1983] 
Shelly — Alpaicia tuutiaho 
125 
Diptera 
nematocerous 
non-nematocerous 
Hymenoptera 
ants 
parasitoids 
Coleoptera 
Frequency 
Figure I. Vertical distributions of the major prey categories. Each value repres- 
ents the total number of individuals captured on 10 sticky traps suspended at a 
particular height. See text for details of sampling method. 
uneaten. Uneaten prey were also examined for evidence of wrap- 
ping. For each web thus sampled, the height of the spider was also 
recorded. Collected prey were later assigned to the appropriate prey 
category and measured to the nearest 0.1 mm. 
Prey selectivity was quantified using Ivlev’s (1961) index of elec- 
tivity. Electivity (E) is calculated as follows: E = (ri — pi)/(ri + pi) 
where rj is the proportion of the predator’s diet represented by prey 
type (or size class) i, and pi is the proportion of the available prey 
represented by prey type (or size class) i. Values of E range from 
— 1.0 (complete avoidance) to +1.0 (complete preference). In this 
study electivity values with absolute values less than 0.40 were not 
considered to differ significantly from zero. In addition, two sets of 
electivity values were calculated. For web selectivity (Ew) ri is the 
proportion of the web contents (both eaten and uneaten items) 
represented by prey type i, and pi is the proportion of available prey 
(as measured by the sticky traps) represented by prey type i. For 
spider selectivity (Eg) ri is the proportion of the spider’s observed 
diet (the eaten prey) represented by prey type i, and pi is the propor- 
tion of the web contents (both eaten and uneaten items) represented 
by prey type i. 
Results 
Alpaicia tuonabo females generally constructed webs in relatively 
open sections of the forest or at the edges of tree-fall gaps. Most web 
