As ecosystems are defined by the network of interactions among organisms, and between organisms and their environment,[4]they can be of any size but usually encompass specific, limited spaces[5](although some scientists say that the entire planet is an ecosystem).[6]

Nebulous- unclear

Anecosystemis acommunityof living organisms (plants, animals and microbes) in conjunction with thenonliving componentsof their environment (things like air, water and mineral soil), interacting as a system.[2]These biotic andabiotic componentsare regarded as linked together through nutrient cycles and energy flows.[3]As ecosystems are defined by the network of interactions among organisms, and between organisms and their environment,[4]they can be of any size but usually encompass specific, limited spaces[5](although some scientists say that the entire planet is an ecosystem).[6]

Energy, water, nitrogen and soil minerals are other essential abiotic components of an ecosystem. The energy that flows through ecosystems is obtained primarily from the sun. It generally enters the system throughphotosynthesis, a process that also capturescarbonfrom the atmosphere. By feeding on plants and on one another,animalsplay an important role in the movement of matter and energy through the system. They also influence the quantity of plant andmicrobialbiomasspresent. By breaking down dead organic matter,decomposersrelease carbon back to the atmosphere and facilitatenutrient cyclingby converting nutrients stored in dead biomass back to a form that can be readily used by plants and other microbes.[7]

Ecosystems are controlled both by external and internal factors. External factors such asclimate, theparent materialwhich forms the soil andtopography, control the overall structure of an ecosystem and the way things work within it, but are not themselves influenced by the ecosystem.[8]Other external factors include time and potentialbiota. Ecosystems are dynamic entitiesinvariably, they are subject to periodic disturbances and are in the process of recovering from some past disturbance.[9]Ecosystems in similar environments that are located in different parts of the world can have very different characteristics simply because they contain different species.[8]Theintroduction of non-native speciescan cause substantial shifts in ecosystem function. Internal factors not only control ecosystem processes but are also controlled by them and are often subject tofeedback loops.[8]While theresourceinputs are generally controlled by external processes like climate and parent material, the availability of these resources within the ecosystem is controlled by internal factors like decomposition, root competition or shading.[8]Other internal factors include disturbance, succession and the types of species present. Although humans exist and operate within ecosystems, their cumulative effects are large enough to influence external factors like climate.[8]

Biodiversityaffects ecosystem function, as do the processes ofdisturbanceandsuccession. Ecosystems provide a variety ofgoods and servicesupon which people depend; the principles ofecosystem managementsuggest that rather than managing individual species,natural resourcesshould be managed at the level of the ecosystem itself. Classifying ecosystems into ecologically homogeneous units is an important step towards effective ecosystem management, but there is no single, agreed-upon way to do this.

Contents

[hide]

1History and development

2Ecosystem processes

2.1Primary production

2.2Energy flow

2.3Decomposition

2.4Nutrient cycling

2.5Function and biodiversity

2.6Ecosystem goods and services

2.7Ecosystem management

3Ecosystem dynamics

3.1Ecosystem ecology

4Classification

4.1Types

5Anthropogenic threats

6See also

7Notes

8References

9Literature cited

10External links

History and development[edit]

The term "ecosystem" was first used in a publication by British ecologistArthur Tansley.[fn 1][10]Tansley devised the concept to draw attention to the importance of transfers of materials between organisms and their environment.[11]He later refined the term, describing it as "The whole system, ... including not only the organism-complex, but also the whole complex of physical factors forming what we call the environment".[12]Tansley regarded ecosystems not simply as natural units, but as mental isolates.[12]Tansley later[13]defined the spatial extent of ecosystems using the termecotope.

G. Evelyn Hutchinson, a pioneeringlimnologistwho was a contemporary of Tansley's, combinedCharles Elton's ideas abouttrophicecology with those of Russian geochemistVladimir Vernadskyto suggest that mineral nutrient availability in a lake limited algalproductionwhich would, in turn, limit the abundance of animals that feed on algae.Raymond Lindemantook these ideas one step further to suggest that the flow of energy through a lake was the primary driver of the ecosystem. Hutchinson's students, brothersHoward T. OdumandEugene P. Odum, further developed a "systems approach" to the study of ecosystems, allowing them to study the flow of energy and material through ecological systems.[11]

Ecosystem processes[edit]

Energyandcarbonenter ecosystems through photosynthesis, are incorporated into living tissue, transferred to other organisms that feed on the living and dead plant matter, and eventually released through respiration.[14]Most mineral nutrients, on the other hand, are recycled within ecosystems.[15]

Ecosystems are controlled both by external and internal factors. External factors, also called state factors, control the overall structure of an ecosystem and the way things work within it, but are not themselves influenced by the ecosystem. The most important of these isclimate.[8]Climate determines thebiomein which the ecosystem is embedded. Rainfall patterns and temperature seasonality determine the amount of water available to the ecosystem and the supply of energy available (by influencing photosynthesis).[8]Parent material, the underlying geological material that gives rise to soils, determines the nature of the soils present, and influences the supply of mineral nutrients.Topographyalso controls ecosystem processes by affecting things likemicroclimate, soil development and the movement of water through a system. This may be the difference between the ecosystem present inwetlandsituated in a small depression on the landscape, and one present on an adjacent steep hillside.[8]

Other external factors that play an important role in ecosystem functioning include time and potentialbiota. Ecosystems are dynamic entitiesinvariably, they are subject to periodic disturbances and are in the process of recovering from some past disturbance.[9]Time plays a role in the development of soil from bare rock and therecovery of a community from disturbance.[8]Similarly, the set of organisms that can potentially be present in an area can also have a major impact on ecosystems. Ecosystems in similar environments that are located in different parts of the world can end up doing things very differently simply because they have different pools of species present.[8]Theintroduction of non-native speciescan cause substantial shifts in ecosystem function.

Unlike external factors, internal factors in ecosystems not only control ecosystem processes, but are also controlled by them. Consequently, they are often subject tofeedback loops.[8]While theresourceinputs are generally controlled by external processes like climate and parent material, the availability of these resources within the ecosystem is controlled by internal factors like decomposition, root competition or shading.[8]Other factors like disturbance, succession or the types of species present are also internal factors. Human activities are important in almost all ecosystems. Although humans exist and operate within ecosystems, their cumulative effects are large enough to influence external factors like climate.[8]

Primary production[edit]

Global oceanic and terrestrialphototrophabundance, from September 1997 to August 2000. As an estimate ofautotrophbiomass, it is only a rough indicator of primary production potential, and not an actual estimate of it. Provided by theSeaWiFSProject,NASA/Goddard Space Flight CenterandORBIMAGE.

Main article:Primary production

Primary production is the production oforganic matterfrom inorganic carbon sources. Overwhelmingly, this occurs through photosynthesis. The energy incorporated through this process supports life on earth, while the carbon makes up much of the organic matter in living and dead biomass,soil carbonandfossil fuels. It also drives thecarbon cycle, which influences globalclimatevia thegreenhouse effect.

Through the process of photosynthesis, plants capture energy from light and use it to combinecarbon dioxideand water to producecarbohydratesandoxygen. The photosynthesis carried out by all the plants in an ecosystem is called the gross primary production (GPP).[16]About 4860% of the GPP is consumed in plant respiration. The remainder, that portion of GPP that is not used up by respiration, is known as the net primary production (NPP).[14]Total photosynthesis is limited by a range of environmental factors. These include the amount of light available, the amount ofleafarea a plant has to capture light (shading by other plants is a major limitation of photosynthesis), rate at which carbon dioxide can be supplied to thechloroplaststo support photosynthesis, the availability of water, and the availability of suitable temperatures for carrying outphotosynthesis.[16]

Energy flow[edit]

Left:Energy flow diagram of a frog. The frog represents a node in an extended food web. The energy ingested is utilized for metabolic processes and transformed into biomass. The energy flow continues on its path if the frog is ingested by predators, parasites, or as a decayingcarcassin soil. This energy flow diagram illustrates how energy is lost as it fuels the metabolic process that transforms the energy and nutrients into biomass.Right:An expanded three link energy food chain (1. plants, 2. herbivores, 3. carnivores) illustrating the relationship between food flow diagrams and energy transformity. The transformity of energy becomes degraded, dispersed, and diminished from higher quality to lesser quantity as the energy within a food chain flows from one trophic species into another. Abbreviations: I=input, A=assimilation, R=respiration, NU=not utilized, P=production, B=biomass.[17]

Main article:Energy flow (ecology)

See also:Food webandTrophic level

The carbon and energy incorporated into plant tissues (net primary production) is either consumed by animals while the plant is alive, or it remains uneaten when the plant tissue dies and becomesdetritus. Interrestrial ecosystems, roughly 90% of the NPP ends up being broken down bydecomposers. The remainder is either consumed by animals while still alive and enters the plant-based trophic system, or it is consumed after it has died, and enters the detritus-based trophic system. Inaquatic systems, the proportion of plant biomass that gets consumed byherbivoresis much higher.[18]In trophic systems photosynthetic organisms are the primary producers. The organisms that consume their tissues are called primary consumers orsecondary producersherbivores. Organisms which feed onmicrobes(bacteriaandfungi) are termedmicrobivores. Animals that feed on primary consumerscarnivoresare secondary consumers. Each of these constitutes atrophic level.[18]The sequence of consumptionfrom plant to herbivore, to carnivoreforms afood chain. Real systems are much more complex than thisorganisms will generally feed on more than one form of food, and may feed at more than one trophic level. Carnivores may capture some prey which are part of a plant-based trophic system and others that are part of a detritus-based trophic system (a bird that feeds both on herbivorous grasshoppers and earthworms, which consume detritus). Real systems, with all these complexities, formfood websrather than food chains.[18]

Decomposition[edit]

See also:Decomposition

The carbon and nutrients indead organic matterare broken down by a group of processes known as decomposition. This releases nutrients that can then be re-used for plant and microbial production, and returns carbon dioxide to the atmosphere (or water) where it can be used for photosynthesis. In the absence of decomposition, dead organic matter would accumulate in an ecosystem and nutrients and atmospheric carbon dioxide would be depleted.[19]Approximately 90% of terrestrial NPP goes directly from plant to decomposer.[18]

Decomposition processes can be separated into three categoriesleaching, fragmentation and chemical alteration of dead material. As water moves through dead organic matter, it dissolves and carries with it the water-soluble components. These are then taken up by organisms in the soil, react with mineral soil, or are transported beyond the confines of the ecosystem (and are considered "lost" to it).[19]Newly shed leaves and newly dead animals have high concentrations of water-soluble components, and includesugars,amino acidsand mineral nutrients. Leaching is more important in wet environments, and much less important in dry ones.[19]

Fragmentation processes break organic material into smaller pieces, exposing new surfaces for colonization by microbes. Freshly shedleaf littermay be inaccessible due to an outer layer ofcuticleorbark, andcell contentsare protected by acell wall. Newly dead animals may be covered by anexoskeleton. Fragmentation processes, which break through these protective layers, accelerate the rate of microbial decomposition.[19]Animals fragment detritus as they hunt for food, as does passage through the gut.Freeze-thaw cyclesand cycles of wetting and drying also fragment dead material.[19]

The chemical alteration of dead organic matter is primarily achieved through bacterial and fungal action. Fungalhyphaeproduce enzymes which can break through the tough outer structures surrounding dead plant material. They also produce enzymes which break downlignin, which allows to them access to both cell contents and to the nitrogen in the lignin. Fungi can transfer carbon and nitrogen through their hyphal networks and thus, unlike bacteria, are not dependent solely on locally available resources.[19]

Decomposition rates vary among ecosystems. The rate of decomposition is governed by three sets of factorsthe physical environment (temperature, moisture and soil properties), the quantity and quality of the dead material available to decomposers, and the nature of the microbial community itself.[20]Temperature controls the rate of microbial respiration; the higher the temperature, the faster microbial decomposition occurs. It also affects soil moisture, which slows microbial growth and reduces leaching. Freeze-thaw cycles also affect decompositionfreezing temperatures kill soil microorganisms, which allows leaching to play a more important role in moving nutrients around. This can be especially important as the soil thaws in the Spring, creating a pulse of nutrients which become available.[20]

Decomposition rates are low under very wet or very dry conditions. Decomposition rates are highest in wet, moist conditions with adequate levels of oxygen. Wet soils tend to become deficient in oxygen (this is especially true inwetlands), which slows microbial growth. In dry soils, decomposition slows as well, but bacteria continue to grow (albeit at a slower rate) even after soils become too dry to support plant growth. When the rains return and soils become wet, theosmotic gradientbetween the bacterial cells and the soil water causes the cells to gain water quickly. Under these conditions, many bacterial cells burst, releasing a pulse of nutrients.[20]Decomposition rates also tend to be slower in acidic soils.[20]Soils which are rich inclay mineralstend to have lower decomposition rates, and thus, higher levels of organic matter.[20]The smaller particles of clay result in a larger surface area that can hold water. The higher the water content of a soil, the lower the oxygen content[21]and consequently, the lower the rate of decomposition. Clay minerals also bind particles of organic material to their surface, making them less accessibly to microbes.[20]Soil disturbance liketillingincrease decomposition by increasing the amount of oxygen in the soil and by exposing new organic matter to soil microbes.[20]

The quality and quantity of the material available to decomposers is another major factor that influences the rate of decomposition. Substances like sugars and amino acids decompose readily and are considered "labile".Celluloseandhemicellulose, which are broken down more slowly, are "moderately labile". Compounds which are more resistant to decay, like lignin orcutin, are considered "recalcitrant".[20]Litter with a higher proportion of labile compounds decomposes much more rapidly than does litter with a higher proportion of recalcitrant material. Consequently, dead animals decompose more rapidly than dead leaves, which themselves decompose more rapidly than fallen branches.[20]As organic material in the soil ages, its quality decreases. The more labile compounds decompose quickly, leaving an increasing proportion of recalcitrant material. Microbial cell walls also contain recalcitrant materials likechitin, and these also accumulate as the microbes die, further reducing the quality of oldersoil organic matter.[20]

Nutrient cycling[edit]

See also:Nutrient cycle,Biogeochemical cycleandNitrogen cycle

Biological nitrogen cycling

Ecosystems continually exchange energy and carbon with the widerenvironment; mineral nutrients, on the other hand, are mostly cycled back and forth between plants, animals, microbes and the soil. Most nitrogen enters ecosystems through biologicalnitrogen fixation, is deposited through precipitation, dust, gases or is applied asfertilizer.[15]Since most terrestrial ecosystems are nitrogen-limited, nitrogen cycling is an important control on ecosystem production.[15]

Until modern times, nitrogen fixation was the major source of nitrogen for ecosystems. Nitrogen fixing bacteria either livesymbioticallywith plants, or live freely in the soil. The energetic cost is high for plants which support nitrogen-fixing symbiontsas much as 25% of GPP when measured in controlled conditions. Many members of thelegumeplant family support nitrogen-fixing symbionts. Somecyanobacteriaare also capable of nitrogen fixation. These arephototrophs, which carry out photosynthesis. Like other nitrogen-fixing bacteria, they can either be free-living or have symbiotic relationships with plants.[15]Other sources of nitrogen includeacid depositionproduced through the combustion offossil fuels,ammoniagas which evaporates from agricultural fields which have had fertilizers applied to them, and dust.[15]Anthropogenic nitrogen inputs account for about 80% of all nitrogen fluxes in ecosystems.[15]

When plant tissues are shed or are eaten, the nitrogen in those tissues becomes available to animals and microbes. Microbial decomposition releases nitrogen compounds from dead organic matter in the soil, where plants, fungi and bacteria compete for it. Some soil bacteria use organic nitrogen-containing compounds as a source of carbon, and releaseammoniumions into the soil. This process is known asnitrogen mineralization. Others convert ammonium tonitriteandnitrateions, a process known asnitrification.Nitric oxideandnitrous oxideare also produced during nitrification.[15]Under nitrogen-rich and oxygen-poor conditions, nitrates and nitrites are converted tonitrogen gas, a process known asdenitrification.[15]

Other important nutrients includephosphorus,sulfur,calcium,potassium,magnesiumandmanganese.[22]Phosphorus enters ecosystems throughweathering. As ecosystems age this supply diminishes, making phosphorus-limitation more common in older landscapes (especially in the tropics).[22]Calcium and sulfur are also produced by weathering, but acid deposition is an important source of sulfur in many ecosystems. Although magnesium and manganese are produced by weathering, exchanges between soil organic matter and living cells account for a significant portion of ecosystem fluxes. Potassium is primarily cycled between living cells and soil organic matter.[22]

Function and biodiversity[edit]

See also:BiodiversityandEcosystem engineer

Loch LomondinScotlandforms a relatively isolated ecosystem. The fish community of this lake has remained stable over a long period until a number ofintroductionsin the 1970s restructured itsfood web.[23]

Spiny forest at Ifaty,Madagascar, featuring variousAdansonia(baobab) species,Alluaudia procera(Madagascar ocotillo) and other vegetation.

Ecosystem processes are broad generalizations that actually take place through the actions of individual organisms. The nature of the organismsthe species,functional groupsand trophic levels to which they belongdictates the sorts of actions these individuals are capable of carrying out, and the relative efficiency with which they do so. Thus, ecosystem processes are driven by the number of species in an ecosystem, the exact nature of each individual species, and the relative abundance organisms within these species.[24]Biodiversity plays an important role in ecosystem functioning.[25]

Ecological theory suggests that in order to coexist, species must have some level oflimiting similaritythey must be different from one another in some fundamental way, otherwise one species wouldcompetitively excludethe other.[26]Despite this, the cumulative effect of additional species in an ecosystem is not linearadditional species may enhance nitrogen retention, for example, but beyond some level of species richness, additional species may have little additive effect.[24]The addition (or loss) of species which are ecologically similar to those already present in an ecosystem tends to only have a small effect on ecosystem function. Ecologically distinct species, on the other hand, have a much larger effect. Similarly, dominant species have a large impact on ecosystem function, while rare species tend to have a small effect.Keystone speciestend to have an effect on ecosystem function that is disproportionate to their abundance in an ecosystem.[24]

Ecosystem goods and services[edit]

Main articles:Ecosystem servicesandEcological goods and services

See also:Ecosystem valuationandEcological yield

Ecosystems provide a variety of goods and services upon which people depend.[27]Ecosystem goods include the "tangible, material products"[28]of ecosystem processesfood, construction material, medicinal plantsin addition to less tangible items like tourism and recreation, and genes from wild plants and animals that can be used to improve domestic species.[27]Ecosystem services, on the other hand, are generally "improvements in the condition or location of things of value".[28]These include things like the maintenance of hydrological cycles, cleaning air and water, the maintenance of oxygen in the atmosphere, crop pollination and even things like beauty, inspiration and opportunities for research.[27]While ecosystem goods have traditionally been recognized as being the basis for things of economic value, ecosystem services tend to be taken for granted.[28]WhileGretchen Daily's original definition distinguished between ecosystem goods and ecosystem services,Robert Costanzaand colleagues' later work and that of theMillennium Ecosystem Assessmentlumped all of these together as ecosystem services.[28]

Ecosystem management[edit]

Main article:Ecosystem management

See also:Ecological economics,SustainabilityandSustainable development

Whennatural resource managementis applied to whole ecosystems, rather than single species, it is termed ecosystem management.[29]A variety of definitions exist:F. Stuart Chapinand coauthors define it as "the application of ecological science to resource management to promote long-term sustainability of ecosystems and the delivery of essential ecosystem goods and services",[30]while Norman Christensen and coauthors defined it as "management driven by explicit goals, executed by policies, protocols, and practices, and made adaptable by monitoring and research based on our best understanding of the ecological interactions and processes necessary to sustain ecosystem structure and function"[27]and Peter Brussard and colleagues defined it as "managing areas at various scales in such a way that ecosystem services and biological resources are preserved while appropriate human use and options for livelihood are sustained".[31]

Although definitions of ecosystem management abound, there is a common set of principles which underlie these definitions.[30]A fundamental principle is the long-term sustainability of the production of goods and services by the ecosystem;[30]"intergenerational sustainability [is] a precondition for management, not an afterthought".[27]It also requires clear goals with respect to future trajectories and behaviors of the system being managed. Other important requirements include a sound ecological understanding of the system, including connectedness, ecological dynamics and the context in which the system is embedded. Other important principles include an understanding of the role of humans as components of the ecosystems and the use ofadaptive management.[27]While ecosystem management can be used as part of a plan forwildernessconservation, it can also be used in intensively managed ecosystems[27](see, for example,agroecosystemandclose to nature forestry).

Ecosystem dynamics[edit]

Temperate rainforeston theOlympic PeninsulainWashington state.

TheHigh Peaks Wilderness Areain the 6,000,000-acre (2,400,000ha)Adirondack Parkis an example of a diverse ecosystem.

Ecosystems are dynamic entitiesinvariably, they are subject to periodic disturbances and are in the process of recovering from some past disturbance.[9]When an ecosystem is subject to some sort ofperturbation, it responds by moving away from its initial state. The tendency of a system to remain close to its equilibrium state, despite that disturbance, is termed itsresistance. On the other hand, the speed with which it returns to its initial state after disturbance is called itsresilience.[9]

From one year to another, ecosystems experience variation in their biotic and abiotic environments. A drought, an especially cold winter and a pest outbreak all constitute short-term variability in environmental conditions. Animal populations vary from year to year, building up during resource-rich periods and crashing as they overshoot their food supply. These changes play out in changes in NPP, decomposition rates, and other ecosystem processes.[9]Longer-term changes also shape ecosystem processesthe forests of eastern North America still show legacies of cultivation which ceased 200 years ago, while methane production in eastern Siberian lakes is controlled by organic matter which accumulated during thePleistocene.[9]

Disturbancealso plays an important role in ecological processes.F. Stuart Chapinand coauthors define disturbance as "a relatively discrete event in time and space that alters the structure of populations, communities and ecosystems and causes changes in resources availability or the physical environment".[32]This can range from tree falls and insect outbreaks to hurricanes and wildfires to volcanic eruptions and can cause large changes in plant, animal and microbe populations, as well soil organic matter content.[9]Disturbance is followed bysuccession, a "directional change in ecosystem structure and functioning resulting from biotically driven changes in resources supply."[32]

The frequency and severity of disturbance determines the way it impacts ecosystem function. Major disturbance like a volcanic eruption or glacial advance and retreat leave behind soils that lack plants, animals or organic matter. Ecosystems that experience disturbances that undergoprimary succession. Less severe disturbance like forest fires, hurricanes or cultivation result insecondary succession.[9]More severe disturbance and more frequent disturbance result in longer recovery times. Ecosystems recover more quickly from less severe disturbance events.[9]

The early stages of primary succession are dominated by species with small propagules (seed and spores) which can be dispersed long distances. The early colonizersoftenalgae, cyanobacteria andlichensstabilize the substrate. Nitrogen supplies are limited in new soils, and nitrogen-fixing species tend to play an important role early in primary succession. Unlike in primary succession, the species that dominate secondary succession, are usually present from the start of the process, often in thesoil seed bank. In some systems the successional pathways are fairly consistent, and thus, are easy to predict. In others, there are many possible pathwaysfor example, the introduced nitrogen-fixing legume,Myrica faya, alter successional trajectories in Hawaiian forests.[9]

Thetheoretical ecologistRobert Ulanowiczhas usedinformation theorytools to describe the structure of ecosystems, emphasizing mutual information (correlations) in studied systems. Drawing on this methodology and prior observations of complex ecosystems, Ulanowicz depicts approaches to determining the stress levels on ecosystems and predicting system reactions to defined types of alteration in their settings (such as increased or reduced energy flow, andeutrophication.[33]

Ecosystem ecology[edit]

Main article:Ecosystem ecology

See also:Ecosystem model

Ahydrothermal ventis an ecosystem on the ocean floor. (The scale bar is 1 m.)

Ecosystem ecology studies "the flow of energy and materials through organisms and the physical environment". It seeks to understand the processes which govern the stocks of material and energy in ecosystems, and the flow of matter and energy through them. The study of ecosystems can cover 10orders of magnitude, from the surface layers of rocks to the surface of the planet.[34]

There is no single definition of what constitutes an ecosystem.[35]German ecologistErnst-Detlef Schulzeand coauthors defined an ecosystem as an area which is "uniform regarding the biological turnover, and contains all the fluxes above and below the ground area under consideration." They explicitly rejectGene Likens' use of entire river catchments as "too wide a demarcation" to be a single ecosystem, given the level of heterogeneity within such an area.[36]Other authors have suggested that an ecosystem can encompass a much larger area, even the whole planet.[6]Schulze and coauthors also rejected the idea that a single rotting log could be studied as an ecosystem because the size of the flows between the log and its surroundings are too large, relative to the proportion cycles within the log.[36]Philosopher of scienceMark Sagoffconsiders the failure to define "the kind of object it studies" to be an obstacle to the development of theory in ecosystem ecology.[35]

Ecosystems can be studied through a variety of approachestheoretical studies, studies monitoring specific ecosystems over long periods of time, those that look at differences between ecosystems to elucidate how they work and direct manipulative experimentation.[37]Studies can be carried out at a variety of scales, frommicrocosmsandmesocosmswhich serve as simplified representations of ecosystems, through whole-ecosystem studies.[38]American ecologistStephen R. Carpenterhas argued that microcosm experiments can be "irrelevant and diversionary" if they are not carried out in conjunction with field studies carried out at the ecosystem scale, because microcosm experiments often fail to accurately predict ecosystem-level dynamics.[39]

TheHubbard Brook Ecosystem Study, established in theWhite Mountains, New Hampshirein 1963, was the first successful attempt to study an entire watershed as an ecosystem. The study used stream chemistry as a means of monitoring ecosystem properties, and developed a detailedbiogeochemical modelof the ecosystem.[40]Long-term researchat the site led to the discovery ofacid rainin North America in 1972, and was able to document the consequent depletion of soilcations(especially calcium) over the next several decades.[41]

Classification[edit]

See also:Ecosystem diversity,Ecoregion,Ecological land classificationandEcotope

FloraofBaja California Desert,Cataviaregion,Mexico.

Classifying ecosystems into ecologically homogeneous units is an important step towards effective ecosystem management.[42]A variety of systems exist, based on vegetation cover, remote sensing, andbioclimatic classificationsystems.[42]American geographerRobert Baileydefines a hierarchy of ecosystem units ranging from microecosystems (individual homogeneous sites, on the order of 10 square kilometres (4sqmi) in area), through mesoecosystems (landscape mosaics, on the order of 1,000 square kilometres (400sqmi)) to macroecosystems (ecoregions, on the order of 100,000 square kilometres (40,000sqmi)).[43]

Bailey outlined five different methods for identifying ecosystems:gestalt("a whole that is not derived through considerable of its parts"), in which regions are recognized and boundaries drawn intuitively; a map overlay system where different layers likegeology,landformsand soil types are overlain to identify ecosystems;multivariate clusteringof site attributes;digital image processingofremotely senseddata grouping areas based on their appearance or otherspectralproperties; or by a "controlling factors method" where a subset of factors (like soils, climate, vegetationphysiognomyor thedistributionof plant or animal species) are selected from a large array of possible ones are used to delineate ecosystems.[44]In contrast with Bailey's methodology, Puerto Rico ecologistAriel Lugoand coauthors identified ten characteristics of an effective classification system: that it be based ongeoreferenced, quantitative data; that it should minimize subjectivity and explicitly identify criteria and assumptions; that it should be structured around the factors that drive ecosystem processes; that it should reflect the hierarchical nature of ecosystems; that it should be flexible enough to conform to the various scales at which ecosystem management operates; that it should be tied to reliable measures of climate so that it can "anticipat[e] global climate change; that it be applicable worldwide; that it should be validated against independent data; that it take into account the sometimes complex relationship between climate, vegetation and ecosystem functioning; and that it should be able to adapt and improve as new data become available".[42]

Types[edit]

Aquatic ecosystem

Marine ecosystem

Large marine ecosystem

Freshwater ecosystem

Lake ecosystem

River ecosystem

Wetland

Terrestrial ecosystem

Forest

Littoral zone

Riparian zone

Subsurface lithoautotrophic microbial ecosystem

Urban ecosystem

Desert

Afreshwaterecosystem inGran Canaria, anislandof theCanary Islands.

Anthropogenic threats[edit]

See also:Planetary boundaries

As human populations grow, so do the resource demands imposed on ecosystems and the impacts of the humanecological footprint. Natural resources are not invulnerable and infinitely available. The environmental impacts ofanthropogenicactions, which are processes or materials derived from human activities, are becoming more apparentair and water quality are increasingly compromised, oceans are beingoverfished, pests and diseases are extending beyond their historical boundaries, anddeforestationis exacerbating flooding downstream. It has been reported that approximately 4050% of Earth's ice-free land surface has been heavily transformed or degraded by anthropogenic activities, 66% of marinefisheriesare eitheroverexploitedor at their limit,atmospheric CO2has increased more than 30% since the advent ofindustrialization, and nearly 25% of Earth's bird species have goneextinctin the last two thousand years.[45]Society is increasingly becoming aware thatecosystem servicesare not only limited, but also that they are threatened by human activities. The need to better consider long-termecosystem healthand its role in enabling human habitation and economic activity is urgent. To help inform decision-makers, many ecosystem services are being assigned economic values, often based on the cost of replacement with anthropogenic alternatives. The ongoing challenge of prescribing economic value to nature, for example throughbiodiversity banking, is prompting transdisciplinary shifts in how we recognize and manage the environment,social responsibility, business opportunities, and our future as a species.

Introduction

The following section describes some of the basic ecological concepts that underlie the ACE Basin ecosystem. Descriptions include an introduction to ecology and ecosystems, habitats,successionandbiodiversity, populations and communities, energy flow through ecosystems, and ecosystem services. Many of these concepts are applicable to the habitats, communities, and ecosystems that are described in the Biological Resources Section and other sections of this product.

What is Ecology?Ecology is the study of living organisms and their interactions with the physical and biological environment. While this involves an incredibly complex network of species, habitats, climates, physical environments, and human uses and concerns, the field of ecology has continued to advance the explanation of biological distributions, chemical cycles, and the interlinked nature of ecosystems. Some of these biological distributions and ecosystem processes (e.g. fish anddecapodcommunities, carbon and nitrogen cycling) are described in other sections of this characterization.

What is an Ecosystem?The ACE Basin contains a diversity of habitats that range fromsubtidalareas and vast wetlands to uplands. These habitats are populated by many different plant and animal species that interact with the physical environment to create the ACE Basin ecosystem. Ecosystems are defined asa set of organisms (community) living in an area, their physical environment, and the interactions between them (Daily 1997). For example, the ecology of Edisto Beach consists of organisms such as fish, insects, shellfish, birds, raccoons, and humans that make up the community; natural features such as the surf zone, front beach, dunes, forested areas and the createdinfrastructureof roads, buildings, and utilities that constitute the physical environment; and the interactions between the community and physical components.

Although it has not always been clearly recognized, we are completely dependent on the ecosystems in which we live. The myriad processes that integrate energy and nutrients flowing through the ACE Basin ecosystem provide its human inhabitants a variety of services. Besides providing food and shelter, the ecosystem provides waste treatment (by way of carbon dioxide consumption; oxygen production; and breakdown of sewage), a water filtration system (by the soil), recreational opportunities, and a basis for economic development. Remove any one of these services and the character and function of the other components can be compromised. See the discussion of ecosystem services below.

Naturalgeomorphic, as well as episodic, events have shaped the overall diversity of habitats and the services they provide. Over the last 10,000 years as early human societies created shellmiddensand set fires intentionally to capture game, and especially over the last 200 years with the advent of extensive forestry and agricultural practices, ecosystems have been significantly altered byanthropogenicfactors. These factors will likely continue to pressure ecosystems in the future. (See related section:History.)

As habitats are modified, ecological processes in these habitats also change and some of these changes may be significant. For example,estuarinemarshes are effective traps for many pollutants. When pollutants are introduced at low levels, they may be bound to sediments or degraded through natural processes, and they are less likely to be transferred up the food chain. If the ability of sediments to trap such pollutants is exceeded, however as has happened in some places in the Charleston Harbor Estuary (DHEC 1998), then pollutants may move up the food chain. Some of the changes may not be immediately obvious, such as a reduction in populations ofbenthicinfauna(small worms, crustaceans, and bivalves). Other impacts, such as the loss of oyster beds resulting in the reduced availability of oysters for recreational or commercial harvest, are much more obvious. Part of the solution to these problems lies in appropriate management decisions made at the federal, state, and local governmental levels, as well as by individual property owners and residents of the ACE Basin. (See related section:Management.)

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Habitat

Habitat Fragmentation

Ecotonal Habitat

A habitat is defined in relation to a plant or animal species and is the location where the species lives. It is a combination of the physical and biological components of the location and ranges from very large and stable (the earth or the open ocean) to very small and ephemeral (a pond in the dunes). A habitat may be a stand of loblolly pine trees with heart-rot where red-cockaded woodpeckers are found, theestuarinepluff mud where mud snails andpolychaeteworms thrive, or the town of Edisto Beach where humans reside. Usually, the more diverse the habitat types within a region, the greater will be the variety of species being supported. Coastal areas, such as the ACE Basin, located between the open ocean and upland areas, have a high diversity of habitats and microhabitats, supporting diverse and abundant communities of plants and animals. However, one of the greatest threats to habitat diversity in the ACE Basin is the conversion of existing habitats to structurally and biologically simpler habitats such as agricultural fields, pine plantations, and urban or residential areas. In addition to the direct loss of existing habitat, the resulting fragmentation of the remaining forested and wetland areas results in decreased species diversity (Odum 1997; Meffe and Carroll 1994).

Habitat FragmentationHabitats are always patchy and fragmented, to some extent, by natural disturbances and subsequentsuccession(see text below). While some of these processes can have global impacts, such as climate change and sea level rise, most disturbances occur on a more local scale. Local examples may include forest fires, hurricanes, and disease. Through successional processes, these habitats revert back to pre-impact states over time periods ranging from years to decades. Low-level patches of disturbance can increase the variety of habitats and therefore provide additional habitat for opportunistic species.

In contrast, due toanthropogenicinfluences much of the change has become much more long-lasting. Forests have been converted to agricultural fields and suburban and urban land, and seldom have the opportunity to revert back to a natural state. Depending on the land use, anthropogenically altered habitats tend to have a simpler structure with lower habitat diversity and increased edge habitats than do natural systems. As a result, biotic communities shift to favor those species that can utilize open, edge, agricultural, or suburban habitats. Species that require interior forest habitats have a harder time finding appropriate food and other required resources. Thus, there has been an overall reduction in populations dependent on these habitats (Meffe and Carroll 1994).

Ecotonal HabitatsAnecotoneis an area of transition between two different environments or habitats. Some ecotones are extreme, such as the shift from anestuarineorriverineenvironment to a forested habitat . In other places, the transition may take place more gradually, shifting from open rivers to forested wetlands and upland areas. One of the most obvious characteristics of an ecotone is the shift in vegetation that occurs between adjacent habitats. These changes reflect similar gradients in less obvious properties such as salinity, moisture, flooding regime, altitude, and other physical and chemical properties. Ecotonal or edge habitats often have a higher diversity of plants and animals relative to the more homogenous habitats on either side. In addition to edge-selected species, species native to each adjacent habitat may occasionally be found in these transition habitats.

One result of fragmented habitats arising from development in the ACE Basin is the change of the character ofecotonalhabitats. Ecotones where the vegetative communities previously shifted slowly from wetland to upland forest have been changed to sharper boundaries between wetland areas and what are now agricultural fields or suburban developments. Many game species utilize these edge habitats and a common practice of wildlife managers is to create edge-habitat. However, many non-game species require less abrupt transition areas and have declined as a result of the loss of these gradual transition zones (Meffe and Carroll 1994).

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Succession

Succession is a process that encompasses the dynamic biological and physical changes that lead to the development of complex, interlinked, biological communities. For example, habitats that are disturbed by fire or storm go through a series of community changes as the habitat recovers from the disturbance. Succession has been viewed as a step-wise process, whereby early communities typically are dominated by a few opportunistic species. The transfer of energy fromprimary producers(plants) to herbivores to predators (each is considered atrophiclevel, see discussion of energy flow through ecosystems below) tends to be less efficient during these early stages. The number oftrophic levelsalso tends to be lower. Early colonizers may change the environment, facilitating later communities of other species to develop and eventually become dominant species. The community of organisms at the final stage ofsuccessionis called the climax community. These communities are generally characterized by a wider range of species, a higher number of trophic levels, and more efficient transfer of energy between trophic levels. In some cases, a sequential process that changes the community of plants and animals occurs in which there is initial colonization by fast growing, opportunistic species followed by species that may grow more slowly but which compete better for limited resources (light, moisture, nutrients). The final climax stage reached is dependent on the pool of species available to colonize the area, and the type, frequency, and intensity of initial disturbance (Christensen 1988). Community succession, therefore, is dependent on both predictable and stochastic events.

A successional series begins when some type of disturbance sets back the clock. Landslides, hurricanes, avalanches, catastrophic forest fires, volcanic eruptions, and meteorite impacts may set the clock back to zero by completely destroying the existing communities. These types of events are relatively rare and there are usually some species (e.g. fire-resistant seeds) adapted to surviving these severe types of disturbances. Less severe disturbances from localized storms, hurricanes, or burned forests are more common and generally result in only partial damage to the community.

In coastal forests of South Carolina, including the ACE Basin, this progression commonly starts with communities dominated by grasses and other fast growing opportunistic weedy species that colonize the area within the first few weeks or months after a disturbance. Over the next year or so, the community is slowly taken over by woody shrubs and young pine trees that grow more slowly than the opportunistic species. Over the next 20-30 years, as the pines begin to grow large enough to shade the ground beneath, shade-tolerant species may become established. Shade-intolerant plants that colonized the open habitat, including young pine trees, can no longer establish themselves under a closed canopy. Shade-tolerant species such as hardwood species (e.g. beech and oak) become established, and the community develops into a Southern mixed hardwood community. Between 50 and 100 years after the disturbance, pine trees begin to slowly die, and the community gradually shifts towards a hardwood dominated community, the common climax community of coastal South Carolina upland areas. (See related section:Plants.)

Although fires and storms still may cause significant disturbance in ACE Basin communities, humans impacts through agriculture and forestry practices and urban development have far greater impact on succession in the ACE Basin. One of theseanthropogenicinfluences is the regulation of fire which may result in changes in communities that are dependent on seasonal fires. Management plans usually prescribe burns during the winter without regard to the natural requirements of the species, because this is a period when areas are wetter and fires are less likely to get out of control. This, in part, explains the reduced dominance of longleaf pine forests that require spring and summer fires in the early part of the growing season. Another impact is the clearing of fields (the initial disturbance) and their maintenance as agricultural land (repeated disturbances) preventing the successional sequence that would return them to a forested landscape if left undisturbed. While some areas have been allowed to develop back into forests, more frequently land has been shifted from forest to agriculture and then on to suburban or urban uses. There are extreme cases, fortunately outside the ACE Basin, where habitats have been so severely impacted through salinization, erosion, or pollution that the areas would take thousands of years to recover and may never revert to the habitat that was there originally (Odum 1997). There is a field of study called restoration ecology that deals with restoration and reclamation of severely degraded habitats.

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Biodiversity

One of the more important characteristics of a habitat is itsbiodiversity. Individual species in a habitat fill different roles or niches includingprimary production, herbivory, predation, and decomposition. In most communities these roles are filled by many species with varied characteristics.

Biologically diverse communities, often occurring in stable environments where complex assemblages of species have time to develop, can provide a wide variety of services to the ecosystem as well as to humans interested in the services. As an example, the potential medicinal value of the plants in the biologically rich tropical regions is well recognized, and the loss of these communities through deforestation may reduce this source of alternative medicines. As another example, the loss of habitat for the Red-cockaded woodpecker is directly related to current forest management practices of harvesting pine forests before they have time to age to the point that woodpeckers can utilize them.

The diversity of a community or habitat is, in part, dependent on the stability of the environment surrounding the habitat. If environmental conditions remain relatively constant, the available resources tend to be divided up between many different species. The transfer of energy betweentrophiclevels tends to be more efficient in communities that have a number oftrophic levels. These conditions are characteristic of climax communities at the late stages ofsuccession. Examples of climax communities are the maritime forest onbarrier islandsand hardwood forests in inland areas that do not burn regularly.

In environments where disturbances are relatively frequent, the diversity of plant and animal species may be less. Frequent disturbance may keep the development of the community in the early stages of succession, which tends to have fewer species and a less efficient transfer of energy between trophic levels. An example of this type of community is the pine flatwood community where forest fires occur every 2-5 years, setting back the successional clock.

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Biological Populations

Reproductive Rate

Growth Rate and "r" and "k" Selected Species

Carrying Capacity: How Many is Too Many?

The thousands of species and billions of individual plants and animals that occupy the ACE Basin can be organized into groups by species (populations),trophiclevels (position in food chain), or habitats (communities). The simplest level of organization of individuals is the population, a group of individuals of one species living in a specific area. Every population has attributes associated with it such as number of individuals (or density), range, habitat requirements, reproductive rates, and dispersal characteristics.

Reproductive RateThe reproductive rate of a population is the inherent or intrinsic growth rate of a population in an unlimited environment. Most environments impose limits to population growth, whether it be nutrients, space or water supply. However, some habitats such as newly formed ponds or newly plowed fields may provide enough nutrients and space that they are functionally unlimited for a short period of time. In these cases, populations with high growth rates and a high reproductive potential can experience explosive population growth and rapidly colonize the habitat.

Growth Rate and r and k selected speciesThe growth rate of a population is a combination of the number of individuals in the population, the death rate, the reproductive rate, and whatever limiting factors act on the population. Growth rate or reproduction rate strategies can be classified along a continuum between two endpoints. Species that are r-selected have a high reproductive potential, producing many offspring. These species, however, devote little energy to protecting their offspring and they experience high mortality rates. Examples of organisms that are r-selected include many plants that are considered weeds as well as many aquatic worms and crustaceans that can rapidly colonize unoccupied habitats. In general these species release large numbers of gametes with minimal parental care. Species that are k-selected have a lower reproductive potential, producing fewer offspring but devote much of their energy towards protecting their offspring until they are ready to fend for themselves. These species may have only one or two offspring every year, mature slowly, and are relatively long-lived. The Florida manatee and humans are examples of k- selected species, with low reproductive potential and long periods of parental care for individual offspring. Other species fall somewhere along the continuum between these two reproductive strategies.

In general, r-selected species tend to be opportunists, rapidly expanding their populations in temporarily unlimited habitats. These species can rapidly establish themselves in newly formed or recently disturbed habitats. After a catastrophic forest fire for example, it is r-selected species that first colonize the site. Similarly, the weeds that attempt to invade a corn field (disturbed every year by site preparation) are usually r-selected species. The conditions these species exploit are often characterized by an abundant resources with a limited number of consumers. While able to rapidly invade an area, r-selected species generally do not compete as well as k-selected species when resources become limited. In the absence of frequent disturbances, r-selected species are out-competed for limiting resources by k-selected species that utilize limited resources more effectively. K- selected species tend to dominate stable habitats such as climax communities, where competition for space, light, and nutrients may be important.

Carrying capacity: How many is too many?The carrying capacity of an environment is a theoretical maximum density of individuals that a particular environment can support. In terrestrial habitats, limiting factors are usually temperature, moisture regime, food, space, or predation. In aquatic systems, especially in small streams and tidal creeks, dissolved oxygen may also limit the number of individuals. Populations tend to fluctuate around the carrying capacity, by exceeding the maximum carrying capacity for short periods and then dropping below it. For food-limited populations, as their population exceeds their food supply (exceeds the carrying capacity) some individuals will starve or emigrate, thereby reducing the population. The population falls and remains below the carrying capacity until food is no longer limited. With adequate food resources, the population will begin to increase again, repeating the pattern. In some cases, the fluctuations are relatively small while other species may experience dramatic oscillations in their population.

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What is a Community?

Any particular location supports populations of different species. Therefore, a community is defined as all the different populations that live together in an area. (Odum 1997). The area comprising the ACE Basin encompasses many different communities. Communities can have unique boundaries, have varied composition of species, and be variable in time and space. A community may be defined as all the plants and animals (including humans) living on a particular barrier island. Alternatively, a community may also be described in a more specific sense, such as all the parasites living in or on a single fish such as a spotted seatrout.

Different communities frequently have similar characteristics. They are usually composed of both common and rare species. Some species, such as deer, are generalists that live in a wide variety of habitats or feed on a wide range of foods; others species are specialists such as the Red-cockaded woodpecker, which requires specific microhabitats or food sources. Some of these specialists are threatened by reductions of their required habitat. The Red-cockaded woodpecker, anendangered speciesonce found in the ACE Basin, requires pine stands with a minimum age of 50-70 years. The loss of this habitat through timber harvesting has resulted in the extirpation of Red-cockaded woodpeckers from the ACE Basin. In contrast, the marsh hen is also a specialist, inhabiting only theSpartinamarshes. But, due to the expanse of this habitat in the ACE basin, this species is very abundant there. National and state level restrictions on impactingSpartinawetlands protect this habitat and therefore protect the marsh hen.

External forces such asgeomorphology(primarily affecting plant communities) and episodic events such as storms or fire may also shape the structure of communities. Low-lying areas are generally wet and support only those plant species that can tolerate wet conditions. Sandy soils with limited organic materials do not hold moisture well, and those habitats are dominated by communities of plants and animals that can withstand dry conditions. Intense storms such as hurricanes may decimate an Atlantic maritime forest dominated by hardwoods allowing faster growing, shade intolerant, pine trees to establish themselves and temporarily dominate the plant community.

In addition to external physical forces, a number of biological processes within a community (such as species interactions) help to establish and maintain its structure. Examples include territorial behavior, predator-prey interactions, inhibitory chemicals used by plants to slow the growth of other plant species, overstory shading that reduces the growth of shade intolerant species, and parasites and diseases. All these processes interact to control the abundance and diversity of the community of plants and animals in an area. Consider the example of Edisto Beach: humans have greatly alteredgeomorphicfeatures and wetlands of the island. The structure of the community has changed considerably through the modifications that humans have made to make the island habitable for them. This may favor raccoons, egrets, and house cats at the expense of salamanders and bald eagles.

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Energy and Trophic Levels

Energy subsidies in Managed Systems

The energy supplied by the sun is the only source of truly renewable energy on the earth. Other sources of energy, such as fossil fuels, are not renewable. Nuclear energy, although potentially unlimited, has disadvantages related to its waste products. Hydroelectric energy is renewable, but is dependent on solar energy and weather patterns to replace the water that flows through the dam. Most of the sunlight falling on the earth is absorbed as thermal energy (Energy Dissipation of Solar Radiation as Percentage of Annual Input into the Biosphere)and this drives physical processes such as thehydrologicalcycle through evaporation and rainfall, and weather patterns through the heating of the air and land. Only about 1-5% of energy from the sun is stored byphotosynthesiswhile the rest is radiated as thermal energy or heat (Odum 1997).

Energy flow through thebiosphere(the thin biological layer at the earths surface) begins with the conversion of the radiant energy of sunlight to chemical energy by organisms calledautotrophs. These include all the species, such as plants,algaeand some bacteria, that can convert solar energy to high-energy molecules through the process of photosynthesis. These species convert raw materials such as elemental nitrogen, carbon dioxide, water, and potassium into organic molecules, and in the process store energy in those molecules. The organic materials synthesized in this way are used by autotrophs to grow and survive. This conversion of raw materials and solar energy to organic materials is calledprimary production. Gross primary production is the total amount of raw materials converted by plants to organic molecules. A percentage of the gross primary production is used to maintain the plants themselves. Any extra production is called net primary production and it is used for growth and reproduction or it may be lost as dissolved organic materials.

Energy stored byprimary producersis used by primary consumers which include herbivores anddetritivores. Some herbivores include deer, rabbits, seed-eating birds, caterpillars, and carp which feed on living plant material. Detritivores are less conspicuous but no less important because they eat dead plant material and start the decomposition processes that reduce the organic material back to simpler, lower energy forms. From an energy storage and transfer point of view, these levels of primary producer, primary consumer, and secondary consumer are calledtrophiclevels. Energy stored in high-energy organic molecules is transferred between these levels by herbivores grazing on plants and carnivores preying on herbivores. If it is hierarchical, from plant to herbivore tocarnivore, this flow of materials is called a food chain. However, movement of materials from primary producers to consumers to decomposers typically follows many different paths resulting in a complex network called the food web as depicted in this figure from Odum (1997).

Energy Subsidies in Managed SystemsIn a natural system that has been undisturbed byanthropogenicimpacts, there is a constant flow of energy, in the form of organic materials, that starts withautotrophsusing raw materials combined with solar energy to produce high-energy organic molecules, which are then transferred up the food chain. As plants and animals excrete wastes or die, decomposers break down these waste materials, extracting the remaining energy from the organic molecules and reducing the material back to raw elements. Almost all of the energy needed to create this flow of energy is provided by solar energy with small amounts coming from geothermal and chemical sources.

Humans have substantially changed the flow of energy in some systems by subsidizing the energy input (Odum 1997). In the course of history, two major changes in energy flow have allowed the human population to expand significantly. The first was during the agricultural revolution, which occurred approximately 8,000 years ago. The primary mechanisms of subsidizing energy flow through agriculture became the addition of fertilizers (energy richorganic material) and removal of competitors (energy removed by unwanted sources such as weeds and pests). The second change occurred with the industrial revolution, when advances in medicines increased human life expectancies and the use of fossil fuels increased the productivity of agriculture through mechanization.

The global economy is currently using more energy than is renewable over the long term and we are therefore heavily dependent on non-renewable fossil fuels and nuclear energy. Our technologically advanced societies are using more energy than can be replaced by renewable energy sources. Thus, energy use is currently subsidized by fossil fuels, a limited resource; and nuclear energy an unlimited resource that has a significant impact on the environment through the release and disposal of radioactive byproducts. Renewable energy sources such as hydroelectric power and solar power, although cleaner, have limitations as well as undesirable impacts on the environment.

Energy use at the local level of the ACE Basin is no exception. Millions of dollars in fuel, fertilizer, and pesticides are used to increase the production of agricultural products well beyond natural levels. When fossil fuels become expensive and scarce, how will the current production levels be maintained on ACE Basin farms? One of the problems faced by society is how to maintain current production levels as non-renewable resources such as fossil fuels become scarce. This issue is not restricted just to the agricultural community but will impact many of the ways that human society uses fossil fuels to subsidize ecosystem services.

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Ecosystem Services

A Global Perspective

Ecosystem services are defined by Daily (1997) as the conditions and processes through which natural ecosystems, and the species that make them up, sustain and fulfill human life. Humans benefit from the materials and processes provided by these services. Some of these materials such as seafood and lumber are clearly apparent while others are less conspicuous including wasteassimilation, carbon cycling, storm buffering, and thehydrologicalcycle.

From a global perspective, ecosystems within the ACE Basin contribute to the maintenance of the atmosphere by removing carbon dioxide and producing oxygen, by transforming nitrogenous wastes into less toxic forms, and by trapping pollutants. Global ecosystem services (Ecosystem services and functions) are large-scale processes that remain stable over long periods of time, thereby allowing biological systems to develop. Loss of these ecosystem services would result in significant changes in the stability of the global ecosystem, affecting all life on earth. However, the scale and complexity of the global ecosystem make it exceedingly difficult to detect changes; to attribute causes for the change; and to stop, or reverse, the processes leading to the change.

ACE Basin PerspectiveThe ACE Basin ecosystem is an integrated network of habitats that exchange nutrients, decompose organicdetritus, convert chemicals from organic andinorganicstates, capture energy, provide food and shelter, detoxify pollutants, and provide economic opportunities. Some of these services, such as food production, are readily apparent and have a market value. In the ACE Basin, commercial fishing is an important means of food production. Likewise, both agriculture and forestry products are produced in the ACE Basin and have a market value. Less apparent services include biological and chemical processes, such as the transfer of energy through the food chain, that operate to produce the fish or agricultural products (Peterson and Lubchenco 1997; Odum 1997). These services are generally taken for granted, yet they may be severely impacted by land use and pollution.

As an example,estuarineecosystems absorb certainanthropogenicwastes (such as nitrogen released from municipal waste-treatment plants and fertilizers applied to agricultural fields) as well as trap and detoxify pollutants. However, if these services are overloaded or the capacity of theestuaryto process these nutrients is reduced through wetland loss, the free service provided by the estuary will have to be replaced by expensive technological substitute services such as more efficient and expensive waste treatment plants.

Another example involves the dunes and maritime forests of the ACE Basin which provide protection from storms. Dune lines serve to buffer coastal areas from high seas and water levels during episodic events such as strong storms and hurricanes. Human activities such as building on dunes, changing the movement of sand with groins or jetties, or removing large areas of maritime forest may compromise this protective buffer allowing increased erosion or greater property damage (Thieler and Bush 1991).

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Wetlands as Contaminant Filters

Wetlands and estuaries trap many pollutants such as oil (PAHs), pesticides (DDT, Chlordane), andheavy metals(lead, copper) in their sediments. Some of these pollutants, such as PAHs, may then be further degraded by natural microbial activity to less toxic byproducts or to simple compounds such as carbon dioxide and water (Peterson and Lubchenco 1997). Pollutants that are not readily degraded (PAHs, chlorinated compounds, and metals) are often bound up with the fine particulates that make up the sediments and therefore are less likely to be absorbed by wildlife. Sediments may temporarily trap the pollutants, but biogenic and oxidative processes periodically facilitate the release ofsediment-associated pollutants. Therefore, pollutants may cause long-term effects on biological resources of the ACE Basin. Although not yet identified as a problem in the ACE Basin, many highly urban areas on the east coast of the United States have exceeded the capability of these services, and are experiencing the undesirable effects of these contaminants being released into the environment and affecting wildlife as well as human populations. These effects are seen in changes in plant and animal populations, increases in fish mortality, reduced growth and deformities, and harmful algal blooms (SCDHEC 1998). (See related section: Phytoplankton:Algal Blooms.)

Some ecosystem services can be difficult to assign a monetary value. Ecologists and economists have made some recent progress in assigning dollar values to ecosystem (Value of biome types) operations or functions to elucidate the economic value of pertinent non-market goods (Colgon 1990). While these estimates are considered rough ones and are thought to underestimate any actual dollar value equivalent of aggregate services of the biome (Costanza et al. 1997), they make the value of these services comparable with more easily recognized services such as the value of commercial fisheries (Total value of commercial fishing in South Carolina.) or the ability of aquatic systems to recycle municipal waste.

Organisms are divided into autotrophs and heterotrophs according to their energy pathways. Autotrophs are those organisms that are able to make energy-containing organic molecules from inorganic raw material by using basic energy sources such as sunlight. Plants are the prime example of autotrophs, usingphotosynthesis. All other organisms must make use of food that comes from other organisms in the form of fats, carbohydrates and proteins. These organisms which feed on others are called heterotrophs.

Aheterotroph(/htrtrof/;heteros= "another", "different" andtrophe= "nutrition") is anorganismthat cannotfix carbonand usesorganiccarbon for growth.[1][2]Heterotrophs can be further divided based on how they obtain energy; if the heterotroph uses light for energy, then it is considered aphotoheterotroph, while if the heterotroph uses chemical energy, it is considered achemoheterotroph.

Heterotrophs contrast withautotrophs, such asplantsandalgae, which can use energy fromsunlight(photoautotrophs) or inorganic compounds (lithoautotrophs) to produceorganic compoundssuch ascarbohydrates,fats, andproteinsfrom inorganiccarbon dioxide. These reduced carbon compounds can be used as an energy source by the autotroph and provide the energy in food consumed by heterotrophs. Ninety-five percent or more of all types of living organisms are heterotrophic.[3]

Anautotroph[]("self-feeding", from theGreekautos"self" andtrophe"nourishing") or "producer", is an organism that produces complexorganic compounds(such ascarbohydrates,fats, andproteins) from simple substances present in its surroundings, generally using energy from light (photosynthesis) or inorganic chemical reactions (chemosynthesis). They are theproducersin afood chain, such asplantson land oralgaein water, in contrast toheterotrophsas consumers of autotrophs. They do not need a living energy or organiccarbonsource. Autotrophs canreducecarbon dioxideto make organic compounds for biosynthesis and also create a store of chemical energy. Most autotrophs use water as thereducing agent, but some can use other hydrogen compounds such as hydrogen sulfide.Phototrophs(green plants and algae), a type of autotroph, convert electromagnetic energy from sunlight into chemical energy in the form ofreduced carbon.

Autotrophs can bephotoautotrophsorchemoautotrophs. Phototrophs use light as an energy source, while chemotrophs utilize electron donors as a source of energy, whether from organic or inorganic sources; however in the case of autotrophs, these electron donors come from inorganic chemical sources. Such chemotrophs arelithotrophs. Lithotrophs use inorganic compounds, such ashydrogen sulfide, elementalsulfur,ammoniumandferrous iron, as reducing agents forbiosynthesisand chemical energy storage. Photoautotrophs and lithoautotrophs use a portion of theATPproduced during photosynthesis or the oxidation of inorganic compounds to reduceNADP+to NADPH to form organic compounds.[1]

Herbivores

Herbivores are animals which only eat plant material. This means leaves, flowers, fruits or even wood. Sheep, horses, rabbits and snails are well known examples of herbivores which eat grass and leaves. A parrot, however, which eats fruits and nuts can also be called a herbivore.

Omnivores

Omnivores eat both plants and meat. Chickens are omnivores. They eat seeds, but they can also eat worms. human beings are also omnivores, although some people choose not to eat meat. These people are called vegetarians.The chimpanzee is omnivorous. It eats fruits, leaves, palm nuts, seeds and stems, as well as ants, birds' eggs, fish and termites. Chimpanzees will occasionally kill and eat baboons and wild pigs.

Carnivores

Carnivores eat meat. A carnivore is a predator because it has to find and catch its prey. Some carnivores, such as wolves, hunt in a group called a pack. They move silently and slowly to form a circle around their prey before they attack.

Johnny'sFactFile No.6The smallest carnivorous mammal is called theleast weasel. This little mammal is found in North America. It's mass is 57 grammes at the most!

Other carnivores, such as the cheetah, usually hunt alone. The cheetah creeps towards its prey without being noticed, until it is 30 metres from it, then the cheetah starts to run.Some insects are carnivores. The dragonfly, which hovers so gracefully above a pond, is hunting for other insects.The eagle is a carnivorous bird. It flies high in the sky looking for animals, such as rabbits. When it finds one it quickly swoops to the ground. It uses its strong feet and pointed claws, called talons, to catch the rabbit. It has a very pointed beak to help it tear off the meat.