Download Fig. 46-12b, p.829

Community Structure &
Biodiversity
Community
 All
the populations that live together in a
habitat
 Type
of habitat shapes a community’s
structure
Factors Shaping
Community Structure
 Climate
and topography
 Available
foods and resources
 Adaptations
 Species
 Arrival
of species in community
interactions
and disappearance of species
 Physical
disturbances
Niche
Sum of activities and relationships in
which a species engages to secure and
use resources necessary for survival and
reproduction
Realized &
Fundamental Niches
 Fundamental

Theoretical niche occupied in the absence of
any competing species
 Realized

niche
niche
Niche a species actually occupies
 Realized
niche is some fraction of the
fundamental niche
Species Interactions
 Most
interactions are neutral; have no
effect on either species
 Commensalism
helps one species and
has no effect on the other
 Mutualism
helps both species
Species Interactions
 Interspecific
competition has a negative
effect on both species
 Predation
and parasitism both benefit one
species at a cost to another
Symbiosis
 Living
together for at least some part of
the life cycle
 Commensalism,
mutualism, and
parasitism are forms of symbiosis
Mutualism
 Both
species benefit
 Some
are obligatory; partners
depend upon each other

Yucca plants and yucca moth

Mycorrhizal fungi and plants
Yucca and Yucca Moth
 Example
 Each
of an obligatory mutualism
species of yucca is pollinated only by
one species of moth
 Moth
larvae can grow only in that one
species of yucca
Fig. 46-3a, p.823
Fig. 46-2b, p.822
Sea Anemone and Fish
Fig. 46-4, p.823
Competition
 Interspecific
- between species
 Intraspecific
- between members of the
same species
 Intraspecific
competition is most intense
Forms of Competition
 Competitors
may have equal access to a
resource; compete to exploit resource
more effectively
 One
competitor may be able to control
access to a resource, to exclude others
Interference Competition
Least chipmunk is
excluded from piñon
pine habitat by the
competitive behavior
Least
Chipmunk
of yellow pine
chipmunks
Yellow Pine
Chipmunk
Fig. 46-5a, p.824
Competitive Exclusion Principle
When two species compete for identical
resources, one will be more successful
and will eventually eliminate the other
Gause’s Experiment
Paramecium caudatum
Species grown together
Paramecium aurelia
Figure 47.6
Page 825
Hairston’s Experiment
 Two
salamanders species overlap in parts
of their ranges
 Removed one species or the other in test
plots
 Control plots unaltered
 5 years later, salamander populations
were growing in test plot
P. glutinosis
P. jordani
Fig. 46-7, p.825
Resource Partitioning

Apparent competitors may
have slightly different
niches

May use resources in a
different way or time

Minimizes competition
and allows coexistence
Figure 47.8
Page 825
Predation
 Predators
are animals that feed on other
living organisms
 Predators
are free-living; they do not
take up residence on their prey
Coevolution
 Joint
evolution of two or more species that
exert selection pressure on each other as
an outcome of close ecological interaction
 As
snail shells have thickened, claws of
snail-eating crabs have become more
massive
Predator-Prey Models

Type I model: Each individual predator will
consume a constant number of prey individuals
over time

Type II model: Consumption of prey by each
predator increases, but not as fast as increases
in prey density

Type III model: Predator response is lowest
when prey density is lowest
Fig. 46-9a, p.826
Fig. 46-9c, p.826
Variation in Cycles
 An
association in predator and prey
abundance does not always indicate a
cause and effect relationship
 Variations
in food supply and additional
predators may also influence changes in
prey abundance
Canadian Lynx
and Snowshoe Hare
 Show
cyclic oscillations
 Krebs studied populations for ten years
 Fencing plots delayed cyclic declines
but didn’t eliminate them
 Aerial predators, plant abundance also
involved
 Three-level model
Fig. 46-10a, p.827
Fig. 46-10b, p.827
Fig. 46-10c, p.827
Prey Defenses
 Camouflage
 Warning
coloration
 Mimicry
 Moment-of-truth
defenses
Camouflage
Fig. 46-11a, p.828
Camouflage
Fig. 46-11b, p.828
Camouflage
Fig. 46-11c, p.828
Mimicry
Fig. 46-12a, p.829
Mimicry
Fig. 46-12b, p.829
Mimicry
Fig. 46-12c, p.829
Mimicry
Fig. 46-12d, p.829
Predator Responses
 Any
adaptation that protects prey may
select for predators that can overcome
that adaptation
 Prey
adaptations include stealth,
camouflage, and ways to avoid chemical
repellents
Fig. 46-13a, p.829
Fig. 46-13b, p.829
Fig. 46-13d, p.829
Parasitism
 Parasites
drain nutrients from their
hosts and live on or in their bodies
 Natural
selection favors parasites that
do not kill their host too quickly
Fig. 46-14a, p.830
Kinds of Parasites
 Microparasites
 Macroparasites
 Social
parasites
 Parasitoids
Fungus and Frogs
 Amphibians
are disappearing even in
undisturbed tropical forests
 Infection
by a parasitic chytrid is one of the
causes of the recent mass deaths
Parasitic Plants
 Holoparasites

Nonphotosynthetic; withdraw nutrients and
water from young roots
 Hemiparasites

Capable of photosynthesis, but withdraw
nutrients and water from host
Devil’s Hair
Fig. 46-15a, p.830
Devil’s Hair
Fig. 46-15b, p.830
Parasitioids
 Insect
larvae live inside and consume all
of the soft tissues of the host
 Used
 Can
as agents of biological control
act as selective pressure on host
Fig. 46-17, p.831
The Cowbird
 Brown-headed
cowbirds lay their eggs in
nests constructed by other “host” bird
species. These hosts are unable to
differentiate between cowbird eggs and
their own
 Cowbird hatchlings shove the other eggs
out of the owner’s nest and demand to be
fed.
The Cowbird
 Parasitic
behavior has perpetuated
cowbird genes for thousands of years
Fig. 46-18a, p.831
Fig. 46-18b, p.831
Ecological Succession
 Change
in the composition of species
over time
 Classical
model describes a predictable
sequence with a stable climax
community
Types of Succession
 Primary
succession - new
environments
 Secondary
succession -
communities were destroyed or
displaced
Pioneer Species
 Species
that colonize barren habitats
 Lichens,
small plants with brief life cycles
 Improve
conditions for other species who
then replace them
Climax Community
 Stable
array of species that persists
relatively unchanged over time
 Succession
does not always move
predictably toward a specific climax
community; other stable communities may
persist
Fig. 46-19a, p.832
Fig. 46-19b, p.832
Cyclic Changes
 Cyclic,
nondirectional changes also shape
community structure
 Tree
falls cause local patchiness in
tropical forests
 Fires
periodically destroy underbrush in
sequoia forests
Fig. 46-20a, p.833
Fig. 46-20b, p.833
Fig. 46-20c, p.833
Restoration Ecology
 Natural
restoration of a damaged
community can take a very long time
 Active
restoration is an attempt to
reestablish biodiversity in an area
 Ecologists
are actively working to restore
reefs, grasslands, and wetlands
Community Instability
Disturbances can cause a community to
change in ways that persist even if the
change is reversed
Keystone Species
A
species that can dictate community
structure
 Removal
of a keystone species can cause
drastic changes in a community; can
increase or decrease diversity
Fig. 46-21a, p.834
Fig. 46-21b, p.834
Lubchenco Experiment
Periwinkles promote or limit diversity in different habitats
Tidepools
Rocks exposed at high tide
Figure 47.21
Page 834
Species Introductions
 Introduction
of a nonindigenous species
can decimate a community
 No
natural enemies or controls
 Can
outcompete native species