Deer, predators, and the emergence of Lyme disease

Paper evaluation #3
Title: Deer, predators, and the emergence of Lyme disease
Authors: Taal Levi, Marm Kilpatrick, Marc Mangel, and Christopher C. Wilmers
Journal: Proceedings of the National Academy of Sciences
Year, volume, pages: 2012, 109, 10942–10947

Objectives of assignment

Throughout the semester we will be reading, summarizing, and discussing peer-reviewed
journal articles. We will use these articles to reinforce important concepts in insect ecology
while exploring how ecological research is performed and communicated. Specifically, this
exercise is designed to increase your familiarity with the primary scientific literature,
improve your reading comprehension, and hone your critical thinking skills.

Description of the assignment

You will complete a written evaluation of the assigned article listed above. Your evaluation
should be singled-spaced, 12 point font (Arial or Times New Roman) with 1 inch margins
on all sides. I do not want a cover page. Simply write your name, date, and “Insect Ecology:
Paper Discussion #3” at the very top of the page, skip a line, and then start writing!
Don’t worry about the statistical analysis portion of the paper. If you have had a class in
statistics and comprehend this part, that’s great.

However, for those who have not, this
should not affect your interpretation. All you truly need to know is that when treatments
are significantly different (p-value less than 0.05) the effect is considered “real” and when
the treatments are not significantly different (p-value greater than 0.05) the effect does not

In figures, authors frequently use letters to denote statistical differences, i.e., if two
bars share the letter ‘a’ then they are not significantly different from one another, whereas
if they do not share a letter (‘a’ on bar 1 vs. ‘b’ on bar 2) they are significantly different.
This goes without saying, but the writing should be entirely your own thoughts. Do not
copy or work with others from the class or from the paper itself! For internet searches (i.e.,
question #1), cite your web source.

There is no specified length that is necessary to answer the questions below;
however, most questions require more lengthy answers, each of which should be
equivalent to a medium sized paragraph (200-300 words).
The assignment is worth 50 points (5 pts for each of 10 questions), which will be
allocated based on your responses to the following specific questions/tasks…

1) List and define all biological terms that you are unfamiliar with in the paper.

Include as many terms as necessary, but you should have at least 5 defined and please do
not include statistical terms. Definitions can be obtained by searching via the internet or
your class texts. For undergraduates who are reading papers for the first time, this is often
the rate-limiting step that slows students down and affects scientific comprehension.

2) This study focuses on the tick
Ixodes scapularis, but due to the relatively brief nature of
the paper the authors do not provide much background information on the ecology of this
species. Please do some background research on this tick and summarize the most
interesting and/or pertinent information you can find on this species, similar to our Bug of
the Day style presentations.

3) The research presented in this paper assumes an underlying knowledge of the
epidemiology of Lyme disease. Draw a diagram that illustrates the complete life cycle of
Ixodes scapularis, including all developmental stages, and note when and where susceptible
ticks become infected with
Borrelia burgdorferi. Which stage is most dangerous for
transmission to humans?

4) The contribution of deer to Lyme disease infection risk is complicated, as noted in the
varying outcomes of this relationship, which range from positive, to negative, to neutral
(see Figs. 3A, 4C-F, 5). Why is the effect of deer so variable? How is the contribution of deer
fundamentally different from the contribution of small mammals? Outline the key pieces of
evidence. Use Fig. 2B to answer the above questions, explaining the importance of the
positive but non-linear (i.e., curved) relationship.

5) What is mesopredator release? When coyote replace fox, wouldn’t small mammal
density simply remain the same (i.e., we replace one rodent predator for another rodent
predator)? Describe at least 3 lines of evidence for why this may or may not be the case.
Can you find any evidence online for a numerical breakdown of the coyote diet (cite your
source here!)? Does this new evidence support or refute the paper’s predictions regarding
shifts in food webs that correspond with coyote invasion?

6) What is an acorn mast and how/why might this affect Lyme disease risk? What
mathematical term does this correspond with the model in Fig. 1A?

7) Figures 1B and 1C show infected nymphs and NIP, respectively, on their y-axis, which
does not affect the general shape of the curves, but does impact the difference between
solid and dashed lines. Why? Why show both of these response variables? Which is more
relevant for Lyme disease transmission to humans?

8) The authors take advantage of three sources of publically available data for their
analyses: hunting records, landowner wildlife surveys, and reported Lyme disease

incidence. For each source, describe (not list, describe) at least two factors that affect the
reliability of these data. Why did the authors focus on Wisconsin, Minnesota, Pennsylvania,
and Virginia as their four focal states? (Note: I highly recommend giving the Methods a
close read before answering these questions).

9) A major strength of the authors’ data are that they span space and time; and both
dimensions generally converge on the same answer. Construct a pro/con table that
describes (not list, describe) at least two pros and two cons for using spatial vs. temporal
data to tease apart these relationships.

10) The study makes an interesting case for the combined role of deer, coyote, fox, small
mammals, and ticks in Lyme disease epidemiology. Pretend that you are a land manager in
one of the affected states. How would use the data shown in this paper to reduce Lyme
disease risk to humans in your area? Develop a management plan. Which of those five
groups of organisms would you focus your management efforts on and why?

Last Updated on February 16, 2018 by Essay Pro