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BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 36
Communities and Ecosystems
Modules 36.1 – 36.4
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
36.1 A community is all the organisms inhabiting a
particular area
• All the organisms in a particular area make up
a community
• A number of factors characterize every
community
– Biodiversity
– The prevalent form of
vegetation
– Response to disturbances
– Trophic structure
(feeding relationships)
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Figure 36.1
• Biodiversity is the variety of different kinds of
organisms that make up a community
• Biodiversity has two components
– Species richness, or the total number of
different species in the community
– The relative abundance of different species
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STRUCTURAL FEATURES OF COMMUNITIES
36.2 Competition may occur when a shared
resource is limited
• Interspecific competition occurs between two
populations if they both require the same
limited resource
• A population's niche is its role in the
community
– The sum total of its use of the biotic and abiotic
resources of its habitat
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• The competitive exclusion principle
– Populations of two species cannot coexist in a
community if their niches are nearly identical
High
tide
Chthamalus
Balanus
Ocean
Low
tide
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Figure 36.2
• Competition between species with identical
niches has two possible outcomes
– One of the populations, using resources more
efficiently and having a reproductive
advantage, will eventually eliminate the other
– Natural selection may lead to resource
partitioning
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36.3 Predation leads to diverse adaptations in both
predator and prey
• Predation is an interaction where one species
eats another
– The consumer is called the predator and the
food species is known as the prey
• Parasitism can be considered a form of
predation
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36.4 Predation can maintain diversity in a
community
• A keystone species exerts strong control on
community structure because of its ecological
role
• A keystone predator may maintain community
diversity by reducing
the numbers of the
strongest competitors
in a community
– This sea star is a
keystone predator
Figure 36.4A
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• Predation by killer whales
on sea otters, allowing sea
urchins to overgraze on kelp
– Sea otters represent the
keystone species
Figure 36.4B
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36.5 Symbiotic relationships help structure
communities
• A symbiotic relationship is an interaction
between two or more species that live together
in direct contact
• There are three main types of symbiotic
relationships within communities
– Parasitism
– Commensalism
– Mutualism
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• Parasitism is a kind of predator-prey
relationship
– The parasite benefits and the host is harmed in
this symbiotic relationship
– A parasite obtains food at the expense of its host
– Parasites are typically smaller than their hosts
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• Commensalism is a symbiotic relationship
where one partner benefits and the other is
unaffected
• Examples of commensalism
– Algae that grow on the shells of sea turtles
– Barnacles that attach to whales
– Birds that feed on insects flushed out of the
grass by grazing cattle
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• Mutualism is a symbiotic
relationship where both
partners benefit
• Examples of
mutualism
– Nitrogen-fixing
bacteria and legumes
– Acacia trees and the
ants of the genus
Pseudomyrmex
Figure 36.5B
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36.6 Disturbance is a prominent feature of most
communities
• Disturbances include events such as storms,
fires, floods, droughts, overgrazing, and human
activities
– They damage
biological
communities
– They remove
organisms from
communities
– They alter the
availability of
resources
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Figure 36.6
• Ecological succession is a transition in the
species composition of a community following a
disturbance
– Primary succession is the gradual colonization
of barren rocks by living organisms
– Secondary succession occurs after a
disturbance has removed the vegetation but left
the soil intact
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ECOSYSTEM STRUCTURE AND DYNAMICS
36.8 Energy flow and chemical cycling are the two
fundamental processes in ecosystems
• A community interacts with abiotic factors,
forming an ecosystem
• Energy flows from the sun, through plants,
animals, and decomposers, and is lost as heat
• Chemicals are recycled between air, water,
soil, and organisms
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• A terrarium ecosystem
Chemical cycling
(C, N, etc.)
Light
energy
Chemical
energy
Heat
energy
Figure 36.8
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36.9 Trophic structure is a key factor in ecosystem
dynamics
• A food chain is the stepwise flow of energy and
nutrients
– from plants (producers)
– to herbivores (primary consumers)
– to carnivores (secondary and higher-level
consumers)
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TROPHIC LEVEL
Quaternary
consumers
Carnivore
Carnivore
Tertiary
consumers
Carnivore
Carnivore
Secondary
consumers
Carnivore
Carnivore
Primary
consumers
Herbivore
Zooplankton
Producers
Plant
Phytoplankton
A TERRESTRIAL FOOD CHAIN
AN AQUATIC FOOD CHAIN
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Figure 36.9A
• Decomposition is the breakdown of organic
compounds into inorganic compounds
• Decomposition is essential for the continuation
of life on Earth
• Detritivores
decompose waste
matter and recycle
nutrients
– Examples: animal
scavengers, fungi,
and prokaryotes
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Figure 36.9B
36.10 Food chains interconnect, forming food webs
• A food web is a network of interconnecting
food chains
– It is a more realistic view of the trophic
structure of an ecosystem than a food chain
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Wastes and
dead organisms
Tertiary
and
secondary
consumers
Secondary
and
primary
consumers
Primary
consumers
Producers
(Plants, algae,
phytoplankton)
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Detritivores
(Prokaryotes, fungi,
certain animals)
Figure 36.10
36.11 Energy supply limits the length of food chains
• Biomass is the amount of living organic
material in an ecosystem
• Primary production is the rate at which
producers convert sunlight to chemical energy
– The primary production of the entire biosphere
is about 170 billion tons of biomass per year
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• A pyramid of production reveals the flow of
energy from producers to primary consumers
and to higher trophic levels
Tertiary
consumers
10 kcal
Secondary
consumers
100 kcal
Primary
consumers
1,000
kcal
Producers
10,000 kcal
1,000,000 kcal of sunlight
Figure 36.11
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• Only about 10% of the energy in food is stored
at each trophic level and available to the next
level
– This stepwise energy loss limits most food
chains to 3 - 5 levels
– There is simply not enough energy at the very
top of an ecological pyramid to support another
trophic level
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36.12 Connection: A production pyramid explains
why meat is a luxury for humans
• The dynamics of energy flow apply to the
human population as much as to other
organisms
– When we eat grain or fruit, we are primary
consumers
– When we eat beef or other meat from herbivores,
we are secondary consumers
– When we eat fish like trout or salmon (which eat
insects and other small animals), we are tertiary
or quaternary consumers
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• Because the production pyramid tapers so
sharply, a field of corn or other plant crops can
support many more vegetarians than meateaters
TROPHIC LEVEL
Secondary
consumers
Primary
consumers
Human
meat-eaters
Human
vegetarians
Cattle
Corn
Corn
Producers
Figure 36.12
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36.13 Chemicals are recycled between organic
matter and abiotic reservoirs
• Ecosystems require daily infusions of energy
– The sun supplies the Earth with energy
– But there are no extraterrestrial sources of
water or other chemical nutrients
• Nutrients must be recycled between organisms
and abiotic reservoirs
– Abiotic reservoirs are parts of the ecosystem
where a chemical accumulates
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• There are four main abiotic reservoirs
– Water cycle
– Carbon cycle
– Nitrogen cycle
– Phosphorus cycle
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35.14 Water moves through the biosphere in a
global cycle
• Heat from the sun drives the global water cycle
– Precipitation
– Evaporation
– Transpiration
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Solar
heat
Water vapor
over the sea
Precipitation
over the sea
(283)
Net movement
of water vapor
by wind (36)
Evaporation
from the sea
(319)
Water vapor
over the land
Evaporation
and
transpiration
(59)
Precipitation
over the land
(95)
Oceans
Flow of water
from land to sea
(36)
Surface water
and groundwater
Figure 36.14
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36.15 The carbon cycle depends on photosynthesis
and respiration
• Carbon is taken from the atmosphere by
photosynthesis
– It is used to make organic molecules
– It is returned to the atmosphere by cellular
respiration
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CO2 in atmosphere
Burning
Cellular respiration
Plants,
algae,
cyanobacteria
Photosynthesis
Higher-level
consumers
Primary
consumers
Wood and
fossil fuels
Decomposition
Detritivores
(soil microbes
and others)
Detritus
Figure 36.15
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36.16 The nitrogen cycle relies heavily on bacteria
• Nitrogen is plentiful in the atmosphere as N2
– But plants cannot use N2
• Various bacteria in soil (and legume root
nodules) convert N2 to nitrogen compounds
that plants can use
– Ammonium (NH4+) and nitrate (NO3–)
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• Some bacteria break down organic matter and
recycle nitrogen as ammonium or nitrate to
plants
• Other bacteria return N2 to the atmosphere
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Nitrogen (N2) in atmosphere
Assimilation
by plants
Amino acids
and proteins in
plants and animals
Denitrifying
bacteria
Nitrogen
fixation
Detritus
Nitrogen-fixing
bacteria in root
nodules of legumes
Nitrates
(NO3–)
Detritivores
Decomposition
Nitrifying
bacteria
Nitrogen-fixing
bacteria in soil
Nitrogen
fixation
Ammonium (NH4+)
Figure 36.16
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36.17 The phosphorus cycle depends on the
weathering of rock
• Phosphates (compounds containing PO43-) and
other minerals are added to the soil by the
gradual weathering of rock
• Consumers obtain phosphorus in organic form
from plants
• Phosphates are returned to the soil through
excretion by animals and the actions of
decomposers
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Uplifting
of rock
Phosphates
in organic
compounds
Weathering
of rock
Phosphates
in rock
Animals
Plants
Runoff
Detritus
Phosphates
in solution
Phosphates
in soil
(inorganic)
Decomposition
Rock
Precipitated
(solid) phosphates
Detritivores
in soil
Figure 36.17
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