Impact of intraguild predators on survival of a forest-floor wolf spider

We investigated the impact of variation in densities of a guild of generali st predators on survival of young wolf spiders of the genus Schizocosa. Num bers of other spiders and centipedes,were reduced by > 80% in fenced 4-m(2) plots in an experiment that was replicated twice in each of three forest l ocations. Schizocosa survival during the Ist month was low (< 50%) in all t hree locations, but did not differ between predator-reduction and control p lots. By the end of the Ist month, densities of the manipulated predators h ad:converged in control and perturbed treatments, most likely because of re duced per capita mortality from lowered rates of intraguild predation and c annibalism in the experimental treatment. During the 2nd month of the exper iment, centipedes and spiders other than Schizocosa again were removed from the experimental plots and, unlike the earlier period, numbers of intragui ld predators in the predator-removal treatment remained lower than in contr ol plots. Reducing densities of intraguild predators during the 2nd month i mproved survival of older juvenile Schizocosa by 75% in two of three locati ons on the forest floor. In addition to this evidence that intraguild preda tion can affect older juvenile Schizocosa, survival of Schizocosa during th e last half of the experiment was negatively correlated with spatial variat ion in densities of gnaphosid and ctenid spiders. These two abundant famili es of cursorial spiders preyed on Schizocosa at a high rate in laboratory t rials. Thus, variation in densities of intraguild predators did not influen ce the youngest Schizocosa, but did influence the survival of older juvenil es, most likely due to variations in densities of other cursorial spiders.