Geoscience Reference
In-Depth Information
Terminology
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The word
habitat
has two distinct usages. The true dictionary definition is the
type of place where an animal normally lives or, more specifically, the collec-
tion of resources and conditions necessary for its occupancy. Following this
definition, habitat is organism specific (e.g., deer habitat, grouse habitat). A
second definition is a set of specific environmental features that, for terrestrial
animals, is often equated to a plant community, vegetative association, or
cover type (e.g., deer use different habitats or habitat types in summer and
winter).
Nonhabitat
could mean either the converse of
habitat
in the first sense
(a setting that an animal does not normally occupy) or the second (a specific
vegetative type that the animal views as unsuitable); here, the two meanings of
habitat
converge (see also pages 392-396 in this volume).
Hall et al. (1997) argue that only the first definition of
habitat
is correct
and that the second represents a confusing misuse of the term. They reviewed
50 articles dealing with wildlife-habitat relationships and, based on their def-
inition, found that 82% discussed habitat vaguely or incorrectly. I suggest that
given the prevalent use of
habitat
to mean habitat type, this alternative defini-
tion is legitimate and well understood in the wildlife literature. Moreover, this
common usage of the term is consistent with the normally accepted meaning
of
habitat use:
the extent to which different vegetative associations are used.
Hall et al. (1997:175) define
habitat use
as “the
way
an animal uses . . . a col-
lection of physical and biological components (i.e., resources)
in
a habitat”
(emphasis mine), which seems difficult to measure.
Habitat selection and preference are also more easily understood in terms
of differential use of habitat types.
Selection
and
preference
are often used inter-
changeably in the wildlife literature; however, they have subtly different mean-
ings. I will adopt the distinction posed by Johnson (1980), who defined
selec-
tion
as the process of choosing resources and
preference
as the likelihood of a
resource being chosen if offered on an equal basis with others. Peek (1986)
suggested that innate preferences exist even for resources not actually available.
Furthering this concept, Rosenzweig and Abramsky (1986) characterized pre-
ferred habitats as those that confer high fitness and would therefore support a
high equilibrium density (in the absence of other confounding factors, such as
competitors). Thus use results from selection, selection results from prefer-
ence, and preference presumably results from resource-specific differential fit-
ness. In controlled experiments, preferences can be assessed directly by offer-
ing equal portions of different resources and observing choices that are made
