Ecosystem

About: Ecosystem is a research topic. Over the lifetime, 25460 publications have been published within this topic receiving 1291375 citations. The topic is also known as: ecological system & Ecosystem.

Stream Ecology: Structure and Function of Running Waters

Abstract: 1 An Introduction to Fluvial Ecosystems An overview of the diversity of rivers and streams, including some of the causes of this diversity, and some of the consequences. The intent is to provide a roadmap for the individual chapters that follow, rather than define terms and explain principles in any detail. 2 Streamflow Fluvial ecosystems exhibit tremendous variability in the quantity, timing and temporal patterns of river flow, and this profoundly influences their physical, chemical and biological condition. This chapter covers the essentials of hydrology, from the global water cycle to the myriad ways that humans alter water flowpaths and river flow. 3 Fluvial Geomorphology Fluvial geomorphology emphasizes the dynamic interplay between rivers and landscapes in the shaping of river channels and drainage networks. It includes study of the linkages among channel, floodplain, network and catchment and helps make sense of the enormous variety exhibited among fluvial systems, and thus the habitat and environmental conditions experienced by the biota. 4 Streamwater Chemistry The constituents of river water include suspended inorganic matter, dissolved major ions, dissolved nutrients, suspended and dissolved organic matter, gases, and trace metals. River chemistry changes temporally under the multiple influences of seasonal changes in discharge regime, precipitation inputs, and biological activity and usually is greatly altered owing to direct and indirect human influences. 5 The Abiotic Environment The abiotic environment includes all physical and chemical variables that influence the distribution and abundance of organisms. Current, substrate and temperature often are the most important variables in fluvial environments, and all organisms show adaptations that limit them to a subset of conditions. Species differ in the specific conditions under which they thrive, and whether those conditionsare narrow or comparatively broad. 6 Primary Producers Primary producers acquire their energy from sunlight and their materials from nonliving sources. The major autotrophs of running waters include the benthic algae and macrophytes in larger rivers, phytoplankton also can be important. Benthic algae occur in intimate association with heterotrophic microbes within an extracellular matrix, referred to as biofilm. Benthic algae are important in fluvial food webs, especially in headwater and midsized streams, and also influence the benthic habitat and nutrient cycling. 7 Detrital Energy Sources Particulate and dissolved organic matter originating both within the stream and in the surrounding landscape is an important basal resource to fluvial food webs. Detritus-based energy pathways can be particularly important, relative to pathways originating from living primary producers, in small streams shaded by a terrestrial canopy and in large, turbid rivers with extensive floodplains. Recent advances in microbial ecology have greatly expanded our understanding of the synergies between autotrophs and heterotrophs. 8 Trophic Relationships The network of consumers and resources that constitute fluvial food webs is supported by a diverse mix of energy supplies that originate within the stream and beyond its banks. These include the living resources of algae and macrophytes, and the non-living resources of particulate and dissolved organic matter. Microorganisms are important mediators of organic matter availability and there is increasing evidence of their importance as a resource to both small and large consumers. Additionally, energy subsidies in the form of falling terrestrial arthropods and the eggs and carcasses of migrating fish contribute to the support of many stream-dwellers. 9 Species interactions The basal resources of algae and detritus and associated microorganisms sustain higher consumers includin

Productivity and sustainability influenced by biodiversity in grassland ecosystems

Abstract: THE functioning and sustainability of ecosystems may depend on their biological diversity1–8. Elton's9 hypothesis that more diverse ecosystems are more stable has received much attention1,3,6,7,10–14, but Darwin's proposal6,15 that more diverse plant communities are more productive, and the related conjectures4,5,16,17 that they have lower nutrient losses and more sustainable soils, are less well studied4–6,8,17,18. Here we use a well-replicated field experiment, in which species diversity was directly controlled, to show that ecosystem productivity in 147 grassland plots increased significantly with plant biodiversity. Moreover, the main limiting nutrient, soil mineral nitrogen, was utilized more completely when there was a greater diversity of species, leading to lower leaching loss of nitrogen from these ecosystems. Similarly, in nearby native grassland, plant productivity and soil nitrogen utilization increased with increasing plant species richness. This supports the diversity–productivity and diversity–sustainability hypotheses. Our results demonstrate that the loss of species threatens ecosystem functioning and sustainability.

Harmful Algal Blooms and Eutrophication: Nutrient Sources, Composition, and Consequences

Abstract: Although algal blooms, including those considered toxic or harmful, can be natural phenomena, the nature of the global problem of harmful algal blooms (HABs) has expanded both in extent and its public perception over the last several decades. Of concern, especially for resource managers, is the potential relationship between HABs and the accelerated eutrophication of coastal waters from human activities. We address current insights into the relationships between HABs and eutrophication, focusing on sources of nutrients, known effects of nutrient loading and reduction, new understanding of pathways of nutrient acquisition among HAB species, and relationships between nutrients and toxic algae. Through specific, regional, and global examples of these various relationships, we offer both an assessment of the state of understanding, and the uncertainties that require future research efforts. The sources of nutrients poten- tially stimulating algal blooms include sewage, atmospheric deposition, groundwater flow, as well as agricultural and aquaculture runoff and discharge. On a global basis, strong correlations have been demonstrated between total phos- phorus inputs and phytoplankton production in freshwaters, and between total nitrogen input and phytoplankton pro- duction in estuarine and marine waters. There are also numerous examples in geographic regions ranging from the largest and second largest U.S. mainland estuaries (Chesapeake Bay and the Albemarle-Pamlico Estuarine System), to the Inland Sea of Japan, the Black Sea, and Chinese coastal waters, where increases in nutrient loading have been linked with the development of large biomass blooms, leading to anoxia and even toxic or harmful impacts on fisheries re- sources, ecosystems, and human health or recreation. Many of these regions have witnessed reductions in phytoplankton biomass (as chlorophyll a) or HAB incidence when nutrient controls were put in place. Shifts in species composition have often been attributed to changes in nutrient supply ratios, primarily N:P or N:Si. Recently this concept has been extended to include organic forms of nutrients, and an elevation in the ratio of dissolved organic carbon to dissolved organic nitrogen (DOC:DON) has been observed during several recent blooms. The physiological strategies by which different groups of species acquire their nutrients have become better understood, and alternate modes of nutrition such as heterotrophy and mixotrophy are now recognized as common among HAB species. Despite our increased un- derstanding of the pathways by which nutrients are delivered to ecosystems and the pathways by which they are assimilated differentially by different groups of species, the relationships between nutrient delivery and the development of blooms and their potential toxicity or harmfulness remain poorly understood. Many factors such as algal species presence/ abundance, degree of flushing or water exchange, weather conditions, and presence and abundance of grazers contribute to the success of a given species at a given point in time. Similar nutrient loads do not have the same impact in different environments or in the same environment at different points in time. Eutrophication is one of several mechanisms by which harmful algae appear to be increasing in extent and duration in many locations. Although important, it is not the only explanation for blooms or toxic outbreaks. Nutrient enrichment has been strongly linked to stimulation of some harmful species, but for others it has not been an apparent contributing factor. The overall effect of nutrient over- enrichment on harmful algal species is clearly species specific.

Biodiversity and ecosystem productivity in a fluctuating environment: The insurance hypothesis

Abstract: Although the effect of biodiversity on ecosystem functioning has become a major focus in ecology, its significance in a fluctuating environment is still poorly understood. According to the insurance hypothesis, biodiversity insures ecosystems against declines in their functioning because many species provide greater guarantees that some will maintain functioning even if others fail. Here we examine this hypothesis theoretically. We develop a general stochastic dynamic model to assess the effects of species richness on the expected temporal mean and variance of ecosystem processes such as productivity, based on individual species’ productivity responses to environmental fluctuations. Our model shows two major insurance effects of species richness on ecosystem productivity: (i) a buffering effect, i.e., a reduction in the temporal variance of productivity, and (ii) a performance-enhancing effect, i.e., an increase in the temporal mean of productivity. The strength of these insurance effects is determined by three factors: (i) the way ecosystem productivity is determined by individual species responses to environmental fluctuations, (ii) the degree of asynchronicity of these responses, and (iii) the detailed form of these responses. In particular, the greater the variance of the species responses, the lower the species richness at which the temporal mean of the ecosystem process saturates and the ecosystem becomes redundant. These results provide a strong theoretical foundation for the insurance hypothesis, which proves to be a fundamental principle for understanding the long-term effects of biodiversity on ecosystem processes.