BI 101 Food webs and Ecosystems - Linn-Benton …cf.linnbenton.edu/mathsci/bio/millern/upload/ecosystems.pdf · Copyright © The McGraw-Hill Companies, Inc. Permission ... cycle through

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BI 101 Food webs and Ecosystems


Learning objectives

• Describe the flow of energy through the ecosystem, and understand how this affects the biomass of tropic levels

• Understand the cycling of nutrients such as carbon and water

• Recognize how impacts to the nutrient cycles affect the whole community


Biosphere

Ecosystem

Community

Population

Organism

What is an ecosystem?

√

√

Levels of study in Ecology


Figure 28-4b A simple marine food chain

(b) A simple marine food chain

quaternary consumer

(5th trophic level)

tertiary consumer

(4th trophic level)

producer

(1st trophic level)

primary consumer

(2nd trophic level)

zooplankton phytoplankton

secondary consumer

(3rd trophic level)


Figure 28-5 A simplified grassland food web


Primary producers—the autotrophs

• Auto = self + trophy = nourishment

• Organisms take nourishment directly from

the environment

http://www.njscuba.

net/biology/eco_wat

er.html

Phytoplankton—ocean Terrestrial plants

http://www.100m

ag.com/know00

2.html


Consumers—heterotrophs

• Hetero = other + trophy = nourishment


8

Trophic levels

within an

ecosystem

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Detrivores (also known as scavengers) are special consumers that eat dead organisms

Decomposers are organism that break down organic substances, making them available to other organisms

bacteria and fungi are the principal decomposers in land

Sun

Fungi

Bacteria Decomposers

Trophic

level 1

Producer

Trophic

level 2

Trophic

level 3

Carnivore

Secondary consumer

Top

carnivore

Trophic

level 4

Tertiary consumer

Herbivore

Primary consumer


Detrital food web


Energy pathways in ecosystems

• All ecosystems need energy so its living

members can grow and reproduce

• Source of energy = the sun

• One-way path

• Flows through various organisms, and

eventually dissipates into the environment

as heat



17%

Growth

33%

Cellular

respiration

50%

Feces

Much of the energy captured by plants is lost as energy passes through the ecosystem

How heterotrophs use (and

lose) food energy

Energy Flows Through

Ecosystems


12

Energy loss in

an ecosystem


Algae and

cyanobacteria

1000 calories

30 calories 6 calories

1.2 calories

Human

Smelt

Small

heterotrophs

Trout

150 calories



Food Supply – Energy Pyramid

Energy is used much more efficiently if humans eat plants

(first tropic level) instead of meat (second tropic level). A given

area of farmland can support more people if the crops are fed

directly to people rather than to livestock that people then eat.

For example if a man needs 3,000 Calories per day, then

30,000 Cal beef are needed, which in turn need 300,000 Cal of

corn. This works out to be 1.5 acres of corn per day per

person. If the person ate corn directly then 10 people could be

supported by the same 1.5 acres of corn.


Biogeochemical Cycles

• In contrast to the one-way flow of energy,

materials (such as water, carbon and

nitrogen) cycle through ecosystems.

– Water cycle

– Carbon cycle

– Nitrogen cycle

– Phosphorus cycle


Figure 28-7 The hydrologic cycle

evaporation

from land and

transpiration

from plants

reservoirs

processes water vapor in

the atmosphere

precipitation

over land

extraction for

agriculture

groundwater,

including

aquifers

evaporation from

lakes and rivers

evaporation

from the

ocean

precipitation

over the ocean

runoff

from rivers

and land water in

the ocean

lakes and rivers

seepage into soil


Burning or clear-cutting forests breaks the

water cycle


Figure 28-8 The carbon cycle

reservoirs

processes

trophic levels

fire

consumers

respiration

CO2 in the

atmosphere

CO2 dissolved

in the ocean

detritus feeders

and decomposers

photosynthesis

producers

burning

fossil fuels

fossil fuels

(coal, oil, natural gas) decomposition


Figure 28-14 Greenhouse gases and global warming

Sunlight energy

enters the atmosphere

1

Most heat is radiated

back into space

Some energy

is reflected back

into space

2

Some atmospheric heat is

retained by greenhouse gases

6

Most sunlight strikes

Earth’s surface and is

converted into heat

3 Heat is

radiated back into

the atmosphere

4

Sun

5

volcanoes forest

fires

homes and

buildings

agricultural

activities

vehicle

emissions

power plants

and factories


Figure 28-15 Global warming parallels atmospheric


Figure 28-9 The nitrogen cycle

reservoirs

processes

trophic levels

N2 in the

atmosphere

ammonia and

nitrates in water

decomposition

burning

fossil fuels

uptake by

producers

application of

manufactured fertilizer

consumers producers

denitrifying

bacteria

detritus feeders

and decomposers

lightning

nitrogen-fixing

bacteria in soil

and legume roots

ammonia

and nitrates

in soil


Figure 28-10 The phosphorus cycle

geological

uplift

reservoirs

runoff

from rivers

producers

phosphate

in water

uptake by

producers

phosphate

in sediment

phosphate

in soil

processes

trophic levels

runoff from

fertilized

fields

consumers

decomposition

phosphate

in rock

application of

manufactured

fertilizer

formation of

phosphate-containing

rock

detritus feeders

and decomposers

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BI 101 Food webs and Ecosystems - Linn-Benton …cf.linnbenton.edu/mathsci/bio/millern/upload/ecosystems.pdf · Copyright © The McGraw-Hill Companies, Inc. Permission ... cycle through