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Chapter 37
Communities and Ecosystems
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Dining In
• Community structure and function depend
on the interactions among organisms
– Example: Apanteles glomeratus wasp,
Pieris rapae butterfly, and other wasps
• Ecosystem structure and function depend
on the interactions of the community with its
abiotic environment
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STRUCTURAL FEATURES OF COMMUNITIES
37.1 A community includes all the organisms
inhabiting a particular area
• Biological community: an assemblage of all the
populations of organisms living close enough
together for potential interaction
• Key characteristics of a community
– Species diversity: variety of different kinds
of organisms
• Species richness
• Relative abundance
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– Dominant species
– Response to disturbances
– Trophic structure: feeding relationships among
species
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37.2 Competition may occur when a shared
resource is limited
• Interspecific competition may play a major role
in structuring a community
– Two species competing for the same limited
resource
– May inhibit growth of one or both species
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• Competitive exclusion principle
– Two species cannot coexist in a community
if their niches are identical
• Niche: species' total use of biotic and
abiotic resources
– Two possible results
• Less competitive species will be driven to
local extinction
• Resource partitioning may evolve
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LE 37-2a
LE 37-2b
37.3 Predation leads to diverse adaptations in
both predator and prey
• Predation is an interaction between species in
which predator kills and eats prey
• Adaptations of both tend to be refined through
natural selection
– Camouflage
– Chemical defense
Video: Seahorse Camouflage
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
– Batesian mimicry
• Palatable species mimics an unpalatable
model
– Mullerian mimicry
• Two unpalatable species mimic each other
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37.4 Predation can maintain diversity in a
community
• Keystone species
– Exerts strong control on community
structure because of its ecological niche
• Keystone predator
– May maintain community diversity by
reducing numbers of the strongest
competitors
– Removal can cause major changes in
community dynamics
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37.5 Herbivores and the plants they eat have
various adaptations
• Herbivores are animals that eat plants or algae
– Have adaptations for locating and eating
vegetation
• Plants have evolved defenses against
herbivores
– Toxic chemicals
– Physical defenses (spines, thorns)
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• Some herbivore-plant interactions illustrate
coevolution
– Reciprocal evolutionary adaptations
– Change in one species acts as a new
selective force on another species
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LE 37-5
Eggs
Sugar
deposits
37.6 Symbiotic relationships help structure
communities
• Symbiotic relationship: interaction between two
or more species that live in direct contact
– Parasitism
• Parasite lives on or near its host
• Parasite obtains nourishment at the
expense of host
• Includes pathogens that may inflict lethal
harm on host
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• Commensalism
– One species benefits without significantly
affecting the other
– Few absolute cases documented
• Mutualism
– Both partners benefit
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Video: Clownfish and Anemone
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37.7 Disturbance is a prominent feature of most
communities
• Disturbances are characteristic of most
biological communities
– Events such as fire, storms, floods
– Damage communities
– Remove organisms from communities
– Alter the availability of resources
– Can have positive effects
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• Ecological succession is a transition in
community species composition following a
major disturbance
– Primary succession: gradual colonization of
barren rocks
– Secondary succession: occurs after a
disturbance has destroyed a community but
left the soil intact
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LE 37-7
Retreating glacier
with moraine in the
foreground
Dryas stage
Spruce starting to appear in the
alder and cottonwood forest
Spruce and hemlock forest
TALKING ABOUT SCIENCE
37.8 Fire specialist Max Moritz discusses the role
of fire in ecosystems
• Dr. Max Moritz studies fire in chaparral
ecosystems
• Fire is a key abiotic factor in many ecosystems
– Important in nutrient cycling
– Creates conditions for regeneration of many
plants
• Dr. Moritz hopes to help people coexist with
cycles of weather, vegetation, growth, and fire
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37.9 Trophic structure is a key factor in
community dynamics
• Trophic structure: a pattern of feeding
relationships consisting of several different
levels
• Food chain: sequence of food transfer up the
trophic levels
– Moves chemical nutrients and energy
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• Producers
– Autotrophs that support all other trophic
levels
– Plants on land
– In water, mainly photosynthetic protists and
cyanobacteria
• Primary consumers
– Herbivores that eat plants, algae, or
phytoplankton
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• Secondary, tertiary, and quaternary consumers
– Eat consumers from the level below them
• Detritivores (decomposers)
– Animal scavengers, fungi, and prokaryotes
– Derive energy from detritus produced at all
trophic levels
– Decomposition is essential for recycling
nutrients in ecosystems
Video: Shark Eating Seal
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LE 37-9
Trophic level
Quaternary
consumers
Hawk
Killer whale
Tertiary
consumers
Snake
Tuna
Secondary
consumers
Herring
Mouse
Primary
consumers
Zooplankton
Grasshopper
Producers
Plant
A terrestrial food chain
Phytoplankton
An aquatic food chain
37.10 Food chains interconnect, forming food
webs
• A food web is a more realistic view of trophic
structure
– Consumers usually eat more than one type
of food
– Each food type is consumed by more than
one type of consumer
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LE 37-10
Quaternary,
tertiary,
and secondary
consumers
Tertiary
and
secondary
consumers
Secondary
and
primary
consumers
Primary
consumers
Producers
(plants)
ECOSYSTEM STRUCTURE AND DYNAMICS
37.11 Ecosystem ecology emphasizes energy
flow and chemical cycling
• An ecosystem consists of all the organisms in
a community and the abiotic factors with which
they interact
• Ecosystem dynamics involve two processes
– Energy flow through the components of the
ecosystem
– Chemical cycling within the ecosystem
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LE 37-11
Chemical
cycling
Energy
flow
Chemical
energy
Light
energy
Heat
energy
Chemical elements
37.12 Primary production sets the energy budget
for ecosystems
• Primary production: amount of solar energy
converted by producers to chemical energy in
biomass
– Biomass: amount of organic material in an
ecosystem
– Net primary production: amount of biomass
produced minus amount used by producers
in cellular respiration
– Varies greatly among ecosystems
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LE 37-12
Open ocean
Estuary
Algal beds and coral reefs
Desert and semidesert scrub
Tundra
Temperate grassland
Cultivated land
Boreal forest (taiga)
Savanna
Temperate deciduous forest
Tropical rain forest
0
500
1,000
1,500
2,000
Average net primary productivity (g/m2/yr)
2,500
37.13 Energy supply limits the length of food
chains
• Only about 10% of the energy stored at each
trophic level is available to the next level
– Pyramid of production shows loss of energy
from producers to higher trophic levels
– Amount of energy available to top-level
consumers is relatively small
• Most food chains have only three to five
levels
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LE 37-13
Tertiary
consumers
Secondary
consumers
Primary
consumers
10 kcal
100 kcal
1,000 kcal
Producers
10,000 kcal
1,000,000 kcal of sunlight
CONNECTION
37.14 A production pyramid explains why meat is
a luxury for humans
• Human meat or fish eaters are tertiary or
quaternary consumers
• Humans eating grain have ten times more
energy available than when they process the
same amount of grain through meat
• Using land to raise animals consumes more
resources than using the land to cultivate
crops
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LE 37-14
Trophic level
Human
meat-eaters
Secondary
consumers
Primary
consumers
Human
vegetarians
Corn
Producers
Cattle
Corn
37.15 Chemicals are recycled between organic
matter and abiotic reservoirs
• Biogeochemical cycles
– Cycle nutrients through both biotic and
abiotic components
– Can be local or global
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LE 37-15
Consumers
Producers
Detritivores
Nutrients
available
to producers
Abiotic
reservoir
37.16 Water moves through the biosphere in a
global cycle
– Solar energy drives the global water cycle
– Precipitation
– Evaporation
– Transpiration
– Water cycles between the land, oceans, and
atmosphere
– Forest destruction and irrigation affect the
water cycle
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LE 37-16
Transport
over land
Solar energy
Net movement of
water vapor by wind
Precipitation
over ocean
Evaporation
from ocean
Precipitation
over land
Evaporation and
transpiration from
land
Percolation
through
soil
Runoff and
groundwater
37.17 The carbon cycle depends on photosynthesis and
respiration
•
Carbon cycles through the atmosphere, fossil fuels,
and dissolved carbon in oceans
– Taken from the atmosphere by photosynthesis
– Used to make organic molecules
– Decomposed by detritivores
– Returned to the atmosphere by cellular respiration
•
Burning of wood and fossil fuels is raising the level of
CO2 in the atmosphere
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LE 37-17
CO2 in atmosphere
Photosynthesis
Cellular
respiration
Burning of
fossil fuels
and wood
Higher-level
Primary
consumers
consumers
Carbon compounds
in water
Detritus
Decomposition
37.18 The nitrogen cycle relies heavily on
bacteria
• Atmospheric N2 is not available to plants
– Soil bacteria convert gaseous N2 to usable
ammonium (NH4+) and nitrate (NO3-)
– Some NH4+ and NO3- are made by chemical
reactions in the atmosphere
• Human activity is altering nitrogen cycle
balance in many areas
– Sewage treatment and fertilization
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LE 37-18
Nitrogen in atmosphere (N2)
Nitrogen
fixation
Assimilation
by plants
Denitrifying
Nitrates bacteria
(NO3–)
Nitrogen-fixing
bacteria in root
nodules of legumes
Detritivores
Decomposition
Ammonium (NH4)
Nitrogen-fixing
soil bacteria
Nitrifying
bacteria
37.19 The phosphorus cycle depends on the
weathering of rock
• Phosphorus and other soil minerals are
recycled locally
• Weathering of rock adds PO43- to soil
– Slow process makes amount of phosphorus
available to plants low
• Human activity has created phosphate
pollution of water
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LE 37-19
Rain
Geologic
uplift
of rocks
Weathering
of rocks
Plants
Runoff
Consumption
Plant uptake
of PO43–
Sedimentation
Soil
Leaching
Decomposition
ECOSYSTEM ALTERATION CONNECTION
37.20 Ecosystem alteration can upset chemical
cycling
• The Hubbard Brook Experimental Forest is a
long-term study of nutrient cycling
– Natural conditions
– Water loss balanced between runoff and
transpiration/evaporation
– Flow of nutrients in and out of
watersheds nearly balanced
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– Logged and sprayed watershed
• Runoff increased 30 -40%
• Net loss of nutrients was huge
• Nitrate concentration in creek was 60 times
greater
– Other long-term findings
• Acid precipitation has resulted in calcium
loss
• Forest plants are not adding new growth
because of calcium deficiency
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Nitrate concentration in runoff (mg/L)
LE 37-20c
80.0
Deforested
60.0
40.0
20.0
4.0
3.0
Completion of
tree cutting
Control
2.0
1.0
1965
1966
1967
1968
TALKING ABOUT SCIENCE
37.21 David Schindler talks about the effects of
nutrients on freshwater ecosystems
• Dr. David Schindler was involved in
environmental research that resulted in the
banning of phosphates in detergents
• Nutrient runoff from agricultural lands and
large livestock operations may cause
excessive algal growth
• This cultural eutrophication reduces species
diversity and harms water quality
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• A combination of factors threaten freshwater
ecosystems
– Acid precipitation
– Climate warming
– Changes in land use
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Figure 37-21b
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