ECOSYSTEM SIZE, BUT NOT DISTURBANCE, DETERMINES FOOD‐CHAIN LENGTH ON ISLANDS OF THE BAHAMAS

Ecologists have long struggled to explain variation in food‐chain length among natural ecosystems. Food‐chain length is predicted to be shorter in ecosystems subjected to greater disturbance because longer chains are theoretically less resilient to perturbation. Moreover, food‐chain length is expected to be longer in larger ecosystems because increasing ecosystem size increases species richness and stabilizes predator–prey interactions, or increases total resource availability. Here we test the roles of disturbance and ecosystem size in determining the food‐chain length of terrestrial food webs on Bahamian islands. We found that disturbance affected the identity of top predators, but did not change food‐chain length because alternative top predators occupied similar trophic positions. On the other hand, a 106‐fold increase in ecosystem size elevated food‐chain length by one trophic level. We suggest that the effect of disturbance on food‐chain length is weak when alternate top predators are trophic omnivores and have similar trophic positions. This and previous work in lakes suggest that ecosystem size may be a strong determinant of food‐chain length in both aquatic and terrestrial ecosystems.