1Predation (Chapter 15) Predator-prey cycles Physical Characteristics AdaptationsFunctional vs. numeric responsesModels of predation
2What is Predation?– one species feeds on another enhances fitness of predator but reduces fitness of prey(+/– interaction)
3Two big themes: Predators can limit prey populations. *This keeps populations below K.
4Predator and prey populations increase and decrease in regular cycles.
5A verbal model of predator-prey cycles: Predators eat prey and reduce their numbersPredators go hungry and decline in numberWith fewer predators, prey survive better and increaseIncreasing prey populations allow predators to increaseAnd repeat…
6Why don’t predators increase at the same time as the prey?
7Factors promoting stability in predator-prey relationships Inefficient predators (prey escaping)less efficient predators allow more prey to survivemore living prey support more predatorsOutside factors limit populationshigher death rate (d) for predatorslower growth rate (r) for prey
8Alternative food sources for the predator less pressure on prey populationsRefuges from predation at low prey densitiesprevents prey populations from falling too lowRapid numeric response of predators to changes in prey population
9Huffaker’s Experiment on Predator-Prey Coexistence 2 mite species (1 predator and 1 prey)Initial experiments – predators drove prey extinct then went extinct themselvesAdding barriers to dispersal allowed predators and prey to coexist.
10Refuges from predation allow predator and prey to coexist.
11Predator-prey cycles can be unstable efficient predators can drive prey to extinctionif the population moves away from the equilibrium, there is no force pulling the populations back to equilibriumeventually random oscillations will drive one or both species to extinction
13Characteristics of Predators Eye Position: Predators’ eyes face forward to give them a clear view of their prey
14Predators’ Eye Position Predators’ eyes face forward so they can see the animals they are chasing. This allows them to focus their vision on just the prey. They have great depth perception, so they can see how close or far away the prey is.Predators have their best vision in their binocular area because they are seeing the prey with both eyes. They don’t see the prey as well in their monocular areas because they can only see with the eye on that particular side.
15Characteristics of Predators 2. Feet: Have sharp claws that the predators use to hold onto the prey while they are killing it
16Characteristics of Predators 3. Teeth: Sharp, pointed teeth for grabbing and cutting their food. Predators don’t usually chew the meat completely. It is swallowed whole or in chunks
17Characteristics of Prey Eyes: Located on the side of the head so they can see if predators are approaching
18Preys’ EyesPreys’ eyes are located at the sides of the head, so they have good side and rear vision. Since prey spend most of their time eating grass and leaves, it is important for them to see to the side and rear without moving their heads to allow them to look out for predators and to eat at the same time. Prey have almost360-degree vision.Prey have monocular vision, meaning they use each eye separately. This allows them to see two different objects on opposite sides of their bodies at the same time.
19Characteristics of Prey 2. Feet: Made for running
20Characteristics of Prey 3. Teeth: Flat teeth used to grind tough plant materialDeer basically have two types of teeth. The front teeth, or incisors, are used for cutting the food. The back teeth, or premolars and molars - are used for chewing and grinding the food. Between the incisors and molars is an open space along the jaw that has no teeth.
21Predator or Prey?By looking at an animal’s feet, eye position, and teeth a person can usually tell if an animal is a predator or prey. See if you can determine which of these animals are predators and which are prey. Remember to look at their feet and eye positions.
22The Predator Becomes the Prey Some animals can be both predators and prey. For example, a Texas horned lizard is a predator when it eats ants, termites, beetles, and grasshoppers. It is also a prey when it is eaten by snakes, bobcats, roadrunners and other birds such as hawks and loggerhead shrikes.A horned lizard is a prey when it is eaten by birds, snakes, wolves, bobcats, and coyotes.The horned lizard is a predator when it eat ants and other insects.
23How has predation influenced evolution? Adaptations to avoid being eaten:spines (cactii, porcupines)hard shells (clams, turtles)toxins (milkweeds, some newts)bad taste (monarch butterflies)camouflageaposematic colorsmimicry
27Mimicry – look like something that is dangerous or tastes bad
28Mimicry – look like something that is dangerous or tastes bad Mullerian mimicry – convergence of several unpalatable species
29Mimicry – look like something that is dangerous or tastes bad Batesian mimicry – palatable species mimics an unpalatable speciesmodelmimicmimicsmodel
30Why are ecological interactions important? Interactions can affect distribution and abundance.
31Changing the number of prey can cause 2 types of responses: Functional response – relationship between an individual predator’s food consumption and the density of preyNumeric response – change in the population of predators in response to prey availability
32Type I functional response: predators never satiate!no limit on the growth rate of predators!
33Type II functional response: – consumption rate increases at first, but eventually predators satiate (upper limit on consumption rate)
34Type III functional response : consumption rate is low at low prey densities, increases, and then reaches an upper limit
35Why type III functional response? at low densities, prey may be able to hide, but at higher densities hiding spaces fill uppredators may be more efficient at capturing more common preypredators may switch prey species as they become more/less abundant
36Functional Responses of Predation Number of Prey ConsumedDensity of Prey Population
37Lotka-Volterra models describe predator and prey population cycling.Real world predator and prey populations can cyclein size.
38The Lotka-Volterra Model: *Predicts oscillations in the abundances of predator and prey populations*Predator numbers lag behind those of their prey*Separate calculations for predators and prey
39The Lotka-Volterra Model: AssumptionsPrey grow exponentially in the absence of predators.Predation is directly proportional to the product of prey and predator abundances (random encounters).Predator populations grow based on the number of prey. Death rates are independent of prey abundance.
40The Lotka-Volterra Model Variables:= changet = timeV = # of prey individuals (“victims”)P = # of predator individualsr = exponential growth rate of preyc = capture efficiency of the predators
41The Lotka-Volterra Model For the Prey:rate of change inthe prey populationintrinsic growthrate of the preyremoval of preyby predators
42The Lotka-Volterra Model For the predators:a = efficiency with which prey consumption results in baby predatorsd = death rate of predatorsdeath rate of predatorsrate of change in thepredator populationconversion of preyinto new predators
43Equilibrium- state of balance between opposing forces populations at equilibrium do not changeIsocline- a line on a graph along which populations will not change over time
44Equilibrium IsoclinePrey population reaches equilibrium when ΔV/Δt = 0Prey population stabilizes based on the size of the predator populationPreyIsoclinePredators (P)Number ofr/cd/acNumber of prey (R)
45Equilibrium IsoclinePredator population reaches equilibrium when ΔP/Δt = 0Predator population stabilizes based on the size of the prey populationPredatorisoclinePredators (P)Number ofd/acNumber of prey (R)
48Predator-prey systems can have multiple stable states Reducing the number of predators can lead to an outbreak of prey
49Keystone species affect community structure Predators can allow coexistence of competing preyStarfishpredatorPisasterNext, I want to turn to how predator behavior can influence interactions between prey speciesIn 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.competitorsBarnacles MusselsBalanusMytilus(Paine 1966)
50How can we test the effect of a predator on community structure? Experiment - Remove the predatorStarfishPisasterNow let’s return the starfish to the community, and see how they affect the interaction between barnacles and mussels.run ecobeaker, keystone predator-2 preynote: show predator action table: specialist on mytiluswith 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 MusselsBalanusMytilus
51Removal experiment - mussels are the dominant competitor - competitive exclusion of barnaclesstarfishremovedmussels%ofinter-tidalzoneNow let’s return the starfish to the community, and see how they affect the interaction between barnacles and mussels.run ecobeaker, keystone predator-2 preynote: show predator action table: specialist on mytiluswith 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.barnaclestime
52What is the effect of the predator on the structure of this community? - starfish allow coexistence of competitorsstarfishremovedmussels%ofinter-tidalzoneNow let’s return the starfish to the community, and see how they affect the interaction between barnacles and mussels.run ecobeaker, keystone predator-2 preynote: show predator action table: specialist on mytiluswith 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.barnaclestime
53How do starfish promote coexistence? PisasterNow let’s return the starfish to the community, and see how they affect the interaction between barnacles and mussels.run ecobeaker, keystone predator-2 preynote: show predator action table: specialist on mytiluswith 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 MusselsBalanusMytilusStarfish are picky – they prefer mussels (dominant competitor),which allows barnacles (weaker competitor) to coexist.
54Keystone species affect community structure disproportionately to their abundance.Picky predators can promote coexistence amongcompeting prey species.Competitive exclusion is prevented when thedominant competitor is the preferred prey.