Geoscience Reference
In-Depth Information
Chapter 4
Delusions in Habitat Evaluation: Measuring Use,
Selection, and Importance
DAVID L. GARSHELIS
Management of wildlife populations, whether to support a harvest, conserve
threatened species, or promote biodiversity, generally entails habitat manage-
ment. Habitat management presupposes some understanding of species'
needs. To assess a species' needs, researchers commonly study habitat use and,
based on the results, infer selection and preference. Presumably, species should
reproduce or survive better (i.e., their fitness should be higher) in habitats that
they tend to prefer. Thus, once habitats can be ordered by their relative prefer-
ence, they can be evaluated as to their relative importance in terms of fitness.
Managers can then manipulate landscapes to contain more high-quality habi-
tats and thus produce more of the targeted species. Habitat manipulations
specifically intended to produce more animals have been conducted since at
least the days of Kublai Khan (
A
.
D
. 1259--1294; Leopold 1933).
However, the processes of habitat evaluation are fraught with problems.
Some problems are specific to the methods used in the data collection or analy-
ses. Many of these problems have already been recognized, and discussions
about them in the literature have prompted a host of evolving techniques.
Other problems are inherent in the two most basic assumptions of this
approach: that researchers can discern habitat selection or preference from
observations of habitat use and that such selection, perceived or real, relates to
fitness and hence to population growth rate.
My goal is to illuminate the scope of the problems involved in habitat eval-
uation. Assessments of habitat selection and presumed importance are done so
often, and study methods have become so routine, that it is apparent that
researchers and managers tend to believe that the major problems have, for the
most part, been overcome. I contend that this view is overly sanguine and pro-
pose a reconsideration of the ways in which habitat evaluations are conducted.
