2EcosystemsPopulation: all the individuals of a certain species that live in a particular areaCommunity: all the different species that interact together within a particular areaEcosystems consist of all the organisms that live in an area along with the nonbiological (abiotic) components.
3Ecosystems Many global environmental problems have emerged recently. Ecosystem ecology follows the flow of energy and nutrients through ecosystemsHumans have artificially affected the flow of these components
4Energy Flow within Ecosystems Energy enters an ecosystem primarily though sunlight:
5Energy Flow and Trophic Structure Species within an ecosystems are classified into different trophic levels:Primary producers: autotrophs, photosynthetic- plants, algae, some bacteriaConsumersPrimary consumers: herbivores that eat producers (plants)- deer, rabbits, etc.Secondary consumers: carnivores that eat herbivores: wolf eating a deerTertiary consumers: carnivores that eat carnivores: a hawk eating a snake that ate a mouseDecomposers: fungi, bacteria that break down organic material (dead plants and animals)
6Different Trophic Levels in an Ecosystem 4321Feeding strategySecondary carnivoreCarnivoreHerbivoreAutotrophGrazing food chainDecomposer food chainCooper’shawkOwlShrewEarthwormDead maple leavesRobinCricketMaple tree leavesFigure: 51.6aCaption:(a) Each trophic level in an ecosystem is defined by a distinct feeding strategy. The organisms illustrated in this table furnish an example for each trophic level in the grazing and decomposer food chains of a temperate-forest ecosystem. Many other species exist at each trophic level in this ecosystem.
7Energy Flow in an ecosystem External energy sourcePRIMARYPRODUCERSCONSUMERSDECOMPOSERSABIOTIC ENVIRONMENTFigure: 51.1Caption:Primary producers harness an external energy source to manufacture ATP and reduced carbon compounds, which are then available to consumers. When primary producers and consumers die, their remains are digested by decomposers. Primary producers, consumers, and decomposers all exchange energy and matter with the soil, atmosphere, water, and other aspects of the abiotic environment.
8Decomposers Predators of decomposers: Primary decomposers: Spider SalamanderCentipedePuffballPuffballMushroomFigure: 51.5Caption:Dead leaves, sticks, and other types of detritus are fed upon by an enormous variety of organisms. These decomposers, in turn, are fed upon by salamanders, shrews, spiders, centipedes, and other predators.EarthwormMillipedePrimary decomposers:Bacteria and archaeaNematodesPillbugs305 nm49.4 µm
9Energy Flow and Trophic Structure Key points about energy flow through ecosystems.Plants use only a tiny fraction of the total radiation that is available to them.Most energy fixed during photosynthesis is used for respiration, not synthesis of new tissues.Only a tiny fraction of fixed energy actually becomes available to consumers.Most net primary production that is consumed enters the decomposer food web.
10Ecological Efficiency: percent of energy transferred from one trophic level to the next Energy source:1,254,000kcal/m2/year0.8% energy captured by photosynthesis. Of this...…45% supports growth(Net primary production)…11% enters grazing food web…34% entersdecomposer food webas dead material…55% lost to respirationFigure: 51.2Caption:In a temperate forest ecosystem, energy from sunlight is transformed to chemical energy by photosynthesis. The products of photosynthesis go, in part, to fuel new plant growth. Plant tissue is either consumed by herbivores in the grazing food web or falls into the decomposer food web when the plant dies.
11Ecosystem ProcessesProduction: rate at which energy/nutrients are converted into growthIncludes Primary Production: growth by autotrophsIncludes Secondary Production - growth by heterotrophsConsumption - the intake and use of organic material by heterotrophsDecomposition - the chemical breakdown of organic material
12Terrestrial productivity Figure 51.3aTerrestrial productivity0–100100–200200–400400–600600–800>800Figure: 51.3aCaption:(a) The terrestrial ecosystems with the highest primary productivity are found in the tropics, where warm temperatures and high moisture encourage high photosynthetic rates. Tundras and deserts have the lowest productivity.Productivity ranges(g/m2/yr)
13Figure 51.3b Marine productivity Productivity ranges (g/m2/yr) <35 35–5555–90>90Figure: 51.3Caption:(b) The highest productivity in the oceans occurs in nutrient-rich coastal areas.Productivity ranges(g/m2/yr)
14Very little of the energy consumed by primary consumers are used for secondary production 80.7% respiration17.7% excretion1.6% growth and reproductionEnergy derived from plantsFigure: 51.4Caption:Very little of the energy consumed by chipmunks, a primary consumer (herbivore), is used for secondary production. Most of the energy is used for cellular respiration.
15Pyramid of productivity 4Secondary carnivore3Carnivore2Herbivore1AutotrophProductivityPyramid of productivityExample: 100g of plant becomes 5-20g of grasshopper then g of mouseFigure: 51.6bCaption:(b) In all ecosystems, productivity is highest at the first trophic level and declines at higher levels. This pattern is called the pyramid of productivity.
16The Different Trophic levels in an ecosystem is often pictured as a Food chain Pisaster(a sea star)Thais(a snail)Bivalves(clams, mussels)Figure: 51.7aCaption:(a) An example of a food chain in an intertidal zone.
17Energy Flow and Trophic Structure Food chains and food websFood chains are typically embedded in more complex food webs.Many organisms feed at more than one trophic level
18Food web Pisaster Thais Limpets Acorn barnacles Gooseneck barnacles Figure: 51.7bCaption:(b) Food chains are embedded in food webs that include more species and different feeding relationships.LimpetsAcornbarnaclesGooseneckbarnaclesChitonsBivalves
19Energy Flow and Trophic Structure Food chains and food websThe maximum number of links in any food chain or web ranges from 1 to 6.Hypotheses offered to explain this:Energy transfer may limit food-chain length.Long food chains may be more fragile.Food-chain length may depend on environmental complexity.
20Food chains tend to have few links. 108642Average numberof links = 3.5StreamsLakesTerrestrialNumber of observationsFigure: 51.7cCaption:(c) The y-axis on this graph plots the number of research studies that described food chains with from 1 to 6 links in stream, lake, and terrestrial habitats.123456Number of links in food chain
21Biogeochemical Cycles The path an element takes as it moves from abiotic systems through living organisms and back again is referred to as its biogeochemical cycle.Examples: nitrogen cycle, carbon cycle, phosphorus cycle
22Figure 51.8 Plants Assimilation Herbivore Feces or urine Death ConsumptionHerbivoreAssimilationFeces or urineDeathFigure: 51.8Caption:Nutrients cycle from organism to organism in an ecosystem as a result of assimilation by primary producers, consumption, and decomposition. Nutrients are exported from ecosystems through the migration of organisms out of the area or, more commonly, in flowing water or groundwater.DeathDetritusUptakeSoil nutrient poolDecomposerfood webLoss to erosion or leaching into groundwater
23Biogeochemical Cycles A key feature in all cycles is that nutrients are recycled and reused.The overall rate of nutrient movement is limited most by decomposition of detritus.
24Boreal forest: nutrients are put back into the soil slowly, so organic material builds up Figure: 51.9a upperCaption:In boreal forests, decomposition rates are limited by cold soil temperatures. The input of detritus into the soil thus exceeds the decomposition rate, and organic matter builds up.
25Tropical rain forest: decomposition is rapid so there is very little organic build up Figure: 51.9 lowerCaption:In tropical rain forests, warm temperatures allow decomposition to proceed rapidly so that organic matter does not build up.Result: if living material is removed from tropical rain forests, the soil is nutrient poor to support new growth
26The rate of nutrient loss is a very important characteristic in any ecosystem. Devegetation experimentChoose two similar watersheds.Document nutrient levels in soil organic matter, plants, and streams.Figure: 51.10a upperCaption:(a) An experiment to test the effects of vegetation removal on nutrient cycling. Question: In effect, this experiment removed one of the arrows in Figure Which one?
27Devegetate one watershed and leave the other intact. ClearcutControlFigure: 51.10a lowerCaption:(a) An experiment to test the effects of vegetation removal on nutrient cycling. Question: In effect, this experiment removed one of the arrows in Figure Which one?Devegetate one watershed and leave the other intact.Monitor the amount of dissolved substances in streams.
28Nutrient export increases dramatically in devegetated plot Net dissolved substance (kg/ha)1965–661966–671967–681968–691969–70Control1000800600400200YearNutrient runoff resultsFigure: 51.10bCaption:(b) Nutrient export increased dramatically in the devegetated watershed.
29Biogeochemical Cycles Nutrient flow among ecosystems links local cycles into one massive global biogeochemical cycle.The carbon cycle and the nitrogen cycle are examples of major, global biogeochemical cycles.Humans are now disrupting almost all biogeochemical cycles. This can have very harmful effects.
30Humans are adding significant amounts of carbon into the atmosphere THE GLOBAL CARBON CYCLEAll values in gigatons of carbon per yearAtmosphere: 750 (in 1990)+3.5 per yearPhotosynthesis:102Respiration:50Fossil fuel use:6.0Deforestation:1.5Physicaland chemical processes: 92Decomposition:50Physicaland chemical processes: 90Land, biota, soil, litter, peat: 2000Figure: 51.11Caption:The arrows in this diagram indicate how carbon moves into and out of ecosystems. Note that deforestation and fossil fuel use are adding 7.5 gigatons of carbon to the atmosphere each year. Of this 7.5 gigatons, two are fixed by photosynthesis in terrestrial ecosystems and two are fixed by physical and chemical processes in the oceans.2Rivers: 1Ocean: 40,000Aquatic ecosystemsTerrestrial ecosystemsHuman–inducedchanges
31Human-induced increases in CO2 flux over time 654321Fossil fuel useAnnual flux of carbon (1015g)Land useFigure: 51.12aCaption:(a) Carbon fluxes from fossil-fuel burning and land-use changes have been increasing since Question Why are atmospheric CO2 concentrations low in the northern hemisphere during the summer and high in winter? What pattern would you expect in the southern hemisphere?1860188019001920194019601980Year
32Figure 51.12b Atmospheric CO2 CO2 concentration (ppm) Year 360 350 340 330320310CO2 concentration (ppm)Figure: 51.12bCaption:(b) Scientists have been collecting air samples and measuring CO2 concentrations at the Mauna Loa Observatory in Hawaii since Because the site is far from large-scale human influence, it should accurately represent the average condition of the atmosphere in the northern hemisphere. Question Why are atmospheric CO2 concentrations low in the northern hemisphere during the summer and high in winter? What pattern would you expect in the southern hemisphere?1960197019801990Year
33THE GLOBAL NITROGEN CYCLE Only nitrogen-fixing bacteria can use N2make ammonia (NH3) or nitrate (NO3)limiting nutrient (demand exceeds supply) for plantsAll organisms require nitrogen to make proteinAnimals get nitrogen from their diets, not the airNitrogenfixing cyanobacteriaMudDecomposition of detritus into ammoniaNitrogen-fixing bacteria in roots and soilProtein andnucleic acid synthesisAtmospheric nitrogen (N2) =78%Bacteria in muduse N-containing molecules as energy sources, excrete (N2)Run–offLightning and rainFigure: 51.13aCaption:(a) Nitrogen enters ecosystems as ammonia or nitrate via fixation from atmospheric nitrogen. Within ecosystems, nitrogen cycles through producers and consumers. Eventually it reaches the decomposer food web. Nitrogen is exported from ecosystems in runoff and as nitrogen gas given off by bacteria that use nitrogen-containing compounds as an electron acceptor.Industrial fixation
34Human activities now fix almost as much nitrogen each year as natural sources Human sourcesAmount of nitrogen (gigatons/year)16014012010080 604020Sources of nitrogen fixationLightningBiological fixationFossil fuelsNitrogen fertilizerNitrogen- fixing cropsFigure: 51.13bCaption:(b) Human activities now fix almost as much nitrogen each year as natural sources. Thus, human activities have almost doubled the total amount of nitrogen available to organisms.