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whereas another habitat that received 45 percent of use was seemingly
“selected against.” In one case banteng were judged to be unselective in their
use of a habitat in which they spent 75 percent of their time. Prayurasiddhi
(1997) recognized these difficulties and decided to evaluate seasonal changes
in habitat selection and habitat-related differences among species based on use
alone, rather than use compared to availability.
In another analogous situation, Macdonald and Courtenay (1996) found
that crab-eating zorros (foxes, Cerdocyon thous ) in Amazonian Brazil spent
most of their time (64 percent) in wooded savanna and scrub habitats; how-
ever, because these two habitats were abundant within the home ranges of
the study animals, they ranked the lowest in apparent preference (sixth and
seventh among seven defined types) based on a comparison of use to availabil-
ity. During the wet season, however, when lowland habitats flooded, the zor-
ros used upland wooded savannas and scrub habitats even more, making the
apparent preference ranking for these rise; in reality, the area of available (not
flooded) lowland habitats diminished, but this reduction could not be mea-
sured and therefore was not taken into account in the use:availability calcula-
tions. The authors realized that the seasonal difference in apparent habitat
preferences was thus an artifact of unmeasured changes in availability.
In another such case, Garrett et al. (1993) found that tidal flats were the
principal foraging habitat for bald eagles ( Haliaeetus leucocephalus ) and ob-
served that nearly one-fourth of their perch sites were within this habitat. That
is, based on use alone, this area was clearly attractive to these birds. However,
because this habitat was so widely available, especially at low tide, a compari-
son of use to availability suggested that the eagles avoided it. Apparent prefer-
ence thus changed radically with tidal fluctuations.
Figure 4.3 (opposite page) The assumed linear relationship between use and availability of
resources arises from a model in which the resources are scattered around in small bits (top panel),
the locations of which are not known to the animal. In the case depicted, the dark-colored resource
(A) is only half as available as the light-colored resource (B), so an animal that randomly encoun-
tered these would be expected to obtain (in the case of food) or use (in the case of habitat) resource
A half as much as resource B. If resource A was used more than that, the animal must have
bypassed B, thus demonstrating selection for A. In the lower panel, the two resources are still in the
same proportions, but are clumped, thus representing a more realistic situation for habitats. An ani-
mal here would not wander around encountering and rejecting or accepting resources in its path,
but would probably know the locations of habitat patches. Thus the time spent in each patch would
be commensurate with the type of activity and attributes of that habitat, which may or may not
include the area of the patch. If, in the case of the lower panel, an animal used (selected) the two
habitats equally, it would be fallacious to assume that it was selecting habitat A over B simply
because A was less available than B.
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