Geoscience Reference
In-Depth Information
exists for a single, precise definition of
home range
and this lack of consensus
leads to some of the confusion regarding home ranges. Many researchers may
be unaware of the confusion. The major confusion appears to be between
those who use a conceptual definition and those who use an operational defi-
nition. Burt's definition is conceptual and has two components: familiarity
and use. Operational definitions and home range estimators quantify use and
may add some estimate of familiarity. The minimum convex polygon estima-
tor assumes that animals are familiar with all areas within the extremes of their
movements but not familiar with any area outside those extremes, no matter
how close. Kernel estimators assume that animals are familiar with, and have
interest in, areas surrounding their movements in a fashion that decreases as
does the shape of the kernels. The only quantification of a home range that
excludes some guess about familiarity would include only areas over which an
animal actually traveled (but what about flight by birds?).
Should areas to which an animal seldom travels but with which the animal
is familiar be included in its home range? This question addresses the difference
between an animal's home range and its cognitive map. An animal's cognitive
map includes all areas for which the animal has information, whereas I consider
its home range to include only the areas with which it maintains familiarity.
Familiarity may be maintained through the senses, without actual visits. In
addition, familiarity is undoubtedly both graded and of a multiscale nature,
making familiarity extremely difficult to quantify. How unused areas are quan-
tified must be considered by researchers. To some extent, how unused areas are
quantified depends on research questions. However, researchers must under-
stand how home range estimators estimate familiarity and must use estimators
that are consistent with their own concepts of home range and with their
research questions. No agreement exists as to how best to quantify familiarity.
What currencies are best for quantifying home ranges and territories?
Home ranges should not always be quantified with respect to the time that an
animal spends, or is predicted to spend, in different places. Most researchers
use time to index importance, but what really counts is fitness. For some ques-
tions, home ranges may need to be quantified by probability density functions
of energy expenditure or energy acquisition. Ultimately, for much research,
home ranges should be quantified as probability density functions for contri-
butions to fitness. How does a person map a home range's contributions to
fitness?
My coworkers and I (Powell et al. 1997) documented a strong correlation
between home range size and the size of the periphery for black bears, suggest-
ing that peripheral parts of home ranges should receive more research atten-
