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Ecology: Succession and Life
Strategies
Interactions within
communities of organisms
Outline
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1. Key concepts
2. Ecosystems and communities
3. Competition, Predation,
Commensalism, Mutualism,
Parasitism
4. Succession
5. Conclusions
Key Concepts:
1. A habitat is the type of place where
individuals of a species normally live
2. Every species in the community has its own
niche
3. Interactions among species influence the
structure of a community
4. The first species to occupy a habitat are
replaced by others
5. Different stages of succession often exist in
the same habitat
Ecosystems and communities
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Ecosystem: all factors affecting an
organism’s survival: abiotic and biotic
Individuals of a species form populations
living in a given habitat
Several populations interact to form
communities within a habitat
Many communities + abiotic factors form
an ecosytem
Everything interacts!
Each organism plays a special
role within a community
Competition
Predation
Commensalism
Mutualism
Parasitism
Competition
Organisms compete for same resources by
innate complex behaviors or by adaptive
fitness
Competitive exclusion: if resources are limited,
the most efficient of two competing species
will eliminate the other species in that location
Competition
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Niches: organism’s place in an ecosystem
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Realized: the niche an organism actually
occupies in a given ecosystem
Fundamental: niche it could occupy in the
absence of competition
Two species cannot occupy exactly the same
niche indefinitely
Competition
Resource Partitioning
Three annual plants in a plowed abandoned field
All require water
and minerals
but differ in
adaptations for
securing them
Predation
Relationship in which an organism of one
species (predator) kills and eats an
organism of another species (prey)
Predator may:
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kill all prey and then die itself (no food)
kill most prey; predator dies; some prey hide
and survive
go through alternating cycles of predation and
recovery along with prey
Predation
Predation
Other factors affecting predator/prey
interaction:
Prey dispersal pattern
Other predators or prey in community
Coevolution: evolutionary adjustment of
characteristics of both predator and prey
Protective Coloration: prey adaptations
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Mimicry of organisms with defenses
Camouflage for concealment
Commensalism
Commensalism: an organism of one species
benefits from its interactions with
another; the other species neither benefits
nor is harmed
EX: epiphytes; barnacles; clownfish and
anemones
Mutualism
A relationship where two species live
together in close association, with
benefits for both
Frequently one species gets protection
and/or support while the other gets food
or a home or transportation
Parasitism
Relationship in which an organism of
one species (the parasite) lives in or on
another (the host). The parasite benefits;
the host is usually harmed
—
successful parasites do not kill the host
Parasites may be viruses, bacteria, fungi,
protists, invertebrates
Host/parasite interactions are examples
of coevolution; dynamic natural
selection
Succession
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Dynamic process of change in an
environment where a sequence of
communities replaces one another over
time
Primary succession: in areas not
previously supporting organisms
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pioneer community
climax community
Secondary succession: in areas originally
occupied but disturbed by humans or
nature
Succession
In Conclusion
1. A habitat is the type of place where
individuals of a given species normally live
2. Each species has its own niche in the
community
3. Mutualism, commensalism, competition,
predation, and parasitism are species
interactions that directly or indirectly link
the populations in a community
In Conclusion
4.Species that require the same limited
resource tend to compete
5.The classical model of ecological succession
explains how a community develops from its
pioneer species to an array of species