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1

Chapter 34 Nature of

Ecosystems

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

34.1 The Biotic Components of

Ecosystems

• Ecosystems

– Abiotic components include sunlight,

inorganic nutrients, soil type, water,

temperature and wind

– Biotic components are the various populations

of species that form a community

34.1 The Biotic Components of

Ecosystems

• Populations Within an Ecosystem

– Autotrophs (producers)

• Require an energy source and inorganic nutrients

to produce organic food molecules

• Manufacture organic nutrients for all organisms

• Green plants and algae carry on photosynthesis

• Some bacteria are chemoautotrophs

34.1 The Biotic Components of

Ecosystems

• Populations of an Ecosystem

– Heterotrophs (consumers)

• Need a preformed source of organic nutrients

• Herbivores: graze directly on plants or algae

• Carnivores: feed on other animals

• Omnivores: feed on both plants and animals

34.1 The Biotic Components of

Ecosystems

• Populations of an Ecosystem

– Decomposers

• Heterotrophic bacteria and fungi

• Break down nonliving organic matter

– They release inorganic matter to be used by producers

• Detritus: partially decomposed matter

– Earthworms and some beetles, termites, and maggots

Producers

Carnivores

Herbivores

Decomposers

34.1 The Biotic Components of

Ecosystems

• Energy flow and chemical cycling

characterizes every ecosystem

– Energy enters ecosystem in the form of sunlight

absorbed by producers

– Chemicals enter when producers take in inorganic

nutrients

34.1 The Biotic Components of

Ecosystems

• Energy Flow and Chemical Cycling

– Producers then make organic nutrients for

themselves and all other organisms in the ecosystem

• Consumers (herbivores and omnivores) gain nutrients and

energy from eating producers

• Higher level consumers (carnivores) then gain nutrients and

energy from eating herbivores and omnivores

– Some energy is released at each level to the

environment in the form of heat and waste products

Energy Flow and Nutrient Cycling Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

heat

heat

heat

producers

consumers

decomposers

energy

nutrients

solar

energy

inorganic

nutrient pool

Energy Balances Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© George D. Lepp/Photo Researchers, Inc.

growth and reproduction Energy to

carnivores

Heat to

environment

Energy

to detritus

feeders

34.2 Energy Flow

• The interconnecting paths of energy flow are

represented by diagramming food webs

– Grazing food webs begin with producers

– Detrital food webs begin with detritus

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

a. Grazing food web

b. Detrital food web

Autotrophs Herbivores/Omnivores Carnivores

deer

rabbits

mice

chipmunks

birds

foxes

skunks

owls

snakes

hawks

detritus

fungi and bacteria invertebrates carnivorous invertebrates salamanders shrews

leaves

mice

fruits and

nuts

leaf-eating

insects

34.2 Energy Flow

• Trophic Level

– Composed of all the organisms that feed at a

particular link in a food chain.

– Grazing food chain

• Leaves → caterpillars → tree birds → hawks

– Detrital food chain

• Detritus → earthworms → shrews

– Primary producers, primary consumers,

secondary consumers

34.2 Energy Flow

• Ecological Pyramids

– Shortness of food chains can be attributed to

the loss of energy between trophic levels

– In general, only about 10% of the energy of

one trophic level is available to the next

trophic level

– Large energy losses depicted as an

ecological pyramid

Ecological Pyramid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

producers

herbivores

carnivores

top carnivores

34.2 Energy Flow

• Ecological Pyramids

– Biomass: the number of organisms at each

level multiplied by their weight

– Biomass of autotrophs much greater than

herbivores

– Biomass of herbivores greater than carnivores

34.2 Energy Flow

• Ecological Pyramids

– Inverted pyramids may be found in aquatic

ecosystems

• Herbivores may have a greater biomass than the

producers

• Over time, algae reproduces and are consumed

rapidly Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

herbivores

producers (algae)

relative

dry weight

34.3 Global Biogeochemical Cycles

• Biogeochemical Cycles

– Pathways by which chemicals circulate

through ecosystems involve both biotic and

abiotic components

• Reservoir: source unavailable to producers

• Exchange pool: source from which organisms take

chemicals

• Biotic community: chemicals move through

community along food chains

Reservoir

• fossil fuels

• mineral

in rocks

• sediment

in oceans Exchange

Pool

• atmosphere

• soil

• water Community

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

34.3 Global Biogeochemical Cycles

• Biogeochemical Cycles

– Two Main Types of Cycles

• Gaseous cycle: chemical element is drawn from

and returns to the atmosphere

• Sedimentary cycle: chemical element is drawn

from soil by plant roots, eaten by consumers,

returned to soil by decomposers

– Exception of water which exists in gas, liquid

and solid forms

34.3 Global Biogeochemical Cycles

• The Water or Hydrologic Cycle

– Freshwater evaporates from bodies of water

– Condensation – gas back to liquid - rain

– Eventually returns to oceans over time via

precipitation

– Human Impact

• In arid West and southern Florida, groundwater

mining is occurring

– Aquifers are being drained faster than they can be

naturally replenished

freshwater runoff

net transport of water vapor by wind

Ocean

Ice

Groundwaters

aquifer

precipitation

over land

transpiration from plants

and evaporation from soil

lake

H2O in Atmosphere

evaporation

from ocean

precipitation

to ocean

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

34.3 Global Biogeochemical Cycles

• The Phosphorus Cycle

– Phosphorus moves from rocks on land to the

oceans

– Gets trapped in sediments

– Phosphorus moves back onto land following a

geological upheaval

– Phosphate is usually a limiting inorganic

nutrient for plants

34.3 Global Biogeochemical Cycles

• The Phosphorus Cycle

– Human Activities

• Phosphates are used in fertilizers, animal feeds,

and detergents

• Excess phosphates in water supplies can lead to

cultural eutrophication (over-enrichment)

– Algal blooms that can lead to massive fish kills

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

biota

sedimentation

plants

decomposers

geological uplift

mineable rock

fertilizer

runoff

phosphate

in soil

animals and

animal wastes Biotic

Community

sewage treatment

plants

phosphate

in solution

detritus

phosphate mining weathering

34.3 Global Biogeochemical Cycles

• The Nitrogen Cycle

– Nitrogen gas makes up about 78% of the

atmosphere

– Plants cannot use nitrogen gas, so nitrogen is

a limiting inorganic nutrient for plants

– Nitrogen Fixation

• Carried out by some cyanobacteria and bacteria

• Conversion of nitrogen gas (N2) to ammonium ions

(NH4+)

– Plants can use ammonium ions

34.3 Global Biogeochemical Cycles

• The Nitrogen Cycle

– Nitrification: production of nitrates (NO3-)

which plants can also use

• Nitrogen gas converted to nitrate in atmosphere by

lightning, meteor trails, cosmic radiation which

provide the high energy needed for N to react with

O

• Ammonium in soil converted to nitrate by nitrifying

bacteria (chemoautotrophs)

– Denitrification: conversion of nitrate back to

nitrogen gas by denitrifying bacteria

34.3 Global Biogeochemical Cycles

• The Nitrogen Cycle

– Human Activities

• Nitrogen is added to fertilizers

– Runoff that contains nitrogen also contributes

to eutrophication

– Fertilizer use also results in the release of

nitrous oxide (N2O), a greenhouse gas

ozone shield depletion

plants

decomposers

NO3

NH4+

NH4+

(ammonium)

decomposers

N2 (nitrogengas) in

Atmosphere

N2 fixation

nitrogen-fixing

bacteria in nodules

and soil

dead organisms

and animal waste

nitrifying

bacteria

NO2

(nitrite) denitrifying

bacteria sedimentation

denitrification

Biotic

Community

NO3

(nitrate)

Biotic

Community

phytoplankton

runoff

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

nitrification

human

activities

cyanobacteria

denitrifying bacteria

denitrification N2 fixation

34.3 Global Biogeochemical Cycles

• The Carbon Cycle • Photosynthesis takes up carbon dioxide from the

atmosphere

• Cell respiration returns it to the atmosphere

– Reservoirs of Carbon

• Dead organisms, fossil fuels, shells, limestone

34.3 Global Biogeochemical Cycles

• The Carbon Cycle

– Human Activities

• More carbon dioxide is being deposited in

atmosphere than is being removed

– Due to deforestation and burning of fossil fuels

• Increased carbon dioxide in atmosphere

contributes to global warming

– Carbon dioxide and other gases absorb and

radiate heat back to Earth – greenhouse effect

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Land plants

Soils

Ocean

combustion

photosynthesis

respiration

decay

runoff

diffusion

sedimentation

coal

oil

natural gas

destruction

of vegetation

CO2 in Atmosphere

bicarbonate (HCO3)

dead

organisms

and animal

waste