Download Interactions Within Communities

Interactions Within Communities
December 1, 2010
Text p. 684-686
Mortality (a) and growth (b) in steelhead trout (Keeley et al. 2001)
Species Interactions
• Populations do not live in isolation
• Interact with other species in the community
• Individual interactions within populations can
shape communities
• One type of interaction: symbiosis
Symbiosis
• Relationship where individuals of two
different species live in close (usually physical)
contact
• At least ONE organism benefits
• 3 categories of symbiosis:
1. Mutualism
2. Commensalism
3. Parasitism
Mutualism
• Both organisms benefit, neither are harmed
• A (+/+) relationship
Lichens
2 Main Types of Mutualisms
• Obligatory
– Neither organism could grow or reproduce
without the other
• Facultative
– One or both organisms can grow or reproduce
without the other
Obligatory Mutualism
Facultative Mutualisms
Ecological Classifications of Mutualism
1. Trophic partnerships
– To obtain energy and nutrients
2. Defensive partnerships
– Provides protection against herbivores, predators
or parasites
3. Dispersive partnerships
– Disperse pollen or seeds, generally for food
reward
Trophic Partnership
Defensive Partnerships
Dispersive Partnerships
• Mutualistic relationships do not have to be
symmetric
– One organism may be obligated to the mutualism,
while the other can live without its mutualistic
partner
Commensalism
• A symbiotic relationship where one organism
benefits and the other is unaffected
• A (+/0) relationship
• Is there really such a thing?
• Not well understood, and difficult to classify
Commensalism
Parasitism
• One organism benefits at the expense of
another organism (the host)
• The other organism is usually never killed but
is often harmed
• A (+/-) relationship
• Come from almost all taxonomic groups
4 Types of Parasitism
1.
2.
3.
4.
Microparasites
Macroparasites
Endoparasites
Ectoparasites
Microparasite
• Microscopic, rapid reproduction rate
• Blood protozoans
• Often requires a vector
Plasmodium
Trypanosoma
Macroparasites
• Larger parasites that are readily visible
Endoparasites
• Live and feed within the host’s body
Ectoparasites
• Live and feed on the outside of the host
Social Parasites
• Complete their life cycle by manipulating the
social behaviour of their hosts
Effects on Host
•
•
•
•
May kill
Reduce fitness
Sterilize
Alter the phenotype
– E.g. alter behaviour of host to benefit parasite but
at host’s expense
Herbivory
• The eating or consumption of plants (primary
producers) by animals known as primary
consumers
– Heterotrophs
– Autotrophs
• Like parasitism & predation, is a (+/-) interaction
• Herbivory is important because plants are the
ultimate source of energy for food webs in most
environments.
Are all herbivores equal?
Feeding Specialization
 Specialists:



Koalas
Monarch caterpillars
Generalists:



Deer
Cows
Leaf-cutter ants
Herbivory
• Alters species dominance patterns
Control of Herbivores?
• Predators and parasites control herbivore
abundance
• Plants defend themselves (particularly
terrestrial plants)
Amensalism
• One species is hurt, but the other does not
benefit
• A (-/0) relationship
Species Interactions
• Interactions can be complex and varied
• Next class... Predators, prey, cycles, defense
mechanisms