How Competition Shapes Communities

ObjectivesDescribe the role of competition in shaping

the nature of communitiesDistinguish between fundamental and

realized nichesDescribe how competition affects an

ecosystem Summarize the importance of biodiversity

Bell RingerWhat do you think would occur when a robin

and a finch both fed exclusively on one type of insect?

What do you think would occur when a robin fed on ground insects and a finch fed on insects in trees?

CompetitionCompetition: when two species use the

same resourcesFood, nesting sites, living space, light, mineral

nutrients, water Occurs for resources in short supply

NicheNiche: functional role of a particular species

in an ecosystemHow an organism lives, “job” it performs

within ecosystemWhat it eats, where it lives, etc.

NicheMay be described in terms of space

utilization, food consumption, temperature range, requirements for moisture or mating

Habitat is a location while niche is pattern of living

NicheFundamental Niche: entire range of

resource opportunities an organism is potentially able to occupy within an ecosystem

Realized Niche: the part of its fundamental niche that a species occupies

NicheSometimes a species won’t use its full

fundamental niche to reduce competition

C = optimal growthWhat is occurring in the diagrams?

Barnacle ExampleChthamalus stellatus (C.S): lives in shallow

water, often exposed to air by receding tidesSemibalanus balanoides (S.B): lives lower

down on rocks, rarely exposed to atmosphere

Barnacle Example

Barnacle ExampleRemoval of S.B from deeper zone allowed

C.S to occupy vacent surfaces Indicated C.S was not intolerant to deeper

environment C.S fundamental niche includes the

deeper zone When S.B reintroduced, it would out

compete C.S by crowding it off the rocks

Barnacle ExampleS.B could not survive when placed in

shallow water habitats where C.S normally occurs

This shows that C.S only occupies a small portion of its fundamental niche

The rest is unavailable because of competition with S.B

Competition can limit how a species use resources

Barnacle Example

Competition without Division of Resources

If two species are competing, the species that uses the resource more efficiently will eventually eliminate the other

Competitive exclusion: the elimination of a competing species

Competitors CoexistIf it is possible for two species to avoid

competition they may coexist

Predation and CompetitionPredation reduces effects of competition Ex. Sea stars

Keystone species: plays large role in ecosystem

Without sea stars, number of prey species in ecosystem fell from 15 to 8

Mussels out competed other species for space

Predation and CompetitionBecause predation can reduce competition, it

can promote biodiversity Biodiversity: variety of living organisms

present in a community Measure of number of different species in

community (species richness) and relative numbers of each species (species diversity)