AN EXPERIMENTAL-ANALYSIS OF INTRAGUILD PREDATION AMONG 3 GENERA OF WEB-BUILDING SPIDERS - HYPOCHILUS, CORAS AND ACHAEARANEA (ARANEAE, HYPOCHILIDAE, AMAUROBIIDAE AND THERIDIIDAE)

We investigated predatory interactions among three species of web-buil ding spiders which co-occur on sandstone outcrops along the Cumberland Plateau in east Tennessee: Hypochilus thorelli (Hypochilidae), Achaea ranea tepidariorum (Theridiidae) and Coras montanus (Amaurobiidae). Pr evious studies have shown that these spiders are essentially ecologica l equivalents with respect to activity, web-site characteristics and p rey capture and that each species preys on the others. This type of pr edatory interaction between potential competitors is referred to as in traguild predation. We performed removal experiments to determine the significance of intraguild predation for each of the species as predat ors and as prey. Three types of treatment plots were established: from each plot two of the three study species were removed (weekly, July-O ctober 1993) and the third remained. Control plots were established fr om which no spiders were removed. We predicted that if the treatments resulted in removal of an important source of prey then: 1) the number of individuals of the remaining species should decline over time as a result of web-relocation, and 2) body condition of spiders remaining should be lower in the treatments than in the controls. If treatments had the effect of removing predation then the number of individuals re maining in treatment plots should increase relative to the controls wh ere intraguild predation could occur. There were no significant differ ences in the number of spiders of the remaining species on treatment v ersus control plots, indicating that the treatment did not result in s pider relocation as a response to potential food removal. However, at the end of the experiment body condition of H. thorelli was significan tly lower on plots from which the other two species were removed than on control plots. This suggests that removal of the other two species may have resulted in removal of a significant source of prey for H. th orelli. In addition, we present evidence that treatments may have remo ved a source of predation on dispersing A. tepidariorum spiderlings.