The effect of predation risk on spider’s decisions on web-site relocation

Abstract

Among the costs associated with animal-built structures, the cost of exposure to predators is important, because it affects the survival of builder animals. When predator risk increases, the builder may change the location of a structure or remain on the structure but modify its behaviour. The main purpose of this study was to examine whether builders leave their current structure locations and relocate to a new location upon predator attacks. To assess this, we used orb-web spiders that regularly renew their webs and occasionally relocates their web site upon web-rebuilding. Specifically, adult females of Cyclosa argenteoalba were exposed to the air-borne vibrations from a tuning fork. These vibrations simulate the vibrations from insect predators’ wings and trigger immediate anti-predator responses (jumping off the web to avoid attacks from predators and shaking webs). Spiders that received these simulated predator stimuli relocated more often on the day after treatment than did spiders that were not exposed to predator stimuli. This indicated that spiders estimated future predation risk from their predator-encounter experience and responded to perceived increase in predation risk at current site by abandoning their web site upon web-rebuilding. In addition, we examined whether the frequency of jumping behaviour and web relocation were correlated, but no significant relationship was detected. This result suggests that immediate anti-predator behaviour at the current site and the decision to relocate were independent of each other.