Showing papers on "Ecosystem published in 1988"

The role of disturbance in stream ecology.

Abstract: We define disturbance in stream ecosystems to be: any relatively discrete event in time that is characterized by a frequency, intensity, and severity outside a predictable range, and that disrupts ecosystem, community, or population structure and changes resources or the physical environment. Of the three major hypotheses relating disturbance to lotic community structure, the dynamic equilibrium hypothesis appears to be generally applicable, although specific studies support the intermediate disturbance hypothesis and the equilibrium model. Differences in disturbance frequency between lentic and lotic systems may explain why biotic interactions are more apparent in lakes than in streams. Responses to both natural and anthropogenic disturbances vary regionally, as illustrated by examples from the mid-continent, Pacific northwest, and southeastern United States. Based on a generalized framework of climatic-biogeochemical characteristics, two features are considered to be most significant in choosing streams...

Effects of Acid Rain on Freshwater Ecosystems

Abstract: Acid-vulnerable areas are more numerous and widespread than believed 7 years ago. Lakes and streams in acid-vulnerable areas of northeastern North America have suffered substantial declines in acid-neutralizing capacity, the worst cases resulting in biological damage. Many invertebrates are very sensitive to acidification, with some disappearing at pH values as high as 6.0. However, the recent rate of acidification of lakes is slower than once predicted, in part the result of decreases in sulfur oxide emissions. A discussion of some of the processes that have contributed to the acidification of lakes as well as those that have protected acid-sensitive freshwaters is presented. The author is in the Department of Fisheries and Oceans, Freshwater Institute, 501 University Crescent, Winnipeg, Manitoba R3T 2N6, Canada.

Arthropod regulation of micro- and mesobiota in below-ground detrital food webs

Abstract: Over the past four decades ecosystem scientists have stressed that biotic and abiotic system components must be studied in concert. This philosophy maintains that an ecosystem is a harmonious interplay between organisms and their environment and possesses cybernetic properties that " . . . make possible the orderly cycle of life" ( 84). Although some researchers have emphasized that organisms and their behavior are the building blocks of an ecosystem (5 8, 105), most ecosystem research has been process rather than entity oriented (93). Functional groups, the basic units of an ecosystem model, have usually been defined by broad taxonomic relationships even though criteria that describe roles in a system would be more suitable. Once there is a clear understanding of what roles organisms have, studies can be· directed at how organisms interact to generate ecosystem dynamics.

Tropical Forests and the Global Carbon Cycle

Abstract: New data on the three major determinants of the carbon release from tropical forest clearing are used in a computer model that simulates land use change and its effects on the carbon content of vegetation and soil in order to calculate the net flux of carbon dioxide between tropical ecosystems and the atmosphere. The model also permits testing the sensitivity of the calculated flux to uncertainties in these data. The tropics were a net source of at least 0.4 x 1015 grams but not more than 1.6 x 1015 grams of carbon in 1980, considerably less than previous estimates. Decreases in soil organic matter were responsible for 0.1 x 1015 to 0.3 x 1015 grams of the release, while the burning and decay of cleared vegetation accounted for 0.3 x 1015 to 1.3 x 1015 grams. These estimates are lower than many previous ones because lower biomass estimates and slightly lower land clearing rates were used and because ecosystem recovery processes were included. These new estimates of the biotic release allow for the possibility of a balanced global budget given the large remaining uncertainties in the marine, terrestrial, and fossil fuel components of the carbon cycle.

Nitrogen cycling in coastal marine environments

Abstract: Pelagic Nitrogen Cycling: Primary Productivity and Pelagic Nitrogen Cycling Pelagic Primary Production in Nearshore Waters Microfauna in Pelagic Food Chains Benthic Nitrogen Cycling: Benthic Primary Production and Oxygen Profiles Benthic Nitrogen Fixation Amino Acids and Amines in Marine Particulate Material and Sediments Distribution and Metabolism of Quaternary Amines in Marine Sediments Benthic Mineralization and Bacterial Production Nitrogen in Benthic Food Chains Nitrification in Estuarine and Coastal Marine Sediments Nitrate Reduction and Denitrification in Marine Sediments Benthic Fauna and Biogeochemical Processes in Marine Sediements: The Role of Burrow Structures Benthic Fauna and Biogeochemical Processes in Marine Sediments: Microbial Activities and Fluxes Models of Nitrogen Cycling: Modelling Benthic Nitrogen Cycling in Temperate Coastal Ecosystems Nitrogen Models at the Community Level: Plant-Animal-Microbe Interactions Nitrogen Biogeochemistry and Modelling of Carmarthen Bay.

Microbial ecosystems of Antarctica

Abstract: Preface 1. Introduction 2. Snow and ice ecosystems 3. Sea-ice ecosystems 4. The marginal-ice zone 5. The open ocean 6. Benthic marine environments 7. Lakes and streams 8. Soil ecosystems 9. Lithic ecosystems: the rock environments 10. Microbial strategies in Antarctica 11. Microbes and humans in Antarctica Glossary Appendixes References Index.

Nitrogen Limitation of Production and Decomposition in Prairie, Mountain Meadow, and Pine Forest

Abstract: The responses of decomposition and primary production to nitrogen supply were investigated in a shortgrass prairie, a mountain meadow, and a lodgepole pine forest. Nitrogen (N) supply was increased by applying ammonium nitrate, or decreased by applying sucrose. The litterbag technique was used to follow decomposition of leaves of the dominant plants: blue grama (Bouteloua gracilis) from the prairie, western wheatgrass (Agropyron smithii) from the meadow, and lodgepole pine (Pinus contorta) from the forest. Soil from beneath the litterbags was sampled at the time of litterbag retrieval in order to detect interactions between decomposition and properties of the underlying soil. There was no consistent effect of soil properties on decomposition rate, but there was a significant effect of litter type on N mineralization in the underlying soil. Decomposition was fastest in the forest, intermediate in the prairie, and slowest in the meadow. Blue grama decomposed faster than the other litters. Each litter type decomposed faster than expected when placed in its ecosystem of origin. This interaction suggests that decomposers in an ecosystem are adapted to the most prevalent types of litter. Nitrogen supply had a small but significant effect on decomposition rate. Within an ecosystem, there was a positive association between decomposition and accumulation of N within the litter, but this relationship was reversed when comparing across ecosystems, possibly because of the overriding effects of differences among ecosystems in abiotic factors. Aboveground net primary production was estimated in the grasslands by a single harvest at the end of the growing season, and growth increment of boles was measured in the forest. These indices of primary production showed a greater relative response to N fertilization than did decomposition, suggesting that primary production is the more N—limited process.

Plant and soil nitrogen dynamics in California annual grassland

Abstract: Seasonal changes in soil water and nitrogen availability were related to the phenology and growth of plants in California annual grassland. Plant accumulation of nitrogen was mainly confined to two short periods of the year: fall and early spring. At these times, plants were in the vegetative growth phase, roots were growing rapidly and soil moisture was high. During these periods, soil nitrate was low or depleted. High flux of nitrogen in this ecosystem, however, is indicated by the rapid disappearance of the previous year's detrital material, high microbial biomass, and high mineralizable nitrogen and nitrification potential. At the end of the summer drought, significant amounts of the previous year's detrital material had disappeared, chloroform-labile N (expressed as microbial biomass N) was at its seasonal maximum, and soil inorganic nitrogen pools were high. This suggests inorganic nitrogen flux during the drought period. The ‘drought escaper’ life history characteristics of annual grasses in California annual grassland, however, may prevent plants from utilizing available nitrogen during a large part of the year.

Phytoplankton community structure and succession in a tropical estuarine complex (central west coast of India)

Abstract: The seasonal distribution of phytoplankton in the Mandovi-Zuari estuarine complex (central west coast of India) from November 1979 to October 1980 is described. Of the 82 species of phytoplankton recorded, diatoms (63 species) showed an overwhelming predominance over dinoflagellates (14 species), blue-green algae (three species) and green algae (two species). Among the several factors affecting phytoplankton, the commencement of the south-west monsoon results in a drastic change in hydrographic conditions which are instrumental in the transformation of the phytoplankton population size and structure. The great variability in the ecosystem is amply illustrated by species succession.

Element interactions in forest ecosystems: succession, allometry and input-output budgets

Abstract: Element interactions within forests differ from those in other major ecosystems for three major reasons: — a greater allocation of carbon to structural material; — a greater element storage within biomass; and — the diversity of carbon- and nutrient-containing metabolites produced. The most important of these differences is structural material, which can lead to C: element ratios in biomass (as a whole) 100 × greater than those in unicellular organisms. Stand allometry causes the amount of carbon stored and C:element ratios in biomass to change in predictable ways in the course of secondary succession. Such changes affect microbial dynamics and C: element interactions within soils. Bicarbonate, organic acids, nitrate, phosphate, and sulfate are major anions within forest soils: they control leaching of both anions and cations. Biotic interactions of C, N, P, and S during both uptake and mineralization control the potential for production of these anions within forests, and geochemical interactions regulate their mobility and loss.

Trophic interactions within pelagic microbial communities: indications of feedback regulation of carbon flow

Abstract: Future considerations of carbon-energy flows within pelagic food webs should include internal, biotic feedback controls, in addition to abiotic forcing functions, in the regulation of these flows. Over the past two decades, research on microbial communities of pelagic ecosystems has yielded data suggestive of cybernetic-like regulation operating within these communities. As presently conceived, phagotrophic protozoa have a pivotal role in such regulation as a consequence of their rapid growth, grazing, and nutrient regenerative capabilities. Feedback controls within microbial food webs may have significant effects on distal portions of pelagic ecosystems, including the fate of organic detritus and metazoan production.

Mediterranean-type ecosystems: a data source book

Abstract: 1. Climate, Vegetation, Vertebrates and Soil/Litter Invertebrates of Mediterranean-Type Ecosystems - Data-Banks.- 2. Vegetation, Nutrition and Climate - Data-Tables.- (1) Natural vegetation - ecomorphological characters.- (2) Foliar analyses.- (3) Species richness.- (4) Climate.- 3. Vegetation, Nutrition and Climate - Examples of Integration.- (1) Mediterranean bioclimate and its variation in the palaearctic region.- (2) Climatic control of ecomorphological characters and species richness in mediterranean ecosystems of Australia.- (3) Leaf structure and nutrition in mediterranean-climate sclerophylls.- 4. Vertebrates.- 5. Soil and Litter Invertebrates.- Systematic index.- General index.

Ecological succession in Phanerozoic reef ecosystems; is it real?

Abstract: I define ecological succession as an orderly, directional, and predictable, pioneer-to-climax process of community and species development. It takes place in an environment where external physico-chemical constraints are not undergoing major change: ecological succession leads naturally to increasing biological control of the environment and a stabilized ecosystem. Ecological succession is an intrinsic feature of reef growth. I present criteria for the recognition of pioneering and climax stages in Phanerozoic reefs at both the species and community level. On the other hand, I use the term community replacement where changing external factors have forced the migration of organisms into an area thereby replacing existing species and communities. Development of reef ecosystems through the Phanerozoic generally follows the pattern of ecological succession but through a time frame of 30 to 10OMa, concluded by a phase of mass extinction. I call such long-term changes erathemic successions. Pioneering recovery of reef ecosystems following extinctions appears to take as much as 8 to 12Ma. Restricted marine environments or global periods of climatic change produce arrested successions-successions essentially halted in initial phases characterized by pioneering species and communities that fail to reach a full climax stage. I outline selective examples of arrested successions. Arrested succession may explain the lack of full reef development within most of the mid-Cambrian to midOrdovician and much of the Carboniferous and may provide a key to explaining global climatic change. Classification of reefs should take into account the role of community structure and ecological succession as these may play a stronger selective role on reef type than tectonic, sedimentological, or physico-chemical constraints.

Grasslands and savannas: regulation of energy flow and nutrient cycling by herbivores

Abstract: Although the importance of herbivores in some terrestrial ecosystems has been questioned, results of research conducted in grasslands and savannas suggest that herbivores may have pervasive effects on ecosystem structure and function. In contrast to many terrestrial ecosystems that support relatively low herbivore loads and annually lose 5-10% or less of their net primary production (NPP) to herbivores (Chew 1974; Wiegert and Evans 1967; Owen and Wiegert 1976), grasslands and savannas typically support heavy herbivore loads. As discussed below, these herbivores may consume half or more of the annual aboveground net primary production (ANPP) and one fourth or more of the annual belowground net primary production (BNPP). As a result of these relatively high rates of consumption, it has been suggested that the structure of grasslands is the result of numerous interactions, many of which are either direct effects of, or mediated by, herbivores (McNaughton 1983). A simplified conceptual model of carbon, mineral nutrients, and water, and a few of the factors affecting their flows in a grazing system, is shown in Figure 7.1.

Temperate forest insect outbreaks, tropical deforestation and migratory birds

Abstract: Ecosystems that are managed for resource production are under continual structural change. Changes imposed by local management aggregate to produce regional patterns and new regionwide responses. Anthropogenic influences on hemispheric and global processes add another level of change. The result is a bewildering variety of real or anticipated changes unique to experience. For example, in the spruce/fir and budworm interaction of eastern North America, a syndrome of causes affects the vulnerability of renewable resources, and the triggers of change can never be predicted. Yet, it is possible to identify key features that affect resilience of ecosystems and robustness of regulation and to reject other possibilities. This approach provides a way to assign priorities for research and for contingency planning to adapt to change.

Shrub-Steppe: Balance and Change in a Semi-Arid Terrestrial Ecosystem

Abstract: 1. Introduction: Shrub-steppe lands (L.E. Rogers, W.H. Rickard). 2. Climate of the Hanford site (W.H. Rickard). Meteorological data base. Climate patterns at the Hanford site. 3. Soils: Carbon and mineral cycling processes (R.E. Wildung, T.R. Garland). Occurrence and distribution of soils. Physiochemical properties. Carbon cycling: Influence of environmental factors. Relationships of carbon cycling to mineral weathering and mobilization. 4. Water Balance (G.W. Gee et al). General principles applicable to arid sites. Microclimatology of the ALE reserve: Data bases. Model simulations. Conclusions. 5. Springs and streams (C.E. Cushing, B.E. Vaughan). Physical and chemical characterization. Biological investigations. Radionuclides as indicators of aquatic ecosystem processes. Summary. 6. Plant communities: Characteristics and responses (W.H. Rickard, B.E. Vaughan). Characteristics of contrasting shrub-steppe plant communities. Responses of plants and plant communities to disturbances. Radionuclides as indicators of biological fate and transport of materials. Summary. 7. Terrestrial animal habitats and population responses (L.E. Rogers et al). Mammals and reptiles. Birds. Insects and related arthropods. Animals as indicators of radionuclide and chemical contamination. 8. Theoretical perspective on ecosystem disturbance and recovery (P.A. Beedlow et al). Concepts of response and recovery. Characterization of disturbance and stress in the shrub-steppe ecosystem. Future research needs. Epilog (L.E. Rogers, W.H. Rickard).

Biota and abiotic environment in the Westerschelde estuary

Abstract: An estuary such as the Westerschelde is a highly dynamic environment, both on an ecological time scale where climatic and hydrodynamic forces, mainly the tides, shape a very variable environment and on a geological, evolutionary time scale, since estuaries are young and very unstable habitats.

Feeding dynamics, nitrogen budgets, and ecosystem role of a desert stream omnivore, Agosia chrysogaster (Pisces: Cyprinidae)

Abstract: Feeding habits, diel periodicity and total daily ingestion, and nitrogen budgets of longfin dace (Agosia chrysogaster) were examined on two occasions when food quality, but not quantity, differed. Agosia chrysogaster was found to be an opportunistic omnivore, consuming primarily insects when the preferred taxon (baetid mayflies) was abundant in the environment, but consuming primarily algae when mayfly abundance was low. Ingestion provided a better measure of diel feeding periodicity than gut fullness; feeding was diurnal on both sample dates, but more markedly so when the primary food was algae. Mean nitrogen content of algal foods was low, and A. chrysogaster apparently compensated for this by increasing its daily ingestion rate when algae were the major food. A reduction in nitrogen content of food during digestion from 4–6% (of dry mass) to less than 1% (in feces) suggested a high assimilation efficiency for nitrogen (nitrogen assimilated/nitrogen consumed = 72–78%). Populations of this abundant and successful cyprinid in Sonoran Desert streams may play an important role in ecosystem nitrogen dynamics. Nitrogen stored in fish biomass comprised 3–6% of the total nitrogen stored in Sycamore Creek, and excretion of ammonia by the fish represented 5–10% of total nitrogen uptake by algae. Such rapid recycling of usable nitrogen to primary producers is significant in this nitrogen limited stream ecosystem.