Geoscience Reference
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both demographic and behavioral, each with potentially different habitat-spe-
cific responses. Controlled experiments should be used more often in assessing
effects of habitat on demographic parameters such as density (Darveau et al.
1995) or reproduction (Vander Haegen and DeGraaf 1996; Siikamäki 1995;
Holt and Martin 1997); however, even elegant experiments may produce
unexpected results in complex natural systems (Wiens et al. 1986).
Where experimentation is unfeasible, comparisons of reproduction and
survival can be made among individuals or groups of individuals with differ-
ent patterns of habitat use. Partridge (1978) warned that such comparisons
may be confounded by competition among individuals: Those living in pre-
ferred habitats may be dominant individuals that are naturally fitter. That is,
they live where they do because they are fitter; they are not fitter because of
where they live. This is an important consideration, but it is not applicable to
all situations; it depends on the social structure and population size relative to
carrying capacity (MacCracken et al. 1997). One way to circumvent the prob-
lem is to compare population parameters across multiple study sites with dif-
fering habitat compositions. Often, though, it may be appropriate to assume
that individual physical differences are not the cause of differences in habitat
use, or even if they are, that the most fit individuals are choosing the best habi-
tats, thereby justifying comparisons within a single study site.
For studies in a single study site, an effective design would be to monitor
habitat use of various individuals (e.g., using radiotelemetry), and then com-
pare their frequency of use of different habitats or the habitat composition of
their home ranges to their eventual reproduction and survival. Many studies of
birds have used this sort of approach to examine relationships between habitat
characteristics of nesting sites and nesting success. However, few attempts have
been made to relate reproduction or survival to variation in habitat use within
home ranges. In one example, Aanes and Andersen (1996) observed a rela-
tionship between survival of roe deer (
Capreolus capreolus
) fawns and the habi-
tat types that they used. Similarly, Aebischer et al. (1993a) found that habitat
use by individual pheasants was related to their survival. In another example,
Fuller (1989) observed that wolf (
Canis lupus
) territories were limited to areas
with low road density (a habitat component that relates to human access) and
then looked for (but did not find) a relationship between survival of radio-
collared wolves and road density within individual territories. In another
study of the same species, Massolo and Meriggi (1998) found relationships
between reproduction (documented presence of pups) and various natural and
anthropic habitat features, including road density. In studies in which data on
