Temporal changes in predator density are linked to shifts in prey behavior, mortality, and abundance in the field

Predators suppress prey populations and elicit defensive phenotypes in prey. The magnitude of predator effects depends upon several factors, including the density of predators, and their cue concentrations, in the environment. Predator density manipulations have often relied on laboratory studies that use unrealistic densities of predators and prey over unnatural temporal and spatial scales. Field studies can provide insights into predator-prey interactions under more realistic scenarios. However, field studies linking predator density and prey populations are limited by the challenge of manipulating predator densities or predicting predator densities in dynamic/stochastic environments. We exploited a somewhat predictable rise in predatory crab communities associated with ocean warming to evaluate the impacts of swimming crab density on ecologically important horn snails. Our approach combined long-term monitoring of crabs and snails with snail behavior surveys and snail tethering exper..., Study system and site
California horn snails (hereafter, horn snails) are ubiquitous in tidal marshes and mudflats across the Southern California Bight (Lorda & Lafferty 2012). Throughout this region, horn snails are prey for several predators (Armitage & Fong 2006; Lorda et al. 2016)and are intermediate hosts for parasitic trematodes (Hechinger & Lafferty 2005; Lafferty et al. 2006b). Horn snails can be predated upon by predatory swimming crabs during high tides, when tidal inundation facilitates crab movements into mud flat and marsh habitats (Cote et al. 2001; Belgrad & Smith 2014). In southern California, the abundance of these swimming crabs (e.g., the Xantus’ swimming crab, Portunus xantusii, and the arched swimming crab, Callinectes arcuatus; hereafter swimming crabs) is connected to sea water temperature. Warm water events (e.g., marine heat waves, El Niños) are associated with influxes of swimming crabs (Zedler et al. 1992; Williams et al. 2001).
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