Download Figure 40-4

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LifeEcology:
Community
Interactions
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Why Are Community Interactions Important?
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The
interactions among populations within a
I community serve to maintain a balance between
O available resources and the number of …
individuals
using them
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As
O the interactions among the populations serve to
limit population size, they also lead to …
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changes in characteristics and behaviors, increasing
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the fitness of the total population. This is …
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evolution
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When
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results in adaptive changes
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in an interacting species ...
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G coevolution has occurred 
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What Are the Effects of Competition
Among Species?
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Competition among species, or
interspecific competition, has such a
strong effect on the species involved that
each evolves ways to reduce any overlap
in needs
In other words, each species specializes
within the community, developing its own
well-defined, ecological niche 
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Adaptations Reduce the Overlap of Ecological
Niches Among Coexisting Species
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The Competitive Exclusion Principle
- no two species can inhabit exactly the
same ecological niche simultaneously and
continuously
- just as no two organisms can occupy
exactly the same physical space
When two or more species with similar
requirements coexist, they typically occupy
a smaller niche than either would if by
themselves. This is …
Resource Partitioning
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Figure 40-2 
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If one of the competing species is
removed from the community, the
other species may expand its niche
since the competition pressure has
been reduced 
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What Are the Results of Interactions
Between Predators and Their Prey?
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Predation interactions have intense effects
on the species involved
Predators have evolved ways to best
capture their prey, while the prey have
evolved mechanisms to elude their
predators
This coevolution has resulted in some very
complex physical characteristics and
behaviors
Know the examples from your text!
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Bats and their moth prey have
developed complex "cat and mouse"
behaviors, while other species
camouflage themselves to avoid
predators or detection by prey
(Figure 40-4)
In contrast to camouflaged species,
others stand out with bright or
warning coloration (Figure 40-7) 
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Figure 40-4
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Figure 40-7
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These species advertise their presence ...
Their warning coloration are bright colors
that warn potential predators that they are
poisonous or otherwise distasteful and are
to be avoided
Species with common characteristics may
share warning patterns as well; for
example, stinging insects tend to be bright
yellow with black stripes, and poisonous
frogs from the tropics display very colorful
skin pigments 
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Some harmless species
have evolved to mimic their
poisonous relatives
Mountain King Snakes (nonvenomous), for example,
have colorful stripes similar
to Coral Snakes
(venomous) (Figure 40-8)
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the poisonous coral snake
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is mimicked by the harmless mountain king snake
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“Devious” predators exists as well:
Aggressive mimicry has evolved among
species that resemble harmless species
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Predators, however, may be caught offguard
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Some prey make use of color patterns that
mimic a larger organism 
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These species use their startle
coloration to scare away predators
(Figure 40-10)
Some prey species have the ultimate
defense: "chemical warfare"
Coevolution, however, has also lead
to a few predator species that are not
harmed by the chemical produced
and may even use it as its own
defense mechanism 
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What Is Symbiosis?
BWithin a community, interacting with other species is
unavoidable; however, some species have such
I close interactions that they have developed
O symbiotic relationships
LWhen one species of the relationship benefits and the
other is unaffected, the relationship is ...
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commensalistic
GIf one species benefits and the other is harmed, the
Y relationship is ...
parasitic
If both species benefit, the relationship is mutualistic
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Let’s Summarize the possible interactions
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among organisms (Table 40-1)
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How Do Keystone Species Influence
Community Structure?
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The influence of species on community
structure is not necessarily equal
When one species has a role that is out of
proportion to its population size, that
species is a keystone in the community 
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Often, a keystone species cannot be
identified until it has actually been …
removed from the community
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At this point it may be too late to reduce the
impact its absence will have on the
community 
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Succession: How Do Community
Interactions
Cause
Change
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Time?
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The interactions among members of a
community lead to structural changes
within that community; changes that are
identified as stages in succession of the
community
Primary succession begins with pioneer
species such as lichen and mosses
establishing a hold on bare rock
Figure 40-15
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As soil slowly forms, additional species move
into the young community in a recognizable
pattern
Secondary succession occurs after an
established community has been disturbed
perhaps by fire, wind storm, or farming
If left undisturbed, succession will continue to a
stable endpoint, the climax, determined in a
large part by ...
the geography and climate of the area
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Figure 40-16 
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If a community is regularly disturbed, it will
be maintained at a succession point below
the climax, a subclimax
Climax communities covering broad
geographical regions are biomes
Biomes are distinguished by specific
climatic conditions and characterized by
specific plant communities 
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Summary: Major Points
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This chapter has covered:
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1. How organisms interact with members of their
own species, as well as with members of
different species
2. That these interactions include mechanisms
that have evolved to deal with competition for
limited resources, predator/prey relationships,
and symbiotic relationships
3. That the species that are present in a
community depends on the ecosystem that is
present
4. How an ecosystem changes over time
(succession) 
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