Chapter 54 Ecosystems

Ecosystems Microcosm: aquarium Lakes, forests Figure 54.1

Dynamics Energy flows Matter cycles

Ecosystem ecologists Monitor energy & matter

Energy flows Light - heat Figure 54.2 Tertiary consumers Microorganisms and other detritivores Detritus Primary producers Primary consumers Secondary consumers Tertiary consumers Heat Sun Key Chemical cycling Energy flow

Decomposition – connects levels Detritivores, (bacteria, fungi) recycle chemical elements Figure 54.3

Primary production Amount of light energy converted to chemical energy by autotrophs during a given time period

Ecosystem Energy Budgets The extent of photosynthetic production Sets the spending limit for the energy budget of the entire ecosystem

The Global Energy Budget Only a small fraction of solar energy Actually strikes photosynthetic organisms

Gross and Net Primary Production GPP – total production Not all stored as organic material in growing plants

Only NPP is available to consumers GPP minus energy used by 1o producers for respiration Only NPP is available to consumers

NPP varies in ecosystems 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)

Gobal NPP Terrestrial 2/3 Marine 1/3 Figure 54.5 180 120W 60W 0 North Pole 60N 30N Equator 30S 60S South Pole

Primary Production in Marine and Freshwater Ecosystems

Light Limitation light penetration Affects primary production throughout the photic zone of an ocean or lake

Limiting nutrient: element that must be added Nutrient limitation Limiting nutrient: element that must be added for production to increase in a particular area Nitrogen and phosphorous most often limit marine production

Nutrient enrichment

Iron may limit PP Table 54.1

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

Eutrophication Sewage runoff may cause eutrophication Figure 54.7

Primary Production in Terrestrial and Wetland Ecosystems Climate factors such as temperature and moisture affect primary production on a large geographic scale

Evapotranspiration measurements Actual evapotranspiration amount of water annually transpired by plants and evaporated from a landscape related to net primary production Figure 54.8 Actual evapotranspiration (mm H2O/yr) Tropical forest Temperate forest Mountain coniferous forest Temperate grassland Arctic tundra Desert shrubland Net primary production (g/m2/yr) 1,000 2,000 3,000 500 1,500

Live, above-ground biomass Nutrients local scale soil nutrient often limiting Figure 54.9 EXPERIMENT Over the summer of 1980, researchers added phosphorus to some experimental plots in the salt marsh, nitrogen to other plots, and both phosphorus and nitrogen to others. Some plots were left unfertilized as controls. RESULTS Experimental plots receiving just phosphorus (P) do not outproduce the unfertilized control plots. CONCLUSION Live, above-ground biomass (g dry wt/m2) Adding nitrogen (N) boosts net primary production. 300 250 200 150 100 50 June July August 1980 N  P N only Control P only These nutrient enrichment experiments confirmed that nitrogen was the nutrient limiting plant growth in this salt marsh.

Between trophic levels < 20% efficient 2o production Energy transfer Between trophic levels < 20% efficient 2o production amount of chemical energy in consumers’ food converted to 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 efficiency of organism Fraction of energy stored in food that is not used for respiration

Trophic Efficiency and Ecological Pyramids percentage of production transferred from one trophic level to the next ranges from 5% to 20%

Pyramids of Production Shows energy loss Figure 54.11 Tertiary consumers Secondary Primary producers 1,000,000 J of sunlight 10 J 100 J 1,000 J 10,000 J

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 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 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

Energy flow dynamics Eating meat important for human population Is a relatively inefficient way of tapping photosynthetic production

Worldwide agriculture could successfully feed many more people If humans all fed more efficiently, eating only plant material Trophic level Secondary consumers Primary producers Figure 54.14

The Green World Hypothesis Terrestrial herbivores consume relatively little plant biomass because they are held in check by a variety of factors

Most terrestrial ecosystems Have large standing crops despite large numbers of herbivores Figure 54.15

Several factors keep herbivores in check Plant defenses Nutrients Abiotic factors Intraspecific competition Interspecific interactions

Biogeochemical cycles Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem Life on Earth Depends on recycling of essential chemical elements

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

Model of nutrient cycling Includes main reservoirs of elements and 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

All elements Cycle between organic and inorganic reservoirs

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

Water moves in a global cycle Driven by solar energy The carbon cycle Reflects the reciprocal processes of photosynthesis and cellular respiration

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

Decomposition and Nutrient Cycling Rates Decomposers (detritivores) play a key role Figure 54.18 Consumers Producers Nutrients available to producers Abiotic reservoir Geologic processes Decomposers

Nutrient cycling rates Are extremely variable, mostly as a result of differences in rates of decomposition

Vegetation and Nutrient Cycling: The Hubbard Brook Experimental Forest Is strongly regulated by vegetation

The research team constructed a dam on the site Hubbard Brook The research team constructed a dam on the site To monitor water and mineral loss Figure 54.19a (a) Concrete dams and weirs built across streams at the bottom of watersheds enabled researchers to monitor the outflow of water and nutrients from the ecosystem.

Trees in one valley were cut down Sprayed with herbicides Figure 54.19b (b) One watershed was clear cut to study the effects of the loss of vegetation on drainage and nutrient cycling.

Nitrate concentration in runoff Net losses of water and minerals Were found to be greater in disturbed area Figure 54.19c (c) The concentration of nitrate in runoff from the deforested watershed was 60 times greater than in a control (unlogged) watershed. Nitrate concentration in runoff (mg/L) Deforested Control Completion of tree cutting 1965 1966 1967 1968 80.0 60.0 40.0 20.0 4.0 3.0 2.0 1.0

We are disrupting chemical cycles throughout the biosphere With human population increase Our activities disrupted trophic structure, energy flow, and chemical cycling of ecosystems in most parts of the world

Nutrient Enrichment Transporting nutrients Adding new materials (some toxic)

Agriculture and Nitrogen Cycling Agriculture constantly removes nutrients from ecosystems That would ordinarily be cycled back into the soil Figure 54.20

Agriculture has a great impact on nitrogen cycle Fertilizer used to replace 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 critical load exceeded Remaining nutrients can contaminate groundwater and freshwater and marine ecosystems

Sewage runoff contaminates freshwater ecosystems Eutrophication Change in species composition or species loss

Combustion of fossil fuels Acid Precipitation Combustion of fossil fuels Is the main cause of acid precipitation

North American and European ecosystems downwind from industrial regions Have been damaged by rain and snow containing nitric and sulfuric acid Figure 54.21 4.6 4.3 4.1 Europe North America

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

In biological magnification Toxins concentrate at higher trophic levels because at these levels biomass tends to be lower 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

In some cases, harmful substances Persist for long periods of time in an ecosystem and continue to cause harm

Atmospheric Carbon Dioxide One pressing problem caused by human activities Is the rising level of atmospheric carbon dioxide

Rising Atmospheric CO2 Due to the increased burning of fossil fuels and other human activities The concentration of atmospheric CO2 has been steadily increasing 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

How Elevated CO2 Affects Forest Ecology: The FACTS-I Experiment The FACTS-I experiment is testing how elevated CO2 Influences tree growth, carbon concentration in soils, and other factors over a ten-year period Figure 54.25

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 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

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

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