Entrapped carrion increases indirect plant resistance and intra-guild predation on a sticky tarweed
LoPresti Eric, Krimmel Billy, Pearse Ian S.
Many plants employ indirect defenses against herbivores; often plants provide a shelter or nutritional resource to predators, increasing predator abundance, and lessening herbivory to the plant. Often, predators on the same plant represent different life stages and different species. In these situations intraguild predation (IGP) may occur and may decrease the efficacy of that defense. Recently, several sticky plants have been found to increase indirect defense by provisioning predatory insects with entrapped insects (hereafter: carrion). We conducted observational studies and feeding trials with herbivores and predators on two sticky, insect-entrapping asters, Hemizonia congesta and Madia elegans, to construct food webs for these species and determine the prevalence of IGP in these carrion-provisioning systems. In both systems, intraguild predation was the most common interaction observed. To determine whether IGP was driven by resource abundance, whether it reduced efficacy of this indirect defense and whether stickiness or predator attraction was induced by damage, we performed field manipulations on H. congesta. Carrion supplementation led to an increase in predator abundance and IGP. IGP was asymmetric within the predator guild: assassin bugs and spiders preyed on small stilt bugs but not vice versa. Despite increased IGP, carrion provisions decreased the abundance of the two most common herbivores (a weevil and a mealybug). Overall seed set was driven by plant size, but number of seeds produced per fruit significantly increased with increasing carrion, likely because of the reduction in the density of a seed-feeding weevil. Observationally and experimentally, we found that carrion-mediated indirect defense of tarweeds led to much intraguild predation, though predators effectively reduced herbivore abundance despite the increase in IGP.