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(i.e., selection for habitats not preferred by the residents). Indeed, one could
reasonably assert that this represents true habitat selection as defined earlier, in
that the disperser chose to avoid habitats with dominant conspecifics and
thereby improved its chance of obtaining resources and not getting killed;
however, one could also legitimately contend that the disperser was simply
exhibiting avoidance of conspecifics, and used whatever cues, including mark-
ings, droppings, and possibly habitat characteristics, to do so.
These are not trivial complications, but rather examples of the intrinsic
ambiguities associated with the application of these concepts. Terms such as
selection
and
preference
can be clearly defined, but not easily measured in the
real world. Moreover, as I will show later, the link between selection, prefer-
ence, and habitat-related fitness may be tenuous.
Methods for Evaluating Habitat Selection, Preference, and Quality
j
Three general study designs have been used to infer habitat quality. The first,
generally called the use-availability design, compares the proportion of time
that an animal spends in each available habitat type (generally judged by the
number of locations, or less commonly, by the distance traveled; e.g., Salas
1996) to the relative area of each type. The second, which I call the site attrib-
ute design, compares habitat characteristics of sites used by an animal to
unused or random sites. These two designs generate measures of selection for
various habitats or habitat attributes, and habitat quality or importance is
inferred from the magnitude of this apparent selection. The third method,
which I call the demographic response design, uses a more direct approach for
assessing habitat quality by comparing the demographics (density, reproduc-
tion, or survival) of animals living in different habitats. This design thus cir-
cumvents the need to interpret animal behavior (habitat choices).
USE-AVAILABILITY DESIGN
Among studies of birds and mammals, the use-availability design is the most
popular. I reviewed habitat-related papers dealing with birds and mammals
published in the
Journal of Wildlife Management
during 1985-1995 and
found that most (90 of 156, or 58 percent) relied on a use-availability study
design to assess habitat selection, preference, or quality. Thomas and Taylor
(1990) further categorized use-availability studies into three approaches: one
in which habitat-use data are collected on animals that are not individually rec-
ognizable (e.g., visual sightings or sign), one in which data are collected on
