Geoscience Reference
In-Depth Information
same number of times, the proportion of locations in the area of overlap will
differ slightly between the two. This approach cannot be used to test whether
two specific individuals attract or avoid each other but can be used to test
whether classes of animals exhibit attraction or avoidance.
Minta (1992) developed further tests for attraction or avoidance to an area
of overlap that allow researchers to test for more specific use of areas of overlap
and that accommodate more diverse data than needed for the approaches used
by Doncaster (1990) and my coworkers and I (Horner and Powell 1990; Pow-
ell et al. 1997). Minta showed how to test whether one animal of a pair is
attracted but the other not, how to test for attraction when animals are not
always located simultaneously, and how to test for attraction when home
ranges are not known but the area of overlap is.
TESTING FOR TERRITORIALITY
For many animals, territory defense is difficult or impossible to document but
patterns of home range overlap can be documented. Such patterns of overlap
can often be used to deduce territorial behavior. Table 3.1 gives overlap index
results for territorial wolves in northeastern Minnesota (Mech, personal com-
munication, unpublished data), for adult female black bears in North Carolina
and in Minnesota that appear to differ in territorial behavior (Powell et al.
1997, Rogers 1977), and for intrasexually territorial stone martens (
Martes
foina
) in Italy (Genovesi and Boitani 1997; Genovesi et al. 1997; Genovesi
personal communication, unpublished data).
Home ranges of wolves in different packs, and pack home ranges (from
combined home ranges of pack members), overlapped little compared to
home ranges of wolves in the same pack (
p
< 0.0001, for each index general
linear model [
GLM
] test). Wolves in the same pack have home ranges that over-
lap extensively and Spearman's
r
is positive, showing significant correlation of
the home ranges of wolves in the same pack and attraction among wolves of
the same pack. Spearman's
r
is negative for wolves of different packs and for
pack home ranges, indicating avoidance by wolves of different packs. Such
quantified patterns of home range overlap and lack of overlap agree with the
extensive field observations that wolves defend territories (Mech 1970; Peters
and Mech 1975; Peterson 1977, 1995).
Overlap of home ranges for bears in the North Carolina site was signifi-
cantly greater than was overlap for bears at the Minnesota site (
p
< 0.01,
GLM
,
for each index, table 3.1; Powell et al. 1997). Productivity of food was signifi-
cantly higher for the North Carolina population (Powell et al. 1997) and anec-
dotal evidence indicates that the lack of home range overlap for the bears in
