Abstract
Multiple predator effects (MPEs) can modify the strength of pest regulation, causing positive or negative deviations from those that are predicted from independent effects of isolated predators. Despite increasing evidence that omnivory can shape predator-prey interactions, few studies have examined the impact of alternative plant food on interactions between multiple predators. In the present study, we examined the effects and interactions of two omnivorous mirids, Μacrolophus pygmaeus and Nesidiocoris tenuis, on different densities of their aphid prey, Myzus persicae. Prey were offered to the to single or pairs of mirid predator individuals, either conspecific or heterospecific on a leaf, while simultaneously adding or excluding a flower as an alternative food resource. Data were compared with calculated expected values using the multiplicative risk model and the substitutive model. We showed that predation of aphids was reduced in the presence of the alternative flower resource in treatments with single M. pygmaeus individuals, but not with single N. tenuis individuals. When the predators had access only to prey, the effects of multiple predation, either conspecific or heterospecific, were additive. The addition of an alternative plant resource differently affected MPEs depending on the nature of predator pairings. Predation risk was increased in conspecific M. pygmaeus treatments at intermediate prey densities, whereas it was reduced in conspecific N. tenuis treatments at high prey densities. Observations of foraging behaviour concerning the location of conspecific pairings revealed that M. pygmaeus individuals showed a clear tendency to reside mainly in the flower, whereas N. tenuis individuals were found to reside at different posts in the dish. We suggest that the competition between omnivorous predators may be mediated through the diversity of their plant feeding preferences, which directly affects the strength of MPEs. Consequently, the preferences of the interacting predators for different plant resources should be considered in studies evaluating the outcomes of MPEs.
Highlights
Intra- and interspecific interactions among organisms influence the complexity and resilience of natural and managed food webs
Multiple-predator effects (MPEs) can be non-additive through either ‘risk enhancement’, in which prey survival in the presence of two predators is reduced as a result of diet complementarity or facilitation between predators, or ‘risk reduction’, in which prey survival in the presence of both predators is higher than predicted from their individual impacts in each single predator treatment [3]
We were interested in measuring multiple predator effects (MPEs) on prey consumption by two mirid bugs commonly used as biocontrol agents, M. pygmaeus and N. tenuis, and how these MPEs could be affected by the presence of an alternative flower resource for doi:10.1371/journal.pone.0138764.g002
Summary
Intra- and interspecific interactions among organisms influence the complexity and resilience of natural and managed food webs (such as agricultural systems). M. pygmaeus has not been seen predating other hemipteran predators [39], it interferes with parasitoid biocontrol agents [32, 40] and displays a cannibalistic behaviour [41] Nesidiocoris tenuis is a plant feeding generalist predator but cannot reach adulthood on plants in the absence of prey [42], this may depend on the plant [43] This species has been reported to benefit tomato plants directly by entomophagy and indirectly by phytophagy, which induces a physiological response in the tomato plant [44]. We addressed the following questions: (a) Do Μ. pygmaeus and N. tenuis show conspecific and heterospesific interactions when foraging in a prey patch? (b) Are the above interactions affected by the level of prey availability? (c) Does flower availability affect the conspecific and heterospesific interactions, if any?
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