Ecosystems

Ecosystems

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 it involves two main processes: energy flow and chemical cycling

©TimErnst

Trophic Relationships • Energy and nutrients pass – From primary producers (autotrophs) to primary consumers (herbivores) and then to secondary consumers (carnivores) – Energy is not reused, but eventually lost as heat. Thus energy flows, but does not cycle.

40.1/40.3

• Energy flows through an ecosystem – Entering as light and exiting as heat Tertiary consumers Microorganisms and other detritivores

Detritus

Secondary consumers

Primary consumers

Primary producers Heat

Key Chemical cycling

40.1

Sun

Energy flow

Detritus – once-living organic matter

Factors Limiting Primary Production • 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 limit for the energy availability of the entire ecosystem

40.2

Global Source of Primary Production North Pole 60°N

30°N

Equator 30°S

60°S South Pole 180°

120°W

60°W

0°

60°E

120°E

180°

• 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

40.4

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

Plant material eaten by caterpillar

200 J

Feces

40.5

67 J

100 J 33 J

Growth (new biomass)

Cellular 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%

40.5

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

Secondary consumers

Primary consumers

Primary producers

40.5

10 J

100 J

1,000 J

10,000 J

1,000,000 J of sunlight

• Most biomass pyramids – Show a sharp decrease at successively higher trophic levels Trophic level Tertiary consumers

1.5

Secondary consumers

11

Primary consumers

37

Primary producers (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.

40.5

Dry weight (g/m2)

809

Pyramids of Numbers • A pyramid of numbers – Represents the number of individual organisms in each trophic level Trophic level

Tertiary consumers

Number of individual organisms 3

Secondary consumers

354,904

Primary consumers

708,624

Primary producers

40.5

5,842,424

• Worldwide agriculture could successfully feed many more people – If humans all fed more efficiently, eating only plant material Trophic level

Secondary consumers

Primary consumers

Primary producers

Chemical Cycling • 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 Reservoir b a between reservoirs Reservoir Organic materials available as nutrients Living organisms, detritus

Assimilation, photosynthesis

40.6

Organic materials unavailable as nutrients

Fossilization

Coal, oil, peat

Respiration, decomposition, excretion

Burning of fossil fuels

Reservoir c

Reservoir d

Inorganic materials available as nutrients

Inorganic materials unavailable as nutrients

Atmosphere, soil, water

Weathering, erosion Formation of sedimentary rock

Minerals in rocks

Biogeochemical Cycles THE CARBON CYCLE

THE WATER CYCLE

• The water cycle and the carbon cycle CO2 in atmosphere

Transport over land

Photosynthesis

Solar energy Cellular respiration

Net movement of water vapor by wind Precipitation Evaporation over ocean from ocean

Precipitation over land Burning of fossil fuels and wood

Evapotranspiration from land

Percolation through soil Runoff and groundwater

40.7/40.8

Higher-level Primary consumers consumers

Carbon compounds in water

Detritus

Decomposition

Biogeochemical Cycles THE PHOSPHORUS CYCLE

THE NITROGEN CYCLE

• The nitrogen cycle and the phosphorous cycle N2 in atmosphere

Rain

Geologic uplift Assimilation Denitrifying NO3− bacteria

Nitrogen-fixing bacteria in root Decomposers nodules of legumes Nitrification Ammonification NH3 Nitrogen-fixing soil bacteria

40.9

NH4+

Nitrifying bacteria

Weathering of rocks Runoff

Plants

Consumption Sedimentation Soil

Plant uptake of PO43−

Leaching

NO2 − Nitrifying bacteria

Decomposition

Acid Precipitation • Combustion of fossil fuels – Is the main cause of acid precipitation – Creates sulfuric and nitric acid from sulfur dioxide and nitrogen oxides

40.10

• 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 4.3

4.1

4.6 Europe

Increasing pH in Industrialized Areas 40.10

North America

Normal rain pH is ~ 5.6

• By the year 2000 – The entire contiguous United States was affected by acid precipitation

40.10

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

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

Concentration of PCBs

– Toxins concentrate at higher trophic levels because at these levels biomass tends to be lower Herring gull eggs 124 ppm

Lake trout 4.83 ppm Smelt 1.04 ppm

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

40.11

Rising Atmospheric CO2 – Due to the increased burning of fossil fuels and other human activities the concentration of atmospheric CO2 has been steadily increasing 1.05 390

CO2 concentration (ppm)

40.11

370

0.75 Temperature

0.60

360

0.45 350 0.30 340 330

CO2

0.15 0

Temperature variation (°C)

0.90

380

320

−0.15

310

− 0.30

300

− 0.45 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 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 40.11

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

40.12

• Satellite studies of the atmosphere – Suggest that the ozone layer has been gradually thinning since 1975 Ozone layer thickness (Dobson units)

350 300 250 200 150 100 50 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

40.12

Year (Average for the month of October)

• The destruction of atmospheric ozone – Probably results from chlorine-releasing pollutants produced by human activity 1 Chlorine from CFCs interacts with ozone (O3), forming chlorine monoxide (ClO) and oxygen (O2). Chlorine atoms

O2 Chlorine

O3

ClO O2

40.12

3 Sunlight causes Cl2O2 to break down into O2 and free chlorine atoms. The chlorine atoms can begin the cycle again.

ClO Cl2O2

Sunlight

2 Two ClO molecules react, forming chlorine peroxide (Cl2O2).

• Scientists first described an “ozone hole” – Over Antarctica in 1985; it has increased in size as ozone depletion has increased

(a) October 1979

40.12

(b) October 2000