Species Interactions:

Interactions classified by mechanisms

Competition

            2 spp. use same limiting resource or limit acquiring resource

Predation

            One animal spp. eats pt of whole another animal

Herbivory

            One spp. eats pt or whole of plant spp.

Parasitism

            One spp. lives in obligatory assoc. with another, metabolically depends host

Disease

            Association b/t pathogenic microorganism & host; host suffers physiologically.

Mutualism

            Two spp. live in assoc. to benefit of both

I. Competition: 2 broad types:

            a.  Resource competition - exploitative: > org. use resource short supply

b. Interference competition - contest: when seek resources harm, may not be limiting resources.

1. Resources involved competition:

            a. Plants: Light, nutrients, water, pollinators, space

            b. Animals: Water, food, mates, space, territory, nesting sites (birds)

2. Classical Models Competition

            a. Lotka-Volterra equations

            b. Based on the logistic curve

            c. Define spp. 1 based on equivalent spp. #2 in terms of resource utilization

3. Competition Equation: Population 1

            a. Changes in species 1 when competing with spp. 2

4. Competition Equation: Population 2

            a. Changes in species 2 when competing with spp. 1

5. Two species together: 3 possible outcomes

            a. Both species coexist

            b. Species 1 go extinct

            c. Species 2 go extinct

6. Graphically depict 2 species change when together in competition

7. Laboratory Experiments: Gause

            a. Gause w/ Yeast cells in pure culture (only one spp.)

            b. Gause w/ Yeast cells 2 spp. together

8. Laboratory Experiments: Birch - grain beetles

            a. Changes one variable influence outcome

            b. Change in intrinsic rate increase for 2 spp.

9. Problem with classical competition equation:

            a. Not mechanistic

            b. No understanding of cause- limiting

            c. "Black box"

10. Natural populations in the Field

            a. Does competitive exclusion occur?  Controversial

            b. Competitive exclusion principle:  Complete competitors cannot coexist

            c. Competitors cannot occupy same niche

                        fundamental vs. realized niche

11. Question?  Does competitive exclusion occur?

            a. When would it not occur?

                        i. Unstable env. never reach equilibrium: primarily colonizing spp.

                        ii. Env. where resources not limiting & spp. do not compete resources

                        iii. Fluctuating env. reverse direction of comp. before extinction

            b. Paradox of Competitive exclusion:

                        i. In lab: Frequent extinction closely related spp.

                        ii. In field: Coexistence of lg.# spp.

            c. Two views:

                        i. Competition is rare in nature - not competing for resources

                        ii. Evolutionary adaptations minimize competitive effects

12. Example field: 5 Warbler spp. boreal forests

            a. All insect eaters ~same size

            b. Why not exclusion?

            c. Different adaptations

13. Adaptations result of competition in past - avoid competition Lack (1944)

            a. Problem in stating competition caused 2 spp. differ

                        i. 2 spp. already different as product of speciation

                        ii. difficult to establish cause & effect from descriptive studies

14. Competition may cause evolution spp. differences:

            a. Example: Resource utilization curves

            b. Important field ecological research "resource partitioning analysis"

            c. Role of competition in defining patterns resource utilization

            d. Same problem - differences may have been caused competition historically

            e. Criteria defining interspecific competition

15. Evolution of competitive ability: Life history strategy

            a. Evolve away from interaction with competitor

                        i. However, may get caught b/t other competitors

            b. Stay and compete - Outcome based on competitive ability

                        i.  Competitive ability: 2 parameters based on Lotka-Volterra equ.

                                    r = rate of increase

                                    K = saturation density

                        ii. Life history either subjected to r selection or K selection

                        iii.         If r selected = Do not evolve mechanisms strong competitors

                                    If K selected = Exist under interspecific/intraspecific competition

                                    > pressure for K-selected to use resources > efficiently

                        iv.         Also have alpha or beta selection: Lotka-Volterra equ.

-Evolve mechanism prevent competitor gaining access resources

                                                -Problem may increase intraspecific competition- offspring

16. Another evolutionary consequence of Competition: Character displacement

            a. Morphological divergence of species

            b. Classical example Darwin's finches on Galapagos Islands

            c. Must show:

                        i. Character not be predictable from variance attribute

                        ii. Local effects eliminated sampling large areas

                        iii. Characteristic must be highly heritable

                        iv. Must show spp are competing and character has relevance