Showing papers on "Ecosystem published in 1980"

Forest Succession Models

Abstract: Studies in succession attempt to determine the changes in species composition and other ecosystem attributes expected to occur over periods of time. Mathematical models developed in forestry and ecology to study ecological succession are reviewed. Tree models, gap models and forest models are discussed. Model validation or testing procedures are described. Model applications can involve evaluating large-scale and long-term changes in the ambient levels of pollutants and assessing the effects of climate change on the environment. (RJC)

The status of three ecosystem-level hypotheses regarding salt marsh estuaries: tidal subsidy, outwelling, and detritus-based food chains

Abstract: During the first 10 years of salt marsh research at Sapelo Island (1952–1962), three general hypotheses emerged as follows: (1) tides provide an energy subsidy that enhances productivity, (2) organic matter is exported from productive estuaries to offshore waters (outwelling), and (3) detritus rather than grazing food chains predominate in the salt marsh ecosystem. These hypotheses, which we judge to be “emergent properties” of the salt marsh estuary as a whole, have now been challenged and tested in many places up and down the coast. The tidal subsidy hypothesis has been verified sufficiently to stand as a general principle. Outwelling seems to be strictly a local question depending on relative productivity of inshore and offshore waters and the magnitude of water flow in and out of the estuary; some estuaries export while some import, and the material exported (or imported) may involve nutrients, organic matter, or organisms. Although dominance of detritus-based food chains has been verified for most shallow water estuaries (in contrast to dominance of the grazing food chain in open water marine habitats), recent work has indicated that detritus complexes are like autotroph-heterotroph microcosms with algae, protozoa, fungi and bacteria providing major energy sources for detritus consumers which in turn are the chief food for fish and higher trophic levels in general.

Influence of Amphibian Larvae on Primary Production, Nutrient Flux, and Competition in a Pond Ecosystem

Abstract: In a pond ecosystem near St. Louis, Missouri, natural variations in tadpole biomass during 1971-1972 were accompanied by shifts in patterns of nutrient cycling and primary production, particularly when metamorphoses caused abrupt removal of these transient consumers. In the field, increased tadpole biomass was associated with: (I) reduced standing crop of suspended particles, including phytoplankton, the tadpoles' major food source; (2) a shift in the state of nitrogen from largely particulate to largely dissolved; (3) reduced rates of primary production, from both H14CO:t uptake and diurnal oxygen methods; (4) a nonlinear effect on phytoplankton specific growth rates; (5) a shift in phytoplankton community structure away from filamentous blue-green algae; and (6) a reduced proportion of active chlorophyll a in the photosynthetic pigments of phytoplankton. From laboratory experiments, the potential impact of tadpoles on nitrogen flux, through feeding and nutrient release, was estimated. Several conclusions were made: (1) Suspension feeding by tadpoles reduced concentrations of suspended particles. Under condi- tions of low particles:high tadpoles, the specific growth rates of tadpoles were reduced. Recruitment was absent except under conditions of high particles:low tadpoles; the most diverse community of new tadpole recruits (four species) was observed under such conditions. All four species (three genera) had similarly sized particles in their guts. These field observations are consistent with an hypothesis of competition among the tadpoles. (2) Tadpoles apparently were regulatory consumers; they became a large component with respect to phytoplankton. Nitrogen flux through tadpoles was within the same order of magnitude, and some- times exceeded the estimated N uptake by phytoplankton. (3) Tadpoles probably regulated primary production by both reducing standing crop and altering specific growth rates of algae. At maximum tadpole biomass, suspended particle concentrations were stabilized near the laboratory-determined threshold concentration for feeding by these Rana tadpoles. When metamorphosis removed these transient consumers, rates of primary production increased dramatically. (4) Interactions within the pond ecosystem apparently determined aquatic-terrestrial nutrient bal- ances for the amphibian communities. Some species deposited more nutrient in their eggs than was assimilated by larvae, but the community as a whole extracted nutrient from the ecosystem. Nutrient input in eggs was much less than that assimilated by autotrophs.

Marine Benthic Dynamics

Abstract: The proceedings from this symposium contain an overview of the benthic ecosystem. The structure, population dynamics, and secondary production of benthic ecosystems are discussed in light of the role of detritus and nutrient cycling in the food chain. The twenty three articles of presentation are grouped by categories of secondary production, population studies, nutrient cycling, and detritus and are summarized and indexed with an abstract for each presentation. (DS)

The dynamics of a grassland ecosystem: botanical equilibrium in the park grass experiment

Abstract: SUMMARY (1) The published results of the Park Grass Experiment (PGE), begun in 1856, provide up to 30 yr of annual data which may be used to determine whether the botanical composition of these grasslands was at equilibrium. Data covering a period exceeding 80 yr are available to test for relationships between hay yield (biomass), species diversity, species number and time. (2) Species diversity and species number show negative relationships with plot biomass and with pH. These relationships were constant over time. The effects of biomass and pH on species number and species diversity were additive. (3) Analysis of the flora of nine plots, each divided into grasses, legumes and a miscellaneous component showed that these components were at equilibrium. (4) The effect of various endogenous factors on this botanical equilibrium was examined. No regular or irregular cycles of component biomass operating between years were detected and it is inferred that populations were regulated by processes operating within individual years. (5) The biomasses of all three components were positively correlated within an unfertilized plot but the floristic components of plots receiving a fertilizer treatment showed few within-plot correlations. By contrast between-plot correlations of components were common for all plots with the exception of those recel.iig nitrogen fertilizer. (6) The mechanisms of population regulation which maintained the Park Grass ecosystem at equilibrium are discussed and tests for these are proposed.

Abundance, biomass and contribution to energy flow by soil nematodes in terrestrial ecosystems

Abstract: A review is made of quantitative estimations on abundance and biomass of nematode faunas from different ecosystems. A great dispersion of the values from different authors is probably to some extent caused by differences in the efficiency of the extraction methods. The mean values of numerical abundance for different types of ecosystems ranged from 7.6 -10 m-2 for semideserts to 9.2 106 m-2 for temperate grasslands. The respiratory metabolism in more productive sites corresponded to an energy emittance of about 20-60 kcal m-2 and year whereas in cold or dry sites it amounted to 7-10 kcal m-2 and year. The contribution of nematodes to the total soil respiration is rather slight; probably in many cases under 1%. The accuracy of estimations on the total energy flow through the soil populations is discussed. Probably the microbial feeders have a high assimilation efficiency whereas the production efficiency is more varying depending upon the food supply which in the soil possibly

Watersheds as the Basic Ecosystem: this Conceptual Framework Provides a Basis for a Natural Classification System

Abstract: A scheme is outlined to classify watersheds as ecosystems, based on their natural attributes. Two physical factors of the environment, climate and geology, are selected as state factors. Climate is the master factor that supplies energy and water to all ecosystems; geologic structure supplies the materal from which the forces of climate carve landforms to establish ecosystems. At the next lower level, soil and vegetation interact in a succession of transactions to produce a mosaic of tesseras within each watershed. It is these interacting tesseras that moderate climate and store energy within the ecosystem that influences the embedded stream. At the bottom of the scale is the stream with its passive role and inability to interact with the higher factors of the ecosystem. Thus, we have a controlling force consisting of two elements (climate and geology), a reacting force (soil and vegetation) that responds by circular conditioning to controlling forces, and at the lowest level, the stream which responds to all factors of the living system within its watershed.

Functional complexity and ecosystem stability

Abstract: The hypothesis that complexity and stability are positively correlated was experimentally tested at the ecosystem level of organization using intact terrestrial microcosms. Power spectral densities of hourly CO/sub 2/ efflux, from 11 old-field microcosms, were analyzed for the number of low-frequency components. We postulate that the number of peaks is related to functional interactions among system components (i.e., population interactions, physical-chemical reactions, and biological turnover rates) influenced by nonlinearities, feedbacks, and time delays. Thus, the number of low-frequency peaks can be taken as an index of functional complexity. Relative stability was based on the capacity of the system to retain essential nutrients and was measured by net loss of calcium after the system was stressed with a heavy metal, cadmium. Rank correlation supported the hypothesis that increasing ecosystem functional complexity leads to increasing ecosystem stability.

Nutrient scavenging of rainfall by the canopy of an Amazonian rain forest.

Abstract: Fluxes of nutrient elements entering the forest canopy by rainfall are compared with fluxes to the forest floor by throughfall, for two tropical rain forest types growing on soils of low nutrient content in southern Venezuela. In contrast with other forests, total yearly rainfall fluxes of calcium, sulfur, and phosphorus were greater than corresponding throughfall fluxes. For other elements, rainfall fluxes were occasionally greater than throughfall fluxes. We hypothesize that these nutrients are intercepted in the canopy by algae and lichens growing on leaf surfaces, resulting in nutrient conservation in this nutrient-limited ecosystem. THE RAIN FOREST WHICH COVERS much of the central and eastern portion of the Amazon Basin grows on soils low in essential nutrient elements (Sioli 1975, Klinge and Ohle 1964). Despite the low nutrient content of the soils, the forests appear large and vigorous. The question of how the forests survive in the nutrient-poor environment has interested ecologists for many years, and it has been hypothesized (Richards 1952) that nutrient-conserving mechanisms evolved in these ecosystems which have enabled these forests to survive and grow in this nutrient-poor environment. In order to study the structure and function of the Amazon rain forest, including nutrient-conserving mechanisms, an ecological project has been established near San Carlos de Rio Negro, Venezuela, lat. 20N, 67?W (Medina et al. 1977). The area is within the northern part of the drainage basin of the Amazon River. Some of the initial results of the project have shown that there is virtually no nutrient input to the ecosystem from the mineral soil and subsoil (Klinge et al. 1977, Stark and Jordan 1978, Stark and Spratt 1977). This finding means that atmospheric input must be a major source of nutrients for the central Amazon forests. In this paper we report that nutrients are filtered out of the rainwater as the water passes through the forest canopy, and we hypothesize that this interception is an important nutrient-conserving mechanism for the Amazonian

The Role of Protozoa in Nutrient Cycling and Energy Flow

Abstract: Nutrient cycling and energy flow are centered on photosynthesis and plant growth, for plant tissue forms the greater part of the earth’s biomass. But all organisms participate, and their role is determined not simply by their biomass but by their catalytic reaction in different ecosystems. The major nutrient cycles are the carbon cycle, in which the organic energy cycle is implicit, the nitrogen cycle, the sulfur cycle, and the phosphorus cycle. The major energy cycles are the solar cycle and the hydrological cycle that is not only the source of the major part of living matter but also provides the medium for all organic cycles. The geometry of nutrient cycling is determined by the nature and distribution of sources and sinks, the most important being the atmosphere, the ocean and soil, and the availability of the major, minor, and trace elements, and other growth factors.

Nutrient Budget Studies for Forests Along an Elevational Gradient in New Mexico

Abstract: Element budgets are presented for watersheds which differ markedly in vegetation biomass, structure, productivity, soil development and hydrology. The net organic matter increment of one of the watersheds has been estimated to be negative. The patterns in the output and net change of Ca, Mg, K and Na among watersheds are related to soil chemistry and stream discharge rates. These factors may not be related to the net organic matter increment of the ecosystem. Actual atmospheric inputs of these elements to some of the ecosystems may be an order of magnitude greater than those measured in bulk precipitation. Nitrogen outputs in stream water are strongly regulated by all of the watershed ecosystems including the one which appears to have a negative net organic increment. Low losses of nitrogen in stream water, however, do not mean a system will minimize other types of N losses (e.g., denitrification). Nutrient budgets generated from bulk precipitation and stream water discharge in the Southwest cannot prove or disprove hypotheses about nutrient regulation by net organic matter increment. Additional inputs (aerosol impaction, weathering, N fixation, NH3 absorption) and outputs (denitri- fication, aerosols) must be quantified before a valid test can be made of these hypotheses.

Environmental Quality and Natural Biota

Abstract: Public desire for a healthful, pleasing environment makes preservation of environmental quality a recognized objective of national policy. Maintenance of a quality environment depends upon a myriad of complex natural systems composed of more than 200,000 species of plants, animals, and protists (HEW 1969, King et al. 1979). We cannot survive with only our crop and livestock species, but we do not know how many of the 200,000 species native to the United States are absolutely essential to our survival. Natural biota, the nonmanipulated or uncultivated organisms, perform many essential functions for agriculture, forestry, and other segments of human society, such as preventing the accumulation of wastes; cleaning water and soil of pollutants; recycling vital chemical elements within the ecosystem, including biotic nitrogen as fertilizer; buffering air pollutants and moderating climatic change; conserving soil and water; serving as sources of certain medicines, pigments, and spices; preserving genetic material for agriculture; and supplying food via the harvest of fish and other wildlife. In addition to these important ecosystem functions, the natural biota are of great aesthetic value to society. Concern for preserving the natural environment is reflected in recent passage of numerous state and federal laws, including the National Environmental Policy Act (NEPA) of 1969, the Marine Mammal Protection Act of 1972, the Endangered Species Act of 1973, and the Fishery Conservation and Management Act of 1976. NEPA mandates that national government agencies by concerned with any "major Federal actions significantly affecting the quality of the human environment . .." (Orloff and Brooks 1980). This interest manifests itself in the activities of the U.S. Environmental Protection Agency and the preparation of environmental impact statements (EIS). On the federal level, EIS preparation is coordinated by the Council on Environmental Quality (CEQ). Many state agencies and some locales also are legally directed to prepare similar statements. CEQ has directed that attention be paid to such aspects as the social, economic, physical, and biological effects that proposed environmental manipulations might have. Biological factors have included possible effects on fish and wildlife, plant conservation, and endangered species. No mention is made of microorganisms, pollinators, and many other small species of life, though the general nature of the guidance does not exclude their consideration. If environmental policy is to include all "significant impacts" of an action, then it should consider the potential impacts on all organisms vital to the total ecosystem. We must assess and understand the ecological role of major species groups, especially in relation to the vitality of the total ecosystem, so that we can identify those that are essential for a viable ecosystem. To make this assessment, we will need all the available, though limited, data concerning the abundance, distribution, and roles of all natural biota. The preliminary survey reported here attempts to ascertain the relative importance of major species groups in the ecosystem and to identify potential human impacts upon these biota. Although this information clearly highlights the need for additional data, it should be helpful to those making policy decisions concerning the priorities accorded to various natural biota that are essential to a quality environment.

Biomass Distribution and Production Budget for a Nonaggrading Forest Ecosystem

Abstract: A fundamental question in current ecosystem research is the extent to which net organic matter increment (net ecosystem production, NEP) controls nutrient input—output behavior. The large uncertainties associated with net primary production (NPP) and heterotrophic respiration (RsH) make it very difficult to verify statistically an ecosystem as steady—state (NPP — RsH = 0). The aspen (Populus tremuloides Michx.) ecosystem reported on here appears to be degrading (i.e., negative NEP), a condition which would allow an important test of the influence of NEP on the nutrient regulation of an ecosystem. Total NPP was estimated at 11 740 kg°ha—1°yr—1, RsH was 13 800 kg°ha—1°yr—1, and NEP was —2060 kg°ha—1°yr—1. The standard error of the estimate for the sum of woody biomass increment and litter fall was 119 kg°ha—1°yr—1. Extravagant estimates were used for other components of NPP and underestimates used for components of RsH to ensure a conservative estimate of a degrading condition. See full-text article at JSTOR

Herbivorous Mammals Along a Montane Sere: Community Structure and Energetics

Abstract: All common herbivorous mammals were censused along a successional gradient in northern Utah in order to assess some of the changes in ecosystem attributes predicted to occur by Odum (1969). Biomass (B) and energy flow [Production (P), Respiration (R), and P + R (e)] through each of nine species in each of four serai stages (montane meadow, Populus -dominated forest, Abies -dominated forest, and Picea -dominated forest) were estimated. Tests of eight predicted trends were supportive in five cases (P/R ratio, P/B ratio, B/e ratio, net community production, and species richness), inconsistent in two cases (total organic matter and species evenness/general diversity) and ambiguous in one (size of organism). Community stability, as measured by changes in average community biomass between years of relatively normal and extremely low precipitation, increased with ecosystem maturity. Individual species, however, fluctuated greatly in biomass between the 2 years. Our results are consistent with the hypothesis that mammals are determinants of successional patterns only insofar as they affect plant colonization. However, a continuum probably exists between completely passive species and those that strongly influence successional patterns in plant communities through their effects on plant recruitment and/or mortality. Changes in the plant community in turn affect the composition of the herbivorous mammal community.

The nutrient status of subarctic woodland soils

Abstract: Five sites are examined near Schefferville, Quebec; two sites represent mature open spruce-lichen woodlands and the remaining three sites are regenerating woodlands. The soils are acid and have very low amounts of available macro-nutrients (Ca, Mg, K, P, and N). The nutrient inputs into the soil through precipitation, spruce canopy drip and stemflow are low, as are the leaching losses from the soil. The spruce trees act as the major nutrient accumulators in the ecosystem and the soil around the trees shows increased nutrient availability. Although burning increases the pH and available nutrient status of the soil, this increase is short-lived (less than 5 yr) and smaller than observed in other ecosystems. The soils remain oligotrophic.

Birds as marine organisms: a review

Abstract: Only 9 of 156 avian families are specialized as seabirds. These birds are involved in marine energy cycles during all aspects of their lives except for the 10% of time they spend in some nesting activities. As marine organisms their occurrence and distribution are directly affected by properties of their oceanic habitat, such as water temperature, salinity, and turbidity. In their trophic relationships, almost all are secondary or tertiary carnivores. As a group within specific ecosystems, estimates of their feeding rates range between 20 and 35% of annual prey production. Their usual prey are abundant, schooling organisms such as euphausiids and squid (invertebrates) and clupeids, engraulids, and exoccetids (fish). Their high rates of feeding and metabolism, and the large amounts of nutrients they return to the marine environment, indicate that seabirds are probably imKortant components in pelagic ecosystems. As such they have been strongly affected by human fisheries; for example, decline in the size of Peruvian anchovy and South African sardine populations have led to tremendous reductions in associated bird numbers. Evidence indicates that seabirds could provide an understanding of fish stock dynamics prior to overexploitation by man. RESUMEN