AN EXPERIMENTAL-ANALYSIS OF INTRAGUILD PREDATION AMONG 3 GENERA OF WEB-BUILDING SPIDERS - HYPOCHILUS, CORAS AND ACHAEARANEA (ARANEAE, HYPOCHILIDAE, AMAUROBIIDAE AND THERIDIIDAE)
Ma. Hodge et Sd. Marshall, AN EXPERIMENTAL-ANALYSIS OF INTRAGUILD PREDATION AMONG 3 GENERA OF WEB-BUILDING SPIDERS - HYPOCHILUS, CORAS AND ACHAEARANEA (ARANEAE, HYPOCHILIDAE, AMAUROBIIDAE AND THERIDIIDAE), The Journal of arachnology, 24(2), 1996, pp. 101-110
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.