Interactions Within Communities (III) December 3, 2010 Text p

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 CompetitionHeavy 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

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

Schoener, 1968 Anolis sp. A. sagrei -Partly terrestrial -Small and large low perches A. angusticeps -Small twigs at great heights A. distichus -Trunks and large branches A. carolinensis - Leaves and adjacent twigs

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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