Geoscience Reference
In-Depth Information
Figure 10.5
Considerations in scoring indices of association are illustrated by the comings and
going of farm cats at a resource center. Observations may be biased by the observer's success in
seeing them or by genuine differences in individuals' attendance records, but the time for which the
two cats are simultaneously present defines the opportunity for interacting in the calculation of the
example association index.
with A is not necessarily so, and vice versa. For example, if cat A is at the
resource center 40 times out of 40 scan censuses and cat B is there 10 times out
of the same 40 scan censuses, and they actually sit together during 8 scans,
then according to the simple association index, their association index is [8/(8
+ 30 + 0 + 2)] = 8/40 = 0.2. However, looking at this another way, it is also true
that while at the resource center cat A sits with cat B only 20 percent of its
time, whereas cat B spends 80 percent of its time sitting with cat A. This asym-
metry is accommodated if we calculate an association index for each cat rather
than for each pair of cats. Thus cat A's association with cat B is [
x
/(
x
+
ya
+
yab
)] = 0.2, whereas cat B's association with cat A is [
x
/(
x
+
yb
+
yab
)] = 0.8.
Kerby and Macdonald (1988) and Macdonald et al. (in press) took scan
samples of presence and proximity of cats at 30-min intervals at three colonies
(small, medium, and large memberships), and made ad libitum records of the
social interactions of focal cats. Data were summarized for each cat each month,
and statistical analyses used these individual summary scores to avoid problems
associated with pooling data (Machlis et al. 1985; Leger and Didrichsons
1994). Some generalizations spanned all colonies: the sexes did not differ sig-
