Spatial refuge influences the distribution of predators during tidal disturbance.
Lewis, Danny*,1, Denno, Robert1, 1 University of Maryland, College Park, MD
ABSTRACT- Abiotic disturbance is known to affect the distribution of predators and thus the intensity of predation on many marine populations. By contrast, much less is known about disturbance effects on predators in terrestrial systems and how they might decouple predator-prey interactions. In a previous observational survey we showed that one form of physical disturbance, tidal inundation, promoted the concentration of two important arthropod predators (the wolf spider Pardosa littoralis and the mirid bug Tytthus vagus) in areas of high-profile vegetation (tall-form Spartina) on Atlantic coast salt marshes. This response suggested that such vegetation provided a vertical refuge for these predators from tide waters. Notably, the spatial distribution of their prey (Prokelisia planthoppers) did not change in response to rising tide waters, resulting in high predator-prey ratios in refuge habitats and lower ratios in areas of short-profile vegetation with less vertical refuge. To experimentally test the role of vertical refuge, we created artificial refuges consisting of upright dried reeds in experimental plots and observed their effect on the abundance of predators and prey. In areas of intense tidal inundation, predators were more abundant in plots supplied with an artificial vertical refuge than in refuge-free controls. Planthopper prey remained unaffected by the treatment, and as a result predator-to-prey ratios were significantly higher in refuge plots than in areas lacking vertical refuge. There was no treatment effect in areas of the marsh experiencing only minimal tidal inundation, confirming that vertical refuge affected predator density only through its interaction with tidal inundation. The temporary spatial decoupling of predators from their prey can have important local consequences for predator-prey interactions and the outbreak dynamics of insect herbivores on the marsh.
Key words: spatial refuge, pardosa littoralis, tytthus vagus
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