Download Interactions Within Communities (III)

Interactions Within Communities (III)
December 3, 2010
Text p. 676-680
Re-Visit: Mullerian Mimicry
• Predators and prey can protect themselves through
mimicry
• Unrelated species that resemble each other and
are all poisonous or “distasteful”
• Why Mullerian? If predator is confused between 2
species, means both are more likely to survive
• To understand competition, must look at
the ecological niche
Ecological Niche
• The use of, and interaction with, abiotic
and biotic resources in its environment
Habitat = organism’s “address”
Ecological Niche = organism’s “occupation”
Ecological Niche
• Can include:
– Prey
– Predators
– Reproductive methods
– Temperature range
– Habitat
– Behaviour
Fundamental Niche
• Biological characteristics of the organism
and the set of resources individuals in the
population are theoretically capable of
using under ideal conditions
• Ideal conditions
– Abundant resources
– No competition from other species
Realized Niche
• What the organism actually uses under
prevailing environmental conditions
• Because of competition with other
organisms for similar resources, a species
can only use a portion of its fundamental
niche
Competition
• Interaction within communities
• May be detrimental to one or both species
• Two Types:
– Interspecific – interactions between
individuals of different species for an essential
common resource that is in limited supply
– Intraspecific – interactions between
individuals of the same species or population
competing for resources in their habitats
Interspecific Competition
• Purpose: to restrict population growth
• 2 Types:
– Interference competition
– Exploitative competition
Interference Competition
• Aggression between individuals of different
species, fighting over the same resource
• Typically detrimental to both individuals of the
different species involved
• Asymmetric – one species has an advantage
over the other
Exploitative Competition
• Consumption of resources by two species,
but one species may limit resource
availability to other species
• One species more efficiently uses a
resource
Reduction in Survival
Principle of Competitive Exclusion
• THEORY: if resources are limited, no two species
can remain in competition indefinitely
Species A
Niche
Species B
Niche
Competition
Heavy competition leads to
competitive exclusion –
one species must go
Gause
• Russian Ecologist G.F. Gause
• Competitive Exclusion aka Gause’s Principle
– Two species with similar requirements could not
coexist in the same community
Paramecium sp.
Red Squirrel
Grey Squirrel
Introduced between 1876-1929
Related Types of Interspecific
Competition
• Apparent competition
– 2 species share a predator
– The two prey can compete with each other to
make themselves less available for
consumption
• Scramble competition
– Inadequate resource for both species
– Receive equal amounts, but not enough
Results of Interspecific
Competition
• Population size of weaker competitor
could decline
• One species could change behaviour to
survive using different resources
• Individuals in one population could migrate
where resources are more plentiful
Resource Partitioning
• Avoidance or reduction of competition for
similar resources by different species
through the use of non-overlapping
ecological niches
Anolis sp.
A.
carolinensis
- Leaves and
adjacent twigs
A. distichus
- Trunks and
large
branches
A. angusticeps
-Small twigs at
great heights
A. sagrei
- Partly
terrestrial
- Small and
large low
perches
Schoener, 1968
Foxtail
Indian Mallow
Smartweed
Evolutionary Adaptation
• Interspecific competition is driving force for
species to evolve adaptations for
continued survival
Classic Interspecific Competition Example:
Connell’s Field Experiments
The Keystone Species
• Plays a critical role in the community
• Impact is greater than expected, based on
its size or abundance
• Predator-Prey – usually is a predator
acting on prey with no other predators
• Good target species for conservation
Intraspecific Competition
• Individuals of same population (and
species) competing for same resources
– Food
– Shelter
– Mates
• As population density increases there is
more competition among individuals for
resources and growth rate slows
• Classic territorial behavioural
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