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Slide 83 -
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Chapter 54 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 Ecosystems can range from a microcosm, such as an aquarium
To a large area such as a lake or forest Figure 54.1 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
Ecosystem ecologists view ecosystems
As transformers of energy and processors of matter 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 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 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 Figure 54.3 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 the energy budget of the entire ecosystem 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 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 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 0 10 20 30 40 50 60 0 500 1,000 1,500 2,000 2,500 0 5 10 15 20 25 Percentage of Earth’s net
primary production Key Marine Freshwater (on continents) Terrestrial 5.2 0.3 0.1 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 0.4 125 360 1,500 2,500 500 3.0 90 2,200 900 600 800 600 700 140 1,600 1,200 1,300 2,000 250 5.6 1.2 0.9 0.1 0.04 0.9 22 7.9 9.1 9.6 5.4 3.5 0.6 7.1 4.9 3.8 2.3 0.3 65.0 24.4 Figure 54.4a–c Percentage of Earth’s
surface area (a) Average net primary
production (g/m2/yr) (b) (c) 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 180 North Pole 60N 30N Equator 30S 60S South Pole Primary Production in Marine and Freshwater Ecosystems In marine and freshwater ecosystems
Both light and nutrients are important in controlling primary production Light Limitation The depth of light penetration
Affects primary production throughout the photic zone of an ocean or lake Nutrient Limitation More than light, nutrients limit primary production
Both in different geographic regions of the ocean and in lakes 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 Nutrient enrichment experiments
Confirmed that nitrogen was limiting phytoplankton growth in an area of the ocean 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. Figure 54.6 Figure 54.6 (a) Phytoplankton biomass and phosphorus concentration (b) Phytoplankton response to nutrient enrichment Great
South Bay Moriches
Bay Shinnecock
Bay Starting
algal
density 2 4 5 11 30 15 19 21 30 24 18 12 6 0 Unenriched control Ammonium enriched Phosphate enriched Station number Phytoplankton
(millions of cells per mL) 8 7 6 5 4 3 2 1 0 2 4 5 11 30 15 19 21 8 7 6 5 4 3 2 1 0 Inorganic phosphorus
(g atoms/L) Phytoplankton
(millions of cells/mL) Station number 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. Phytoplankton Inorganic
phosphorus 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 (NH4) caused heavy phytoplankton growth in bay water, but the addition of phosphate (PO43) did not induce algal growth (b). Experiments in another ocean region
Showed that iron limited primary production Table 54.1 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 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 The contrast between wet and dry climates
Can be represented by a measure called actual evapotranspiration Actual evapotranspiration
Is the amount of water annually transpired by plants and evaporated from a landscape
Is related to net primary production 0 On a more local scale
A soil nutrient is often the limiting factor in primary production Figure 54.9 Concept 54.3: 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 The production efficiency of an organism
Is the fraction of energy stored in food that is not used for respiration Trophic Efficiency and Ecological Pyramids Trophic efficiency
Is the percentage of production transferred from one trophic level to the next
Usually ranges from 5% to 20% 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
consumers Primary
consumers 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 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 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 The dynamics of energy flow through ecosystems
Have important implications for the human population
Eating meat
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 Figure 54.14 Trophic level Secondary
consumers Primary
consumers Primary
producers The Green World Hypothesis According to 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 the large numbers of herbivores Figure 54.15 The green world hypothesis proposes several factors that keep herbivores in check
Plants have defenses against herbivores
Nutrients, not energy supply, usually limit herbivores
Abiotic factors limit herbivores
Intraspecific competition can limit herbivore numbers
Interspecific interactions check herbivore densities Concept 54.4: 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 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 Organic
materials
unavailable
as nutrients Coal, oil,
peat Inorganic
materials
available
as nutrients Inorganic
materials
unavailable
as nutrients 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 Precipitation
over land Percolation
through
soil Runoff and
groundwater CO2 in atmosphere Photosynthesis Cellular
respiration Burning of
fossil fuels
and wood Higher-level
consumers Primary
consumers 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
bacteria Nitrifying
bacteria Nitrification Nitrogen-fixing
soil bacteria Nitrogen-fixing
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 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 The rates at which nutrients cycle in different ecosystems
Are extremely variable, mostly as a result of differences in rates of decomposition Vegetation and Nutrient Cycling: The Hubbard Brook Experimental Forest Nutrient cycling
Is strongly regulated by vegetation Long-term ecological research projects
Monitor ecosystem dynamics over relatively long periods of time
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 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. In one experiment, the trees in one valley were cut down
And the valley was 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. 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 Figure 54.19c Concept 54.5: 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 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 and Nitrogen Cycling Agriculture constantly removes nutrients from ecosystems
That would ordinarily be cycled back into the soil Figure 54.20 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 Sewage runoff contaminates freshwater ecosystems
Causing cultural eutrophication, excessive algal growth, which can cause significant harm to these 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 Figure 54.21 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 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 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 0 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 ClO Cl2O2 O2 Chlorine atoms Scientists first described an “ozone hole”
Over Antarctica in 1985; it has increased in size as ozone depletion has increased Figure 54.28a, b (a) October 1979 (b) October 2000
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