Download Bio 150: Ecology Study Questions Week 7: Predation 1. What

Bio 150: Ecology
Study Questions Week 7:
Predation
1. What evidence is there that predators affect prey density?
2. Are predators always bad for potential prey populations? (By potential prey, I mean things the
predator could eat but does not necessarily eat. Hint: the seastar removal experiment provides an
answer)
3. What is an ‘isocline’? Draw and identify prey and predator isoclines on a phase diagram of prey
and predator population size for the basic Lotka-Volterra predation model (i.e. NOT competition).
Identify the joint equilibrium. Any nudge of the populations will produce stable limit cycles. For
such a situation, show using thin arrows for the change in each species numbers on each side of their
isocline. Use fat arrows to show the joint movement (the vectors) of predator and prey numbers.
4. What is the most important basic conclusion from the simple models like Lotka-Volterra and the
one you examined in the lab with respect to the influence of predation on simple predator-prey
systems? Do laboratory studies support or refute this conclusion?
5. Distinguish between a functional response and a numerical response by predators.
6. Modeling has also taught us that the behavior of predators can stabilize population dynamics,
particularly with respect to the efficiency with which individuals capture individual prey and how
this changes with prey density. This relation between rate of prey capture per predator and prey
density is called the functional response. With graphs, illustrate the three types of functional
responses (I, II, and III; in predator-prey context). Show the corresponding relationships when
these are graphed in terms of proportion of the prey population consumed, instead of the number
of prey consumed per predator. With these second graphs, explain with reference to density
dependence why a type III functional graph can stabilize prey populations (i.e. why predators can
impose density-dependent mortality that brings the prey population to an equilibrium. Describe two
mechanisms that can produce a type III functional response.
7. Geographic variation in the pattern of vole population dynamics within Fennoscandia provide
support for the idea that simple one-predator one-prey systems are unstable and, moreover, that prey
switching behavior by predators can stabilize prey population dynamics? Describe the patterns that
led to this conclusion.
8. On your trip to Alaska you discover a lemming that shows dramatic and regular population
fluctuations. Two different mechanisms could account for these fluctuations, one involving
interactions among species, one involving interactions within species. Describe these explanations
and what you could do to distinguish between them.
9. There are many ways that animals can potentially reduce the risk of predation (as demonstrated in
lecture). List four of these possible mechanisms. For one of these mechanisms, outline an
experiment you could conduct to test whether the mechanism is actually operating in a species, and
clearly identify the result of your experiment that would support the hypothesized mechanism.
10. Toxic snakes like coral snakes are provide good examples of (i) aposomatic coloration, (ii)
Batesian mimicy and (iii) Mullerian mimicry. What do each of these terms refer to? Illustrate these
terms using coral snakes and their mimics. Describe an experiment you could conduct to determine
if coral snake aposomatic warning colors actually deter predation. Describe an experiment you could
conduct to determine how a bird predator could know to avoid coral snake warning colors (i.e., is
the knowledge of the warning colors innate or it learned)?