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

2. Types of predators Carnivores – kill the prey during attack
Herbivores – remove parts of many prey,
rarely lethal.
Parasites – consume parts of one or few prey,
Parasitoids – kill one prey during prolonged
attack.
Start with definition. Unlike competition, here we have clear winners and losers in the fitness arena.
Classification: Based on effects of predators on prey.
Clearly, prey can compensate for some forms of predation (grazing) but not others (true predation).
Take home message.
different kinds of predation, in this classification elicit different coping responses on the part of the prey.
by the way, which kind of predator would you try to choose to control populations of a pest?
go for specificity and lethality, parasitoids.
Let’s look at some examples of these different interactions.

3. Diet breadth consumes only one prey type specialist generalist
narrow
diet
specialist
an alternative way to classify predators concerns their diet. In particular, whether their diet is diverse (broad) or specific to one food source (narrow).
This classification scheme is useful if we are trying to understand predator behavior and prey choice.
Diet width of predators varies along a continuum.
On the one hand we can find examples of animals who have specialized morphological adaptations that make for very high efficiency in consuming a particular kind of prey.
at the expense of diversity in their diet (monophagous)
On the other hand, we have predators (like our crayfish) that consume a diversity of prey, that vary spatially and seasonally.
One question is, what kinds of behaviors give rise to different diet widths.
What behavior would cause an animal to specialize?
discrimination among alternative prey types or preference.
generalist
broad diet
consumes many prey types

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

5. 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

6. Camouflage – blending in

7. Aposematic colors – warning

8. Is he crazy???

9. Mimicry – look like something that is dangerous
or tastes bad

10. Mimicry – look like something that is dangerous or tastes bad
Mullerian mimicry – convergence of several
unpalatable species

11. Mimicry – look like something that is dangerous or tastes bad
Batesian mimicry – palatable species mimics an
unpalatable species
model
mimic
mimics
model

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

13. Predator-prey population dynamics are connected
Predators kill prey  affects prey death rate
dNprey/dt = rNprey
– pNpreyNpredator
change in prey population
deaths due to predation
per capita rate of growth without predation

14. Predator-prey population dynamics are connected
Predators kill prey  affects prey death rate
dNprey/dt = rNprey
– pNpredatorNprey
predation rate
prey population size depends on number of predators
with few predators, prey population grows
with many predators, prey population shrinks

15. births due to predation
Predator-prey population dynamics are connected
Predators eat prey  affects predator birth rate
dNpredator/dt = cpNpreyNpredator – dNpredator
change in
predator population
death rate
births due to predation

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

17. Predator-prey population dynamics are connected
 affects prey death rate
 affects predator birth rate
Predators kill and eat prey
dNprey/dt = rNprey
– pNpredatorNprey
dNpredator/dt = cpNpreyNpredator – dNpredator
with few predators, prey population grows
with many prey, predator population grows
with many predators, prey population shrinks
with few prey, predator population shrinks N
time

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

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

20. Keystone species affect community structure
Predators can allow coexistence of competing prey
Next, I want to turn to how predator behavior can influence interactions between prey species
In particular I want to ask, how can preference for a dominant competitor influence species coexistence?
We might expect predators to show preference for dominant competitors over subordinate species.
Why? What makes a dominant competitor? High intrinsic rate of increase, capacity to monopolize scarce resources, ergo relatively high abundance.
What makes an energetically profitable prey source?
all else being equal, relatively high abundance. Why, smaller search time.
So, let’s see what happens to a prey community in the presence of a picky predator. We reach into our virtual zoo and pull out barnacles, (balanus), mussels (mytilus), and starfish (pisaster).
This is the virtual inter tidal zone, where sea meets rocky shore.
it, and this particular community, were made famous in a classic paper by Robert Paine in the mid-60s. Paine’s study was the first to experimentally manipulate species abundances as a way of testing the factors controlling community composition.
you have the reference on a list we passed out in lab this week.
competitors
Barnacles Mussels
Balanus
Mytilus
(Paine 1966)

21. Keystone species affect community structure
Predators can allow coexistence of competing prey
Starfish
predator
Pisaster
Next, I want to turn to how predator behavior can influence interactions between prey species
In particular I want to ask, how can preference for a dominant competitor influence species coexistence?
We might expect predators to show preference for dominant competitors over subordinate species.
Why? What makes a dominant competitor? High intrinsic rate of increase, capacity to monopolize scarce resources, ergo relatively high abundance.
What makes an energetically profitable prey source?
all else being equal, relatively high abundance. Why, smaller search time.
So, let’s see what happens to a prey community in the presence of a picky predator. We reach into our virtual zoo and pull out barnacles, (balanus), mussels (mytilus), and starfish (pisaster).
This is the virtual inter tidal zone, where sea meets rocky shore.
it, and this particular community, were made famous in a classic paper by Robert Paine in the mid-60s. Paine’s study was the first to experimentally manipulate species abundances as a way of testing the factors controlling community composition.
you have the reference on a list we passed out in lab this week.
competitors
Barnacles Mussels
Balanus
Mytilus
(Paine 1966)

22. How can we test the effect of a predator on community structure?
Experiment - Remove the predator
Starfish
Pisaster
Now let’s return the starfish to the community, and see how they affect the interaction between barnacles and mussels.
run ecobeaker, keystone predator-2 prey
note: show predator action table: specialist on mytilus
with selective predation of the top competitor, the subordinate (barnacles) persists.
What controls the population of the subordinate (barnacles)
Intraspecific competition and interspecific competition. Watch squares.
Barnacles Mussels
Balanus
Mytilus

23. Removal experiment - mussels are the dominant competitor
- competitive exclusion of barnacles
starfish
removed
mussels % of
inter-
tidal
zone
Now let’s return the starfish to the community, and see how they affect the interaction between barnacles and mussels.
run ecobeaker, keystone predator-2 prey
note: show predator action table: specialist on mytilus
with selective predation of the top competitor, the subordinate (barnacles) persists.
What controls the population of the subordinate (barnacles)
Intraspecific competition and interspecific competition. Watch squares.
barnacles
time

24. What is the effect of the predator on the structure of this community?
- starfish allow coexistence of competitors
starfish
removed
mussels % of
inter-
tidal
zone
Now let’s return the starfish to the community, and see how they affect the interaction between barnacles and mussels.
run ecobeaker, keystone predator-2 prey
note: show predator action table: specialist on mytilus
with selective predation of the top competitor, the subordinate (barnacles) persists.
What controls the population of the subordinate (barnacles)
Intraspecific competition and interspecific competition. Watch squares.
barnacles
time

25. How do starfish promote coexistence?
Pisaster
Now let’s return the starfish to the community, and see how they affect the interaction between barnacles and mussels.
run ecobeaker, keystone predator-2 prey
note: show predator action table: specialist on mytilus
with selective predation of the top competitor, the subordinate (barnacles) persists.
What controls the population of the subordinate (barnacles)
Intraspecific competition and interspecific competition. Watch squares.
Barnacles Mussels
Balanus
Mytilus
Starfish are picky – they prefer mussels (dominant competitor),
which allows barnacles (weaker competitor) to coexist.

26. Keystone species affect community structure
disproportionately to their abundance.
Picky predators can promote coexistence among
competing prey species.
Competitive exclusion is prevented when the
dominant competitor is the preferred prey.