Co-occurrence among Intraguild Predators: Avoidance or Aggregation?

Intraguild predation (IGP) may interact with prey availability to structure predator communities. However, if predators are able to avoid each other, its effect on predator community structure may be minimized or absent. To determine whether co-occurrence among IG predators is limited, we estimated co-occurrence among predators in experimental plots of maize and soybean. These crops provide high densities of shared resources (aphids) as well as known IG predators (primarily coccinellids). Despite documented intraspecific and interspecific avoidance behaviors, aggregation to patchy resources could bring IG predators into contact. We, therefore, hypothesized that despite documented intraspecific avoidance behaviors, aphidophagous IG coccinellid predators would not significantly avoid co-occurrence, making IGP likely. Co-occurrence was estimated from visual counts of aphid predators and their prey on randomly selected plants over the course of the growing season. For each habitat, we used maximum likelihood analysis to determine whether observed co-occurrence deviated significantly from that expected for each possible pairwise combination of IG predators. We repeated this analysis using published data on co-occurrence among aphid predators on tansy. We found that most co-occurrence among IG predators was random, suggesting that avoidance does not limit co-occurrence. Failure to limit co-occurrence could be the result of ineffective avoidance mechanisms or because predators balance aggregating on shared resources with avoiding IG predators.