ChapterChapter 5454 Ecosystems

PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Overview: Ecosystems, Energy, and Matter

• An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with which 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 chemical cycling • Energy flows through ecosystems while matter cycles within them Concept 54.1: Ecosystem ecology emphasizes energy flow and chemical cycling

• Ecologists view ecosystems as transformers of energy and processors of matter Ecosystems and Physical Laws

• Laws of physics and chemistry apply to ecosystems, particularly energy flow • 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 through an ecosystem, entering as light and exiting as heat • Nutrients cycle within an ecosystem LE 54-2

Tertiary consumers

Microorganisms and other detritivores Secondary consumers

Detritus Primary consumers

Primary producers

Heat Key

Chemical cycling Sun Energy flow Decomposition

• Decomposition connects all trophic levels • Detritivores, mainly bacteria and fungi, recycle essential chemical elements by decomposing organic material and returning elements to inorganic reservoirs

Concept 54.2: 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 Ecosystem Energy Budgets

• The extent of photosynthetic production sets the spending limit for an ecosystem’s energy budget The Global Energy Budget

• The amount of solar radiation reaching the Earth’s surface limits photosynthetic output of ecosystems • Only a small fraction of solar energy actually strikes photosynthetic organisms Gross and Net Primary Production

• Total primary production is known as the ecosystem’s gross primary production (GPP) • Net primary production (NPP) is GPP minus energy used by primary producers for respiration • Only NPP is available to consumers • Ecosystems vary greatly in net primary production and contribution to the total NPP on Earth LE 54-4

Open ocean 65.0 125 24.4 Continental shelf 5.2 360 5.6 Estuary 0.3 1,500 1.2 Algal beds and reefs 0.1 2,500 0.9 Upwelling zones 0.1 500 0.1 Extreme desert, rock, sand, ice 4.7 3.0 0.04 Desert and semidesert scrub 3.5 90 0.9 Tropical rain forest 3.3 2,200 22 Savanna 2.9 900 7.9 Cultivated land 2.7 600 9.1 Boreal forest (taiga) 2.4 800 9.6 Temperate grassland 1.8 600 5.4 Woodland and shrubland 1.7 700 3.5 Tundra 1.6 140 0.6 Tropical seasonal forest 1.5 1,600 7.1 Temperate deciduous forest 1.3 1,200 4.9 Temperate evergreen forest 1.0 1,300 3.8 Swamp and marsh 0.4 2,000 2.3 Lake and stream 0.4 250 0.3 0 10 20 30 40 50 60 0 500 1,0001,500 2,000 2,500 0 5 10 15 20 25 Key Percentage of Earth’s Average net primary Percentage of Earth’s net surface area production (g/m2/yr) primary production Marine Terrestrial Freshwater (on continents) • Overall, terrestrial ecosystems contribute about two-thirds of global NPP • Marine ecosystems contribute about one-third LE 54-5

North Pole

60°N

30°N

Equator

30°S

60°S

South Pole 180° 120°W 60°W 0° 60°E 120°E 180° Primary Production in Marine and Freshwater Ecosystems

• In marine and freshwater ecosystems, both light and nutrients control primary production Light Limitation

• Depth of light penetration affects primary production in the photic zone of an ocean or lake Nutrient Limitation

• More than light, nutrients limit primary production in geographic regions of the ocean and in lakes • A limiting nutrient is the element that must be added for production to increase in an area • Nitrogen and phosphorous are typically the nutrients that most often limit marine production • Nutrient enrichment experiments confirmed that nitrogen was limiting phytoplankton growth in an area of the ocean LE 54-6

30 21 and g Isl Shinnecock Lon 19 15 Bay 5 ay 4 h B 11 Moriches Bay out t S rea 2 G Atlantic Ocean

Coast of Long Island, New York

8 Phytoplankton 8 7 Inorganic 7 6 phosphorus 6 5 5 4 4 3 3 (µm atoms/L) Phytoplankton 2 2

(millions of cells/mL) (millions 1 1 Inorganic phosphorus Inorganic 0 0 2 4 5 113015 19 21 Station number Great Moriches Shinnecock South Bay Bay Bay

Phytoplankton biomass and phosphorus concentration

30 Ammonium enriched Phosphate enriched Unenriched control 24

18

12 Phytoplankton 6 (millions of cells per mL) per of cells (millions 0 Starting 2 4 5 11 30 15 19 21 algal Station number density

Phytoplankton response to nutrient enrichment • Experiments in another ocean region showed that iron limited primary production

• The addition of large amounts of nutrients to lakes has a wide range of ecological impacts • In some areas, sewage runoff has caused eutrophication of lakes, which can lead to loss of most fish species

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 scale • Actual evapotranspiration can represent the contrast between wet and dry climates • Actual evapotranspiration is the water annually transpired by plants and evaporated from a landscape • It is related to net primary production LE 54-8 3,000 Tropical forest /yr) 2

2,000

Temperate forest 1,000 Mountain coniferous forest

Desert Temperate grassland shrubland Net primary production (g/m production Net primary Arctic tundra 0 0 500 1,000 1,500 Actual evapotranspiration (mm/yr) • On a more local scale, a soil nutrient is often the limiting factor in primary production LE 54-9

300

N + P 250 ) 2 200

150 N only (g dry wt/m

100 Control

Live, above-ground biomass Live, above-ground 50 P only

0 0 June July August 1980 Concept 54.3: Energy transfer between trophic levels is usually less than 20% efficient

• Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time Production Efficiency

• When a caterpillar feeds on a leaf, only about one- sixth of the leaf’s energy is used for secondary production • An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration LE 54-10

Plant material eaten by caterpillar

200 J

67 J Cellular 100 J respiration Feces 33 J

Growth (new biomass) Trophic Efficiency and Ecological Pyramids

• Trophic efficiency is the percentage of production transferred from one trophic level to the next • It usually ranges from 5% to 20% Pyramids of Production

• A pyramid of net production represents the loss of energy with each transfer in a food chain LE 54-11

Tertiary 10 J consumers

Secondary 100 J consumers

Primary 1,000 J consumers

Primary producers 10,000 J

1,000,000 J of sunlight Pyramids of Biomass

• In a biomass pyramid, each tier represents the dry weight of all organisms in one trophic level • Most biomass pyramids show a sharp decrease at successively higher trophic levels LE 54-12a

Trophic level Dry weight (g/m2)

Tertiary consumers 1.5 Secondary consumers 11 Primary consumers 37 Primary producers 809

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. • Certain aquatic ecosystems have inverted biomass pyramids: Primary consumers outweigh the producers LE 54-12b

Trophic level Dry weight (g/m2)

Primary consumers (zooplankton) 21 Primary producers (phytoplankton) 4

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). Pyramids of Numbers

• A pyramid of numbers represents the number of individual organisms in each trophic level LE 54-13

Trophic level Number of individual organisms

Tertiary consumers 3 Secondary consumers 354,904 Primary consumers 708,624 Primary producers 5,842,424 • Dynamics of energy flow in ecosystems have important implications for the human population • Eating meat is a relatively inefficient way of tapping photosynthetic production • Worldwide agriculture could feed many more people if humans ate only plant material LE 54-14

Trophic level

Secondary consumers

Primary consumers

Primary producers The Green World Hypothesis

• Most terrestrial ecosystems have large standing crops despite the large numbers of herbivores

• The green world hypothesis proposes several factors that keep herbivores in check: – Plant defenses – Limited availability of essential nutrients – Abiotic factors – Intraspecific competition – Interspecific interactions Concept 54.4: Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem

• Life depends on recycling chemical elements • Nutrient circuits in ecosystems involve biotic and abiotic components and are often called biogeochemical cycles A General Model of Chemical Cycling

• Gaseous carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally • Less mobile elements such as phosphorus, potassium, and calcium cycle on a more local level • 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 LE 54-16 Reservoir a Reservoir b

Organic Organic materials materials available unavailable as nutrients as nutrients Fossilization Living organisms, Coal, oil, detritus peat

Respiration, Assimilation, decomposition, photosynthesis excretion Burning of fossil fuels

Reservoir c Reservoir d

Inorganic Inorganic materials materials available Weathering, unavailable as nutrients erosion as nutrients

Atmosphere, Minerals soil, water Formation of in rocks sedimentary rock Biogeochemical Cycles

• In studying cycling of water, carbon, nitrogen, and phosphorus, ecologists focus on four factors: 1. Each chemical’s biological importance 2. Forms in which each chemical is available or used by organisms 3. Major reservoirs for each chemical 4. Key processes driving movement of each chemical through its cycle LE 54-17a

Transport over land Solar energy

Net movement of water vapor by wind

Precipitation Precipitation Evaporation over land over ocean from ocean Evapotranspiration from land

Percolation through soil Runoff and groundwater LE 54-17b

CO2 in atmosphere Photosynthesis

Cellular respiration

Burning of fossil fuels and wood Higher-level Primary consumers consumers

Carbon compounds Detritus in water

Decomposition LE 54-17c

N2 in atmosphere

Assimilation Denitrifying bacteria – NO3 Nitrogen-fixing bacteria in root Decomposers nodules of legumes Nitrifying Ammonification bacteria Nitrification

+ – NH3 NH4 NO2 Nitrogen-fixing Nitrifying soil bacteria bacteria LE 54-17d

Rain

Geologic Weathering uplift of rocks Plants

Runoff

Consumption

Sedimentation Plant uptake of PO 3– Soil 4 Leaching

Decomposition Decomposition and Nutrient Cycling Rates

• Decomposers (detritivores) play a key role in the general pattern of chemical cycling • Rates at which nutrients cycle in different ecosystems vary greatly, mostly as a result of differing rates of decomposition LE 54-18

Consumers

Producers

Decomposers

Nutrients available to producers

Abiotic reservoir

Geologic processes Vegetation and Nutrient Cycling: The Hubbard Brook Experimental Forest

• Vegetation strongly regulates nutrient cycling • Research projects monitor ecosystem dynamics over long periods • The Hubbard Brook Experimental Forest has been used to study nutrient cycling in a forest ecosystem since 1963 • The research team constructed a dam on the site to monitor loss of water and minerals LE 54-19

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. One watershed was clear cut to study the effects of the loss of vegetation on drainage and nutrient cycling.

80.0 Deforested 60.0 40.0 20.0

(mg/L) 4.0 Completion of tree cutting 3.0 Control 2.0 1.0 Nitrate concentration in runoff concentration Nitrate 0 1965 1966 1967 1968

The concentration of nitrate in runoff from the deforested watershed was 60 times greater than in a control (unlogged) watershed. • In one experiment, the trees in one valley were cut down, and the valley was sprayed with herbicides • Net losses of water and minerals were studied and found to be greater than in an undisturbed area • These results showed how human activity can affect ecosystems Concept 54.5: The human population is disrupting chemical cycles throughout the biosphere

• As the human population has grown, our activities have disrupted the trophic structure, energy flow, and chemical cycling of many ecosystems Nutrient Enrichment

• In addition to transporting nutrients from one location to another, humans have added new materials, some of them toxins, to ecosystems Agriculture and Nitrogen Cycling

• Agriculture removes nutrients from ecosystems that would ordinarily be cycled back into the soil • Nitrogen is the main nutrient lost through agriculture; thus, agriculture greatly impacts the nitrogen cycle • Industrially produced fertilizer is typically used to replace lost nitrogen, but effects on an ecosystem can be harmful

Contamination of Aquatic Ecosystems

• Critical load for a nutrient is the amount that plants can absorb without damaging the ecosystem • When excess nutrients are added to an ecosystem, the critical load is exceeded • Remaining nutrients can contaminate groundwater and freshwater and marine ecosystems • Sewage runoff causes cultural eutrophication, excessive algal growth that can greatly harm freshwater ecosystems 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 LE 54-21

4.6

4.3 4.6 4.3 4.6 4.1 4.3 4.6 Europe

North America • By the year 2000, acid precipitation affected the entire contiguous United States • Environmental regulations and new technologies have allowed many developed countries to reduce sulfur dioxide emissions LE 54-22

5.0 5.3 5.4 5.1 5.6 5.2 5.5 5.3 6.1 5.2 5.3 5.3 4.8 4.5 4.7 5.4 5.1 4.6 5.2 5.2 5.2 5.5 5.2 5.0 4.8 5.2 4.7 4.5 4.6 5.2 4.9 4.8 4.3 4.5 4.5 5.5 5.6 5.5 4.5 5.2 4.7 4.5 5.6 5.3 4.9 4.7 4.5 4.6 5.4 5.3 5.5 4.5 4.34.4 4.6 5.1 4.7 4.6 4.5 5.4 4.7 6.0 4.1 4.4 4.5 5.5 5.3 5.3 4.6 4.8 4.4 4.4 5.9 4.3 4.6 5.3 4.6 4.6 4.5 4.4 6.3 5.1 5.4 4.7 4.5 4.5 5.3 5.0 4.54.5 4.7 5.2 4.7 4.6 5.3 5.1 4.9 5.6 4.8 5.7 5.0 5.4 5.4 4.6 4.6 5.4 5.0 4.8 4.6 4.5 4.5 4.9 4.7 4.5 4.9 4.8 4.5 4.6 5.4 4.5 5.3 4.5 4.7 Field pH 5.7 5.0 4.7 4.8 4.7 4.7 5.0 4.8 4.7 5.0 5.2 5.1 ≥5.3 4.7 4.7 5.0 5.2–5.3 5.0 5.0 5.4 4.9 4.7 4.6 4.7 5.4 5.1 4.8 5.1–5.2 5.1 4.8 4.7 5.3 4.9 4.8 4.8 5.0–5.1 4.7 4.9–5.0 5.7 4.7 4.8 4.9 5.1 4.8–4.9 5.0 4.8 4.7 4.7 4.7–4.8 4.6–4.7 5.0 4.7 4.5–4.6 4.9 4.4–4.5 4.3–4.4 <4.3 Toxins in the Environment

• Humans release many toxic chemicals, including synthetics previously unknown to nature • In some cases, harmful substances persist for long periods in an ecosystem • One reason toxins are harmful is that they become more concentrated in successive trophic levels • In biological magnification, toxins concentrate at higher trophic levels, where biomass is lower LE 54-23

Herring gull eggs 124 ppm

Lake trout 4.83 ppm

Smelt 1.04 ppm Concentration of PCBs Concentration

Zooplankton Phytoplankton 0.123 ppm 0.025 ppm Atmospheric Carbon Dioxide

• One pressing problem caused by human activities is the rising level of atmospheric carbon dioxide Rising Atmospheric CO2

• Due to the burning of fossil fuels and other human activities, the concentration of atmospheric CO2 has been steadily increasing 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

The Greenhouse Effect and Global Warming

• The greenhouse effect caused by atmospheric

CO2 keeps Earth’s surface at a habitable temperature

• Increased levels of atmospheric CO2 are magnifying the greenhouse effect, which could cause global warming and climatic change Depletion of Atmospheric Ozone

• Life on Earth is protected from damaging effects of UV radiation by a protective layer or ozone molecules in the atmosphere • Satellite studies suggest that the ozone layer has been gradually thinning since 1975 LE 54-26

350

300

250

200

150

100 Ozone layer thickness (Dobson units) Ozone layer 50

0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Year (Average for the month of October) • Destruction of atmospheric ozone probably results from chlorine-releasing pollutants produced by human activity LE 54-27 Chlorine from CFCs interacts with ozone

(O3), forming chlorine monoxide (CIO) and oxygen (O ). Chlorine atoms 2

O2

Chlorine O3

CIO

O2

Sunlight causes CIO Cl2O 2 to break down into O2 and free chlorine atoms. Cl O Two CIO molecules The chlorine atoms 2 2 react, forming chlorine can begin the cycle peroxide (Cl2O 2). again. Sunlight • Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased LE 54-28

October 1979 October 2000