Ecosystems & Climate Change PDF

Overview: Ecosystems Chapter 55 An ecosystem consists of all the organisms living in a community, as well as the abiotic f...

Overview: Ecosystems Chapter 55 An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with which Ecosystems they interact. Ecosystems range from a microcosm, such as an aquarium, to a large area such as a lake or forest. Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and PowerPoint® Lecture Presentations for chemical cycling. Biology Energy flows through ecosystems while matter cycles Eighth Edition Neil Campbell and Jane Reece within them. Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Physical laws govern energy flow and chemical Conservation of Mass cycling in ecosystems Laws of physics and chemistry apply to the The law of conservation of mass states that transformations of energy and matter within the matter cannot be created or destroyed. ecosystems, particularly energy flow. The first law of thermodynamics states that energy Chemical elements are continually recycled cannot be created or destroyed, only transformed. within ecosystems. Energy enters an ecosystem as solar radiation, is conserved, and is lost from organisms as heat. In a forest ecosystem, most nutrients enter as The second law of thermodynamics states that every dust or solutes in rain and are carried away in exchange of energy increases the entropy of the water. universe. In an ecosystem, energy conversions are not completely efficient, and some energy is always Ecosystems are open systems, absorbing lost as heat. energy and mass and releasing heat and waste products. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Energy, Mass, and Trophic Levels Autotrophs build organic molecules themselves Detritivores, or decomposers, are consumers using photosynthesis or chemosynthesis as an that derive their energy from detritus, nonliving energy source. organic matter. Heterotrophs depend on the biosynthetic Prokaryotes and fungi are important output of other organisms. detritivores. Energy and nutrients pass from primary producers (autotrophs) to primary Decomposition connects all trophic levels. consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (carnivores that feed on other carnivores). Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fungi Energy and Nutrient decomposing Dynamics in an Ecosystem a dead tree Tertiary consumers Microorganisms and other detritivores Secondary consumers Detritus Primary consumers Primary producers Heat Key Chemical cycling Sun Energy flow Energy and other limiting factors control primary Gross and Net Primary Production production in ecosystems Primary production in an ecosystem is the amount of Total primary production is known as the light energy converted to chemical energy by ecosystem’s gross primary production = GPP autotrophs during a given time period. The extent of photosynthetic production sets the spending limit for Net primary production = NPP is GPP minus an ecosystem’s energy budget. energy used by primary producers for respiration. The amount of solar radiation reaching the Earth’s NPP = GPP - Respiration surface limits photosynthetic output of ecosystems. Only NPP is available to consumers. Only a small fraction of solar energy actually strikes photosynthetic organisms, and even less is of a Standing crop is the total biomass of usable wavelength. photosynthetic autotrophs at a given time. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Global net primary production in 2002 Tropical rain forests, estuaries, and coral reefs are among the most productive ecosystems per unit area. Marine ecosystems are relatively unproductive Global net primary production in 2002 per unit area, but contribute much to global net primary production because of their volume. Net primary production (kg carbon/m 2·yr) · 0 1 2 3 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Primary Production in Aquatic Ecosystems Nutrient Limitation In marine and freshwater ecosystems, both More than light, nutrients limit primary production light and nutrients control primary production. in geographic regions of the ocean and in lakes. Depth of light penetration affects primary A limiting nutrient is the element that must be production in the photic zone of an ocean or added for production to increase in an area. lake. Nitrogen and phosphorous are typically the nutrients that most often limit marine production. Nutrient enrichment experiments confirmed that nitrogen was limiting phytoplankton growth. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Relationship between net primary production and actual evapotranspiration in six Primary Production in Terrestrial Ecosystems terrestrial ecosystems 3,000 Tropical forest Net primary production (g/m2··yr) In terrestrial ecosystems, temperature and moisture affect primary production on a large scale. 2,000 Actual evapotranspiration can represent the contrast between wet and dry climates. Temperate forest Actual evapotranspiration is the water 1,000 Mountain coniferous forest annually transpired by plants and evaporated Desert Temperate grassland from a landscape. It is related to net primary shrubland production. Arctic tundra 0 On a local scale, a soil nutrient is often the 0 500 1,000 1,500 limiting factor in primary production. Actual evapotranspiration (mm H2O/yr) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Energy transfer between trophic levels is typically Energy only 10% efficient partitioning within a link of the food Secondary production of an ecosystem is the chain amount of chemical energy in food converted Plant material to new biomass during a given period of time. eaten by caterpillar When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for 200 J secondary production. An organism’s production efficiency is the 67 J Cellular fraction of energy stored in food that is not Feces 100 J respiration 33 J used for respiration. Growth (new biomass) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Trophic Efficiency and Ecological Pyramids Tertiary consumers 10 J Trophic efficiency is the percentage of production transferred from one trophic level to Secondary the next. 10% Law of Energy Transfer consumers 100 J Trophic efficiency is multiplied over the length of a food chain. Primary 1,000 J consumers Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer. Primary producers 10,000 J A pyramid of net production represents the loss of energy with each transfer in a food chain. 1,000,000 J of sunlight Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Biological and geochemical processes cycle Biogeochemical Cycles nutrients between organic and inorganic parts of an ecosystem Gaseous carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally. Life depends on recycling chemical elements. Less mobile elements such as phosphorus, Nutrient circuits in ecosystems involve biotic potassium, and calcium cycle on a more local and abiotic components and are often called level. biogeochemical cycles. A model of nutrient cycling includes main reservoirs of elements and processes that transfer elements between reservoirs. All elements cycle between organic and inorganic reservoirs. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Nutrient Reservoir A Reservoir B Cycling Organic Organic materials materials available as nutrients unavailable as nutrients In studying cycling of water, carbon, nitrogen, Living Fossilization and phosphorus, ecologists focus on four Coal, oil, organisms, detritus peat factors: – Each chemical’s biological importance Respiration, Assimilation, decomposition, photosynthesis excretion Burning – Forms in which each chemical is available or of fossil fuels Reservoir C Reservoir D used by organisms Inorganic Inorganic materials materials – Major reservoirs for each chemical available Weathering, unavailable as nutrients erosion as nutrients – Key processes driving movement of each Atmosphere, Minerals chemical through its cycle. soil, water Formation of in rocks sedimentary rock Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Nutrient Cycles: The Water Cycle Water Cycle Transport Water is essential to all organisms. Solar energy over land 97% of the biosphere’s water is contained in Net movement of water vapor by wind the oceans, 2% is in glaciers and polar ice Precipitation caps, and 1% is in lakes, rivers, and Precipitation Evaporation over ocean from ocean over land groundwater. Evapotranspiration from land Water moves by the processes of evaporation, Percolation transpiration, condensation, precipitation, and through soil movement through surface and groundwater. Runoff and groundwater Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Nutrient The Carbon Cycle Cycles: Carbon CO2 in atmosphere Carbon-based organic molecules are essential Cycle Photosynthesis to all organisms. Photo- Cellular synthesis respiration Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and animal biomass, and the atmosphere. Burning of fossil fuels Phyto- and wood plankton Higher-level CO2 is taken up and released through Primary consumers consumers photosynthesis and respiration; additionally, Carbon compounds Detritus in water volcanoes and the burning of fossil fuels contribute CO2 to the atmosphere. Decomposition Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Nutrient The Terrestrial Nitrogen Cycle Cycles: Nitrogen Nitrogen is a component of amino acids, proteins, and Cycle N2 in atmosphere nucleic acids The main reservoir of nitrogen is the atmosphere (N2), though this nitrogen must be converted to NH4+ or NO3– for uptake by plants, via nitrogen fixation by Assimilation Denitrifying bacteria. NO 3– bacteria Nitrogen-fixing bacteria Organic nitrogen is decomposed to NH4+ by Decomposers Nitrifying bacteria ammonification, and NH4+ is decomposed to NO3– by Ammonification Nitrification NH3 nitrification. NH4+ NO2– Nitrogen-fixing Nitrifying soil bacteria bacteria Denitrification converts NO3– back to N2 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Nutrient The Phosphorus Cycle Cycles: Phosphorous Phosphorus is a major constituent of nucleic Cycle Precipitation acids, phospholipids, and ATP. Geologic Weathering uplift of rocks Phosphate (PO43–) is the most important Runoff inorganic form of phosphorus. Consumption Decomposition Plant uptake The largest reservoirs are sedimentary rocks of Plankton Dissolved PO43– of PO43– Soil marine origin, the oceans, and organisms. Uptake Leaching Sedimentation Phosphate binds with soil particles, and movement is often localized. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Decomposition and Nutrient Cycling Rates Case Study: Nutrient Cycling in the Hubbard Brook Experimental Forest Decomposers = detritivores play a key role in Vegetation strongly regulates nutrient cycling. the general pattern of chemical cycling. Research projects monitor ecosystem Rates at which nutrients cycle in different dynamics over long periods. ecosystems vary greatly, mostly as a result of differing rates of decomposition. The Hubbard Brook Experimental Forest has been used to study nutrient cycling in a forest The rate of decomposition is controlled by ecosystem since 1963. temperature, moisture, and nutrient availability. The research team constructed a dam on the Rapid decomposition results in relatively low site to monitor loss of water and minerals. levels of nutrients in the soil. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Nutrient Cycling in the In one experiment, the trees in one valley were cut Hubbard Brook Experimental down, and the valley was sprayed with herbicides. Net Forest: an losses of water and minerals were studied and found example of (a) Concrete dam and weir to be greater than in an undisturbed area. long-term ecological These results showed how human activity can affect research (b) Clear-cut watershed ecosystems. As the human population has grown, our activities Nitrate concentration in runoff 80 Deforested 60 40 have disrupted the trophic structure, energy flow, and 20 chemical cycling of many ecosystems. (mg/L) 4 Completion of tree cutting 3 2 Control In addition to transporting nutrients from one location 1 to another, humans have added new materials, some 0 1965 1966 1967 1968 of them toxins, to ecosystems. (c) Nitrogen in runoff from watersheds Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Agriculture and Nitrogen Cycling Contamination of Aquatic Ecosystems The quality of soil varies with the amount of Critical load for a nutrient is the amount that organic material it contains. plants can absorb without damaging the ecosystem. Agriculture removes from ecosystems nutrients that would ordinarily be cycled back into the When excess nutrients are added to an soil. ecosystem, the critical load is exceeded. Nitrogen is the main nutrient lost through Remaining nutrients can contaminate agriculture; thus, agriculture greatly affects the groundwater as well as freshwater and marine nitrogen cycle. ecosystems. Industrially produced fertilizer is typically used Sewage runoff causes cultural eutrophication, to replace lost nitrogen, but effects on an excessive algal growth that can greatly harm ecosystem can be harmful. freshwater ecosystems. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Toxins in the Environment Biological Magnification of PCBs in a Humans release many toxic chemicals, including Great Lakes Herring synthetics previously unknown to nature. In some food web gull eggs 124 ppm cases, harmful substances persist for long periods in an ecosystem. Lake trout 4.83 ppm One reason toxins are harmful is that they become more concentrated in successive trophic levels. Smelt 1.04 ppm Biological magnification concentrates toxins at higher trophic levels. PCBs and many pesticides such as DDT are subject to biological magnification in ecosystems. Zooplankton Phytoplankton 0.123 ppm 0.025 ppm Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Greenhouse Gases and Global Warming The Greenhouse Effect and Climate One pressing problem caused by human CO2, water vapor, and other greenhouse gases activities is the rising level of atmospheric reflect infrared radiation back toward Earth; this carbon dioxide. is the greenhouse effect. Due to the burning of fossil fuels and other This effect is important for keeping Earth’s human activities, the concentration of surface at a habitable temperature. atmospheric CO2 has been steadily increasing. Increased levels of atmospheric CO2 are magnifying the greenhouse effect, which could cause global warming and climatic change. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Depletion of Atmospheric Ozone Increasing concentration of atmospheric CO2 is linked to increasing global temperature. Northern coniferous Life on Earth is protected from damaging forests and tundra show the strongest effects of global effects of UV radiation by a protective layer of warming. ozone molecules in the atmosphere. A warming trend would also affect the geographic Satellite studies suggest that the ozone layer distribution of precipitation. has been gradually thinning since 1975. Global warming can be slowed by reducing energy needs and converting to renewable sources of energy. Destruction of atmospheric ozone probably results from chlorine-releasing pollutants such Stabilizing CO2 emissions will require an international as CFCs (chloroflorocarbons) produced by effort. human activity. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings How free chlorine in the atmosphere destroys ozone Chlorine atom O2 Scientists first described an “ozone hole” over Chlorine O3 Antarctica in 1985; it has increased in size as ozone depletion has increased. ClO Ozone depletion causes DNA damage in plants O2 and poorer phytoplankton growth. ClO An international agreement signed in 1987 has Cl2O2 resulted in a decrease in ozone depletion. Sunlight Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Erosion of Earth’s ozone shield (a) September 1979 (b) September 2006