Ecosystems. Chapter 55. Ecosystem Ecology Ecosystems, Energy, and Matter An ecosystem consists of

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1 Chapter 55 Ecosystems Ecosystem Ecology Ecosystems, Energy, and Matter An ecosystem consists of All the organisms living in a community, and All the abiotic factors with which they interact PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Ecosystem Ecology Ecosystems can range from a microcosm, such as an aquarium To a large area such as a lake or forest Figure 5.1 Energy Flow and Nutrient Cycles Regardless of an ecosystem s size, ecosystem ecology emphasizes two main processes Energy flows through ecosystems Nutrients (matter) cycles within ecosystems Ecosystem ecologists view ecosystems as Transformers of energy, and Ecosystems and Physical Laws The laws of physics and chemistry apply to ecosystems Particularly in regard to the flow of energy Energy is conserved But degraded to heat during ecosystem processes (entropy) Processors of matter 1

2 Trophic Relationships Energy and nutrients pass from primary producers (autotrophs) To primary (herbivores) and then To secondary (carnivores), etc. Trophic Structure, Energy Flow & Nutrient Cycles Energy flows through an ecosystem Entering as light and exiting as heat Tertiary Microorganisms and other detritivores Secondary Detritus Primary Primary producers Key Heat Chemical cycling Energy flow Sun Figure 5.2 Nutrient Cycles A general model of nutrient cycling Reservoir a Reservoir b Organic Organic un Fossilization Living organisms, Coal, oil, detritus peat Respiration, Assimilation, decomposition, Burning photosynthesis excretion of fossil fuels Reservoir c Reservoir d Weathering, un erosion Decomposers Decomposers, mainly bacteria and fungi, recycle essential chemical elements, returning Dead organic material to inorganic reservoirs May account for 5% of energy transfers from primary producers Figure 5.16 Atmosphere, soil, water Formation of sedimentary rock Minerals in rocks Figure 5.3 Detritivores Detritus consists of dead organic matter and the decomposers on it Bacteria and Fungi Detritivores feed on detritus Gain energy contained in decomposers Process dead organic matter for further decomposition Primary Production: The Energy of Ecosystems Physical and chemical factors limit primary production in ecosystems Primary production in an ecosystem Is the amount of light energy converted to chemical energy by autotrophs during a given time period Sets the energy budget of the ecosystem Detritivores & Decomposers may process 5% of an ecosystems chemical energy 2

3 The Global Energy Budget The amount of solar radiation reaching the surface of the Earth Limits the photosynthetic output of ecosystems Only a small fraction of solar energy Actually strikes photosynthetic organisms Gross and Net Primary Production Total primary production in an ecosystem is the Ecosystem s gross primary production (GPP) Only some of this production is stored as organic material in the growing plants Net primary production (NPP) Is equal to GPP minus the energy used by the primary producers for respiration Only NPP is to Global NPP: Net Primary Production of the Earth Different ecosystems vary considerably in their net primary production & contribution to global NPP Open ocean Continental shelf Estuary Algal beds and reefs Upwelling zones Extreme desert, rock, sand, ice Desert and semidesert scrub Tropical rain forest Savanna Cultivated land Boreal forest (taiga) Temperate grassland Woodland and shrubland Tundra Tropical seasonal forest Temperate deciduous forest Temperate evergreen forest Key Marine Swamp and marsh Lake and stream , 1,5 2, 2, (a) Percentage of Earth s surface area Terrestrial Freshwater (on continents) Figure 5.a c (b) ,2 1,5 1,3 Average net primary production (g/m 2 /yr) 1,6 2,5 2,2 2, (c) Percentage of Earth s net primary production 22 Global NPP: Net Primary Production of the Earth Terrestrial ecosystems contribute about 2/3 s of global NPP; Marine ecosystems about 1/3 North Pole 6 N 3 N Equator 3 S 6 S South Pole W 6 W 6 E 12 E 18 Figure 5.5 Marine and Freshwater Ecosystems Light and nutrients limit primary production in aquatic ecosystems Light is absorbed by water Photosynthesis is limited to surface waters Nutrient Addition Experiments Confirmed nitrogen was the limiting resource for phytoplankton growth off Long Island, NY EXPERIMENT Pollution 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. Nutrients limit primary production A limiting nutrient (resource) is the element that must be added for production to increase Nitrogen & phosphorous most often limit marine production Coast of Long Island, New York. The numbers on the map indicate the data collection stations. 2 Long Island 5 Great South Bay Shinnecock Bay Moriches Bay Atlantic Ocean 3

4 Marine Ecosystems may be limited by Nitrogen RESULTS Phytoplankton abundance parallels the abundance of phosphorus in the water (a). Nitrogen, however, is immediately taken up by algae, and no free nitrogen is measured in the coastal waters. The addition of ammonium (NH + ) caused heavy phytoplankton growth in bay water, but the addition of phosphate (PO 3+ ) did not induce algal growth (b). Addition Experiments in the Sargasso Sea Iron limits primary production Phytoplankton (millions of cells/ml) 8 Phytoplankton 7 6 phosphorus Station number Great Moriches South Bay Bay phosphorus (µg atoms/l) 1 Shinnecock Bay Phytoplankton (millions of cells per ml) Ammonium enriched Phosphate enriched Unenriched control Starting algal Station number density (a) Phytoplankton biomass and phosphorus concentration (b) Phytoplankton response to nutrient enrichment CONCLUSION Since adding phosphorus, which was already in rich supply, had no effect on Nannochloris growth, whereas adding nitrogen increased algal density dramatically, researchers concluded that nitrogen was the nutrient limiting phytoplankton growth in this ecosystem. Figure 5.6 Table 5.1 In some areas, sewage runoff Has caused eutrophication of lakes, which can lead to the eventual loss of most fish species from the lakes Primary Production in Terrestrial & Wetland Ecosystems In terrestrial and wetland ecosystems climatic factors Such as temperature and moisture, affect primary production on a large geographic scale The contrast between wet and dry climates Can be represented by a measure called actual evapotranspiration Figure 5.7 Actual evapotranspiration Is the amount of water annually transpired by plants and evaporated from a landscape Is related to net primary production Figure 5.8 Net primary production (g/m 2 /yr) 3, 2, 1, Desert shrubland Arctic tundra Temperate forest Mountain coniferous forest Temperate grassland 5 1, 1,5 Actual evapotranspiration (mm H 2O/yr) Tropical forest On local scales, soil nutrients often are the limiting factor in primary production Live, above-ground biomass (g dry wt/m 2 ) Adding nitrogen (N) boosts net primary production. Experimental plots receiving just phosphorus (P) do not outproduce the unfertilized control plots. N + P June July August 198 N only Control P only

5 Energy Transfers Limit Trophic Structure Energy transfer between trophic levels Is the percentage of production transferred from one trophic level to the next Usually ranges from 5% to 2% (~ 1%) Production Efficiency When a caterpillar feeds on a plant leaf Only about one-sixth of the energy in the leaf is used for secondary production The secondary production of an ecosystem Plant material eaten by caterpillar Is the amount of chemical energy in food that is converted to their own new biomass during a given period of time Feces 1 J 2 J 33 J 67 J Cellular respiration Figure 5.1 Growth (new biomass) Pyramids of Production This loss of energy with each transfer in a food chain Can be represented by a pyramid of net production Tertiary 1 J The dynamics of energy flow through ecosystems Have important implications for the human population Secondary Primary 1 J 1, J Eating meat Is a relatively inefficient way of tapping photosynthetic production Primary producers 1, J Figure ,, J of sunlight Worldwide agriculture could successfully feed many more people If humans all fed more efficiently, eating only plant material Trophic level Secondary Primary Primary producers Figure 5.1 Nutrient Cycles Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem Life on Earth Depends on the recycling of essential chemical elements Nutrient circuits that cycle matter through an ecosystem Involve both biotic and abiotic components and are often called biogeochemical cycles 5

6 A General Model of Chemical Cycling Gaseous forms of carbon, oxygen, sulfur, and nitrogen Occur in the atmosphere and cycle globally Less mobile elements, including phosphorous, potassium, and calcium Nutrient Cycles A general model of nutrient cycling Reservoir a Reservoir b Organic Organic un Fossilization Living organisms, Coal, oil, detritus peat Cycle on a more local level Assimilation, photosynthesis Respiration, decomposition, excretion Burning of fossil fuels All elements Cycle between organic & inorganic reservoirs Reservoir c Weathering, erosion Reservoir d un Figure 5.16 Atmosphere, soil, water Formation of sedimentary rock Minerals in rocks Biogeochemical Cycles The water cycle and the carbon cycle Water moves in a global cycle THE WATER CYCLE THE CARBON CYCLE Driven by solar energy Transport over land CO 2 in atmosphere Photosynthesis The carbon cycle Precipitation over ocean Solar energy Net movement of water vapor by wind Evaporation from ocean Evapotranspiration from land Precipitation over land Burning of fossil fuels and wood Cellular respiration Higher-level Primary Reflects the reciprocal processes of photosynthesis and cellular respiration Runoff and groundwater Percolation through soil Carbon compounds Detritus in water Decomposition Figure 5.17 The nitrogen cycle and the phosphorous cycle THE NITROGEN CYCLE THE PHOSPHORUS CYCLE Most of the nitrogen cycling in natural ecosystems N 2 in atmosphere Rain Involves local cycles between organisms and soil or water Assimilation Denitrifying NO - bacteria 3 Nitrogen-fixing bacteria in root Decomposers nodules of legumes Nitrifying Nitrification bacteria Ammonification Geologic uplift Weathering of rocks Runoff Sedimentation Soil Leaching Plants Consumption Plant uptake of PO 3- The phosphorus cycle Is relatively localized NH 3 NH + NO 2 - Nitrogen-fixing soil bacteria Nitrifying bacteria Decomposition Figure

7 Decomposition and Nutrient Cycling Rates Decomposers and Detritivores play a key role In the general pattern of chemical cycling Humans and the Biosphere The human population is disrupting chemical cycles throughout the biosphere As the human population has grown in size Consumers Producers Nutrients to producers Decomposers Our activities have disrupted the trophic structure, energy flow, and chemical cycling of ecosystems in most parts of the world Abiotic reservoir Figure 5.18 Geologic processes Nutrient Enrichment and Acid Rain Sewage runoff contaminates freshwater ecosystems Biological Magnification: DDT, PCBs Toxins concentrate at higher trophic levels because at these levels biomass tends to be lower Causing eutrophication, excessive algal growth, which can cause significant harm to these ecosystems Herring gull eggs 12 ppm Combustion of fossil fuels Is the main cause of acid precipitation Concentration of PCBs Smelt 1. ppm Lake trout.83 ppm Figure 5.23 Zooplankton.123 ppm Phytoplankton.25 ppm Rising Atmospheric CO 2 and Global Warming Due to the increased burning of fossil fuels and other human activities atmospheric CO 2 has been steadily increasing Depletion of Atmospheric Ozone An atmospheric ozone layer protects life on earth from harmful UV radiation, but the The ozone layer has been thinning since CO 2 concentration (ppm) Temperature CO Temperature variation ( C) Ozone layer thickness (Dobson units) Figure Year Figure Year (Average for the month of October) 7

8 The destruction of atmospheric ozone Probably results from chlorine-releasing pollutants produced by human activity Scientists first described an ozone hole Over Antarctica in 1985; it has increased in size as ozone depletion has increased Chlorine atoms 1 Chlorine from CFCs interacts with ozone (O 3 ), forming chlorine monoxide (ClO) and oxygen (O 2 ). O 2 Chlorine O 3 ClO O 2 3 Sunlight causes Cl 2 O 2 to break ClO Figure 5.27 down into O 2 and free chlorine atoms. The chlorine atoms can begin the cycle again. Sunlight Cl 2 O 2 2 Two ClO molecules react, forming chlorine peroxide (Cl 2 O 2 ). (a) October 1979 (b) October 2 Figure 5.28a, b Global Warming & Climate Change Anthropogenic release of greenhouse gases has increased average global temperatures Increased average global temperatures will Intensify the water cycle and atmospheric activity Raise sea-level Change local climates The Intergovernmental Panel on Climate Change The IPCC is a UN-sponsored body made up of scientists and representatives of 188 countries Creates Consensus Assessment Reports The Fourth Assessment Report (AR) was completed in early 27[11]. Like previous assessment reports, it consists of four reports, three of them from its working groups. Stress local ecosystems and communities IPCC th Assessment Report: Climate Change 27 Part I "Physical Science Basis of Climate Change." Warming of the climate system is unequivocal. Most of the observed increase in globally averaged temperatures since the mid-2th century is very likely due to the observed increase in anthropogenic (human) greenhouse gas concentrations. Anthropogenic warming and sea level rise would continue for centuries due to the timescales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilized, although the likely amount of temperature and sea level rise varies greatly depending on the fossil intensity of human activity during the next century (pages 13 and 18)[13]. IPCC th Assessment Report: Climate Change 27, cont. The probability that this is caused by natural climatic processes alone is less than 5%. World temperatures could rise by between 1.1 and 6. C (2. and 11.5 F) during the 21st century (table 3) and that: Sea levels will probably rise by 18 to 59 cm (7.8 to in) [table 3]. There is a confidence level >9% that there will be more frequent warm spells, heat waves and heavy rainfall. There is a confidence level >66% that there will be an increase in droughts, tropical cyclones and extreme high tides. 8

9 IPCC th Assessment Report: Climate Change 27, cont. Both past and future anthropogenic carbon dioxide emissions will continue to contribute to warming and sea level rise for more than a millennium (1+ yrs) Global atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased markedly as a result of human activities since 175 and now far exceed pre-industrial values over the past 65, years In IPCC statements "most" means greater than 5%, "likely" means at least a 66% likelihood, and "very likely" means at least a 9% likelihood. Focus the Nation Nation-wide educational event, Jan Focus attention on the problem Develop the political will to act Video (background) 9