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Community Ecology
Chapter 52
Community:
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All the populations in an ecosystem
Difficult to study
Can be large or small
Have a wide range of interactions
Are rarely isolated
Community structure and
functioning
 Niche vs. habitat
 Niche = role
 Habitat = local environment (part of an
organism’s niche)
 Fundamental niche – all the basic parts of
the ecosystem that it could use; reduced by
competition with other species
 Realized niche – the parts of the ecosystem
that the organism actually uses
Interspecific competition
 Two or more species attempting to use the
same limited resource
 Competitive exclusion: two species cannot
share the same resource at the same time
– one will be excluded
 Resource partitioning – competing species each
use only part of the available resource so they
can coexist
 Character displacement – a physical change in
an organism’s appearance as a result of
competition reduction
Predator/Prey
 Coevolution – each one changes in
response to the other
 Predator strategies: pursuit vs.
ambush
 Prey strategies:
 Plants – physical or chemical defenses
 Animals – physical, mechanical,
chemical, cryptic coloration, mimicry
Symbiosis
 Mutualism – both benefited
 Nitrogen-fixing bacteria and legumes
 Commensalism – one benefits, the
other is neither harmed nor helped
 Tree and epiphyte
 Parasitism – one harms the other
 Tapeworm and host
Keystone species
 A crucial species – determines the
characteristics of the rest of the
community
 Many times are the top predator in
the ecosystem
 Without their presence the shape of
the entire community changes
Dominant species
 Also greatly impact their community
– but because of their high number
 Forests – trees, coral reef - coral