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Dryad

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

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Jan 30, 2023 version files 79.32 KB

Abstract

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 experiments repeated during and after a marine heat wave. Near the end of a marine heat wave in 2016, swimming crabs were found in 25% of marsh tidal creeks. No swimming crabs were found in these tidal creeks during cooler water conditions in 2012 and 2021. When swimming crabs were more abundant (e.g. 2016), horn snails experienced 7,533% more mortality and were 91% less abundant. The proportion of snails climbing vegetation was 454% higher when swimming crabs were more abundant. Thus, higher predator densities occurring during a marine heat wave were associated with changes in snail abundance, mortality, and behavior. Such changes could influence marsh food webs and nutrient cycling. Our findings highlight the value of exploiting climatic anomalies to understand ecological patterns linked to the top-down effects in ecosystems - a critical need in predator-prey ecology.