Species Interactions (cont.)

Predation

            One animal spp. eats pt of whole another animal

Herbivory

            One spp. eats pt or whole of plant spp.

1. Predation Important

            a. Restrict distribution, abundance

                        i. pest - useful, biocontrol

                        ii. resource- undesirable - sheep

            b. Interactions affect community organization

            c. Major selective force, > adaptation predator-prey coevolution

2. Simple Models - Predator-prey systems assume isolation

            a. Discrete Generations (t to t+1) or overlapping generations

            b. Based on logistic models

            c. Produce oscillations but > variance

            d. Discrete generation predator-prey models variety dynamic

                        behaviors similar discrete pop. growth models

3. Continuous Generations (overlapping): Prey Isoclines Examined Behavior

            a. Simple horizontal prey isocline Lotka & Volterra:

-predators population high prey decline

            b. More complex hump isocline Rosenweig-MacArthur Model

                        -prey become density limited at high population levels

                        - Predators keep prey low-few reproduce

4. Continuous Generations (overlapping): Predator Isoclines Examined Behavior

            a. Simple horizontal predator isocline Lotka & Volterra

            b. More realistic curve isocline Rosenweig-MacArthur Model

                        -Predator density dependent competition decreases predators

5.  Superimposing 2 Isoclines: Graphic model predator-prey interaction

            -2 equilibrium points where predator & prey # fixed

6.  Superimposing 2 Isoclines: Graphic model predator-prey interaction

            -Limit cycles if predator 0 isocline left of hump

            -Limit cycles: Prey goes up � Predator goes up-Prey declines-Predator declines

-Magnitude of amplitude cycle more likely for extinction

7. Laboratory studies:

            a. Gause (1934) w/ Protozoans

                        i. Paramecium as Prey

                        ii. Didinium as Predator

                        iii. Need refuge survive

                        iv. Need immigration/emigration cycles

            b. Huffaker (1958) Questioned Gauses experiments

                        i. Idea self-annihilating patterns w/o interference

                        ii. Worked with 2 mites

                                    -Prey phytophagous on oranges

                        iii. Only extremely complex configuration cycles

                        iv. Similar to refuge concept - still predators died 70 wks

                        v. Still required immigration/emigration

8. Some lab experiments have shown oscillations � many generations

Utida 1957 � host-parasitoid system bean weevil & wasp

9. Field Experiments, Studies:

            a. Predator removal experiments

                        i. If remove predator will prey increase

                        ii. Study remove bird predators affects on salmon

                                    -Year 1937 before 1,834 smolt going to sea

                                    -Year 1938 after 4,065

                        iii. Problems:

                                    -could have been a good year "highly variable"

                                    -more smolt not always translate > adults

                        iv. Elson (1962) six year study

                        v. Skunk removal for improvement of duck nesting success

                                    -Waterfowl areas of N. Dakota

                        vi. Density red kangaroo vs dingo fence +/-

                        vii. Serengeti Plains E Africa > lg. mammals predators:

                                    -lions, leopards, cheetahs, hyenas etc.

                                    -little impact on lg. mammal prey

                                    -focus surplus, injured, diseased animals

                        viii. Predators can maintain populations & keep starvation

                                    -Caribou herds with and without wolves or predators

            b. Predator introductions

                        i. Sea lamprey lake trout in upper Great Lakes

                        ii. Blocked by Niagara fall until Welland Canal

                        iii. Within 20yrs crash trout pop.

10. Key Question: Do predators control prey densities?

            a. Only first part of sigmoid curve

            b. At high prey densities pred. exert no controlling influence on prey

            c. Endemic phase - prey pop. controlled by pred.

            d. Epidemic phase - not controlled by pred.

11. Classic predator-prey models based on oscillations

            a. Example field support idea: lynx & hares

                        i. Peaks @ 9-10 yrs; suggested function hare decline b/c pred.

                        ii. Alternative hypothesis food shortage for hares

                        iii. Other examples Tawny Owl do not show oscillations

12. Population stability field contrasts oscillation models

            a. Evolutionary selection

                        i. Evolution of predator-prey systems

                        ii. Co-evolution two interacting species

            b. Predators

                        i. > efficient catching prey

                        ii. if too efficient starvation

            c. Prey

                        i. better escaping predation

            d. Predator-prey evolution "arms race"

            e. "life dinner" principle - selection stronger for prey

            f. Depends on if tight relationship b/t pred-prey system

13. Prey also develop Antipredator defense strategies other escape

            a. Warning (Aposematic) coloration, Models and Batesian mimics

            b. Group living

                        i. early detection

                        ii. mobbing - birds, primates

                        iii. confusion in flight (fish, herds)

                                    -position important