The strength and outcome of mutualistic interactions can be highly dependent on the combination of traits of the species involved. Distinct foraging strategies (e.g. hunting mode) of mutualistic predators may mediate the basis of variation in predator-prey interactions. We investigated the strength of spider-plant mutualistic interactions by focusing on contrasting hunting modes of spider partners: an active hunter (lynx spider, Peucetia sp.,) and a sit-and-wait (crab spider, Misumenops argenteus). We manipulated spider species by assigning each plant to one of the following treatments: (1) no spiders; (2) crab spiders; (3) lynx spiders; (4) lynx and crab spiders. We then examined the independent and interactive effects of spiders on floral herbivory and fitness of the glandular trichome-bearing plant, Trichogoniopsis adenantha (Asteraceae).
Results/Conclusions
Spiders increased plant fitness indirectly by suppressing herbivores and increasing ovary fertilization, but the overall net benefit of spiders was contingent on spider identity. Sit-and-wait crab spiders increased plant fitness by consuming herbivores and triggering strong predation risk cues. In contrast, actively hunting lynx spiders benefitted plants by mainly reducing the number of herbivores, likely inducing evasive predation risk cues. The combined impact of spider species was merely additive on herbivores, whereas it was slightly antagonistic on plant fitness. We conclude that the strength of spider-plant mutualisms depends on the combination and hunting mode of spider partners involved by operating distinctively on the consumptive and non-consumptive components of predators. These findings offer a general framework for understanding the critical role of predator foraging mode in trophic cascades.