The midterm will include three of the following
questions. The instructions will be:
Answer two out of three. Each answer is limited to a single
page. Take a few minutes before you start writing to organize
your answer. Use examples and/or diagrams to illustrate your answers
where appropriate. Please underline the two most important sentences in
each essay.
- Very simple epidemic models predict that a parasite can never drive
its host population extinct, yet we do see examples in nature of
parasite-driven host extinction (or near-extinction). List some
important processes that are missing from the simple models, and explain
how they might allow parasite-mediated extinction. If you can, give an
example of a host-parasite system where each applies.
- Explain the concept of levels of selection in
evolution. Use at least two examples from host-parasite systems to
illustrate how it works.
- Describe box models for disease. What do boxes, solid lines, and
dashed lines usually represent? Construct a box model for an epidemic of
gonorrhea in a heterosexual population where you keep track of males and
females separately (assume that gonorrhea can be treated with
antibiotics, but treated [recovered] people do not develop immunity).
Write down a set of equations that corresponds to these boxes.
- Define the difference between microparasites and macroparasites,
both in terms of how they have classically been used, in terms of their
population dynamics and transmission, and how these two definitions are
related. Give some examples. What are the differences between them in
terms of ecology and evolution, and how they are modeled?
- Describe how we can use phylogenetic comparative methods to
establish the evolutionary history of an organismal trait (such as a
parasitic lifestyle). What data do we need? Make up an example showing
how we would infer that a gut parasite evolved from a free-living
ancestor by way of a commensal stage.
- Describe and explain as many methods as you can remember (at least
three) for estimating R0 from different types of data on epidemics;
explain which approaches would be most important for different types of
diseases (human vs wildlife, epidemic vs endemic, etc.)
- Discuss the roles of theoretical (model-based), lab experiments,
field experiments, and observational data in understanding ecological
and evolutionary systems. What are the costs/benefits or
advantages/disadvantages of each kind of information? Give at least one
example of each level of information and how it applies to our knowledge
of a particular host-parasite system; for at least one system, contrast
the contribution of two different levels.
- Discuss the difference between establishing how parasites tip the
balance between competitors in natural systems (e.g. moose-deer-P.
tenuis) and laboratory systems (e.g. flour beetles
(Tribolium)-sporozoan parasite). Describe and compare the
methods can we use to understand what’s going on in each case, and the
kind of insights we gain (or can’t gain) in each case.
Last updated 28 Sep 2025