1. Predation – one species feeds on another  enhances fitness of predator but reduces fitness of prey ( +/– interaction)

2. Diet breadth consumes only one prey type consumes many prey types broad diet narrow diet specialist generalist

3. How has predation influenced evolution? Adaptations to avoid being eaten: spines (cactii, porcupines) hard shells (clams, turtles) toxins (milkweeds, some newts) bad taste (monarch butterflies) camouflage aposematic colors mimicry

4. Predator-prey population dynamics are connected Predators kill prey  affects prey death rate dN prey /dt = rN prey change in prey population per capita rate of growth without predation deaths due to predation – pN prey N predator

5. Predator-prey population dynamics are connected Predators kill prey  affects prey death rate dN prey /dt = rN prey – pN predator N prey predation rate prey population size depends on number of predators with few predators, prey population grows with many predators, prey population shrinks

6. Predator-prey population dynamics are connected Predators eat prey  affects predator birth rate dN predator /dt = cpN prey N predator – dN predator births due to predation change in predator population death rate

7. Predator-prey population dynamics are connected Predators eat prey  affects predator birth rate dN predator /dt = cpN prey N predator – dN predator predation rate conversion rate of prey to baby predators predator population size depends on number of prey with many prey, predator population grows with few prey, predator population shrinks

8. Predator-prey population dynamics are connected Predators kill and eat prey dN predator /dt = cpN prey N predator – dN predator with few predators, prey population grows with many prey, predator population grows with many predators, prey population shrinks with few prey, predator population shrinks  affects prey death rate  affects predator birth rate dN prey /dt = rN prey – pN predator N prey N time

9. Lotka-Volterra models describe predator and prey population cycling. Real world predator and prey populations can cycle in size.

10. Why are ecological interactions important? Interactions can affect distribution and abundance. Interactions can influence evolution.

11. Keystone species affect community structure Predators can allow coexistence of competing prey competitors Barnacles Mussels BalanusMytilus (Paine 1966)

12. Keystone species affect community structure Predators can allow coexistence of competing prey Sea Star competitors predator Pisaster Barnacles Mussels BalanusMytilus (Paine 1966)

13. Barnacles Mussels Balanus Mytilus How can we test the effect of a predator on community structure? Experiment - Remove the predator Sea Star Pisaster

14. Removal experiment time Sea Star removed % of inter- tidal zone mussels - mussels are the dominant competitor - competitive exclusion of barnacles barnacles

15. time Sea Star removed % of inter- tidal zone mussels barnacles What is the effect of the predator on the structure of this community? - Sea Star allow coexistence of competitors

16. Barnacles Mussels Sea Star Pisaster Sea Stars are picky – they prefer mussels (dominant competitor), which allows barnacles (weaker competitor) to coexist. How do Sea Stars promote coexistence? BalanusMytilus