Geoscience Reference
In-Depth Information
Chapter 11
Modeling Species Distribution with GIS
FABIO CORSI, JAN DE LEEUW, AND ANDREW SKIDMORE
From the variety of checklists, atlases, and field guides available around the
world it is easy to understand that distribution ranges are pieces of information
that are seldom absent in a comprehensive description of species. Their uses
range from a better understanding of the species biology, to simple inventory
assessment of a geographic region, to the definition of specific management
actions. In the latter case, knowledge of the area in which a species occurs is
fundamental for the implementation of adequate conservation strategies.
Conservation is concerned mostly with fragmentation or reduction of the dis-
tribution as an indication of population viability (Maurer 1994), given that,
for any species, range dimension is considered to be correlated to population
size (Gaston 1994; Mace 1994).
Unfortunately, animals move and this poses problems in mapping their
occurrence. Traditional methods used to store information on species distri-
butions are generally poor (Stoms and Estes 1993). Distributions have been
described by drawing polygons on a map (the “blotch”) to represent, with
varying approximations, a species' ranges (Gaston 1991; Miller 1994). The
accuracy of the polygons relies on the empirical knowledge of specialists and
encloses the area in which the species is considered likely to occur, although
the probability level associated with this “likelihood” is seldom specified. A
more sophisticated approach divides the study area into subunits (e.g., admin-
istrative units, equal-size mesh grid), with each subunit associated with infor-
mation on the presence or absence of the species. In this case the distribution
range of a species is defined by the total of all subunits in which presence is
confirmed; however, blank areas are ambiguous as to whether the species is
absent or no records were available (Scott et al. 1993).
