Title:
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The evolutionary ecology of small mammals.
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The thesis aims to relate variation in life history and population variables to ecological factors. Data on
small mammal were extracted from published reports and
this information supplemented by measurements on specimens
at the British museum (Natural History).
Species are classified into ecological types accord-
-1ng 'to habitat, diet, zonation, activity rhythm and nest
site Latitude and breeding and growing season lengths of
the habitat are also recorded.
To avoid statistical difficulties, techniques removed
the effects of both size and taxon. From comparisons of
genera in different ecological classes, variation in life
histories is closely related to diet: folivores, which
have an abundant, low quality but highly predictable food,
have shorter lifespans, are weaned earlier and reach
maturity earlier than granivores and insectivores. When
brain size is compared across the same ecological groups,
fol1vores have relatively small brains. This may result
from their less complex feeding niches.
Developmental stages, such as the ages at ear and eye
opening, vary only with nest site. Precocious young are
associated with open terrestrial nests and altricial young
with burrows. Increased predator pressure may select for
faster development in exposed sites.
Both home range size and population density are
influenced by diet. Granivores and insectivores have
relatively larger home ranges and 10Vier population densities.
Fluctuations in density are greater for folivores and for
populations living at high latitudes.
Variation in body size is associated with diet,
vegetation and sometimes climate. The calorific content
of the food is negatively correlated with body size both
within and across taxa. A set of hypotneses to explain
variation in tae degree of sexual dimorphism in body size
are reviewed. Some of these are tested and the results
discussed in terms of the different selective pressures
operating on different groups.
Finally, two pervasive aspects of the analysis are
discussed. The explanations for widespread differences
between t:'xonomic groups are reviewed. The interrelation-
-ships of diet, brain size, life histories and density
fluctuations are discussed in the light of various
explanations for their association.
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