Chapter 17 Section 2

1. 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)