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

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.

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

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

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

Camouflage – blending in

Aposematic colors – warning

Is he crazy???

Mimicry – look like something that is dangerous or tastes bad

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

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

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

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

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

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

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

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

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

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

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)

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)

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

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

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

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.

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.