Chapter 55 Ecosystems
Overview: Ecosystems, Energy, and Matter An ecosystem consists of all the organisms living in a community As well as all the abiotic factors with which they interact Regardless of an ecosystem’s size Its dynamics involve two main processes: energy flow and chemical cycling Energy flows through ecosystems IN ONE DIRECTION ONLY while matter CYCLES within them
Visual Overview: Energy Flow
Ecosystems and Physical Laws Ecosystem ecology emphasizes energy flow and chemical cycling Ecosystem ecologists view ecosystems As transformers of energy and processors of matter 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
Trophic Relationships Energy and nutrients pass from primary producers (autotrophs) To primary consumers (herbivores) and then to secondary consumers (carnivores) Energy flows IN ONE DIRE CTION ONLY through an ecosystem entering as light and exiting as heat – decomposition connects all trophic levels Nutrients CYCLE within ecosystems
Energy Flow & Nutrient Cycles Figure 54.2 Microorganisms and other detritivores Detritus Primary producers Primary consumers Secondary consumers Tertiary consumers Heat Sun Key Chemical cycling Energy flow
Recycling Nutrients Detritivores, mainly bacteria and fungi, recycle essential chemical elements By decomposing organic material and returning elements to inorganic reservoirs Figure 54.3
Primary Production in Ecosystems Photosynthesis Involves the use of light energy in the conversion of inorganic carbon into organic carbon. Photosynthetic organisms include: terrestrial plants, seaweeds, phytoplankton, blue-green algae, and zooxanthellae.
Primary Productivity in 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 The extent of photosynthetic production sets the spending limit for the energy budget of the entire ecosystem 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
Fate of Solar Energy
Gross Primary Productivity (GP) The rate of production of organic matter from inorganic materials by autotrophic organisms Respiration (R) The rate of consumption of organic matter (conversion to inorganic matter) by organisms. Net Primary Productivity (NP) The net rate of organic matter produced as a consequence of both GP and R.
Primary Productivity: Formula
Gross and Net Primary Production Total primary production in an ecosystem Is known as that ecosystem’s gross primary production (GPP) Not all 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 available to consumers
NPP of Varying Ecosystems Different ecosystems vary considerably in their net primary production and in their contribution to the total NPP on Earth Lake and stream 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 Tundra Tropical seasonal forest Temperate deciduous forest Temperate evergreen forest Swamp and marsh Woodland and shrubland 10 20 30 40 50 60 500 1,000 1,500 2,000 2,500 5 15 25 Percentage of Earth’s net primary production Key Marine Freshwater (on continents) Terrestrial 5.2 0.3 0.1 4.7 3.5 3.3 2.9 2.7 2.4 1.8 1.7 1.6 1.5 1.3 1.0 0.4 125 360 3.0 90 2,200 900 600 800 700 140 1,600 1,200 1,300 250 5.6 1.2 0.9 0.04 22 7.9 9.1 9.6 5.4 0.6 7.1 4.9 3.8 2.3 65.0 24.4 Figure 54.4a–c Percentage of Earth’s surface area (a) Average net primary production (g/m2/yr) (b) (c)
Terrestrial Ecosystems Overall, terrestrial ecosystems contribute about two-thirds of global NPP and marine ecosystems about one-third Figure 54.5 180 120W 60W 0 60E 120E North Pole 60N 30N Equator 30S 60S South Pole
Environmental Factors Effect Production
Primary Production in Marine and Freshwater Ecosystems Both light and nutrients are important in controlling primary production The depth of light penetration Affects primary production throughout the photic zone of an ocean or lake More than light, nutrients limit primary production Both in different geographic regions of the ocean and in lakes
Limits to Marine & Freshwater Ecosystems A limiting nutrient is the element that must be added In order for production to increase in a particular area Nitrogen and phosphorous Are typically the nutrients that most often limit marine production The addition of large amounts of nutrients to lakes has a wide range of ecological impacts
Algal Blooms When an aquatic ecosystem receives a large input of a limiting nutrient, the result is often an immediate increase in the amount of algae & other producers Leads to algal blooms Algal blooms occur because there are suddenly more nutrients available…so producers can grow and reproduce more quickly…and if there aren’t enough consumers to eat the producers, then algal blooms can cover the surface of the water. Runoff from heavy fertilizers can lead to algal blooms
Eutrophication In some areas, sewage runoff has caused eutrophication of lakes, which can lead to the eventual loss of most fish species from the lakes Figure 54.7
Primary Production in Terrestrial and Wetland Ecosystems In terrestrial and wetland ecosystems climatic factors Such as temperature and moisture, affect primary production on a large geographic scale On a more local scale A soil nutrient is often the limiting factor in primary production
Efficiency of Energy Transfer in Ecosystems Energy transfer between trophic levels is usually less than 20% efficient The secondary production of an ecosystem Is the amount of chemical energy in consumers’ food that is converted to their own new biomass during a given period of time
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 Figure 54.10 Plant material eaten by caterpillar Cellular respiration Growth (new biomass) Feces 100 J 33 J 200 J 67 J
Production & Trophic Efficiency The production efficiency of an organism Is the fraction of energy stored in food that is not used for respiration Trophic efficiency Is the percentage of production transferred from one trophic level to the next Usually ranges from 5% to 20% Decreases moving between trophic levels because much energy is used for metabolism and life processes, and much is lost as entropy (heat waste)
Pyramids of Production This loss of energy with each transfer in a food chain Can be represented by a pyramid of net production Figure 54.11 Tertiary consumers Secondary Primary producers 1,000,000 J of sunlight 10 J 100 J 1,000 J 10,000 J
Pyramids of Biomass One important ecological consequence of low trophic efficiencies can be represented in a biomass pyramid Most biomass pyramids show a sharp decrease at successively higher trophic levels Figure 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 level Dry weight (g/m2) Primary producers Tertiary consumers Secondary consumers Primary consumers 1.5 11 37 809
Certain aquatic ecosystems have inverted biomass pyramids Pyramids of Biomass Certain aquatic ecosystems have inverted biomass pyramids Figire 54.12b Trophic level Primary producers (phytoplankton) Primary consumers (zooplankton) (b) In some aquatic ecosystems, such as the English Channel, a small standing crop of primary producers (phytoplankton) supports a larger standing crop of primary consumers (zooplankton). Dry weight (g/m2) 21 4
Number of individual organisms Pyramids of Numbers A pyramid of numbers represents the number of individual organisms in each trophic level Figure 54.13 Trophic level Number of individual organisms Primary producers Tertiary consumers Secondary consumers Primary consumers 3 354,904 708,624 5,842,424
Biogeochemical 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
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 Cycle on a more local level
Biogeochemical Cycles A general model of nutrient cycling Includes the main reservoirs of elements and the processes that transfer elements between reservoirs Figure 54.16 Organic materials available as nutrients Living organisms, detritus unavailable Coal, oil, peat Inorganic Atmosphere, soil, water Minerals in rocks Formation of sedimentary rock Weathering, erosion Respiration, decomposition, excretion Burning of fossil fuels Fossilization Reservoir a Reservoir b Reservoir c Reservoir d Assimilation, photosynthesis
Biogeochemical Cycles The water cycle and the carbon cycle Figure 54.17 Transport over land Solar energy Net movement of water vapor by wind Precipitation over ocean Evaporation from ocean Evapotranspiration from land Percolation through soil Runoff and groundwater CO2 in atmosphere Photosynthesis Cellular respiration Burning of fossil fuels and wood Higher-level consumers Primary Detritus Carbon compounds in water Decomposition THE WATER CYCLE THE CARBON CYCLE
Biogeochemical Cycles Water moves in a global cycle Driven by solar energy The carbon cycle Reflects the reciprocal processes of photosynthesis and cellular respiration
Biogeochemical Cycles The nitrogen cycle and the phosphorous cycle Figure 54.17 N2 in atmosphere Denitrifying bacteria Nitrifying Nitrification Nitrogen-fixing soil bacteria bacteria in root nodules of legumes Decomposers Ammonification Assimilation NH3 NH4+ NO3 NO2 Rain Plants Consumption Decomposition Geologic uplift Weathering of rocks Runoff Sedimentation Plant uptake of PO43 Soil Leaching THE NITROGEN CYCLE THE PHOSPHORUS CYCLE
Biogeochemical Cycles Most of the nitrogen cycling in natural ecosystems Involves local cycles between organisms and soil or water The phosphorus cycle Is relatively localized
Decomposition and Nutrient Cycling Rates Decomposers (detritivores) play a key role In the general pattern of chemical cycling Figure 54.18 Consumers Producers Nutrients available to producers Abiotic reservoir Geologic processes Decomposers
As the human population has grown in size The human population is disrupting chemical cycles throughout the biosphere As the human population has grown in size Our activities have disrupted the trophic structure, energy flow, and chemical cycling of ecosystems in most parts of the world
In addition to transporting nutrients from one location to another Nutrient Enrichment In addition to transporting nutrients from one location to another Humans have added entirely new materials, some of them toxins, to ecosystems Agriculture constantly removes nutrients from ecosystems That would ordinarily be cycled back into the soil
Nitrogen is the main nutrient lost through agriculture Thus, agriculture has a great impact on the nitrogen cycle Industrially produced fertilizer is typically used to replace lost nitrogen But the effects on an ecosystem can be harmful
Contamination of Aquatic Ecosystems The critical load for a nutrient Is the amount of that nutrient that can be absorbed by plants in an ecosystem without damaging it When excess nutrients are added to an ecosystem, the critical load is exceeded And the remaining nutrients can contaminate groundwater and freshwater and marine ecosystems
Contamination of Ecosystems Sewage runoff contaminates freshwater ecosystems Causing cultural eutrophication, excessive algal growth, which can cause significant harm to these ecosystems Combustion of fossil fuels Is the main cause of acid precipitation
Contamination of Ecosystems By the year 2000, the entire contiguous United States was affected by acid precipitation Figure 54.22 Field pH 5.3 5.2–5.3 5.1–5.2 5.0–5.1 4.9–5.0 4.8–4.9 4.7–4.8 4.6–4.7 4.5–4.6 4.4–4.5 4.3–4.4 4.3
Contamination of Ecosystems Environmental regulations and new industrial technologies Have allowed many developed countries to reduce sulfur dioxide emissions in the past 30 years
Toxins in the Environment Humans release an immense variety of toxic chemicals Including thousands of synthetics previously unknown to nature One of the reasons such toxins are so harmful Is that they become more concentrated in successive trophic levels of a food web
Biological Magnification In biological magnification toxins concentrate at higher trophic levels because at these levels biomass tends to be lower In some cases, harmful substances persist for long periods of time in an ecosystem and continue to cause harm Figure 54.23 Concentration of PCBs Herring gull eggs 124 ppm Zooplankton 0.123 ppm Phytoplankton 0.025 ppm Lake trout 4.83 ppm Smelt 1.04 ppm
Dichloro-diphenyl-trichloro-ethane (DDT): Toxins can become concentrated in successive trophic levels of food webs! Halogenated hydrocarbons or organochlorines: Include DDT and PCBs, which are slow to biodegrade Dichloro-diphenyl-trichloro-ethane (DDT): used as a pesticide from 1939-late 1960s fat soluble compound the world’s production has substantially decreased since it was banned in the West detected in mud of deep sea and snow & ice of Antarctica
Effect of PCBs & DDT Polychloronated biphenyls (PCBs) Toxins can become concentrated in successive trophic levels of food webs! Effect of PCBs & DDT Polychloronated biphenyls (PCBs) produced since 1944 banned in U.S. by 1979 used in production of electrical equipment, paints, plastics, adhesives, and coating compounds… found everywhere in the ocean released in env. by unregulated incineration of discarded products DDT & PCBs affects: copepod and oyster development death of shrimp and a variety of fish
Biomagnification In biomagnification, there is a tendency for pollutants to concentration as they move from one link in a food chain to another…top level carnivores suffer the most harmful effects of biomagnification.
Atmospheric Carbon Dioxide One pressing problem caused by human activities Is the rising level of atmospheric carbon dioxide Due to the increased burning of fossil fuels and other human activities The concentration of atmospheric CO2 has been steadily increasing
Rising Atmospheric CO2 Figure 54.24 CO2 concentration (ppm) 390 380 370 360 350 340 330 320 310 300 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 1.05 0.90 0.75 0.60 0.45 0.30 0.15 0.15 0.30 0.45 Temperature variation (C) Temperature CO2 Year
The Greenhouse Effect and Global Warming The greenhouse effect is caused by atmospheric CO2 But is necessary to keep the surface of the Earth at a habitable temperature Increased levels of atmospheric CO2 are magnifying the greenhouse effect Which could cause global warming and significant climatic change
Depletion of Atmospheric Ozone Life on Earth is protected from the damaging effects of UV radiation By a protective layer or ozone molecules present in the atmosphere Satellite studies of the atmosphere Suggest that the ozone layer has been gradually thinning since 1975
Depletion of Atmospheric Ozone Figure 54.26 Ozone layer thickness (Dobson units) Year (Average for the month of October) 350 300 250 200 150 100 50 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Depletion of Atmospheric Ozone The destruction of atmospheric ozone probably results from chlorine-releasing pollutants produced by human activity Figure 54.27 1 2 3 Chlorine from CFCs interacts with ozone (O3), forming chlorine monoxide (ClO) and oxygen (O2). Two ClO molecules react, forming chlorine peroxide (Cl2O2). Sunlight causes Cl2O2 to break down into O2 and free chlorine atoms. The chlorine atoms can begin the cycle again. Sunlight Chlorine O3 O2 ClO Cl2O2 Chlorine atoms
Depletion of Atmospheric Ozone Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased (a) October 1979 (b) October 2000 Figure 54.28a, b