Getting ready for invasions: can background level of risk predict the ability of naïve prey to survive novel predators?

Abstract

Factors predicting the outcome of predator invasions on native prey communities are critical to our understanding of invasion ecology. Here, we tested whether background level of risk affected the survival of prey to novel predators, both native and invasive, predicting that high-risk environments would better prepare prey for invasions. We used naïve woodfrog as our prey and exposed them to a high or low risk regime either as embryos (prenatal exposure) or as larvae (recent exposure). Tadpoles were then tested for their survival in the presence of 4 novel predators: two dytiscid beetles, crayfish and trout. Survival was affected by both risk level and predator type. High risk was beneficial to prey exposed to the dytiscids larvae (ambush predators), but detrimental to prey exposed to crayfish or trout (pursuit predators). No effect of ontogeny of risk was found. We further documented that high-risk tadpoles were overall more active than their low-risk counterparts, explaining the patterns found with survival. Our results provide insights into the relationship between risk and resilience to predator invasions.

Figure 1. Comparison of mean survival (± SE where applicable) of tadpoles exposed to high risk vs low risk as embryos (left panels) or as tadpoles (right panel).

Survival trials were setup with rainbow trout (top panels), crayfish (middle panel) or dytiscid beetles (bottom panels). Measurement of survival varied with each specific experimental setup (see text for details) (photos: AC, MF).

Figure 2. Mean proportion (± SE) of active tadpoles in each of the high- and low-risk treatments (N = 40/treatment).