchronously. The correlation models of ecosystem respiration with environmental factors were established, and the respiration rate of each component of the ecosystem was estimated based on the vegetation characteristics of the broadleaved Korean pine forest. The results showed that the annual total respiration rate of the ecosystem was 1602. 8 g C x m(-2), with a mean of (4. 37+/-2. 98) micromol x m(-2) x s(-1) , and the respiration of soil, foliage, and stem and branch contributed about 63% , 21% , and 16% of the total, respectively. There was a significant correlation between system respiration and daily mean air and soil temperature, and about 87% and 95% of the ecosystem respiration could be explained by the air and soil temperature, respectively.

China↗

PubMed1976

Snakes as indicators of environmental contamination: relation of detoxifying enzymes and pesticide residues to species occurrence in three aquatic ecosystems.

Pesticide detoxifying enzymes and residues of p,p'-DDE and PCB were measured in snakes of two genera collected in three aquatic ecosystems in central Texas. Snake genera were Agkistrodon (water moccasins and copperheads) and Natrix (water snakes). One collecting site had heavy exposure to insecticides, one to PCBs and one to neither. Objectives were to correlate pesticide residues and detoxifying enzymes with species occurrence in different ecosystems, to evaluate the usefulness of snakes as indicators of environmental contamination, and to establish a biochemical basis for the differential distribution of snakes between ecosystems. Agkistrodon spp. had several times the NADPH-dependent oxidative detoxifying activity of Natrix spp. Within Natrix, oxidase activity was significantly higher in erythrogaster and fasciata than in rhombifera. Alkyltransferase activity was higher in A. piscivorus (water moccasins) than in any other species. There were no consistent differences between sexes in levels of detoxifying enzymes and enzyme activity was similar in snakes of each species from all collecting sites, indicating no induction had occurred as a result of heavy exposure to insecticides or PCBs. DDE residues were highest in snakes collected adjacent to a cotton agro-ecosystem. PCB residues occurred only in snakes collected near a heavily-traveled highway. Residues in A. piscivorus were only half those in Natrix spp. from the same site, indicating the former is more efficient as disposing of residues. The data indicate that snakes with high levels of detoxifying enzymes, particularly microsomal oxidases, are more likely to occur in a contaminated ecosystem than snakes with less active detoxifying enzymes and that residues are lower in the better detoxifiers. Snakes are apparently excellent indicators of environmental contaminated by insecticides and other persistent chemicals.

Adipose Tissue↗

PubMed2000

FORUM: Balancing Endangered Species and Ecosystems: A Case Study of Adaptive Management in Grand Canyon.

/ Adaptive ecosystem management seeks to sustain ecosystems while extracting or using natural resources. The goal of endangered species management under the Endangered Species Act is limited to the protection and recovery of designated species, and the act takes precedence over other policies and regulations guiding ecosystem management. We present an example of conflict between endangered species and ecosystem management during the first planned flood on the Colorado River in Grand Canyon in 1996. We discuss the resolution of the conflict and the circumstances that allowed a solution to be reached. We recommend that adaptive management be implemented extensively and early in ecosystem management so that information and working relationships will be available to address conflicts as they arise. Though adaptive management is not a panacea, it offers the best opportunity for balanced solutions to competing management goals.

Journal Article↗

PubMed1997

Ecosystem Manipulation Experimentation as a Means of Testing a Biogeochemical Model

/ Numerical simulation models have found increased usage in the past decade for projecting the environmental effects of ecosystem perturbations such as atmospheric deposition of sulfur and nitrogen, increased atmospheric CO2 concentration, and global or regional temperature change. Such model projections are frequently used as the basis or justification for public policy decisions and legislation. A substantial need has therefore arisen to test and substantiate the veracity of mathematical model projections. Unfortunately, environmental models can never be truly validated because natural systems are never closed and model solutions are always nonunique. Partial model confirmation is possible, however, and entails demonstration of agreement between prediction and observation. Experimental ecosystem manipulation provides one of the best, and in many cases only, available basis for model confirmation. The use and potential misuse of data from experimental ecosystem manipulations for model testing is explored using examples drawn from the application of an acid-base chemistry model, MAGIC. As model projections provide an increasingly important basis for public policy decisions, and as both the scientific questions and the models become increasingly complex, it will become critical to provide data from a suite of well-designed ecosystem manipulation experiments in order to evaluate the quality and uncertainty of those model projections and the models upon which they are based.KEY WORDS: Modeling; Model testing; Acidification; Ecosystem manipulation

Journal Article↗

PubMed1999

Institutional Analysis and Ecosystem-Based Management: The Institutional Analysis and Development Framework.

/ Scholars, government practitioners, and environmentalists are increasingly supportive of collaborative, ecosystem-based approaches to natural resource management. However, few researchers have focused their attention on examining the important administrative and institutional challenges surrounding ecosystem-based management. This paper describes how the institutional analysis and development (IAD) framework can be used to better understand the institutional arrangements used to implement ecosystem-based management programs. Some of the observations emanating from previous research on institutional design and performance are also discussed. The paper's central argument is that if this new resource management paradigm is to take hold and flourish, researchers and practitioners must pay closer attention to the questions surrounding institutional design and performance. This should help improve our understanding of the relationship between science and human values in decision making. It should also help researchers avoid making faulty policy recommendations and improve the implementation of ecosystem-based management programs.KEY WORDS: Ecosystem management; Watershed management; Common pool resources; Implementation; Institutional analysis; Evaluation; Policy analysishttp://link.springer-ny.com/link/service/journals/00267/bibs/24n4p449.html</HEA

Journal Article↗

PubMed1989

Environmental stress in five aquatic ecosystems in the floodplain of the River Rhine.

General theories of stress ecology were applied to aquatic communities in the floodplain of the polluted River Rhine. These communities inhabited (i) a brackish section of the Ems-Dollard estuary with large intertidal flats, (ii) the coastal waters of the North Sea and the adjacent Wadden Sea, (iii) a former estuary of the Rivers Rhine and Meuse: the newly endiked Lake Grevelingen, (iv) the shallow Loosdrecht Lakes, and (v) the lower River Rhine. These systems are characterized by natural perturbations, such as suspension of sediments and flushing of the shallow waters. Organic pollution, eutrophication and chemical pollution reinforce the natural tendency to severe selection in the communities, in extreme cases leading to an abundance of small and opportunistic species participating in relatively simple food chains. Signs of ecosystem distress, as defined by Rapport et al., were detectable in all five ecosystems. The application of the theory of Odum et al. on stimulation and inhibition of ecosystems helped in identifying the positive impact of man. The role of stress in natural aquatic ecosystems in the delta, together with observations on ecological recovery under reduced man-made perturbation, suggest that there is scope for effective water management that exploits the resilience of these ecosystems.

Animals↗

PubMed1990

A baseline-ecosystem approach to the analysis of ecotoxicological effects.

Since 1980 the German Ministry of Research has sponsored a number of ecotoxicological research projects aimed at the analysis of effects of environmental chemicals on terrestrial ecosystems. Some of these field studies were conducted by using a baseline-ecosystem approach, the theoretical framework of which is given. It is demonstrated by the baseline ecosystem derived from a ruderal site. The results from the German ecotoxicology program concerning some features of structural and functional responses of ecosystems to chemicals are summarized. Many effects observed in "real nature" could be attributed to the substances under study as side effects due to the integrative approach. This means that without knowledge of the structure and function of a biogeocoenosis reliable predictions of chemically induced changes at the ecosystem level will not be possible.

Ecology↗

PubMed2000

Quantifying simultaneous fluxes of ozone, carbon dioxide and water vapor above a subalpine forest ecosystem.

Assessing the long-term exchange of trace gases and energy between terrestrial ecosystems and the atmosphere is an important priority of the current climate change research. In this regard, it is particularly significant to provide valid data on simultaneous fluxes of carbon, water vapor and pollutants over representative ecosystems. Eddy covariance measurements and model analyses of such combined fluxes over a subalpine coniferous forest in southern Wyoming (USA) are presented. While the exchange of water vapor and ozone are successfully measured by the eddy covariance system, fluxes of carbon dioxide (CO(2)) are uncertain. This is established by comparing measured fluxes with simulations produced by a detailed biophysical model (FORFLUX). The bias in CO(2) flux measurements is partially attributed to below-canopy advection caused by a complex terrain. We emphasize the difficulty of obtaining continuous long-term flux data in mountainous areas by direct measurements. Instrumental records are combined with simulation models as a feasible approach to assess seasonal and annual ecosystem exchange of carbon, water and ozone in alpine environments. The viability of this approach is demonstrated by: (1) showing the ability of the FORFLUX model to predict observed fluxes over a 9-day period in the summer of 1996; and (2) applying the model to estimate seasonal dynamics and annual totals of ozone deposition and carbon, and water vapor exchange at our study site. Estimated fluxes above this subalpine ecosystem in 1996 are: 195 g C m(-2) year(-1) net ecosystem production, 277 g C m(-2) year(-1) net primary production, 535 mm year(-1) total evapo-transpiration, 174 mm year(-1) canopy transpiration, 2.9 g m(-2) year(-1) total ozone deposition, and 1.72 g O(3) m(-2) year(-1) plant ozone uptake via leaf stomata. Given the large portion of non-stomatal ozone uptake (i.e. 41% of the total annual flux) predicted for this site, we suggest that future research of pollution-vegetation interactions should relate plant response to actively assimilated ozone by foliage rather than to total deposition. In this regard, we propose the Physiological Ozone Uptake Per Unit of Leaf Area (POUPULA) as a practical index for quantifying vegetation vulnerability to ozone damage. We estimate POUPULA to be 0.614 g O(3) m(-2) leaf area year(-1) at our subalpine site in 1996.

Journal Article↗

PubMed2000

Acclimation of ecosystem CO2 exchange in the Alaskan Arctic in response to decadal climate warming

Long-term sequestration of carbon in Alaskan Arctic tundra ecosystems was reversed by warming and drying of the climate in the early 1980s, resulting in substantial losses of terrestrial carbon. But recent measurements suggest that continued warming and drying has resulted in diminished CO2 efflux, and in some cases, summer CO2 sink activity. Here we compile summer CO2 flux data for two Arctic ecosystems from 1960 to the end of 1998. The results show that a return to summer sink activity has come during the warmest and driest period observed over the past four decades, and indicates a previously undemonstrated capacity for ecosystems to metabolically adjust to long-term (decadal or longer) changes in climate. The mechanisms involved are likely to include changes in nutrient cycling, physiological acclimation, and population and community reorganization. Nevertheless, despite the observed acclimation, the Arctic ecosystems studied are still annual net sources of CO2 to the atmosphere of at least 40 g C m(-2) yr(-1), due to winter release of CO2, implying that further climate change may still exacerbate CO2 emissions from Arctic ecosystems.

Journal Article↗

PubMed1997

Plant diversity and ecosystem productivity: theoretical considerations.

Ecosystem processes are thought to depend on both the number and identity of the species present in an ecosystem, but mathematical theory predicting this has been lacking. Here we present three simple models of interspecific competitive interactions in communities containing various numbers of randomly chosen species. All three models predict that, on average, productivity increases asymptotically with the original biodiversity of a community. The two models that address plant nutrient competition also predict that ecosystem nutrient retention increases with biodiversity and that the effects of biodiversity on productivity and nutrient retention increase with interspecific differences in resource requirements. All three models show that both species identity and biodiversity simultaneously influence ecosystem functioning, but their relative importance varies greatly among the models. This theory reinforces recent experimental results and shows that effects of biodiversity on ecosystem functioning are predicted by well-known ecological processes.

Journal Article↗

PubMedDate not supplied

A general biogeochemical model describing the responses of the C and N cycles in terrestrial ecosystems to changes in CO(2), climate, and N deposition.

A model that simulates carbon (C) and nitrogen (N) cycles in terrestrial ecosystems is developed. The model is based on the principle that the responses of terrestrial ecosystems to changes in CO(2), climate, and N deposition will encompass enzymatic responses, shifts in tissue stoichiometry, changes in biomass allocation among plant tissues, altered rates of soil organic matter turnover and N mineralization, and ultimately a redistribution of C and N between vegetation and soils. The model is a highly aggregated, process-based, biogeochemical model designed to examine changes in the fluxes and allocation of C and N among foliage, fine roots, stems, and soils in response to changes in atmospheric CO(2) concentration, temperature, soil water, irradiance, and inorganic nitrogen inputs. We use the model to explore how changes in CO(2) concentration, temperature, and N inputs affect carbon storage in two ecosystems: arctic tundra and temperate hardwood forest. The qualitative responses of the two ecosystems were similar. Quantitative differences are attributed to the initial distribution of C and N between vegetation and soils, to the amounts of woody tissue in the two ecosystems, and to their relative degree of N limitation. We conclude with a critical analysis of the model's strengths and weaknesses, and discuss possible future directions.

Journal Article↗

PubMed1992

Evaluation of aquatic sediment microcosms and their use in assessing possible effects of introduced microorganisms on ecosystem parameters.

In this paper we describe a sediment microcosm system consisting of 20 undisturbed, layered sediment cores with overlying site water which are incubated under identical conditions of temperature, light, stirring rate of overlying water, and water exchange rate. Ecosystem parameters (nutrient level, photosynthetic potential, community structure of heterotrophic bacteria, thymidine incorporation rate, and oxygen microgradients) of the laboratory microcosms and the source ecosystem were compared and shown to be indistinguishable for the first 2 weeks. In weeks 3 and 4, small differences were detectable in the nutrient level, community structure of heterotrophic bacteria, and thymidine incorporation rate. However, the photosynthetic potential, depth profiles of heterotrophic bacterial community structure, and oxygen microgradients were maintained throughout the incubation period and did not differ between laboratory microcosms and the source ecosystem. The microcosm system described here would thus appear to be a valid model of aquatic sediments for up to 4 weeks; the actual period would depend on the sediment source and incubation temperature. The validated systems were used with Rhine river sediment to assess possible effects on ecosystem parameters of Pseudomonas sp. strain B13 FR1(pFRC20P), a genetically engineered microorganism (GEM) that had been constructed to degrade mixtures of halo- and alkylbenzoates and -phenols. The GEM survived in the surface sediment at densities of 5 x 10(4) to 5 x 10(5)/g (dry weight) for 4 weeks and degraded added chloro- and methylaromatics. The GEM did not measurably influence ecosystem parameters such as photosynthesis, densities of selected heterotrophic bacteria, thymidine incorporation rate, and oxygen microgradients. Thus, the microcosm system described here would seem to be useful for the study of the ecology of biodegradation and the fate and effect of microorganisms introduced into the environment.

Bacteria↗

PubMed2006

Predators have large effects on ecosystem properties by changing plant diversity, not plant biomass.

Cascading effects of predators on total plant trophic-level biomass tend to be weaker in terrestrial than in aquatic systems. Accordingly, it is hypothesized that top predator effects on terrestrial plant diversity and on ecosystem function should likewise be weak or unimportant. This report presents a test of this hypothesis using data from a long-term field experiment. The five-year experiment manipulated the trophic structure of an old field ecosystem by excluding either predators or predators and herbivores relative to an unmanipulated, natural control. Long-term manipulations led to systematic treatment effects on community properties (plant trophic-level biomass, plant species biomass, plant species evenness) and on ecosystem properties (supply rate of solar radiation, N mineralization rate). The strengths of top predator effects on community properties were modest compared with nonterrestrial systems. But, predator-caused changes in plant community structure via alteration of plant dominance, and hence plant species evenness, strengthened effects on ecosystem properties. Counter to the hypothesis, weak trophic cascades do not necessarily lead to weak indirect effects of predators on ecosystem properties.

Animals↗

PubMed1971

Theoretical and experimental decisions in the creation of an artificial ecosystem for human life support in space.

All of man's former space flights were not real ventures into space in the biological sense, as his life was supported with unregenerated earth supplies. The coming stage of space exploration requires man's long existence in the cosmos and on the other planets. This stage of man's activity outside the earth become possible only by creating small man-made ecosystems, permitting the support of his metabolism by the recycling of substances of the terrestrial biosphere. Creation of such systems is a new scientific and technical task. Man-made ecosystems are a new product of man's activity, which have no complete analogy, either in nature, or in technology. Stochastic mechanisms, which stabilize biogeocenosis, cannot be effective in small ecosystems. A technique of parametric control over biosynthesis made it possible to calculate, and put to practice, an ecosystem for man with a cyclic regeneration of the atmosphere, water and, partially, food. The specific bio-technological properties of small man-made ecosystems are being analysed. The possibility of their application for man's excursions into space and for the settlement of other planets is being considered.

Bacteria↗

PubMedDate not supplied

[Variants of the control over a gas-exchange closed ecosystem with a periodically operating autotrophic component].

The paper discusses the problem of how to control a gas exchange closed ecosystem that consists of autotrophic and heterotrophic components and operates periodically in the light or in the dark. The purpose of the control is to maintain the steady state of an ecosystem with a man-oriented atmosphere. This problem of control has different solutions each of which is characterized by a set of six dimensionless variables associated with three equations--steady-state conditions. The physical characteristics of the variables and conditions of similarity of ecosystems are described. The resultant methods of control are evaluated from the point of view of economic operation of the ecosystem and the level of stability of its amosphere. The class of ecosystems for which the results obtained are valid in the event of accidental perturbations is presented.

Air↗

PubMed1983

Radionuclide transport processes in terrestrial ecosystems.

Some major principles and the status of knowledge concerning the transport of radionuclides through terrestrial ecosystems are reviewed. Fundamental processes which control the flow of radionuclides between ecosystem components such as air, soil, plants, and animals are described, with emphasis on deposition, resuspension, plant uptake, ingestion, and assimilation. Properties of radionuclides, organisms, and ecosystems are examined in relation to their influence on the accumulation of radioactive materials by plants and animals. The effects of the physicochemical nature of the radionuclide; morphology, physiology, and behavior of the organism; and soil, nutrient, and trophic characteristics of the ecosystem are highlighted. Observations in natural ecosystems on radionuclides such as 137Cs, 90Sr, 131I, 3H, and 239Pu are used to illustrate current concepts. An assessment of the degree to which the processes controlling radionuclide behavior are understood and of our ability to simulate and predict such behavior with computerized models is offered. Finally, brief comments are made on research needs.

Air Pollutants↗

PubMed2002

Integration of aquatic fate and ecological responses to linear alkyl benzene sulfonate (LAS) in model stream ecosystems.

An integrated model stream ecosystem fate and effect study of dodecyl linear alkylbenzene sulfonate (C(12)LAS) was performed in the summer and fall of 1996. The study addressed responses of periphytic microbes, immature benthic fauna including abundance, drift, and emergence of adult insects in a 56-day exposure. Exposures ranged from 126 to 2978 microg/L and were continuously presented in a single-pass, flow-through test system. Microbial heterotrophs acclimated to C(12)LAS exposure quickly (14 days) and biodegraded C(12)LAS at all concentrations. Blue-green algae responded by increasing in abundance with increasing C(12)LAS concentration. Invertebrates responded by increased drift and reduced benthic abundances at concentrations exceeding 293 microg/L. Emergence at 927 microg/L also declined relative to the control. Adverse responses for mayflies and chironomids were indicated using univariate statistical techniques. Multivariate techniques indicated these taxa plus mollusks, aquatic worms, caddisflies, and stoneflies were impaired at some concentrations. Bioavailability of C(12)LAS was investigated in streams as a function of the total suspended solid load in the water column driven by local weather and watershed patterns. A continuous bioavailability model indicated exposure was reduced by an average of 8.5+/-8.9%. A model ecosystem no-observed-effect concentration (NOEC) was concluded to be 293 microg/L based on measured water column exposure and adjusted to 268 microg/L by the bioavailability model. A literature review of 13 available model ecosystem studies was conducted and NOEC conclusions were adjusted by a structure-activity relationship to a dodecyl chain length (sulfophenyl position and distribution being ignored due to lack of information in the reviewed studies). Lentic studies (n=7) were found to have higher NOECs than lotic studies (n=6) and were more variable. Mean NOECs+/-SD for all studies, lentic studies only, and lotic studies only were 3320+/-6040, 5720+/-7640, and 530+/-430 microg/L, respectively. Interpretation of results for anomalies from specific studies suggests the importance of experimental design, use of laboratory versus natural surface water, biological complexity of the test system, and physical test system design as relevant factors for consideration. The specific results of the new model ecosystem study presented in this article can be well defended on the basis of a robust experimental and physical design and because the system contained a diverse and sensitive aquatic community. A low or no uncertainty factor could be applied to the result.

Adsorption↗