Abstract: Wolf Spiders Show Graded Antipredator Behavior in the Presence of Chemical Cues from Different Sized Predators.

The wolf spider, Pardosa milvina, displays effective antipredator behavior (reduced activity) in the presence of silk and excreta cues from adults of another co-occurring wolf spider, Hogna helluo. However, Pardosa and Hogna engage in size-structured intraguild predation where Pardosa may be either the prey or predator of Hogna. We tested the ability of adult female Pardosa to vary antipredator responses toward kairomones produced by Hogna that vary in size. Hogna were maintained on filter paper for 24 hours. We then presented the paper to adult female Pardosa simultaneously paired with a blank sheet of paper. One treatment had two sheets of blank paper to serve as a control. The Hogna stimulus treatments were as follows (N = 15/treatment): 1) 1 Hogna half the mass of Pardosa; 2) 1 Hogna equal mass of a Pardosa; 4) 1 adult Hogna, 30 times the mass of Pardosa, and 5) 8 Hogna each 0.25 the mass of Pardosa. Pardosa significantly decreased activity in the presence of kairomones from Hogna of equal or larger size than themselves, but showed no change in activity in the presence of a blank control or from a single Hogna smaller than itself. Pardosa showed a significant reduction in activity in the presence of cues from eight small Hogna. Pardosa avoided substrates with adult Hogna cues, but showed no avoidance response to any other treatment. These results suggest that Pardosa are likely showing graded antipredator behavior relative to the quantity of predator kairomones present rather than directly discriminating between the different sizes of the predator.