Transcript 14.4 Interactions within Communities

Interactions within
Communities
Interactions within Communities
• A community consists of all populations
of different species that interact together in
a given ecosystem.
• Some organisms within communities
cannot exist independently of one another
and work together for survival.
Niches
• Ecological Niche:
– An organisms use of and interaction with abiotic and
biotic resources in its environment that influences its
growth, survival and reproduction.
• Fundamental Niche:
– The physical conditions under which a species might
live, in the absence of interactions with other species.
• Realized Niche:
– The actual niche of a species whose distribution is
restricted by biotic interactions such as competition,
predation, disease and parasitism.
Niches
• Intraspecific and interspecific interactions
influences population dynamics of
individual species.
• Interactions between two species and their
effects on population density calssified into
5 categories:
– Competition, Predation, Symbiosis
(Parasitism, Mutualism, Commensalism).
Interspecific Competition
• Occurs between individuals of different
populations.
• Serves to restrict population growth.
• Consists of:
– Interference Competition: involves
aggression and fighting.
– Exploitative Competition: involves
consumption/use of shared resources
Interspecific Competition
• Strongest competition occurs between
species when niches overlap.
• Principle of Competitive Exclusion:
– If resources are limited, no two species can
remain in competition for exactly the same
niche indefinitely.
– Outcome?
• Population decline in weaker species; migration;
change in behaviour.
Interspecific Competition
• Resource partitioning reduces competition
between different species occupying the same
habitat.
Interspecific Competition
• Considered to be a driving force for
evolution of adaptations that enable
species to use resources for continued
survival.
• See the example on the two barnacle
species on page 680 of your textbook.
Predation
• Population density of predator increases at
the expense of its prey.
• As prey ↑, there is more food for the
predator.
• As the predator ↑, the prey ↓.
• As the prey ↓, the predator ↓.
• When the predator population is low, the
prey population can grow.
Predation
• The predator patterns tend to lag behind
the prey patterns.
Defense Mechanisms (Plants)
• Defense mechanisms in prey have evolved
through repeated encounters with predators.
• Plants use morphological defenses (thorns,
hooks, spines, needles) and chemical
defenses.
Defense Mechanisms (Animals)
• Defensive mechanisms brought out by
coevolution between plants and animals.
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Camouflage.
Bright colouration as a warning signal.
Mimicry.
Hiding
Fleeing from predators.
Bright Colours = Dangerous
Camouflage
Defense Mechanisms: Mimicry
Batesian Mimicry
• A palatable/harmless species mimics an
unpalatable/harmful organism.
Mullerian Mimicry
• Unpalatable species that resemble one
another.
• Several species have the same
appearance to the predator, reducing the
impact on each individual species.
Symbiosis (“living together”)
• Mutualism
• Commensalism
• Parasitism
Mutualism
• Both organisms benefit from relationship.
• Obligatory mutualism: neither species involved
could survive without the other.
• Examples:
– Bacteria in guts of herbivores digest cellulose.
– Bacteria in human large intestine produce vitamins B
and K.
– Oxpecker birds feed on backs of grazing animals.
– Lichens – relationship between fungi and
cyanobacteria.
Commensalism
• One organism benefits and the other
remains unaffected.
• Example:
– Remora suction themselves to
sharks…do not have to
expend energy to travel!
– Barnacles also attach
themselves to whales.
Parasitism
• One organism (the parasite) benefits at the
expense of another (the host).
• The host is often harmed or killed.
• Microparasites (microscopic) vs. macroparasites
(readily visible).
• Endoparasites (live & feed
inside host) vs. ectoparasites
(live & feed on host).
Parasitism
• Social parasites complete life cycle by
manipulating social behaviour of host.
• Example:
– Cowbirds lay eggs in other nests…no energy
expended on building a nest and caring for
young.
– Cowbird egg hatches earlier, so larger chick
receives more food, resulting in higher death
rate of host eggs.