Download Ch 54 * Community Ecology

Ch 53 – Community Ecology
What is a community?
• A group of populations of different species
living close enough to interact
1. Interspecific interactions
• Interspecific – between species
• Can be:
– Positive (+)
– Negative (-)
– Neutral (0)
• for each species
Interspecific competition
• Competition (-/-)
• Result
of resources in short supply
http://www.youtube.com/watch?v=rqoqfLzCN6M
• http://www.youtube.com/watch?v=igkjcuw_n_U
• http://www.youtube.com/watch?v=EzLADnLsNRs
• Competitive exclusion principle– Two species competing for the same limiting
resources cannot coexist. Eventually one will have a
selective advantage that will eliminate the other.
Resource partitioning
• Differentiation of
niches that allow
similar species to
coexist in a
community
A. distichus perches on A. insolitus usually
fence posts and other
perches on shady
sunny surfaces.
branches.
A. ricordii
A. insolitus
A. aliniger
A. distichus
A. christophei
A. cybotes
A. etheridgei
Niche
• Ecological niche – the sum total of a species’
use of the biotic and abiotic resources in its
environment
• Fundamental niche – the niche potentially
occupied by a species
• Realized niche – the portion of the
fundamental niche the species actually
occupies
EXPERIMENT
For example, the
presence of one
barnacle species
limits the realized
niche of another
barnacle species
Chthamalus
Balanus
High tide
Chthamalus
realized niche
Balanus
realized niche
Ocean
Low tide
RESULTS
High tide
Chthamalus
fundamental niche
Predation
• Predator eats prey (+/-)
• Predator adaptations:
– Acute senses to locate and identify prey
• Many have forward facing eyes & ears (i.e. fox)
– Adaptations to help catch & subdue prey:
• Stingers, teeth, fangs, poisons, etc.
• http://www.youtube.com/watch?v=pNcIUIULafw
Prey defense
• Cryptic coloration
• Aposematic coloration
• camouflage
• warning coloration
• Batesian mimicry
• Mullerian mimicry
• Unharmful mimics harmful
• 2 unpalatable species mimic each
other
Behavioral defenses
Herbivory
• Herbivore eats part of
plant or alga (+/-)
• Animal – distinguish
non-toxic from toxic
plants
• Plant – defense through
toxins, spines, thorns
Symbiosis
• When individuals of two species live in direct
contact with each other
• Parasitism – parasite gets nourishment from
host (+/-)
• Mutualism – interspecific interaction that
benefits both species (+/+)
• Commensalism – benefits one species, neither
helps nor harms other species (+/0)
• Symbiotic relationships – blind shrimp & goby:
• http://www.animalplanet.com/tvshows/animal-planet-presents/videos/top-10odd-animal-couples-shrimp-a-goby.htm
2. Communities are characterized by
Diversity & trophic structure
• Species diversity –
• Species richness – number of species
• relative abundance – how common or rare species is
• Dominant species – have the highest biomass, or
are most abundant
• Keystone species – exert strong control on
community structure by their ecological roles or
niches (not necessarily the most abundant)
Trophic structure
• The feeding relationships among organisms in a
community
• Trophic levels – the links in the trophic structure
of a community
• Food chains- what eats what
• Food webs – two or more food chains connected
3. Disturbance and community
structure
• Disturbance – an event that damages a
community
• Natural or human activities
• Intermediate disturbance hypothesis –
• Moderate levels of disturbance create
conditions that foster greater species diversity
(vs. High or Low levels of disturbance)
Ecological succession
• Transitions in species composition over ecological
time
• Primary succession –
• Occurs where soil has not yet formed
• Secondary succession –
• Occurs where existing community cleared but soil is
intact
Mt. St. Helen’s
• http://www.youtube.com/watch?v=4RsMyVav
T2Q
• http://www.youtube.com/watch?v=gQ9fV35D
xLY
• Yellowstone Forest Fire succession
• http://www.youtube.com/watch?v=AQQupOY
onRo
4. Biogeographic factors affecting
community diversity
• Two key factors:
• Latitude of community
– More abundant & diverse life in tropics vs. poles
– Area of the community
• Larger the geographic area of a community, the more
species
Island biogeography
• Two factors:
• Size of island – the greater the size, the higher
the immigration rates, lower rates of
extinction
• Distance from mainland – rate of immigration
falls, extinction rates increase
• http://virtualbiologylab.org/Models/Model_
IslandBioGeography.html