Effects of Predation Risk and Prey Availability on the Foraging Activity of Desert Scorpions

A. Bouskila, H. Shamir, A. Bachi and Y. Hadar

When a forager emerges from its shelter to forage, it increases the probability of finding food, but it may also increase the chances of getting killed by its predators. In this project the investigators study simultaneously three trophic levels: scorpions, their predators and prey.The aim of this study is to understand the components in the trade-off between predation risk and energy gain of the nocturnal scorpions. Hila Shamir (M.Sc. student) quantified the risk of predation on the desert scorpion Buthus occitanus near the Sede Boqer Campus and found that the main predator in the field site is the desert hedgehog, Paraechinusaethiopicus. She also found that the probability per night of getting killed varies greatly, but cannot be explained by moonlight. She is now investigating the influences of both the internal state of the scorpionand the environmental conditions on the scorpion's foraging activity. Alona Bachi found that another scorpion at the same site, Scorpiomaurus, modifies its foraging activity in response to artificial enrichment of prey. She also found that the prey of scorpions (otherarthropods) reduce their activity on moonlit nights, thus providing a possible explanation for the reduction in activity that was previously observed in scorpions on moonlit nights.

In order to understand in more details the risk of predation imposed by the main predator of the scorpion B. occitanus in our field site,Yuval Hadar is monitoring the activity of hedgehogs P. aethiopicus and how it varies in time and in space. Hedgehogs are marked by radiotelemetry, and are followed during their main activity hours atnight. We are also looking at the effects of external factors such as temperature, relative humidity and moonlight on the movements and habitatuse of the hedgehogs.