How Competition Shapes Communities Chapter 17 Section 2 How Competition Shapes Communities

Objectives Describe the role of competition in shaping the nature of communities Distinguish between fundamental and realized niches Describe how competition affects an ecosystem Summarize the importance of biodiversity

Bell Ringer What 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?

Competition Competition: when two species use the same resources Food, nesting sites, living space, light, mineral nutrients, water Occurs for resources in short supply

Niche Niche: functional role of a particular species in an ecosystem How an organism lives, “job” it performs within ecosystem What it eats, where it lives, etc.

Niche May 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

Niche Fundamental 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

Niche Sometimes a species won’t use its full fundamental niche to reduce competition C = optimal growth What is occurring in the diagrams?

Barnacle Example Chthamalus stellatus (C.S): lives in shallow water, often exposed to air by receding tides Semibalanus balanoides (S.B): lives lower down on rocks, rarely exposed to atmosphere

Barnacle Example

Barnacle Example Removal 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 Example S.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 Coexist If it is possible for two species to avoid competition they may coexist

Predation and Competition Predation 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 Competition Because 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)