Showing papers on "Ecosystem published in 1978"

The effect of fire on nutrients in a chaparral ecosystem

Abstract: The distribution of nutrients in plants, litter, and soil were studied before and after a prescribed burn in southern California chaparral. Total N, P, K, Na, Mg, and Ca were measured. The various nutrients were distributed differently in the plant parts and the litter before fire and this affected their redistribution by fire. Measurable losses of only 2 nutrients occurred–N (146 kg/ha) and K (49 kg/ha). Erosional losses of nutrients during the first rainy season after fire are also reported.

Measuring the Inertia and Resilience of Ecosystems

Abstract: The resilience of natural ecosystems is a property of keen interest to both theoretical and applied ecologists. Resilience, in this context, refers to the degree, manner, and pace of restoration of initial structure and function in an ecosystem after disturbance. It is an important ecological characteristic, reflecting ultimately the nature and complexity of homeostatic processes in an ecosystem. Discussions of the concept of ecosystem resilience are relatively recent, and a variety of terms has been proposed for properties of resilience. The ability of a natural ecosystem to restore its structure following acute or chronic disturbance (natural or human-induced) is here termed resilience, consistent with the use of Clapham (1971). This same set of properties is subsumed under the term stability by May (1973), Holling (1973), and Orians (1975) and termed elasticity by Cairs and Dickson (1977). Given the definition of resilience above, it would seem useful to limit "stability" to the pattern of fluctuations in a relatively unimpacted ecosystem over time, a usage consistent with the first eight properties of stability discussed by Whittaker (1975a). Traditionally, fluctuations in ecosystem structure have referred to variations in population densities of component species, but in theory other measures of ecosystem structure or function (e.g., biomass, net primary production, nutrient stocks, species richness) could be used. Since different properties of ecosystem structure and function will not necessarily vary at parallel rates, however, the ecosystem parameters chosen for study will have a

The dynamics of crayfish and their role in ecosystems.

Abstract: An understanding of the population dynamics of crayfish and their trophic position is critical to understanding energy transformation in lakes. In many lakes crayfish dominate the annual production of the benthic biomass, at times reaching mean biomass values of 1000 1400 kg/ha and numerical densities of 15/m2. Density determines the rate of growth of various populations and determines reproductive capacity, age at maturity and life span. For Orconectes virilis, within the lakes we studied, population stability was mostly due to the short lag between a change in population density and an adjustment in fecundity. As a result, these populations appear to be self-regulated through density-dependent control of brood stock size. In Orconectes virilis, annual production was a function of mean annual biomass. Examination of available data on the ratio between other species showed them to fall within the same range as O. virilis. It seems that the evolutionary strategy governing crayfish biomass replacement and energy turnover has remained essentially unchanged. As regards their role in the community, crayfish do not fit the trophic level concept. Attempts to quantify their food habits show them to be polytrophic and a key energy transformer between various trophic links through utilization of all the trophic levels in lakes. Because of the multiple trophic roles of the crayfish, a comparison with the bioenergetics of various freshwater crust?cea is difficult. Crayfish may be most important in lakes with low phytoplankton production. In such lakes detritus and benthic algae, both of which are ingested by the crayfish, are important sources of overall energy flow. Since crayfish also function as major predators on the benthos, they most likely contribute to the stability of lake communities by interacting with a whole subweb of species ranging from large benthic invertebrates and submerged higher aquatics to the periphytic microcommunity. Hence, crayfish act as an important mechanism contributing to the regulation of most production processes and most specifically to the regulation of benthic production available to fish. In low nutrient lakes, because of their biomass dominance and functional role, crayfish greatly surpass the usual role assigned to them from their occurrence in fish diets. Manipulation of the benthic food chain would seem to be the most appropriate strategy to increase the fish production of such lakes. However, a greater appreciation of the complexity of the trophic organization of such food webs is necessary before such modifications can be attempted. 1 A contribution under Dingell-Johnson Project F-30-R, Michigan. 2 Present address: Department of Biology, Lakehead University, Thunder Bay, Ontario, Canada.

Trophic and spatial interrelationships in the fish species of an Ontario temperate lake

Abstract: Analysis of the fish faunas of Lake Opinicon and other small, cold temperate Ontario water bodies shows that the component species differ in body size, morphology, abundances, habitats, diurnal and seasonal habitat utilization patterns, diets, dietary changes with age, reproductive strategies, and population turnover rates. These differences are detailed. The number of species occurring in a lake is partly due to historic factors, the number of habitats available, and morphological, behavioral and ecological adaptations that, by channelling their owners towards alternative resources, permit species to co-occur. Diet overlap values between most species are low except for the congeneric bluegill and pump-kinseed sunfishes, where values are moderate. These are the two commonest species in the lake and other parameters must increase the ecological differences between these two species. Lake Opinicon is a highly variable ecosystem. Part of this variability stems from the seasonal nature of the environment and the fact that different resources reach their peak abundance at different times of the year. Ecological overlap levels between fish species fluctuate greatly in the course of the season as species switch from, or move on to, different resources. Population levels in different habitats also vary seasonally. Species adaptations and interaction patterns were presumably evolved over a long period; most of these adaptations undoubtedly developed before the component species colonized the lake.

Production Ecology of British Moors and Montane Grasslands

Abstract: I. The Moor House Programme.- 1. Introduction and Site Description.- 2. Field Estimates of Primary Production.- 3. Physiological Aspects of Bog Production at Moor House.- 4. Ecology of Moorland Animals.- 5. Microbial Populations in Peat.- 6. Nutrient Availability and Other Factors Limiting Microbial Activity in the Blanket Peat.- 7. A Study of the Rates of Decomposition of Organic Matter.- 8. A Simulation of Production and Decay in Blanket Bog.- 9. A Model of Peat Bog Growth.- 10. The Blanket Bog as Part of a Pennine Moorland.- II. Supporting Studies-Dwarf Shrub Communities.- 11. The Productivity of a Calluna Heathland in Southern England.- 12. Production in Montane Dwarf Shrub Communities.- 13. Heather Productivity and Its Relevance to the Regulation of Red Grouse Populations.- III. Snowdonia Grasslands.- 14. Snowdonia Grassland: Introduction, Vegetation and Climate.- 15. Physiography, Geology and Soils of the Grassland Site at Llyn Llydaw.- 16. Primary Production, Mineral Nutrients and Litter Decomposition in the Grassland Ecosystem.- 17. The Role of Slugs in an Agrostis-Festuca Grassland.- 18. Sheep Population Studies in Relation to the Snowdonian Environment.- 19. The Grazing Intensity and Productivity of Sheep in the Grassland Ecosystem.- 20. The Distribution and Transfer of Energy and Nutrients in the Agrostis-Festuca Grassland Ecosystem.- References.

Soil Organisms as Components of Ecosystems

Abstract: This book is the Proceedings of the 6th International Soil Zoology Colloquium held in Uppsala in June 1976. The major theme is the interactions of plant roots, microorganisms, and soil animals. Four subthemes were chosen for the plenary sessions. These were: (i) Community structure and niche separation; (ii) The role of soil organisms in nutrient cycling; (iii) Plant roots in the soil system; and (iv) Models of soil organisms and their environment. In addition tothe 51 papers (14, 16, 13, and 8) presented in the above sessions, there are summarized versions of 41 papers given in poster session. The individual papers range from excellent to poor, with about one-fourth in the poor category. About half the remainder are autecological in subject matter treatment and lack the perspective promised in the colloquium title. Most of the papers in the first plenary session are on niche exploitation and responses by members of the soil fauna rather than on their roles as ecosystem components. The papers on nutrient cycling are, with few exceptions, excellent contributions. Particularly commendable is the comprehensive discussion offered by D. E. Reichle. The bulk of the papers in the third session concern either the activities or the effects on plants of rhizophagic invertebrates. Good discussions are given by Vancura and associates on quantitative aspects of root exudation and by Sihanonth and Todd on transfer of nutrients by ectomycorrhizal fungi. Readers expecting to find any noteworthy array of simulation models on soil organisms will be disappointed. Most of the papers in this session might have been placed just as appropriately in some other session. The closing session address by J. E. Satchell is thought-provoking as well asentertaining. The reader, while being told that earthworms are the trombones of the grave, gains the impression that as a group, the soil zoologists are alive and well. Mechanistically the book is soft cover and generally excellently edited. There are about 200 illustrations, mostly line graphs and histograms, but also some light microscope and scanning electron micrographs. Unfortunately, some of the hand-drawn diagrams are so overcrowded with small-scale details as to be practically unreadable. This volume belongs primarily in the personal libraries of invertebrate zoologists. Its reading by systems ecologists and soil scientists will be, in part, time well spent.--FRANCIS E. CLARK, Federal Research, Western Region, U.S. Department of Agriculture, P.O. Box E, Fort Collins, CO 80522.

The phenology, growth and ecosystem dynamics of Erythronium americanum in the northern hardwood forest.

Abstract: In the northern hardwood forest, growth of vernal photosynthetic herbs is temporally restricted to the period between spring snowmelt and summer canopy development. This characteristic suggests that several unique adaptations exist which allow the species to complete their life cycles, and that temporal separation of production in the herbaceous layer may add to structural and functional complexity of the ecosystem. Erythronium americanum Ker. (Liliaceae) was examined in central New Hampshire with respect to its natural history, growth characteristics and influence on energy flow and mineral cycling in the deciduous forest ecosystem. Growth leading to the early spring development of photosynthetic tissue begins with fall root growth and continues through a long winter phase during which the shoot elongates from the perennating organ, through the soil and into the snowpack. Following snowmelt, the shoots begin rapid unfurling and maturation of the photosynthetic tissue. The length of the mature leaf phase is controlled by the timing of snowmelt and canopy development, and may be quite variable between successive years. During the short period of production, total biomass increased by 190% in 1972 and 338% in 1973; however, plant weight at the end of the winter period in 1973 had decreased to 28% of the spring 1972 maximum. In the annual energy cycle, biomass losses during the nonphotosynthetic period may amount to more than production during the preceding spring. In comparison with summer green herbs, Erythronium shoot tissue contained significantly higher concentrations of N but lower levels of K, Mg and Ca, suggesting that the spring adaptation may be oriented toward higher N levels of the soil during the spring period as well as higher light levels at the forest floor. Significant correlations of biomass of vernal photosynthetic herbs with summer green species imply that temporally separated species may utilize the same physical site and resources. This adds to the structural complexity and production of the herbaceous layer; however, the vernal photosynthetics account for only 0.5% of total aboveground primary production of the ecosystem. The temporal character of Erythronium's growth and its capacity for rapid biomass accumulation combine to make it a significant factor in nutrient dynamics in the deciduous forest. Uptake of N and K during spring flushing of nutrients from the ecosystem and later release through senescence of shoot tissue appear to reduce gross ecosystem losses of these elements.

Nitrogen Fixation by Actinomycete-Nodulated Angiosperms

Abstract: Nitrogen fixation by symbiotic associations between soil bacteria belonging to the actinomycetes and root systems of a diversified group of woody dicotyledonous plants is less generally well known than that by the legume-Rhizobium symbiosis. The fixation of dinitrogen by nodulated legumes is a major mechanism for entry of reduced nitrogen into agricultural lands and, to a much lesser extent, to wooded ecosystems. For forested areas, woodlands, wetlands, and fields, nodulated plants like the alders (Alnus), bog plants like sweet gale (Myrica gale), and roadside and disturbed area invaders such as sweet fern

Community and Population Level Responses to Fertilization in an Old‐Field Ecosystem

Abstract: The effects of nutrient enrichment by 2 applications of N—P—K pebble fertilizer (November and April) on the plant community of an 8—year old—field successional ecosystem were studied in 2 adjacent 1—acre [=.4047 hectares] experimental plots in Georgia. Net primary production, standing crop biomass, turnover and dominance increased, while all components of diversity decreased as a result of the treatment. These responses generally support Odum's (1969) model of ecosystem development, if the assumption is that eutrophication should involve a "set back" in development to earlier (younger) stages of autogenic succession. However, species composition was not set back since species characteristic of earlier successional stages (i.e., Ambrosia) exhibited reduced importance in the treated areas, while dominants more characteristic of the 8—year stage increased in importance. Results of this study suggest that fertilization has its major effect through competition—altered changes in the organization of realized ni...

Detritus in the Lake Ecosystem

Abstract: Present views of the roles of detritus are not consistent with the ecosystem concept, and result in an underestimation of the importance of carbon and energy pathways involving detritus. Nonpredatory losses from a plant-herbivore transfer, particularly as dissolved organic matter and egestion, may be greater than the amount of material and energy transmitted up the grazer food chain. Ecosystem efficiencies are significantly higher than Lindeman (food chain) efficiencies. Benthic anaerobic metabolism (CO2 production) is greater than benthic oxygen uptake estimates indicate, and the energy-rich intermediate products which undergo deferred respiration (O2 uptake) far from their origin may create redox gradients, drive chemosynthesis, and subsidize bacterial photosynthesis in the water column. Thus, aquatic detrital material, particulate and dissolved, and its metabolism create a dynamic structure in lake sediments and water somewhat analogous to the trophic-dynamic aspect of the biota. However, detrital-dyna...

A Study of the Rates of Decomposition of Organic Matter

Abstract: The previous chapters analyse the faunal and microbial populations in the bog ecosystem. The combined activities of these populations result in the decomposition of the plant remains and, under the influence of environmental factors, result in variation in the rate of decomposition in time and space.

Nitrogen budget of a shortgrass prairie ecosystem.

Abstract: A N budget is presented for a shortgrass prairie ecosystem. The grassland was ungrazed by domestic herbivores. The quantities of N in various plant, animal, microorganism, and soil components of the ecosystem are estimated for the date when aboveground living biomass was at its maximum for the growing season of 1973. Annual transfers of N between the various compartments were also estimated.

The Lake Washington Ecosystem: The Perspective from the Fish Community Production and Forage Base

Abstract: In Lake Washington, fish production through detritus-based food chains is substantially greater than fish production through the grazing food chain. The lack of significant grazing by fish on the z...

Primary production ecology in southern Africa

Abstract: ‘Perhaps the most fundamental dimension of an ecosystem is its productivity — the rate of creation of organic material, by photosynthesis primarily, per unit area and time’ (Whittaker 1970). Of importance are the structural parameter, biomass, and the functional parameter, production (Odum 1962), both essential in the process of ecosystem analysis (Reichle 1975). Economic requirements for increased food and structural material production have long drawn attention to the importance of understanding and optimizing primary production within different ecosystems.

Nitrogen Fixation in Arctic and Alpine Tundra

Abstract: The role of biological nitrogen fixation in tundra ecosystems was studied in order to determine the quantitative input of nitrogen from this source, the organisms involved, and the ecological interactions between these organisms and the tundra vegetative community. We were especially concerned with the environmental factors which influence nitrogen fixation rates. Very early in the study it became apparent that although the total amount of nitrogen entering the system through fixation was rather low, nevertheless this represented the major input, especially in low, mossy areas. Possibly the ecological significance is greater than would be assumed from the amount of nitrogen involved, since this nitrogen is in a mobile pool and subject to short-term cycling, whereas the bulk of the nitrogen in tundra soils is tied up in relatively unavailable forms.

Principal-Components and Factor Analysis for the Description of Microbial Populations

Abstract: The ecosystem ecologist and the population ecologist often set out to describe the structure and function of an ecosystem or of a population. The biotic structure is given by a description of the species present and their abundance, while the function of the biotic component of the ecosystem calls for a fairly detailed analysis of the role of individual populations (species or functional groups) in, for example, energy flow or nutrient cycling.

Foods and Habitats of Aquatic Snakes (Reptilia, Serpentes) in a Louisiana Swamp

Abstract: The foods and habitats of seven species of aquatic snakes were investigated in a Louisiana swamp, the Atchafalaya River Basin. Nerodia rhombifera was the most abundant species, and N. cyclopion, the second most common species, was an ecological associate. Stomachs of 796 aquatic snakes were examined. N. rhombifera and N. cyclopion fed mainly upon fish, and Agkistrodon piscivorus fed upon fish and other vertebrates. Catfish were frequently ingested by N. rhombifera, and A. piscivorus, but rarely by N. cyclopion. N. fasciata showed preferences for anurans and fish, and N. erythrogaster for anurans. Regina grahami and R. rigida fed upon crayfish. N. rhombifera and N. fasciata were observed utilizing crayfish burrows, and individuals of all seven aquatic species occasionally moved considerable distances overland. In the ecosystem under consideration, N. rhombifera and N. cyclopion are habitat generalists and food specialists; A. piscivorus is a habitat specialist and probably a food generalist.

Inputs and cycling of mineral nutrients in a coastal subtropical eucalypt forest

Abstract: (1) Nutrient budgets have been estimated for eleven elements in a Eucalyptus signatadominated forest 15 m tall, growing on infertile podzolized sands on North Stradbroke Island in subtropical Australia. (2) No single component of the ecosystem rainfall, salt spray, soil or litter mass is sufficient to provide all the net annual nutrient demands of the forest. Although recirculation of mineral nutrients is therefore essential to the maintenance of the forest, turnover of nutrients from the vegetative standing stock is slow relative to deciduous forests on more fertile soils. (3) Rainfall and salt spray provide significant inputs to the forest, especially of chloride, manganese, nitrogen and sodium. Substantial quantities of mineral nutrients from salt spray are subsequently transferred to the forest floor with throughfall (68% of rainfall volume) and stem-flow (677%), but these evergreen trees appear more resistant to leaching losses than deciduous trees observed in temperate regions. (4) The forest dominant exhibits advantageous patterns of nutrient flow relative to its major competitors, by assimilating a smaller amount of nutrients relative to its mass, and by channelling more salt-laden waters to its roots via stem-flow. (5) The decrease in forest stature on older dunes on North Stradbroke Island (500 000 years old or more) may be due in part to gradual loss of nutrients from the ecosystem. Supplies of exchangeable potassium and available phosphorus, for example, are very low relative to uptake demands in the younger pyric-climax forest studied.

The input of gaseous and particulate sulfur to a forest ecosystem

Abstract: Sulfate is the predominant anion in precipitation entering the Hubbard Brook Experimental Forest, a northern hardwood forest in north-central New Hampshire. Sulfur is also the dominant element in airborne particulate matter. Losses of sulfur from the ecosystem in stream water exceed inputs in precipitation plus that released from weathering. Using the ecosystem method, it is possible to estimate (by difference) that 6.1 kg/ha/yr of sulfur is obtained from dry deposition on the ecosystem. The deposition velocity for particulate sulfur is estimated to be about 0.1 cm/s and the deposition velocity for sulfur dioxide is 0.9 cm/s. Some biogeochemical relationships of sulfur for the Hubbard Brook Forest are presented. DOI: 10.1111/j.2153-3490.1978.tb00872.x

Nitrogen Fixation by Soil Algae of Temperate and Tropical Soils

Abstract: Blue-green algae are common components of the microbial flora of the soil in many parts of the world (7,8,18,30) In the tropics most attention has been paid to their role in rice paddy soils where, free-living (26,27) and in symbiotic association with the water-fern Azolla (3,19,21,36) they contribute substantial amounts of nitrogen to the ecosystem In this paper we present information on the occurrence, activity, and factors affecting soil algae from tropical savanna regions of Nigeria and from the Amazon region of Brazil The findings are compared with observations made on algae from temperate soils in Scotland These studies complement ones from tropical (eg 22,26,27,37) and temperate (eg 6,9,12,28) regions

Nutrient Cycling in a Eucalyptus obliqua (L'hérit.) Forest. II. A Study in a Small Catchment

Abstract: The geochemical balance of cations (input in rainwater-output in stream-water) in a mature E obliqua forest is shown to be dependent primarily on the amount of 'stream-water' leaving the catchment at the weir During the 3 complete years of the study, the annual balance of calcium was positive, the annual balance of magnesium was negative, and there was either a net gain or net loss of sodium and potassium depending on the amount of stream-flow The order of mobility is sodium > potassium > magnesium > calcium, in accord with physicochemical properties More calcium than sodium is returned annually from plant to soil by litter fall and leaching (biogeochemical cycling), yet the rate of loss of calcium in stream-water is less than one-twentieth that of sodium The ecosystem is described as 'tight' in respect to calcium (the annual geochemical balance is con- sistently small relative to the amount cycled biogeochemically) and 'loose' in respect to sodium (the annual geochemical balance is highly variable with a range equal to the annual biogeochemical cycle) The annual turnover in litter fall and leaching of calcium plus magnesium plus potassium represents 9% of the amount of these elements in the above-ground biomass The geochemical balance, however, is only +0 13 % of the amount in the biomass, and thus the biogeochemical cycling of these elements in the mature forest appears to be at equilibrium Introduction

Ecosystem Processes in Semiarid Grasslands. I Primary Production and Water Use of two Communities Possessing Different Photosynthetic Pathways

Abstract: Above- and below-ground productivity and estimated evapotranspiration rates of a C3 native grassland and a sown C4 buffel grassland community growing on sandy red earth soils at Charleville were studied over a 12-month period. Resistance to water vapour transfer from leaves of both species was measured in the field and glasshouse. Although buffel grass had the highest maximum above-ground growth rate in summer, the most striking difference between the two communities was the much greater standing root crop and root production of the C4 community. Above-ground growth rates were very low in winter, and the differences in rates between communities were small. Over the summer growing period the water use efficiency of the C3 community was about 60 % the value for the Cd community. Leaf resistance of the latter species was found to be greater under conditions of limiting and non-limiting water supply. The role of external factors influencing the distribution of these grasslands, as well as the agronomic implications of the study, are discussed.

Land floras: the major late phanerozoic atmospheric carbon dioxide/oxygen control.

Abstract: Since at least the late Mesozoic, the abundance of terrestrial vegetation has been the major factor in atmospheric carbon dioxideloxygen fluctuations. Of modern ecosystem types occupying more than 1 percent of the earth's surface, productivity/area ratios of terrestrial ecosystems (excepting tundra and alpine meadow, desert scrub, and rock, ice, and sand) exceed those of marine ecosystems and probably have done so for much of late Phanerozoic time. Reduction of terrestrial ecosystems during marine transgression would decrease the world primary productivity, thus increasing the atmospheric carbon dioxide concentration and decreasing the oxygen concentration. Regression would produce opposite effects.

Lake grevelingen: A case study of ecosystem changes in a closed estuary

Abstract: 1. Grevelingen estuary, formerly in open connection with the rivers Rhine and Meuse and with the North Sea, was closed by a dam in May 1971, excluding influences both from the rivers and from the sea (tides dropped out); brackish Lake Grevelingen originated. 2. A number of changes took place in the environment, on species level, on community level and on ecosystem level. 3. Changes on species level. The life cycles of certain species were blocked, because their food disappeared, the particle size spectrum of the food changed, or their migration routes were blocked. It was found that (1) species richness decreased; (2) shifts in numbers per species took place; (3) species with broad ecological tolerance remained; (4) brackish water species appeared. 4. Changes on community level. Structural aspects: (a) habitats disappeared; (b) pattern diversity decreased; (c) habitat-bound species disappeared. Functional aspects (trophic relations): (a) the energy subsidy from the North Sea was blocked; (b) the amount of organic matter decreased; (c) the production of some primary consumer groups decreased (d) tertiary and some secondary consumers disappeared; (e) the food chains shortened. 5. Changes on ecosystem level. The overall ecosystem simplified, both in structure and in functioning. The impact of the shallow macrophyte dominated subsystem increased.