Undergraduate Research: An Archive - 2021 Program

Ingrid Koester ’21
ECOLOGY AND EVOLUTIONARY BIOLOGY
Certificate in Environmental Studies
BIODIVERSITY AND
CONSERVATION
THESIS TITLE
But Do You Recall, Why
Reindeer Populations
Rise and Fall? A
Theoretical Model of
Reindeer (Rangifer
tarandus) and Warble
Flies (Hypoderma
tarandi)
ADVISER
Andrew Dobson,
Professor of Ecology
and Evolutionary
Biology
While multiple mechanisms may contribute
to the long-term population fluctuations of
reindeer (Rangifer tarandus), the parasitic warble
fly (Hypoderma tarandi) may be an overlooked
contributor. I investigated this possibility by first
constructing a basic theoretical model of this
host/parasite system using the work of Crofton
and May as a foundation, and then introducing
additional nuance through host age-structure,
parasite predators and climatic data. The model
constructions were subsequently fit to observed
field data of eight reindeer herds using both
single-input projections (fitting the model to the
entire time-series) and forecasting predictions
(fitting the model to half of the time-series).
The average normalized RMSD value (root
mean square deviation between observed and
expected population sizes) across all herds was
0.3797 for the single-input projections and was
0.7036. for the forecasting predictions. Changes
in latitude, herd status and herd ecotype show
statistically significant correlations with changes
in the normalized RMSD values. This study
demonstrated that warble flies may be critical
regulators of long-term reindeer population
cycles. The models produced stable oscillations
and have a predictive ability for some reindeer
herds, particularly for herds with migratory
tundra as its dominant ecotype. Future research
should confirm these results through empirical
parasite-removal experiments.
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