Food Web Dynamics on Bahamian Islands

We here summarize and integrate findings in our studies of food-web interactions on Bahamian islands conducted over a 40-year timespan. Results obtained in a series of field experiments, taken together, provide compelling evidence that predatory lizards reduce herbivory and thereby have a positive indirect effect on plants, even though lizards also reduce web spiders which eat herbivores. Two exogenous factors, hurricanes and allochthonous resource pulses, play a significant role in structuring island communities and produce major temporal fluctuations in food-web dynamics. Following hurricanes, herbivory increased substantially on severely damaged plants due at least in part to enhanced susceptibility of resprouting foliage to herbivores. The top-down effect of lizards on herbivory was stronger after the hurricanes than before. Allochthonous resource pulses in the form of seaweed deposition events cause a sequential series of bottom-up and top-down effects that propagate throughout the food web. In the short-term, lizards shift from eating local prey (including terrestrial herbivores) to eating mostly marine detritivores, leading to increased herbivory and weakening the trophic cascade from lizards to plants. In the long-term, decomposing seaweed adds nutrients to plants, increasing their growth rate, and a numerical response by lizards to marine detritivores strengthens the trophic cascade.