Document: RON-3-42-44

Seedling establishment in a tropical maritime forest: The relative role of crab herbivory on seedling growth and survival.

LINDQUIST, E.S.* and C.R.CARROLL

University of Georgia, Athens GA 30602 USA ¹

Abstract:
Both top-down (predators) and bottom-up (resource limitation) forces have been found in previous studies to have large impacts on seedling establishment, growth, and survival. In tropical maritime forests, Hermit crabs, Coenobita compressus (Coenobitidae) and burrowing Harlequin crabs, Gecarcinus quadratus (Gecarcinidae), are very abundant and may be important predators of seeds and seedlings. In secondary forest of variable canopy height and cover, light may also affect seedling establishment and growth. In Cabo Blanco Absolute Reserve of Costa Rica, tree density and richness of all size classes is significantly lower in the secondary maritime forest than in the upland forest of the same age. To determine the relative effects of bottom-up and top-down factors on native tree seedling establishment in the maritime forest, we conducted a factorial experiment. Through the use of natural gaps and exclosures, we manipulated light regime and crab predation pressure at sites where we then placed potted germinated seeds of the native tree (Enterolobium cyclocarpus). After one month, we found that crabs do predate intensively on seedlings. No seedlings that were accessible to crabs remained, while 75 percent of those protected from crabs but accessible to other potential herbivores survived. Contrary to our prediction, high light levels negatively affected seedling survival and growth. The lower survivorship and growth in the gap sites may have been caused by a high evaporation rate during the dry season experiment, and unlikely due to light intolerance under natural conditions. The information we obtained in this study enhances our understanding of the natural limitations to seedling establishment. Follow-up studies are planned to further investigate the impact of multiple factors at different stages of recruitment for native trees in the successional maritime forest.

Keywords:

This abstract is being presented at: 3:30 PM in session:
HERBIVORE EFFECTS ON PLANTS