Effects of Web Design on the Prey Capture Efficiency of the Uloborid Spider Octonoba sybotides under Abundant and Limited Prey Conditions

Abstract

The influence of web design on prey capture efficiency was investigated in the orb-webs of Octonoba sybotides under different prey conditions (abundant and limited). The insects captured by artificial traps under limited prey conditions were smaller than those captured under abundant prey conditions. O. sybotides webs with spiral stabilimenta (SP webs) have a narrower mesh and a larger catching area than webs with linear stabilimenta (LN webs). Previous studies have shown that the form of the stabilimentum is changed in response to the internal energetic state of individual spiders. Food-deprived spiders tend to construct SP webs, and food-satiated spiders tend to construct LN webs. The total thread length of SP webs is significantly longer than that of LN webs; so food-deprived spiders seem to invest more energy in foraging than do satiated spiders. When prey was abundant, prey sizes and capture rates for SP webs and LN webs were similar. LN webs may have an advantage over SP webs in prey capture when prey is abundant, because SP webs appear to be more costly than LN webs. On the other hand, SP webs caught more prey than LN webs under limited-prey conditions, when the prey was smaller than under abundant-prey conditions. The average size of prey captured on SP webs was smaller than that on LN webs; SP webs seem to catch more prey than LN webs by catching smaller prey efficiently in prey-limited conditions. Since the food-deprived and food-satiated conditions of spiders in the field may correspond to the potential prey abundance in their habitat, O. sybotides seems to change its web dimensions in order to capture prey efficiently under different prey conditions.