Many natural systems exhibit transient dynamics in which populations fluctuate substantially. Understanding the role of predators in modulating transient food-web dynamics is needed to evaluate the general importance of trophic cascades in nature. We studied a system of highly fluctuating populations, the moth Achyra rantalis feeding on the plant Sesuvium portulacastrum, on small subtropical islands of the Bahamas. The plant is a prostrate inhabitant of shorelines, and consequently moths are highly vulnerable to being consumed by the often ground-foraging predatory lizard Anolis sagrei. We measured the percent ground cover of Sesuvium and abundance of Achyra on 11 islands with lizards present and 21 islands without lizards annually for 10 consecutive years. We predicted that mean temporal variability in percent cover would be higher on no-lizard islands because many would be in an “outbreak-dieback” phase or in a “regrowth” phase in which the moth populations had crashed and the plants were recovering. During the study, the area was impacted by a series of hurricanes which washed away much of the Sesuvium on the islands. This enabled us to measure a different type of phenomenon: the effect of lizards on the resilience of Sesuvium following hurricanes.
Overall abundance of Achyra was 4.6 times higher on no-lizard islands than on lizard islands. Temporal variability of Sesuvium percent cover was lower on lizard islands when the study site was undisturbed by hurricanes, and recovery rate of Sesuvium was higher on islands with lizards following hurricanes. We suggest that both of these stabilizing phenomena are linked to a trophic cascade in which predatory lizards control herbivore populations and thereby suppress outbreaks and enhance plant recovery following physical disturbance. Most theoretical and empirical studies of trophic cascades focus on steady-state equilibrium abundances of producers. However, we need to focus on non-equilibrium conditions as well, in which populations may fluctuate dramatically due to erratic outbreaks and disturbances. During this time of increasing frequency of many types of disturbances, strategies for sustainable management of ecosystems should focus on maintaining resilience. The findings of this study imply that preserving healthy predator populations may mitigate the negative impacts of global change on ecosystems.