Document: WAL-3-42-31

Do ground-dwelling mammals promote high tropical tree diversity: Testing Janzen-Connell at the community level.

CARSON, W.P.*, S.SCHNITZER and H.STEVENS

University of Pittsburgh, Pittsburgh, PA 15260, USA ¹

Abstract:
We have been excluding ground-dwelling mammals with exclosures for 6-years in the understory at two old-growth forest sites in Panama. Excluding mammalian seed and seedling predators has led to the establishment of dense seedling carpets of a number of tree species. These seedling carpets have now persisted for many years, even through a severe El Nino drought. Species richness of seedlings on a per stem basis increased for three years, but now has returned to control levels. This suggests that there is a substantial lag time before species richness actually declines following the exclusion of mammals, which is consistent with predictions of the Janzen-Connell Hypothesis. Overall, predation and browsing have reduced seedling growth and survivorship, demonstrating that these factors are important following seedling establishment. At very high seedling densities inside exclosures, however, we have detected density dependent mortality, suggesting that in the absence of seed predators and herbivores, seedlings begin to compete even under fairly dense shade. Thus, predation and browsing on many species of seedlings is as important as light availability with regard to establishment and persistence in the shaded understory. A clear confirmation of the Janzen-Connell hypothesis (i.e., significantly lower diversity inside exclosures in the understory) will likely require at least several more years of experimental exclusion of mammals.

Keywords: Herbivory, tropical forest, diversity, seed predation

This abstract is being presented at: 1:30 PM in session:
Oral Session #17: Mammalian Herbivory.