Population ecology of landlocked Arctic charr, Salvelinus alpinus L., in the Canadian High Arctic.
The thesis describes fieldwork conducted during the Joint Services Expeditions to
Ellesmere Island 1988, 1991 and subsequent modelling activities. Four landlocked
populations of Arctic charr, Salvelinus alpinus L., were surveyed at 81 oN, close to the
northerly extreme of the species range. They were single-species populations consisting
of two distinct size modes, "Dwarf" and "Normal" charr, but with major differences
both in size and relative numbers between the lakes. Tentative correlations between
population structure, growth rate variation and possible genetic divergence are suggested
by this fieldwork and the models examine their credibility. The key hypothesis is that
the alternative life history strategies represented by Dwarf and Normal charr represent
different solutions to the problem of energy limitation within a size-structured
population. Major findings of the models are that alternative life history strategies
should be expected to be optimised at different growth rates; density dependence implies
that Dwarfs and Normals have equal fitness; a high average juvenile growth rate is likely
to lead to a large number of Normals relative to Dwarfs; and that maximum individual
fitness is probably achieved in bimodal populations within a "semi-speciated" condition.
A combination of evidence further suggests that cannibalism is a likely mechanism for
maintenance of the bimodal population structures; and the form of a reaction norm for
choice of life history strategy is predicted and found to be similar to one experimentally
determined for smolting in Atlantic salmon, Safmo safar L ..