Geoscience Reference
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for analysis and the available habitat is considered to be the same for all, yet
some individuals may not even have all habitat types within their home range.
Johnson (1980) suggested that the habitat composition of home ranges
compared with the habitat composition of some broader area should indicate
the level of selection animals exercise when establishing their home range.
Often the broader available area is considered to be that encompassed by the
composite of the home ranges of all study animals. However, there are several
problems with this.
First, animals cannot really select their ideal mix of habitats to compose
their home range. Animals can only choose home range borders that encom-
pass the best mix of habitats from what exists on the landscape; they cannot
alter the mix to suit their needs. By analogy, a person may pick a town to live
in, among several available, based on the resources available. One may also
choose where to live within the town, but one cannot alter the layout of the
town or the array of features available.
Second, animals may not have free and equal access to all areas when estab-
lishing their home range. Home ranges may be established near the natal area
just because of familiarity with resources or neighboring animals, not any
choice related to habitat composition. Analogously, people might remain in
their home state or country not because they consciously chose it among all
others, but because they never had the opportunity to visit other places, or
because moving elsewhere, even if it seemed desirable in some respects, had
too many costs. Social constraints also may dictate choice of a home range by
precluding access to certain areas. Extending the analogy with people, consider
a house to be like a home range and a neighborhood a composite home range.
The first few residents of a neighborhood might have selected where to live
among houses that differed in various ways; however, as more people moved
in, the choices narrowed, until no choice remained for the last resident. If all
houses were used, regardless of their quality, one could not discern after the
fact which houses were preferred unless the “colonization” process was
observed. Fretwell and Lucas (1970) proposed a corresponding model for ani-
mal populations. In an expanding population, preferred habitats are settled
first, but as these are taken, animals are forced to settle in poorer and poorer
areas. However, unless they are strictly territorial, their ranges can overlap, so
unlike the human example, they can choose to live in a preferred area even
though another animal is already there. As animal density increases in the most
preferred habitat, however, resources become less available to each individual,
so the quality of the habitat from each resident's perspective diminishes. Thus
unless individuals benefit from the presence of others (Smith and Peacock
