10/25/2013

1

Ecosystems

Chapter 42

42.1 Ecosystems

Ecosystem

• An array of organisms and their physical and

chemical environment

Inputs and outputs of energy and nutrients

• Energy flows one way, into and out of an

ecosystem

• Materials are cycled among resident species

10/25/2013

2

Energy Sources

Sunlight supplies energy to most ecosystems

Primary producers

• Convert energy of sunlight into chemical energy

(autotrophs)

• Take up nutrients that all living organisms require

Energy Sources

Consumers - get energy from food

• Herbivores – feed on producers

• Carnivores – eat herbivores and other consumers

• Flesh of animals

• Omnivores – eat animals and plants

• Decomposers – feed on organic waste and

remains. It is broken down into inorganic building

blocks

• Detritivores- eat small particles of organic matter

(crabs and earthworms)

10/25/2013

3

Fig. 42.2, p.734

Nutrient

cycling

Energy

input,

from

sun

Producers and then

consumers concentrate

nutrients in their tissues.

Some nutrients released by

decomposition get cycled

back to producers.

Energy inputs from the

environment flow through

producers, then consumers.

All energy that entered this

ecosystem eventually flows

out of it, mainly as heat.

Energy output (mainly metabolic heat)

Consumers

Detritivores, Decomposers

Primary Producers

Plants, Other Photoautotrophs

Energy efficiency is not 100%. All energy eventually lost

– most as heat from metabolism.

Trophic Levels

Organisms in an ecosystem are classified by

trophic levels (feeding levels)

• Organisms at the same trophic level are the same

number of steps away from the energy input

• Approximately 10% of the energy is transferred

from one energy level to the next.

A food chain shows who eats whom

• Path of energy and nutrient flow among

organisms

10/25/2013

4

Fig. 42.3b, p.735

big bluestem grass

Fourth Trophic Level

carnivore (third-level consumer)

coyote

Third Trophic Level

carnivore (second-level consumer)

Second Trophic Level

herbivore (primary consumer)

First Trophic Level

autotroph (primary producer)

sparrow

grasshopper

Food chains

or trophic

levels

Key Concepts:

ORGANIZATION OF ECOSYSTEMS

An ecosystem consists of a community and its

physical environment

A one-way flow of energy and a cycling of raw

materials among its interacting participants

maintain it

It is an open system, with inputs and outputs of

energy and nutrients

10/25/2013

5

42.2 Food Webs

Food chains interconnect as food webs

Most ecosystems support only four or five

trophic levels away from original energy source

• Efficiency of energy transfer is low

• Energy lost limits the length of the chain

42.2 Food Webs

Shorter in habitats that change widely over time

Longer in stable habitats

• Ocean depths

If there are a large number of connections then

there will be more herbivores

If there are fewer number of connections then

there will be more carnivores

10/25/2013

6

Types of Food Webs

Type of energy varies with season.

Most of the energy stored in producers moves

through the detrital food web.

42.3 Biological Magnification

A chemical substance is passed from organisms

at each trophic level to those above, becoming

increasingly concentrated in body tissues

• Pesticides (herbicides, insecticides, fungicides)

• Industrial pollutants

• Toxic metals (lead, mercury)

DDT – in raptors

10/25/2013

7

Key Concepts:

FOOD WEBS

Food chains are linear sequences of feeding

relationships, from producers through

consumers, decomposers, and detritivores

The chains cross-connect as food webs

Most energy that enters a food web returns to

the environment, mainly as metabolic heat

Key Concepts:

FOOD WEBS (cont.)

Most nutrients are cycled; some reenter the

environment

Biological magnification is the increasing

concentration of a substance in tissues of

organisms as it moves up food chains

10/25/2013

8

42.4 Energy Flow Through Ecosystems

Primary productivity of a system

• The rate at which producers capture and store

energy in their tissues

• Depends on number of producers and balance

between energy stored and energy used

• Varies with climate, seasonal changes, nutrient

availability, and other factors

42.4 Energy Flow Through Ecosystems

Gross primary production – all energy trapped

by the producers

Net primary production – the fraction of trapped

energy that producers funnel into growth and

reproduction.

10/25/2013

9

42.4 Energy Flow Through Ecosystems

Net ecosystem production – gross primary

production minus the energy that producers,

detritivores, and decomposers require.

• Subtracted because it is NOT availabel to next

trophic level

Ecological Pyramids

Energy pyramids and biomass pyramids

• Depict how energy and organic compounds are

distributed among organisms of an ecosystem

Energy pyramids are largest at their base

• Usually primary producers

• Always largest at the base

10/25/2013

10

Ecological Pyramids

Biomass pyramids

• Dry weight of all organisms at each trophic level

in a specific ecosystem

• Common

• Primary producers – most biomass

• Carnivores – least biomass

• may be upside down

• Consumer biomass can exceed that of producers

• Producers are eaten almost as fast as they grow

and reproduce and cannot accumulate

Fig. 42.10a, p.740

1.5 top carnivores

(gar and bass)

carnivores (smaller

fishes, invertebrates)

herbivores

(plant-eating fishes,

invertebrates, turtles)

producers (mainly

algae and eel grass)

detritivores (crayfish) and

decomposers (bacteria)

5

809

37

11

Small biomass (g/m squared) on

aquatic system of Florida. Producers

bulk.

10/25/2013

11

Ecological Efficiency

Only about 10% of energy transferred from

trophic level to trophic level

Influences amount of energy transferred

• Proportion of digestible biomass

• Amount of energy lost by the animals

• Warm-blooded loose faster then cold blooded

• Active animals loose mere than less active

animals

Higher efficiency of transfer allows for longer

food chains

Key Concepts:

PRIMARY PRODUCTIVITY

Primary productivity is the rate at which an

ecosystem’s producers capture and store

energy in their tissues during a given interval

The number of producers and the balance

between photosynthesis and aerobic respiration

influence the amount stored

10/25/2013

12

42.5 Biogeochemical Cycles

In biogeochemical cycles, water or a nutrient

moves from an environmental reservoir, through

organisms, then back to the environment

• Hydrologic cycle

• Carbon cycle

• Nitrogen cycle

• Phosphorus cycle

42.5 Biogeochemical Cycles

Transfer to and from reservoirs are far slower

than rates of exchange among organisms of an

ecosystem.

• Minerals enter and leave rocks slowly

• Nutrient cycles depend on decomposers

10/25/2013

13

42.5 Biogeochemical Cycles

Hydrologic cycle – oxygen and hydrogen moving

at a global scale

Atmospheric cycle – gaseous form of a nutrient

available to ecosystems

• Carbon and nitrogen

Sedimentary cycle – nutrients that do not often

occur as gases

• Phosphorus

42.5 Biogeochemical Cycles

Cycles –

• Hydrologic cycle

• Carbon cycle

• Nitrogen cycle

• Phosphorus cycle

10/25/2013

14

42.6 The Hydrologic Cycle

Evaporation, condensation, and precipitation

move water from its main reservoir (oceans) into

the atmosphere, onto land, and back to oceans

42.6 The Hydrologic Cycle

Evaporation –

• driven by the sun

• Liquid to a vapor

Transpiration-

• Evaporation of water from plant parts

10/25/2013

15

42.6 The Hydrologic Cycle

Condensation-

• Water vapors form drops as it cools

• Gives rise to clouds

Precipitation – clouds releasing water

• Rain

• Snow

• Hail

42.6 The Hydrologic Cycle

Evaporation, condensation, and precipitation move

water from its main reservoir (oceans) into the

atmosphere, onto land, and back to oceans

• A watershed area drains into a waterway

• Valley to Amazon river basin

• Aquifers – permeable rock layers that hold water

• Groundwater includes water in soil and aquifers

• Runoff flows over ground into a waterway when

saturated

10/25/2013

16

The Hydrologic Cycle - FYI

A Global Water Crisis

Humans are disrupting the water cycle

• Salinization of soil due to uptake of water and

evaporation

• Stunts plant growth and decreases yields

• Pollution of groundwater drinking supplies

10/25/2013

17

A Global Water Crisis

• Contaminants disrupt aquatic ecosystems, drive

vulnerable species to local extinction

• Desalinization of seawater increases freshwater

supplies, but uses fossil fuels

• EXSPENSIVE

A Global Water Crisis

• Water overdrafts from aquifers (saltwater

intrusion)

• Water is drawn from aquifers faster than natural

processes replenish it.

• Near the coast salt water is drawn into aquifer

• Ogallala aquifer is half depleted

• Supplies 20% of nations crops

• Withdrawal exceeds replenishment by a factor of

10

10/25/2013

18

A Global Water Crisis

• Water to regulate political behavior –

• Turkey has built dam sites at headwaters of

Tigris and Euphrates rivers

• In the words of one of the dam site

managers, “Turkey can shut off water flow

into Syria and Iraq ‘ to regulate their

political behavior.’”

42.7 The Carbon Cycle

Carbon cycle

• Carbon moves from reservoirs in rocks and

seawater, through its gaseous form (CO2) in the

atmosphere, and through ecosystems

Carbon-oxygen cycle

• Carbon moves in and out of ecosystems

combined with oxygen in carbon dioxide,

bicarbonate, and carbonate

10/25/2013

19

Fig. 42.15a, p.744

sedimentation

bicarbonate and carbonate dissolved in ocean water

marine food webs producers, consumers,

decomposers, detritivores

marine sediments, including formations with fossil fuels

diffusion between atmosphere and ocean

photosynthesis aerobic respiration

incorporation into sediments

death, sedimentation

uplifting over geologic time

combustion of fossil fuels

F

Y

I

Fig. 42.15b, p.745

volcanic action

terrestrial

rocks

weathering

soil water

(dissolved carbon)

leaching,

runoff

photosynthesis

atmosphere

(mainly carbon dioxide)

land food webs producers, consumers,

decomposers, detritivores

death, burial, compaction over geologic time peat,

fossil fuels

deforestation

combustion of wood (for clearing

land; or for fuel)

aerobic respiration

combustion of fossil

fuels

10/25/2013

20

Carbon Cycling

between Ocean and Atmosphere

Deforestation and burning of wood and fossil

fuels are adding more carbon dioxide to the

atmosphere than oceans can absorb

The Greenhouse Effect

Natural processes and human activities add

more greenhouse gases to the atmosphere

• Gases that can profoundly influence the average

temperatures of the Earth’s surface

• Carbon dioxide, CFCs, methane, nitrous oxide

• Greenhouse Effect-

• Named because gasses act as a pane of glass in a

greenhouse

•

10/25/2013

21

The Greenhouse Effect

• Gasses absorb wavelengths of visible light and

transmit them toward Earth’s surface

• The surface absorbs the wavelength and then

emits longer , infrared wavelengths – heat.

• Greenhouse gasses impede the escape of heat

energy form Earth into space and increases

temperature.

• It has to have some gasses or the Earth would be

too cold to support life.

42.8 The Greenhouse Effect

Greenhouse gases trap heat in the lower

atmosphere

10/25/2013

22

The Greenhouse Effect

CO2 follow annual cycles of primary production

• Decline in summer due to photosynthesis

increase

• Rise in winter when photosynthesis declines

Global Warming

Global Warming

• Long term increase in temperature near Earth’s

surface

• Evaporation increases – precipitation increases

• Causing flooding in some areas and droughts in

others

10/25/2013

23

42.9 The Nitrogen Cycle

Plants can’t use atmospheric N2

Nitrogen fixation (soil bacteria) takes up N2 (gas)

and forms ammonia

Denitrification (denitrifying bacteria) returns

some nitrogen to the atmosphere

42.9 The Nitrogen Cycle

Denitrification (denitrifying bacteria) returns

some nitrogen to the atmosphere

Farmers must counter act loss of nitrogen when

they plant crops that use a lot of nitrogen

• Plant rotation

10/25/2013

24

The Nitrogen Cycle - FYI

Disruption by Human Activities

Human activities add nitrogen to ecosystems

• Examples: Fertilizer application and fossil fuel

burning (releases nitrogen oxides)

10/25/2013

25

42.10 The Phosphorus Cycle

Phosphorus moves in a sedimentary cycle

• Mainly stored as phosphate in rocks

• Earth’s crust is the largest reservoir

Phosphorus is often the limiting factor for plant

growth and algal producers

Required for energy (ATP adenosine

triphosphate)

42.10 The Phosphorus Cycle

Subtropical and tropical ecosystems have limited

amounts of phosphorus available for plants

• Most is tied up in plants

Developed countries have too much phosphorus

• Heavily fertilized fields

• At one point soaps –

• Moves to water ways and causes algal blooms

10/25/2013

26

The Phosphorus Cycle - FYI

Eutrophication

Excessive nutrient

enrichment of an

ecosystem

• Example:

Phosphorus in

aquatic ecosystems

Natural

But, exacerbated by

humans

10/25/2013

27

Key Concepts:

CYCLING OF WATER AND NUTRIENTS

Availability of water, carbon, nitrogen, phosphorus, and other substances influences primary productivity

Ions or molecules of these substances move slowly in global cycles, from environmental reservoirs, into food webs, then back to reservoirs

Human activities can disrupt these cycles