High predator-to-prey ratios promote the suppression of some herbivorous insects, and disturbance events (harsh winters, cold snaps, fires, storms) can lead to outbreaks of herbivores by diminishing the relative abundance of predators. This study assessed the effect of one kind of disturbance, tidal inundation, on food-web structure as indexed by changes in predator-prey ratios along an elevational gradient in a mid-Atlantic salt marsh community. Planthoppers, the major herbivores in the community, often reach outbreak densities in low marsh habitats. We hypothesized that two of the most abundant predators of planthoppers, the lycosid spider Pardosa littoralis and the mirid egg predator Tytthus vagus, respond differently to rising tidewaters due to differences in their mobility. We measured densities of naturally-occurring populations of planthoppers and their predators over a range of elevations during different phases of the tide cycle. The mirid population showed a clear response to the highest tides, with a significant portion shifting from low to high-elevation habitats. The spider response was more complex, showing a bimodal distribution caused by larger numbers leaving intermediate elevations than lower elevations where tall plants offer spiders a spatial refuge. These predator responses may create temporary spatial refuges for planthoppers and help explain their outbreak dynamics in low marsh habitats.
Species 1: Aranea Lycosidae Pardosa littoralis
Species 2: Hemiptera Miridae Tytthus vagus
Species 3: Hemiptera Delphacidae Prokelisia marginata
Keywords: Tidal disturbance, Predator-prey interaction
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