FIELD OBSERVATIONS ON THE POPULATION-STRUCTURE OF 3 CTENID SPIDERS (CUPIENNIUS, ARANEAE, CTENIDAE)

The population structure of three large species of the genus Cupienniu s was evaluated. Although solitary, 45% of C. coccineus, 40% of C. sal ei and 30% of C. getazi spiders were found on plants together with one or more conspecifics. The adult sex ratio (males : females) was 1:1.2 for C. salei (1989, n = 52), 1:1.3 for C. coccineus (1990, n = 75) an d 1:1.6 for C. getazi (1990, n = 29). The ratio of adults : immatures was 1:0.5 for C. salei, 1:1.8 for C. coccineus and 1:13 for C. getazi. The two sympatric species, C. coccineus and C. getazi, sometimes occu r on the same plants and are therefore considered syntopic. In all thr ee species spider density is correlated with the number of the retreat s offered by their dwelling plants. We found up to 0.2 adults/plant fo r C. salei and 0.3 adults per plant for C. coccineus and C. getazi. Cu piennius spiders, particularly the males, change their dwelling plants quite often. On average, C. salei males could only be found for 0.5 d ay on the same plant without interruption (five days observation time) , C. coccineus males for one day (21 days observation time) whereas fe males with eggsacs of these two species stay significantly longer (3.5 days and 8 day, respectively; 21 days observation time). Considering the rather high population density and the frequent changes of the dwe lling plants (the males in particular), interactions between spiders s eem very likely. In the lab, male competition in addition to courtship between the sexes is elicited by male vibratory courtship signals. Ov ert fights between males were observed in the field.