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  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.

ScienceShare.co.uk Shared Resource Presentation Transcript

  • 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, rarely lethal. Parasitoids – kill one prey during prolonged attack.
  • 3. Diet breadth consumes only one prey type consumes many prey types broad diet narrow diet specialist generalist
  • 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 c o l o r s mimicry
  • 6. Camouflage – blending in
  • 7. Aposematic c o l o r s – 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 model mimics
  • 12. Lotka-Volterra models describe predator and prey population cycling. Real world predator and prey populations can cycle in size.
  • 13. Keystone species affect community structure Predators can allow coexistence of competing prey competitors Barnacles Mussels Balanus Mytilus (Paine 1966)
  • 14. Keystone species affect community structure Predators can allow coexistence of competing prey Starfish competitors predator Pisaster Barnacles Mussels Balanus Mytilus (Paine 1966)
  • 15. Barnacles Mussels Balanus Mytilus How can we test the effect of a predator on community structure? Starfish Pisaster Experiment - Remove the predator
  • 16. Removal experiment time starfish removed % of inter- tidal zone mussels - mussels are the dominant competitor - competitive exclusion of barnacles barnacles
  • 17. time starfish removed % of inter- tidal zone mussels barnacles What is the effect of the predator on the structure of this community? - starfish allow coexistence of competitors
  • 18. Barnacles Mussels Starfish Pisaster Starfish are picky – they prefer mussels (dominant competitor), which allows barnacles (weaker competitor) to coexist. How do starfish promote coexistence? Balanus Mytilus