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Chapter 8
Community Ecology:
Structure, Species
Interactions, Succession,
and Sustainability
Miller – Living in the Environment
13th Edition
ECOTONE
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transition zone or boundary between two
ecosystem, merging area
may be narrow or sharp (b/n woodlandgrassland)
may be gradual or wide (estuary to ocean)
greater number of species along with
greater pop. density in an ecotone than in
either single ecosystem
Most Species Rich Environments
Tropical rainforests
Coral reefs
The deep sea
Large tropical lakes
What are Edge Effects?
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EDGE EFFECTS = changes occurring at
boundaries or edges b/n habitats, there are
changes in community structure and physical
properties (sunlight, temp, wind)
favorable habitat for edge species (ex. Deer)
Roles of Species in Ecosystems
 native
 non-native
 indicator
 keystone
Native and Non-native Species
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Native species
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Species that normally live and thrive in a
particular ecosystem
Non-native (exotic or alien) species
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Species that migrate into an ecosystem or
are deliberately or accidentally introduced
into an ecosystem
Cane toads, Zebra Mussels, Kudzu, Water
Hyacinth
Indicator Species
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Species that serve as early warning of
environmental damage to an
ecosystem(most sensitive),
environmental health gauge
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Birds (canary in a coal mine)
Fish (trout)
Amphibians
Herps
Indicators of thing like . . .
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Adult frog
(3 years)
Tadpole
develops
Into frog
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Young frog
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sperm
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Sexual
reproduction
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Fertilized egg
development
Tadpole
Egg hatches
Eggs
Organ formation
Habitat loss
Drought
Pollution
UV radiation
Parasitism
Over-hunting
Diseases
Immigration or
introduction of
predators or
competitors
Keystone Species
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Species that play roles affecting many other
organisms in an ecosystem
Strong interaction with other species affect health
and survival of species
species whose removal would effect many others as they
play a critical role
loss of species can result in population crash or extinction
critical roles: involve pollination, predation, nutrient recyclers
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Species Interactions
 competition
 predation
 parasitism
 mutualism
 commensalism
Competition
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Intraspecific competition – competition
between members of the same species
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Gain a competitive advantage (Plants)
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Chemical inhibitors
Seed dispersal
Territoriality (Animals)
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Patrol or mark an area
Defend an area
Competition
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Interspecific competition – competition
between members of two or more different
species
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Abundant commonly used resources (food,
sunlight, water, soil nutrients, space, nesting
sites)
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Fundamental niche
Limited resources
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Overlap of fundamental niches
Competitive Exclusion Principle
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The niches of two species cannot
overlap completely or significantly for
very long.
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one species excluded/eliminated from
niche by competition for limited resources
Paramecium
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Paramecium Experiment = grown separately,
then together
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p. 174
RESULTS = two species needing same resource
CANNOT coexist due to limited resources, niches
of two species CANNOT overlap completely or
indefinitely
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HOW DO WE SURVIVE????
Resource Partitioning
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organisms access slightly different
resources to coexist (ADAPT & EVOLVE)
use resources in different ways, from
different areas, or at different times
thus resources are partitioned
EX. Spruce forest warblers: distinct feeding
habits
Resource Partitioning
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Each species minimizes
competition with the
others for food by
spending at least half its
feeding time in a distinct
portion of the spruce tree
and by consuming
somewhat different insect
species.
Number of individuals
© 2004 Brooks/Cole – Thomson Learning
Resource Partitioning
Species 1
Species 2
Region
of
niche overlap
Number of individuals
Resource use
Niche Specialization
Species 1
Species 2
Resource use
Predator – Prey Relationship
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Predation – members of one species
(predator) feed directly on all or part of a
living organism of another species (prey).
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Benefits from reducing prey population
 Gives remaining prey greater access to
food supply
 Can improve the genetic stocks of the
prey population
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PREDATOR STRATEGIES include:
Pursuit and Ambush ~ traits that increase
hunting efficiency
(ex. Speed, intelligence, camouflage,
attractions, trickery)
Predator Tactics
Pursuit
Cheetah
Eagle
Wolves
Ambush
Preying Mantis
Snowy Owls
Humans
Prey Strategies
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Escapism ~ traits that increase ability to FLEE!
Sensory alertness ~ sight/smell alerts of predators
lurking
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Protective outer
armor ~ shells,
spines, thorns,
bark for
protection
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Unique adaptations
lizard tails that break
away
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Camouflage
chameleons, arctic
fox
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Chemical Warfare ~
poisons (toxic,
irritating, bad tasting)
excreted when
threatened
Behavioral Strategies
~ scare off predators
by behavioral activity
(puff body, spreading
wings, herds,
mimicry)