RELATIVE SEASONAL ABUNDANCE OF FIVE SPIDER SPECIES IN THE NEGEV DESERT: INTRAGUILD INTERACTIONS AND THEIR IMPLICATIONS

ABSTRACT

Current models indicate that intraguild predation is most likely to occur in communities with intermediate levels of productivity. Desert communities fit this criterion and also contain a disproportional amount of generalist predacious arthropods, in particular spiders, suggesting a high degree of intraguild predation in these communities. In this study we looked at intraguild predation in the Negev highlands among five species of spiders, two of which (Poecilochroa senilis, Gnaphosidae and Thyene imperialis, Salticidae) are predators of one or more of the other three (Latrodectus revivensis, Theridiidae; Stegodyphus lineatus, Eresidae; and Mogrus sp., Salticidae). However, unlike the simple interactions frequently modeled, we found complex interactions among the species which enhance coexistence. For example, evidence of higher-order interactions between Mogrus and Stegodyphus apparently enhanced the survival of Stegodyphus: during an annual cycle Mogrus, the preferred prey of Poecilochroa, was able to escape predation as juveniles by becoming scarce in the preferred habitat of Poecilochroa (which then mainly attacked Stegodyphus); when Mogrus returned to the habitat as adults, it relieved Stegodyphus from predation pressure at a time when the Stegodyphus population was most vulnerable (juveniles still in their dead mother's nest). Mogrus did not gain relief from predation by changing habitats as Thyene readily attacked the juveniles in the second habitat. The relationship between Poecilochroa and Latrodectus is also complex. Poecilochroa readily preyed on Latrodectus spiderlings and were often found overwintering in Latrodectus eggsacs. However, adult Latrodectus may themselves prey on Poecilochroa during summer. Thus the presence of a potential predator (Latrodectus) may enhance the survival of Poecilochroa during the winter by being a source of food.