Ecosystems EcologyEcosystems An energy processing and nutrient generating system

Biosphere- part of the Earth, including air, land, surface rocks and water, within which life occurs.

From the broadest biophysiological point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, hydrosphere, and atmosphere.

Lithosphere rocky material about 100km deep first 1000m is substrate of life primary source of nutrients

Hydrosphere body of liquid oceans, lakes, rivers, aquifers, frozen water (ice caps, glaciers) and water vapour

The Earths Life-Support SystemsTroposphereStratosphereHydrosphereLithosphereBiosphere

The Nature of EcologyOrganismsPopulationsCommunitiesEcosystemsBiosphere

All Ecosystems consist of 3 basic componentsProducers autotrophs energy capturing green plants, algae, diatomsConsumers (including decomposers) heterotrophs utilise food/energy stored in producersThose that feed on living tissueDecomposers break down dead organic matter (detritus) into inorganic substances basis for nutrient cyclingInorganic and dead organic matter (plant and consumers) in soil matrix and aquatic systems

Essential Processes in EcosystemsEnergy and nutrients are incorporated into ecosystems via photosynthesis and ends with decompositionPhoto fixes light & incorporates nutrients into tissue C3, C4 and CAM, Diatoms, Algae Decomposition dissipates energy and reduces organic matter to inorganic substances CO2, H2O, PO4, SO4 + heat

Energy flows through an ecosystemEntering as light and exiting as heatFigure 54.2Microorganismsand otherdetritivoresDetritusPrimary producersPrimary consumersSecondaryconsumersTertiary consumersSunKeyChemical cyclingEnergy flowHeat

Ecosystems can range from a microcosm, such as an aquariumTo a large area such as a lake or forestFigure 54.1

Regardless of an ecosystems sizeIts dynamics involve two main processes: energy flow (1) and chemical cycling (2)Energy flows through ecosystems (1)While matter cycles within them (2)The biotic and abiotic exchange energy and matter

Sustaining Life of EarthOne-way flow of energyCycling of matter

Ecosystem ecology emphasizes energy flow and chemical cycling

Ecosystem ecologists view ecosystemsAs transformers of energy and processors of matter

Ecosystems and Physical LawsThe laws of physics and chemistry apply to ecosystemsParticularly in regard to the flow of energy

Energy is conserved (neither created nor destroyed)It may change form, pass from one place to another and act upon matter in various wayBut degraded to heat during ecosystem processesThe First Law of Thermodynamics

The two laws of thermodynamics

Trophic RelationshipsEnergy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) and then to secondary consumers (carnivores)

Trophic Relationships

Primary consumerSecondary consumerSecondary consumerPrimary consumer

The Biotic Components of EcosystemsProducers (autotrophs)PhotosynthesisConsumers (heterotrophs)Aerobic respirationDecomposers

Trophic Levels (Consumer)Primary consumer (herbivore)Secondary consumer (carnivore)Tertiary consumer (top predator)OmnivoreDetritivores and scavengersDecomposers

Connections: Food Webs and Energy Flow in EcosystemsFood chainsFood webs

DecompositionDecompositionConnects all trophic levels

Detritivores, mainly bacteria and fungi, recycle essential chemical elementsBy decomposing organic material and returning elements to inorganic reservoirs

DecomposersMicroflora (bacteria and fungi that inhabit an area)Bacteria aerobic (facultative or obligate) , anaerobic (fermentation) Dominant decomposers of animal matterFungi dominant decomposers of plant matterDetritivores or detritus feeder (play the role as decomposer)4 major groups soil microfauna (protozoans), soil mesofauna (nematodes), soil macrofauna (earthworm), soil megafauna (earthworm or small invertebrate)Microbivores (microorganism feeding on decomposer) mesofauna & macrofauna feed on bacteria & fungi and are important for dispersal of fungal spores in soil

Ecosystem Energy BudgetsThe extent of photosynthetic productionSets the spending limit for the energy budget of the entire ecosystem

The Global Energy BudgetThe amount of solar radiation reaching the surface of the EarthLimits the photosynthetic output of ecosystems

Only a small fraction of solar energyActually strikes photosynthetic organisms

The Source of Energy

Physical and chemical factors limit primary production in ecosystems

Primary production in an ecosystemIs the amount of light energy converted to chemical energy by autotrophs during a given time periodLight energy converted to product

Gross and Net Primary ProductionTotal primary production in an ecosystemIs known as that ecosystems gross primary production (GPP)GPP is total rate of the photosynthesis or energy assimilated by the autotroph

Not all of this productionIs stored as organic material in the growing plantsOnly NPP is available to consumers

NPP = GPP - R

GPP measures the total amount of organic matter produced by the autotroph in the ecosystem. This includes the matter that plants use for respiration. NPP measures the total amount of matter produced that is available to heterotrophs. The GPP minus the matter used (respiration) by the plant is the NPP.

Gross and Net Primary Production

Secondary ProductivityAmount of production/energy available to heterotrophs 1) Energy (in the form of plant) consumed passes from the body as waste products (feces and urine)2) Part is used as heat for metabolism (respiration) 3) The remainder is available for maintenance- capturing or harvest food, perform muscular work- usually lost to the env. as heatEnergy left from maintenance and respiration goes into production - growth of new tissue and production of young This net energy of production is called secondary productionAka the rate of biomass accumulation by heterotrophs (herbivores, carnivores and detritivores).

Example of Primary ProductivityIn tropical forests and in marshlands, between 1500 and 3000 grams of organic material are normally produced per square meter per year. Corresponding figures for other communities are: temperate forests, 1100 to 1500 grams; dry deserts, 200 grams. For such highly productive communities as estuaries, coral reefs, and sugarcane fields, the figures may range from 10 to 25 grams per day, for comparable annual yields of 3600 to 9100 grams.

Overall, terrestrial ecosystemsContribute about two-thirds of global NPP and marine ecosystems about one-third

Primary Production in Marine and Freshwater Ecosystems

Primary Production in Terrestrial and Wetland Ecosystems

Primary Production in Marine and Freshwater EcosystemsIn marine and freshwater ecosystemsBoth light and nutrients are important in controlling primary production

1. Light LimitationThe depth of light penetrationAffects plant primary production throughout the photic zone of an ocean or lake

2. Nutrient LimitationMore than light, nutrients limit primary productionBoth in different geographic regions of the ocean and in lakes

A limiting nutrient is the element that must be addedIn order to increase production in a particular ecosystemsNitrogen and phosphorousAre typically the nutrients that most often limit marine production

Nutrient enrichment experimentsConfirmed that nitrogen was limiting phytoplankton growth in an area of the oceanGross primary productivityEXPERIMENTPollution from duck farms concentrated near Moriches Bay adds both nitrogen and phosphorus to the coastal water off Long Island. Researchers cultured the phytoplankton Nannochloris atomus with water collected from several bays.Coast of Long Island, New York. The numbers on the map indicate the data collection stations.Long IslandGreat South BayShinnecock BayMoriches BayAtlantic Ocean3021191511542

PhytoplanktonInorganicphosphorusRESULTS (a) Phytoplankton abundance parallels the abundance of phosphorus in the water. Nitrogen, however, is immediately taken up by algae, and no free nitrogen is measured in the coastal waters. (b) The addition of ammonium (NH4) caused heavy phytoplankton growth in bay water, but the addition of phosphate (PO43) did not induce algal growth.

The addition of large amounts of nutrients to lakesHas a wide range of ecological impacts

In some areas, sewage effluent and runoff lawn fertilizers into natural waters (rivers or coasts) Has caused eutrophication in which increasing in chemical nutrients typically compounds nitrogen or phosphorusThree particularly troubling ecological impacts: decreased biodiversity, changes in species composition and dominance, and toxicity effects. Other effects are:Increased biomass of phytoplankton Toxic or inedible phytoplankton species Increases in blooms of gelatinous zooplankton Decreased biomass of benthic and epiphytic algae Color, smell, and water treatment problems Dissolved oxygen depletion Increased incidences of fish kills Decreases in perceived aesthetic value of the water body

Primary Production in Terrestrial and Wetland EcosystemsIn terrestrial and wetland ecosystems climatic factorsSuch as temperature and moisture, affect primary production on a large geographic scale

The contrast between wet (wetland) and dry (terrestrial) climatesCan be represented by a measure called actual evapotranspirationRun off occurs when soil is infiltrated to full capacity and excess water, from rain, snowmelt, or other sources flows over the land. Groundwater recharge a hydrologic process where water moves downward from surface water to groundwaterWater cycle of the earth's surface, showing the individual components of transpiration and evaporation that make up evapotranspiration. Other closely related processes shown are runoff and groundwater recharge.

On a more local scaleA soil nutrient is often the limiting factor in primary productionRESULTSExperimental plots receiving just phosphorus (P) do not out produce the unfertilized control plots.CONCLUSIONLive, above-ground biomass(g dry wt/m2)Adding nitrogen (N) boosts net primaryproduction.300250200150100500JuneJulyAugust 1980N PN onlyControlP only These nutrient enrichment experiments confirmed that nitrogen was the nutrient limiting plant growth in this salt marsh.

The production efficiency of an organismIs the fraction of energy stored in food that is not used for respirationFraction of energy stored in food that will be efficient for the consumerProduction Efficiency

Production EfficiencyWhen a caterpillar feeds on a plant leafOnly about one-sixth of the energy in the leaf is used for secondary production (biomass)

NPP- total amount of matter produced that is available to heterotrophs.

Ecological PyramidsTrophic EfficiencyPyramid of productivityPyramid of biomassPyramid of numbersFig. 4-20 p. 79

1. Trophic EfficiencyTrophic efficiencyIs the percentage of production transferred from one trophic level to the nextUsually ranges from 5% to 20%only 5% to 20% of primary producer biomass consumed is converted into new consumer biomass

2. Pyramids of ProductionThis loss of energy with each transfer in a food chainCan be represented by a pyramid of net productionFigure 54.11TertiaryconsumersSecondaryconsumersPrimaryconsumersPrimaryproducers1,000,000 J of sunlight10 J100 J1,000 J10,000 J

3. Pyramids of BiomassShows the relationship between biomass and trophic level - by quantifying the amount of biomass present at each trophic level. Typical units for a biomass pyramid could be grams per meter2, or calories per meter2.Can be represented in a biomass pyramid

Most biomass pyramidsShow a sharp decrease at successively higher trophic levelsFigure 54.12a(a) Most biomass pyramids show a sharp decrease in biomass at successively higher trophic levels, as illustrated by data from a bog at Silver Springs, Florida.Trophic levelDry weight(g/m2)Primary producersTertiary consumersSecondary consumersPrimary consumers1.51137809

Certain aquatic ecosystemsHave inverted biomass pyramids(b) In some aquatic ecosystems, such as the English Channel, small standing crop of primary producers (phytoplankton) supports a larger standing crop of primary consumers (zooplankton).Consequently, aquatic biomass pyramids can seemingly be upside down if net primary productivity does not accumulate in the ecosystem within primary producers (i.e., primary producers are eaten as fast as they grow/reproduce)

4. Pyramids of NumbersA pyramid of numbersRepresents the number of individual organisms in each trophic levelFigure 54.13Trophic levelNumber of individual organismsPrimary producersTertiary consumersSecondary consumersPrimary consumers3354,904708,6245,842,424

The dynamics of energy flow through ecosystemsHave important implications for the human populationEating meatIs a relatively inefficient way of tapping photosynthetic production

Worldwide agriculture could successfully feed many more peopleIf humans all fed more efficiently, eating only plant materialFigure 54.14

The Green World HypothesisAccording to the green world hypothesisTerrestrial herbivores consume relatively little plant biomass because they are held in check by a variety of factors

Most terrestrial ecosystemsHave large standing crops despite the large numbers of herbivores

The green world hypothesis proposes several factors that keep herbivores in checkPlants have defenses against herbivoresNutrients usually limit herbivoresAbiotic factors (temperature, moisture, light) limit herbivoresIntraspecific competition can limit herbivore numbersInterspecific interactions check herbivore densities

Concept 54.4: Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystemLife on EarthDepends on the recycling of essential chemical elementsNutrient circuits that cycle matter through an ecosystemInvolve both biotic and abiotic components and are often called biogeochemical cycles

A General Model of Chemical CyclingGaseous forms of carbon, oxygen, sulfur, and nitrogenOccur in the atmosphere and cycle globallyLess mobile elements, including phosphorous, potassium, and calciumCycle on a more local level

A general model of nutrient cyclingIncludes the main reservoirs of elements and the processes that transfer elements between reservoirsAssimilation: the conversion of nutrient into the fluid or solid substance of the body, by the processes of digestion and absorption

All elementsCycle between organic and inorganic reservoirs

Biogeochemical Cycles4b. Evaporation From the sea4a. Evaporation from land

Water cycle- Water moves in a global cycle- Driven by solar energy

The carbon cycleReflects the reciprocal processes of photosynthesis (use) and cellular respiration (return bck)

The carbon cycle

The carbon cycleThe carbon cycle depends on photosynthesis and respiration.

Carbon also enters the atmosphere when fossil fuels burn and when volcanoes erupt.

Sediments and rocks hold most of the carbon, followed by the ocean, then soil, the atmosphere and biomass on land.

Most atmospheric carbon occurs in the form of carbon dioxide (CO2).

Carbon dissolved in the ocean is mainly in the forms of bicarbonate and carbonate.

The carbon cycleCarbon compounds in detritus (animal wastes, plant litter, dead organisms) are consumed and decomposed by detritivores.Detritivores respiration returns CO2 to the atmosphere.

The return of CO2 to the atmosphere by respiration closely balances its removal by photosynthesis.

The increased burning of wood and fossil fuels is raising the level of CO2 in the atmosphere.

Nitrification

Nitrogen cycleEarths atm-80% nitrogen, however mostly in the form of nitrogen gas (N2)N2 -unavailable to consumers of plantsFour processes participate in nitrogen cycle: Nitrogen fixationDecayNitrificationDenitrification Nitrogen enters atm through 2 ways:1. Atm deposition2. Nitrogen fixation

Nitrogen cycle- Atm deposition5-10% through atm deposition

NH4+ (ammonium) and NO3- (nitrate), the 2 forms available to plants-added to soil by dissolving in rain or settling as dust or particles

Some plants, epiphytic bromeliads-have aerial roots that can take up NH4+ and NO3- directly from moist atm

1. Nitrogen FixationThe ability to fix nitrogen is found only in certain bacteria and archaea. Some live in a symbiotic relationship with plants of the legume family (e.g., soybeans, alfalfa).Some establish symbiotic relationships with plants other than legumes (e.g., alders). Some establish symbiotic relationships with animals, e.g., termites and "shipworms" (wood-eating bivalves). Some nitrogen-fixing bacteria live free in the soil.

Although the first stable product of the process is ammonia, this is quickly incorporated into protein and other organic nitrogen compounds.

2. DecayThe proteins made by plants enter and pass through food webs just as carbohydrates do. At each trophic level, their metabolism produces organic nitrogen compounds that return to the environment, chiefly in excretions. The final beneficiaries of these materials are microorganisms of decay. They break down the molecules in excretions and dead organisms into ammonia.

3. Nitrification1. This is accomplished in two steps:

Bacteria of the genus Nitrosomonas oxidize ammonia (NH3) to nitrites (NO2). Bacteria of the genus Nitrobacter oxidize the nitrites to nitrates (NO3).These two groups of autotrophic bacteria are called nitrifying bacteria. Through their activities (which supply them with all their energy needs), nitrogen is made available to the roots of plants.

Both soil and the ocean contain archaeal microbes, assigned to the Crenarchaeota, that convert ammonia to nitrites. They are more abundant than the nitrifying bacteria and may turn out to play an important role in the nitrogen cycle.

Many legumes, in addition to fixing atmospheric nitrogen, also perform nitrification converting some of their organic nitrogen to nitrites and nitrates. These reach the soil when they shed their leaves.

Since most soils are acidic:- NH3 released to soil, picks up ion (H+)-form ammonium (NH4+)- NH4+ can be used directly by plants

Nitrogen cycle- Nitrification

4. DenitrificationThe three processes above remove nitrogen from the atmosphere and pass it through ecosystems.

Denitrification reduces nitrates to nitrogen gas, thus replenished the atmosphere.

Once again, bacteria are the agents. They live deep in soil and in aquatic sediments where conditions are anaerobic. They use nitrates as an alternative to oxygen for the final electron acceptor in their respiration.

Thus they close the nitrogen cycle.

Phosphorus cycleDont involve atmosphere!!

Plants absorb phosphorous in the form of PO43- (phosphate) - then absorb form organic synthesis

Weathering of rocks-add phosphate to soil

Producers-incorporate phosphorous into biological molecules-transferred to consumers in organic form-added back to soil by excretion of phosphate by animals and by the action of bacteria and fungi decomposers

Phosphorus cyclePhosphate that reach the ocean- accumulates in sediment- incorporated in rocks

Phosphate -recycles among soil, plants and consumers

Most of the nitrogen cycling in natural ecosystemsInvolves local cycles between organisms and soil or waterThe phosphorus cycleIs relatively localized

Decomposition and Nutrient Cycling RatesDecomposers (detritivores) play a key roleIn the general pattern of chemical cycling

The rates at which nutrients cycle in different ecosystemsAre extremely variable, mostly as a result of differences in rates of decomposition

Ecosystem Servicesand SustainabilityFig. 4-34 p. 92

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