Survey of IGP datasets
We surveyed papers in online, digitally-available journals through the University of California Berkeley library with "intraguild pre*" in the title. We restricted this search to years since 1989 when G. Polis and colleagues published their influential Annual Review of Ecology and Systematics article (Polis et al. 1989). This search, while not exhaustive, provides a representative sample of recent empirical studies of IGP. Because studies examining biological control systems were most likely to quantify the basal resource density, we added 8 studies specifically examining the effect of IGP on the basal resource that did not match our original search criteria.