1983] 
Shelly — Alpaicia tuonaho 
131 
Table 3. Web selectivity ( values for size classes of nematocerous Diptera and 
ants collected from webs of A. tuonaho. 
a. Nematocerous Diptera 
Size (mm) 
Collected from webs 
(eaten and uneaten) 
no. rj 
Captured on traps 
no. Pi 
Ew 
O-I 
1 18 
71.9 
138 
40.7 
+0.28 
1-2 
40 
24.4 
163 
48.1 
-0.33 
2-3 
4 
2.4 
31 
9.1 
-0.58 
>3 
2 
1.2 
7 
2.1 
-0.27 
b. Ants 
Collected from webs 
Captured on traps 
Size (mm) 
(eaten and uneaten) 
no. 
n 
no. 
Pi 
Ew 
0-1 
0 
0.0 
0 
0.0 
1-2 
17 
13.3 
43 
36.7 
-0.47 
2-3 
II 
8.6 
46 
39.3 
-0.64 
3-4 
21 
16.4 
7 
6.0 
+0.46 
4-5 
16 
12.5 
3 
2.6 
+0.65 
5-6 
10 
7.8 
3 
2.6 
+0.50 
6-7 
24 
18.7 
7 
6.0 
+0.51 
7-8 
13 
10.2 
2 
1.7 
+0.71 
>8 
16 
12.5 
6 
5.1 
+0.42 
caught in the web but ignored. Spider selectivity for larger prey has 
also recently been demonstrated for Micrathena gracilis (Uetz and 
Biere 1980). 
Second, A. tuonabo did not construct their webs at heights where 
total prey abundance was greatest. Since the taxonomic and size 
composition of the flying insect fauna varied only slightly with 
height, A. tuonabo was apparently not responding to the vertical 
distribution of a particular type or size of prey. Several factors 
potentially affect web height in A. tuonabo. First, although females 
use various support structures, the number of suitable “web spaces” 
may be limited (Lubin pers. comm.). Also, other species of similar 
size (e.g. Pronous tuberculifer, Edricus crassicaudus, and Leucauge 
sp.) construct webs closer to the ground (Lubin 1978; Shelly pers. 
obs.). Thus, the higher webs of A. tuonabo may reflect a behavioral 
means to lessen interspecific competition for food. In addition. 
