Geoscience Reference
In-Depth Information
calls has defined territoriality clearly in many birds (e.g., nectarivorous birds,
reviewed by Hixon 1980; Hixon et al. 1983; blackbirds, reviewed by Orians
1980). For many species, however, apparent lack of overlap of home ranges is
the only evidence of territorial behavior. For many carnivorous mammals, ter-
ritory defense and responses to scent marks are difficult to document. For such
species, home range overlap can be quantified in an objective manner that
weighs probability of use of different parts of a home range or territory. Home
range overlap can then be compared statistically among populations or species
that appear to differ in territorial behavior but for whom territorial behavior
has not been manipulated experimentally.
Doncaster (1990) defined two types of overlap, called static and dynamic
interactions. Static interaction is the spatial overlap of two home ranges and
dynamic interaction involves interdependent movements of the two animals
whose home ranges overlap. These types of overlap can be quantified in several
different ways.
STATIC INTERACTIONS
Area of overlap is a poor estimate of the effect or importance of the overlap on
two individuals whose home ranges overlap. Areas of overlap vary in probabil-
ity of use and the two individuals may have a large overlap of areas used little
by each or a small overlap of areas used intensively by each. Although Genovesi
and Boitani (1997) found that area overlap of minimum convex polygons cor-
related strongly with weighted overlap, this need not be the case for all popu-
lations or individuals.
I have used two indices of pairwise overlap of home ranges using 95 per-
cent probability density functions for each animal's home range. Such proba-
bility density functions could be generated by a fixed kernel home range esti-
mator or by any other estimator that produces accurate utility distributions.
The first,
I
p
, is
k
e
0
P
ki
ยท
k
e
0
P
kj
I
p
=
k
e
k
e
0
0
where
p
ki
and
p
kj
are the independent probabilities that at any arbitrary time
animals
i
and
j
are in cell
k
of a study area that has a grid superimposed on it
and that cell
k
is within the area of overlap,
O
, of the animals' home ranges.
I
p
ranges from 0 to 1. This index is the simple probability that the two animals
i
