Agricultural diversification can increase the abundance and diversity of predators, affecting predator-predator interactions. In the belowground food web, predators exert top-down control of microbivorous arthropods and can indirectly influence the dynamics of soil microbial communities and soil organic matter (SOM) formation. Since SOM is critical for soil fertility, it is necessary to understand how interspecific predator-predator interactions affect microbivores, like Collembola, in diversified agroecosystems. In soils of Inland Pacific Northwest agroecosystems, predatory beetles (Coleoptera: Staphylinidae: Xantholinus linearis linearis (Olivier 1795)) and predatory mites (Mesostigmata: Laelapidae sp.) are abundant predators and regulators of Collembola populations. Using this two-predator study system, we investigated the influence of predator-predator interactions on Collembola (Onychiuridae sp.) populations in laboratory microcosms. Collembola were exposed to predators individually and in combination. Individual predators significantly reduced Collembola populations. The two-predator treatment resulted in intraguild predation of mites by beetles, which influenced Collembola mortality. Non-consumptive effects could also regulate interactions between predators in our system. Using the same microcosm design, we immobilized beetle mouthparts and observed their non-consumptive effects on Collembola and mites. Predatory beetles exert non-consumptive effects on their intraguild prey, mesostigmatid mites, and Collembola. Together, these predators may act non-additively to suppress Collembola in microcosms, suggesting intraguild interference (consumptive and non-consumptive) can occur within the soil food web with possible cascading effects on microbial communities and soil health processes. A better understanding of these interactions will augment our limited knowledge of soil arthropod food webs and their influence on soil health in diversified agroecosystems.
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