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Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 41
Community Ecology
(Sections 41.1 - 41.5)
Albia Dugger • Miami Dade College
41.2 Community Structure
• Symbiosis (“living together”) refers to a relationship in which
two species have a prolonged close association
• Two species that interact closely for generations can coevolve
– an evolutionary process in which each species acts as a
selective agent on the other
• symbiosis
• One species lives in or on another in a commensal,
mutualistic, or parasitic relationship
Species Interactions
• Species interactions can be mutually beneficial, mutually
harmful, or benefit one species while harming the other
• Example: Commensal ferns attached to the trunk of a tree;
the fern benefits from the light, and the tree is unaffected
• commensalism
• Species interaction that benefits one species and neither
helps nor harms the other
Commensalism
• A tree with a
commensal fern
• The fern benefits by
growing on the tree,
which is unaffected by
the presence of the fern
41.3 Mutualism
• In a mutualistic interaction, two species benefit by taking
advantage of one another
• Example: Pollinators eat nectar and pollen, and plants
receive pollen from other plants of the same species
• mutualism
• Species interaction that benefits both species
Mutualism and Defense
• For some mutualists, the main benefit is defense
• Example: Sea anemone and anemone fish
• An anemone fish has a mucus layer that shields it from
stinging cells (nematocysts) of a sea anemone
• Tentacles of the anemone protect the fish from predators
• The anemone fish chases away the few fishes that are
able to eat sea anemone tentacles
Sea Anemone and Anemone Fish
41.4 Competitive Interactions
• Each species has an ecological niche defined by physical
and biological factors; the more similar the niches of two
species are, the more intensely they will compete
• An animal’s niches include the temperature range it can
tolerate, species it eats, and places it can breed
• A flowering plant’s niche would include its soil, water, light,
and pollinator requirements
• ecological niche
• All of a species’ requirements and roles in an ecosystem
Effects of Competition
• Species compete most intensely when a shared resource is
the main limiting factor for both
• Whenever two species require the same limited resource to
survive or reproduce, the better competitor will drive the less
competitive species to extinction in that habitat
• competitive exclusion
• Process whereby two species compete for a limiting
resource, and one drives the other to local extinction
Experiment: Competitive Exclusion
• EX: with an invasive
species
• Two Paramecium
species compete for the
same food (bacteria)
• Each species thrives
when grown alone
• When grown together,
P. aurelia drove P.
caudatum to extinction
Experiment: Competitive Exclusion
Experiment: Competitive Exclusion
Fig. 41.6.1, p. 695
Experiment: Competitive Exclusion
Fig. 41.6.2, p. 695
Experiment: Competitive Exclusion
Fig. 41.6.3, p. 695
0
4
8 12 16 20 24
Time (days)
0
P. aurelia alone
4
8 12 16 20 24
Time (days)
Relative
population density
P. caudatum alone
Relative
population density
Relative
population density
Experiment: Competitive Exclusion
0
Both species together
4
8 12 16 20 24
Time (days)
Stepped Art
Fig. 41.6, p. 695
ANIMATION: Competitive Exclusion
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Invasive Species
• Gypsy moths
native to Europe
and Asia feed on
oaks through
much of the
United States
Invasive Species
• Nutrias native to
South America are
abundant in
freshwater
marshes of the
Gulf States
Resource Partitioning
• Resource partitioning is an evolutionary process by which
species become adapted to use a shared limiting resource in
a way that minimizes competition
• Example: Three plant species growing in the same field
• resource partitioning
• Species become adapted in different ways to access
different portions of a limited resource
• Allows species with similar needs to coexist
Resource Partitioning
• Roots of each species
take up water and
mineral ions from a
different soil depth
• Reduces competition
among the species and
allows them to coexist
ANIMATION: Resource Partitioning
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41.6 Parasites, Brood Parasites,
and Parasitoids
• Some plants and animals benefit by withdrawing nutrients
from other species
• Some species trick others into providing parental care
Parasitism
• With parasitism, one species (the parasite) feeds on another
(the host), without immediately killing it
• Endoparasites live and feed inside their host
• Ectoparasites feed while attached to a host’s external
surface
• parasitism
• Relationship in which one species withdraws nutrients
from another species, without immediately killing it
41.1 Fighting Foreign Fire Ants –
Biological Controls
• NOT 41.6 BUT SUPPORTIVE STORY FROM 41.1:
• Red imported fire ants, Solenopsis invicta, have a venomous
sting, disrupt native wildlife communities, and are not
controlled by pesticides
• Biological control involves phorid flies, specialized parasites
(parasitoids) that kill their host by laying an egg in the ant’s
tissues – the larvae eats its way through the fire ant and
undergoes metamorphosis in its head
• community
• All species that live in a particular region
Phorid Fly and Fire Ant
• Phorid flies insert a
fertilized egg into an
ant’s thorax
• Parasitized ant that lost
its head after a
developing fly larva
moved into it
Fighting Foreign Fire Ants (revisited)
• Red imported fire ants (RIFAs) did not evolve in North
America, so there are few predators, parasites, or pathogens
to hold them in check
• Global climate change is expected to help RIFAs extend their
range in the US
ANIMATION: Succession
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41.7 Ecological Succession
• Species often alter the habitat in ways that allow other
species to replace them (ecological succession)
• The first, opportunistic colonizers of new or newly vacated
habitats are pioneer species, which have high dispersal
rates, grow and mature fast, and produce many offspring
• pioneer species
• Species that can colonize a new habitat
• Mosses, lichens, some flowering annuals
Primary Succession
• Primary succession begins when pioneer species colonize a
barren habitat with no soil, such as a new volcanic island or
land exposed by the retreat of a glacier
• Pioneers help build and improve the soil
• primary succession
• A new community becomes established in an area where
there was previously no soil
Primary Succession
Secondary Succession
• In secondary succession, a disturbed area within a
community recovers.
• Occurs in abandoned agricultural fields and burned forests
• secondary succession
• A new community develops in a site where the soil that
supported an old community remains