Ants vs crabs: competition over seeds on a tropical island ecosystem

Seed dispersal by ants plays a major role globally in plant dynamics for many angiosperms and can be influenced by multiple factors. One of those factors is competition between ants and other organisms for gaining access to seeds. A habitat with high abundance of potential competitors for ants is forests in marine coast ecosystem, where there is a high abundance of terrestrial crabs that functionally act as seed predators. In a coastal forest on Coiba Island, Panama, we measured seed removal rates at increasing intervals from the coast towards the interior of the forest, representing a decreasing gradient in ant–crab competition. We found that seed removal was dominated by hermit crabs near the coast, and while ants moved more seeds as the distance from the coast increased. We expect that this differential removal should generate varying levels of seed predation and seedling establishment, with crabs acting mainly as seed and seedling predators. This study provides insights into how ant–crab dynamics may play a role in maintaining the vegetation gradients in coastal ecosystems.