Rodents as conditional mutualists of trees: When are agoutis effective seed dispersers?

Abstract

Seed dispersal and seed predation are key ecological processes
that play important roles in plant population dynamics and community
composition, and are partly responsible for the maintenance of high levels of tree species coexistence in tropical forests. The ecological role of scatter-hoarding rodents is controversial in this regard, having been argued as good for trees, bad for trees, or conditionally mutualistic depending on local food or predators. I present results from experiments with agoutis and palm seeds on Barro Colorado Island, Panama, where we used new tracking technologies and large-scale gradients to determine whether and how agoutis can be effective seed dispersers, despite being seed predators. The hypothesis was that the
rodent-tree interaction is most beneficial to trees in situations with low relative seed abundance and high rodent predation rates. Here, competition for seeds results in rapid and extensive scatterhoarding, and high mortality of rodents subsequently allows cached seeds to escape consumption. This pattern may contribute to the negative density dependence of tree performance.