Geoscience Reference
In-Depth Information
defend territories after reproduction has ceased for the year. If bears, hum-
mingbirds, and other animals use food as an index for the potential to produce
offspring, then food can legitimately be considered to be at least a proximately
limiting resource. Fitness is the ultimate currency in biology, and fitness may
be affected by one or more limiting resources that need not be offspring or
other direct components of reproduction. Evolution via natural selection re-
quires heritable variation that affects reproductive output among individuals
in a population. The effects can be via offspring, or they can be via food, nest
sites, tunnel systems, or other potentially limiting resources.
Estimating Animals' Home Ranges
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Added to conceptual problems of understanding an animal's home range are
problems in estimating and quantifying that home range. We may never be
able to find completely objective statistical methods that use location data to
yield biologically significant information about animals' home ranges (Powell
1987). Nonetheless, our goal must be to develop methods that are as objective
and repeatable as possible while being biologically appropriate. When analyz-
ing data, we must use a home range estimator that is appropriate for the hy-
potheses being tested and appropriate for the data.
Reasons for estimating animals' home ranges are as diverse as research and
management questions. Knowing animals' home ranges provides significant
insight into mating patterns and reproduction, social organization and inter-
actions, foraging and food choices, limiting resources, important components
of habitat, and more. A home range estimator should delimit where an animal
can be found with some level of predictability, and it should quantify the ani-
mal's probability of being in different places or the importance of different
places to the animal.
Quantifying an animal's home range is an act of using data about the ani-
mal's use of space to deduce or to gain insight into the animal's cognitive map
of its home (Peters 1978). These data are usually in the form of observations,
trapping or telemetry locations, or tracks. Because at present we have no way
of learning directly how an animal perceives its cognitive map of its home, we
do not have a perfect method for quantifying home ranges. Even if we could
understand an animal's cognitive map, we would undoubtedly find it difficult
to quantify. Many methods for quantifying home ranges provide little more
than crude outlines of where an animal has been located. For some research
questions, no more information is needed. For questions that relate to under-
