Friends of the Osa: Interaction in a Costa Rican Wet Forest

Interaction among landscape heterogeneity, secondary-seed dispersal and forest regeneration in a Costa Rican wet forest

As human induced large-scale disturbances alter natural ecosystems, loss of key species and even entire guilds negatively affect important ecological roles associated to high levels of diversity. Seed dispersal and seed bank creation are two important ecological roles that can be severely affected with diversity reduction. Seed dispersal may help maintain population viability and forest diversity in time. Seed banks are the source that will maintain future forest community structure. These two ecological functions can be affected directly with the extinction of plant species, but can also be drastically modified with the loss of the animal species that directly interact with the seeds.

Large vertebrate species are usually the first animals to disappear under large-scale disturbances. Most of these animals are herbivores that play important roles as seed dispersers or seed predators. The effects on seed dispersal caused by the loss of these organisms are fairly well understood. On the other hand, the impact of invertebrates on seed dispersal, seed burial and seed predation still requires research. Dung beetles (Scarabaeinae), have been used as habitat indicators and are an important guild that interacts with seeds found in dung of large vertebrates. This guild is very sensible to habitat disturbance, and as their community structure is affected by habitat change, their role as secondary dispersers is also negatively altered. As a consequence, seed predation increases and seed germination probability is reduced in disturbed habitats.

The Osa peninsula, Costa Rica, contains the only remaining stand of tropical wet forest in Central America (CEPF 2000). During the 1960’s to the 1990’s the region under went intense land use changes that were controlled later on by the creation of the Corcovado National Park. Today what is left is a landscape with large patches of primary and secondary forest, pastures and tree plantations. This is an excellent setting to study how habitat loss and subsequent forest regeneration led to changes on beetle communities and on their role as secondary seed dispersers. This proposal will study those changes and will evaluate their impact on tropical forest seed bank creation and ultimately on seed germination; processes that will control future forest structure and diversity.

The main questions of my proposal are:

1. How dung beetle communities change with disturbance and regeneration;
2. How these changes influence seed dispersal, burial, predation and germination.