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

2. 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

3. 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?

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

5. 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.

6. 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

7. 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

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

9. 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

10. Barnacle Example

11. 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

13. 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

14. Barnacle Example

15. 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

16. Competitors Coexist
If it is possible for two species to avoid competition they may coexist

17. 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

21. 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)