Understanding how temporal variation in resource availability affects the dynamics of species interactions is a central goal for community ecology. Recently, there has been increasing interest in the effects of resource pulses, defined as ephemeral events of increased resource availability. Resource pulses can influence trophic cascades by driving changes in consumer behavior and abundance, but the time-scale of these effects differs, with behaviorally mediated changes usually occurring on shorter time scales than abundance-mediated changes.
To investigate temporal variation in trophic cascades triggered by resource pulses, we conducted a multi-year experiment using 32 small islands as replicates at a field site in the Bahamas. The experiment comprised four seaweed treatments that differed in the frequency and magnitude of seaweed deposition events (including a no-seaweed control). Lizards were introduced to half of the islands at the start of the experiment in a fully-crossed design, such that there were eight unique lizard-seaweed treatments, each with four replicate islands. We measured herbivory and growth on buttonwood (Conocarpus erectus), one of the commonest shoreline plants in this ecosystem, on one to four plants per island three times each year for the duration of the experiment.
The cascading effect of lizards on plants varied by seaweed treatment. Notably, a single large pulse of seaweed addition diminished the beneficial effects of lizards on plant growth in the first year of the experiment when compared to control islands. In contrast, in years 3 and 4 of the experiment the beneficial effects of lizards were stronger on islands that had received a pulse of seaweed addition than on control islands. This outcome is consistent with theory and with previous experimental studies showing that seaweed addition leads to short-term changes in lizard behavior and diet that reduce their impact on herbivory, and long-term increases in lizard abundance that can increase the effect of lizards on herbivory.