Chapter 55

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPoint® Lecture Presentations for

Biology Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Chapter 55Chapter 55

Ecosystems


Overview: Observing Ecosystems

• An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with which they interact

• Ecosystems can range in size, but regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling

• Energy flows through ecosystems (IN ONE DIRECTION) while matter cycles within them (IN ALL DIRECTIONS)


Concept 55.1: Physical laws govern energy flow and chemical cycling in ecosystems.

• All living systems require a constant input of free energy, and organisms use free energy to maintain organization, grow and reproduce.

• Ecologists study the transformations of energy and matter within their system, and use these studies to suggest the health of an ecosystem.

• Laws of physics and chemistry apply to ecosystems, particularly energy flow.


Conservation of Mass

• The law of conservation of mass states that matter cannot be created or destroyed

• Chemical elements must therefore be continually recycled within ecosystems

• Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products

Fig. 55-4

Microorganismsand other

detritivores

Tertiary consumers

Secondaryconsumers

Primary consumers

Primary producers

Detritus

Heat

SunChemical cycling

Key

Energy flow

Fig. 55-3


Concept 55.2: Energy and other limiting factors control primary production in ecosystems.

• 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 spending limit for an ecosystem’s energy budget

– The amount of solar radiation reaching the Earth’s surface limits photosynthetic output of ecosystems.

– Only a small fraction of solar energy actually strikes photosynthetic organisms, and even less is of a usable wavelength.


Gross and Net Primary Production

• Total primary production is known as the ecosystem’s gross primary production (GPP)

• Net primary production (NPP) is GPP minus energy used by primary producers for respiration

• Only NPP is available to consumers

• Ecosystems vary greatly in NPP and contribution to the total NPP on Earth

NPP = GPP - R

Fig. 55-6

Net primary production (kg carbon/m2·yr)

0 1 2 3

·


Primary Production in Aquatic Ecosystems

• In marine and freshwater ecosystems, both light and nutrients control primary production:

– Depth of light penetration affects primary production in a lake or ocean

– More than light, nutrients limit primary production in geographic regions of the ocean and in lakes

– A limiting nutrient is the element that must be added for production to increase in an area

– Nitrogen and phosphorous are typically the nutrients that most often limit marine and freshwater production

Fig. 55-7

Atlantic Ocean

Moriches Bay

ShinnecockBayLong Island

Great South Bay

A

BC D

EF G

EXPERIMENT

Ammoniumenriched

Phosphateenriched

Unenrichedcontrol

RESULTS

A B C D E F G

30

24

18

12

6

0

Collection site

Ph

yto

pla

nkt

on

den

sity

(mill

ion

s o

f ce

lls p

er m

L)


Primary Production in Terrestrial Ecosystems

• In terrestrial ecosystems, temperature and moisture affect primary production on a large scale:

• Tropical rainforests, with their warm, wet conditions that promote plant growth, are the most productive of all terrestrial ecosystems.

• Low productivity terrestrial ecosystems are generally dry (deserts or the arctic tundra).

• Temperate forest and grassland ecosystems have moderate climates and intermediate productivity.


Concept 55.3: Energy transfer between trophic levels is typically only 10% efficient.

• Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time.


Trophic Efficiency and Ecological Pyramids

• Trophic efficiency is the percentage of production transferred from one trophic level to the next

• It usually ranges from 5% to 20%

• Trophic efficiency is multiplied over the length of a food chain

Fig. 55-10

Primaryproducers

100 J

1,000,000 J of sunlight

10 J

1,000 J

10,000 J

Primaryconsumers

Secondaryconsumers

Tertiaryconsumers

PYRAMID OF NUMBERS

Fig. 55-11

(a) Most ecosystems (data from a Florida bog)

Primary producers (phytoplankton)

(b) Some aquatic ecosystems (data from the English Channel)

Trophic level

Tertiary consumersSecondary consumers

Primary consumersPrimary producers

Trophic level

Primary consumers (zooplankton)

Dry mass(g/m2)

Dry mass(g/m2)

1.5

1137

809

214

What would be the most likely immediate result of a disturbance that reduced the primary producer’s biomass by 50% AND removed all rabbits and insects? Long term result?

Meadow Habitat: Occupies 50.2 km2. Primary Producer Biomass – distributed uniformly and totals 3200 kg/km2.

How much carbon (in g/m2) is released into the atmosphere as a result of the metabolic activity of herbivores?

What % of the biomass in the forest community is tied up in the shrub layer?


Concept 55.4: Biological and geochemical processes cycle nutrients between organic and inorganic parts of an ecosystem.

• Life depends on recycling chemical elements

• Nutrient circuits in ecosystems involve biotic and abiotic components and are often called biogeochemical cycles

– Gaseous carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally

– Less mobile elements such as phosphorus, potassium, and calcium cycle on a more local level

Fig. 55-13Reservoir A Reservoir B

Organicmaterialsavailable

as nutrientsFossilization

Organicmaterials

unavailableas nutrients

Reservoir DReservoir C

Coal, oil,peat

Livingorganisms,detritus

Burningof fossil fuels

Respiration,decomposition,excretion

Assimilation,photosynthesis

Inorganicmaterialsavailable

as nutrients

Inorganicmaterials

unavailableas nutrients

Atmosphere,soil, water

Mineralsin rocks

Weathering,erosion

Formation ofsedimentary rock


• In studying cycling of water, carbon, nitrogen, and phosphorus, ecologists focus on four factors:

– Each chemical’s biological importance

– Forms in which each chemical is available or used by organisms

– Major reservoirs for each chemical

– Key processes driving movement of each chemical through its cycle

Biogeochemical Cycles

Fig. 55-14a

Precipitationover land

Transportover land

Solar energy

Net movement ofwater vapor by wind

Evaporationfrom ocean

Percolationthroughsoil

Evapotranspirationfrom land

Runoff andgroundwater

Precipitationover ocean

Fig. 55-14b

Higher-levelconsumersPrimary

consumers

Detritus

Burning offossil fuelsand wood

Phyto-plankton

Cellularrespiration

Photo-synthesis

Photosynthesis

Carbon compoundsin water

Decomposition

CO2 in atmosphere

Fig. 55-14c

Decomposers

N2 in atmosphere

Nitrification

Nitrifyingbacteria

Nitrifyingbacteria

Denitrifyingbacteria

Assimilation

NH3 NH4 NO2

NO3

+ –

–

Ammonification

Nitrogen-fixingsoil bacteria

Nitrogen-fixingbacteria

Fig. 55-14d

Leaching

Consumption

Precipitation

Plantuptakeof PO4

3–

Soil

Sedimentation

Uptake

Plankton

Decomposition

Dissolved PO43–

Runoff

Geologicuplift

Weatheringof rocks


Decomposition and Nutrient Cycling Rates

• Decomposers (detritivores) play a key role in the general pattern of chemical cycling

• Rates at which nutrients cycle in different ecosystems vary greatly, mostly as a result of differing rates of decomposition

• The rate of decomposition is controlled by temperature, moisture, and nutrient availability

• Rapid decomposition results in relatively low levels of nutrients in the soil

Fig. 55-15Ecosystem typeEXPERIMENT

RESULTS

Arctic

Subarctic

Boreal

TemperateGrassland

Mountain

P

O

D

J

RQ

K

B,C

E,FH,I

LNUS

TM

G

A

A

80

70

60

50

40

30

20

10

0–15 –10 –5 0 5 10 15

Mean annual temperature (ºC)

Per

cen

t o

f m

ass

lost

B

CD

E

F

GH

I

JK

LMN

O

P

QR

S

T

U

Fig. 55-16

1965

(c) Nitrogen in runoff from watersheds

Nit

rate

co

nc

en

tra

tio

n i

n r

un

off

(mg

/L)

(a) Concrete dam and weir

(b) Clear-cut watershed

1966 1967 1968

Control

Completion oftree cutting

Deforested

01

234

20

4060

80


Concept 55.5: Human activities now dominate most chemical cycles on Earth.

• As the human population has grown, our activities have disrupted the trophic structure, energy flow, and chemical cycling of many ecosystems

• In addition to transporting nutrients from one location to another, humans have added new materials, some of them toxins, to ecosystems

• Disruptions that deplete nutrients in one area and increase them in other areas can be detrimental to ecosystem dynamics.

Fig. 55-17: Agriculture & Nitrogen Cycling

Fig. 55-18 – Contamination of Aquatic Ecosystems

Winter Summer


Acid Precipitation


Toxins in the Environment

• Humans release many toxic chemicals, including synthetics previously unknown to nature

• In some cases, harmful substances persist for long periods in an ecosystem

• One reason toxins are harmful is that they become more concentrated in successive trophic levels

• Biological magnification concentrates toxins at higher trophic levels, where biomass is lower

Fig. 55-20

Lake trout4.83 ppm

Co

nce

ntr

ati

on

of

PC

Bs

Herringgull eggs124 ppm

Smelt1.04 ppm

Phytoplankton0.025 ppm

Zooplankton0.123 ppm


Greenhouse Gases and Global Warming

Ozo

ne

lay

er

thic

kn

ess

(D

ob

so

ns)

Fig. 55-23

Year’052000’95’90’85’80’75’70’65’601955

0

100

250

200

300

350

Fig. 55-24

O2

Sunlight

Cl2O2

Chlorine

Chlorine atom

O3

O2

ClO

ClO

Fig. 55-25

(a) September 1979 (b) September 2006

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