and Ecosystems Global Ecology
Nutrient and energy flows Nutrient cycles Global patterns of productivity Human impacts
Why is the ocean blue and the land green?
Figure 54.15
Ecosystems
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
Trophic Relationships
Ecosystem ecology emphasizes energy flow and chemical cycling Ecosystem ecologists view ecosystems
As transformers of energy and processors of matter
Energy flows through an ecosystem Nutrients cycle within an ecosystem
Tertiary consumers Microorganisms and other detritivores
This view de-emphasizes the particular species in an ecosystem in favor of studying nutrient cycles and energy flows
Secondary consumers
Detritus
Primary consumers
Primary producers Heat Sun
Key Chemical cycling Energy flow
Figure 54.2
1
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%
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
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
Feces 100 J
Plant material eaten by caterpillar
200 J
67 J 33 J Growth (new biomass)
Cellular respiration
Figure 54.10
Pyramids of Production
This loss of energy with each transfer in a food chain
Can be represented by a pyramid of net production
Tertiary consumers
Pyramids of biomass
Show a sharp decrease at successively higher trophic levels
10 J
Trophic level
Secondary consumers 100 J
Dry weight (g/m2) 1.5 11 37 809
Tertiary consumers Secondary consumers Primary consumers Primary producers (a) M ost biomass pyramids show a sharp decrease in biomass at successively higher trophic levels, as illustrated by data from a bog at Silver Springs, Florida.
Primary consumers
1,000 J
Primary producers
10,000 J
Figure 54.11
1,000,000 J of sunlight
Figure 54.12a
Certain aquatic ecosystems
Have inverted biomass pyramids
Pyramids of Numbers
A pyramid of numbers
Represents the number of individual organisms in each trophic level
Trophic level
Dry weight (g/m2) 21 4
Primary consumers (zooplankton) Primary producers (phytoplankton)
Trophic level Tertiary consumers Secondary consumers
Number of individual organisms 3 354,904 708,624 5,842,424
(b) I n 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).
Primary consumers Primary producers
Figire 54.12b Figure 54.13
2
The dynamics of energy flow through ecosystems
Have important implications for the human population
Worldwide agriculture could successfully feed many more people
If humans all fed more efficiently, eating only plant material
Trophic l evel
Eating meat
Is a relatively inefficient way of tapping photosynthetic production
Secondary consumers
Primary consumers
Primary producers Figure 54.14
Why is the world green?
Most terrestrial ecosystems
Have large standing crops of primary producers despite the large numbers of herbivores
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 Competition and Predator-prey interactions check herbivore densities
What limits herbivore abundance?
Figure 54.15
Nutrient 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
A nutrient cycle
Includes the main reservoirs of elements and the processes that transfer elements between reservoirs
Reservoir a Organic materials available as nutrients Living organisms, detritus Reservoir b Organic materials unavailable as nutrients Coal, oil, peat Fossilization
Nutrient circuits that cycle matter through an ecosystem
Involve both biotic and abiotic components and are often called biogeochemical cycles
Figure 54.16
Assimilation, photosynthesis
Respiration, decomposition, excretion
Burning of fossil fuels Reservoir d Inorganic materials unavailable as nutrients Minerals in rocks
Reservoir c Inorganic materials available as nutrients Atmosphere, soil, water
Weathering, erosion Formation of sedimentary rock
3
THE WATER CYCLE
THE CARBON CYCLE
The water cycle and the carbon cycle
Transport over land CO2 in atmosphere Photosynthesis Cellular respiration Solar energy Net movement of water vapor by wind Precipitation over ocean Precipitation over land Burning of fossil fuels and wood
The nitrogen cycle and the phosphorous cycle
N2 in atmosphere
THE NITROGEN CYCLE
THE PHOSPHORUS CYCLE
Rain
Evaporation from ocean Evapotranspiration from land
Geologic uplift Assimilation Denitrifying bacteria
Weathering of rocks Runoff
Plants
Higher-level Primary consumers consumers Detritus
Percolation through soil Runoff and groundwater
Carbon compounds in water
Nitrogen-fixing bacteria in root nodules of legumes
NO3 Decomposers Nitrification NO2 Nitrifying bacteria
Consumption Sedimentation Soil Leaching Plant uptake of PO4 3
Ammonification NH3 NH4 +
Nitrifying bacteria
Decomposition
Nitrogen-fixing soil bacteria
Decomposition
Figure 54.17 Figure 54.17
Decomposition
Detritivores, mainly bacteria and fungi, are essential components of nutrient cycles
By decomposing organic material and returning elements to inorganic reservoirs
Gross and Net Primary Production
Total primary production in an ecosystem
Is known as that ecosystems gross primary production (GPP), equivalent to total photosynthesis or carbon fixation
Net primary production (NPP)
Is equal to GPP minus the energy used by the primary producers for respiration
Only NPP
Is available to consumers
Figure 54.3
Ecosystems vary considerably in their net primary production
And in their contribution to the total NPP
Open ocean Continental shelf Estuary Algal beds and reefs Upwelling zones Extreme desert, rock, sand, ice Desert and s emidesert s crub Tropical rain forest Savanna Cultivated land Boreal forest (taiga) Temperate grassland Woodland and shrubland Tundra Tropical seasonal forest Temperate deciduous forest Temperate evergreen forest Swamp and marsh Lake and stream Key Marine Terrestrial Freshwater (on continents) 0 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 10 20 30 40 50 60 0 250 500 1,000 1,500 2,000 2,500 0 140 1,600 1,200 1,300 2,000 3.0 90 2,200 900 600 800 600 700 0.6 7.1 4.9 3.8 2.3 0.3 5 10 15 20 25 7.9 9.1 9.6 5.4 3.5 65.0 125 360 1,500 2,500 500 1.2 0.9 0.1 0.04 0.9 22 5.6 24.4
Aquatic biomes
Dominated by open ocean Most productive acquatic biomes are estuaries, reefs, and algal beds
30 N Tropic of Cancer Equator Tropic of Capricorn 30 S Continental shelf
Key Lakes Rivers Oceanic pelagic zone Estuaries Intertidal z one Abyssal zone (below oceanic pelagic zone)
(a) Percentage of Earth s surface area
(b) Average net primary production (g/m2 /yr)
(c) Percentage of Earth s net primary production
Figure 50.15 Figure 54.4a c
Coral reefs
4
Terrestrial Biomes
Climate has a great impact on the distribution of organisms, and on productivity The distribution of major terrestrial biomes
Desert 30 Temperate grassland Tropical forest
30 Tropic N of Cancer Equator Tropic of Capricorn 30 S
Annual mean temperature (C)
15
Temperate broadleaf forest Coniferous forest
0 Arctic and alpine tundra 15 100 200 300 400
Key Tropical forest Savanna Desert
Chaparral Temperate grassland Temperate broadleaf forest Coniferous forest
Tundra High mountains Polar ice
Figure 50.18
Annual mean precipitation (cm)
Figure 50.19
Actual evapotranspiration
Is the amount of water annually transpired by plants and evaporated from a landscape Is related to net primary production
Overall, terrestrial ecosystems
Contribute about two-thirds of global NPP and marine ecosystems about one-third Much of the ocean is as unproductive as the Sahara Desert
North Pole 60N 30N Equator
3,000 Net primary production (g/m 2/yr)
Tropical forest
2,000
Temperate forest 1,000 Desert shrubland Arctic tundra 0 0 500 1,000 1,500 Actual evapotranspiration (mm H 2 O/yr) Mountain coniferous forest Temperate grassland
30S 60S South Pole 180 Figure 54.5
120W
60W
0
60E
120E
180
Figure 54.8
Why is the open ocean a desert?
Plenty of light Lack of nutrients?
If so, which?
5
Experiments in another ocean region
Also showed that iron limited primary production
Vegetation and Nutrient Cycling: The Hubbard Brook Experimental Forest
The research team constructed a dam on the site
To monitor water and mineral loss
Table 54.1 Figure 54.19a
(a) C oncrete 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
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
Nitrate concentration in runoff (mg/L) 80.0 60.0 40.0 20.0 4.0 3.0 2.0 1.0 0 Completion of tree cutting Deforested
Control
1965
1966
1967
1968
Figure 54.19b
(b) O ne watershed was clear cut to study the effects of the loss of vegetation on drainage and nutrient cycling.
Figure 54.19c
(c) T he concentration of nitrate in runoff from the deforested watershed was 60 times greater than in a control (unlogged) watershed.
Anthropogenic effects
The human population is disrupting chemical cycles throughout the biosphere
About 1/3rd of nitrogen fixation is by humans (for fertilizers, etc.) Carbon emissions causing increase in atmospheric C02 concentrations
Nutrient Enrichment
The addition of large amounts of nutrients to aquatic ecosystems such as lakes and nearshore oceans
Has a wide range of ecological impacts Including eutrophication
In eutrophication, excessive algal production is caused by increased n utrient availability This h as several effects including loss of light in deeper waters, and loss of d issolved oxygen in water due to respiration by alga and decomposers. Anoxic conditions kill fish and o ther aquatic life
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
6
In some areas, sewage runoff
Has caused eutrophication of lakes, which can lead to the eventual loss of most fish species from the lakes
Agricultural inputs of nutrients
Figure 54.7
Cause an anoxic dead zone in the gulf of Mexico each summer which kills fish and shrimp
Acid Precipitation
Combustion of fossil fuels releases sulfur
And 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
4.6
4.3
4.6 4.3 4.6 4.1 4.3 4.6 Europe
Figure 54.21
North America
By the year 2000
The entire contiguous United States was affected by acid precipitation
Acid Rain and Forest Decline
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
7
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
But studies at Hubbard Brook and elsewhere indicate that return of soil nutrients lost due to acidification will take decades or longer
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 l evels 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
Herring gull eggs 124 ppm Concentration of PCBs
Lake trout 4.83 ppm
Smelt 1.04 ppm
Figure 54.23
Zooplankton 0.123 ppm
Phytoplankton 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 increased burning of fossil fuels and other human activities
The concentration of atmospheric CO2 has been steadily increasing
390 380 CO2 concentration (ppm) 370 360 350 0.30 340 330 320 310 300 CO2 0.15 0 1.05 0.90 0.75 Temperature 0.60 0.45 Temperature variation ( C)
0.15 0.30 0.45 1980 1985 1990 1995 2000 2005 Year
1960 1965
1970 1975
Charles Keeling (SIO) 1928-2005
Figure 54.24
8
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 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 causing global warming
Figure 54.25
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
350
Ozone layer thickness (Dobson units)
300
250
200
150
100
50
0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Figure 54.26
Year (Average for the month of October)
The destruction of atmospheric ozone
Probably results from chlorine-releasing pollutants produced by human activity
Scientists first described an ozone hole
Over Antarctica in 1985; it has increased in size as ozone depletion has increased
1 Chlorine from CFCs interacts with ozone (O3), forming chlorine monoxide ( ClO) and oxygen (O2). Chlorine atoms O2 Chlorine O3
ClO O2 3 Sunlight causes Cl 2O 2 to break down into O2 and free chlorine atoms. The chlorine atoms can begin the cycle again.
ClO Cl 2O 2 2 Two ClO molecules react, forming chlorine peroxide (Cl2O 2).
Figure 54.27
Sunlight
(a) October 1979 Figure 54.28a, b
(b) October 2000
9
Summary
Ecosystem science is the study of energy flows and nutrient dynamics The biota of the earth play a critical role in nutrient cycling, while nutrient, water and energy levels determine productivity Humans are altering the levels of nutrients at all spatial scales Anthropogenic changes in the atmosphere are bringing about global warming, with far reaching environmental effects Combining scientific understanding with social policy provides some hope for reducing or ameliorating environmental effects
Why is the ocean blue and the land green?
Figure 54.15
10