Document: WAY-3-42-36

Propagule predation dependent on canopy disturbance controls regeneration of a Caribbean mangrove.

SOUSA, W.P.*

University of California, Berkeley, CA 94720, U.S.A. ¹

Abstract:
Empirical and theoretical studies suggest that seed predation can strongly affect the demography and dynamics of low-density, seed-limited plant populations. However, when plant density is high, competition for microsites suitable for establishment and growth may be more important in determining the number of individuals that reach maturity than the number of surviving seeds. This dichotomous perspective does not account for more complex situations in which the risk of seed predation differs inside versus outside recruitment microsites. Such an interaction between microsite quality and the risk of propagule predation occurs in low intertidal, mangrove forests on the Caribbean coast of Panama, where it appears to play a key role in shaping the demography and dynamics of the red mangrove, Rhizophora mangle. This species' water-borne propagules can establish wherever they strand, but only those that do so in or near lightning-created canopy gaps survive and grow to maturity. These microsites afford better growth conditions than the surrounding understory, but as importantly, provide a refuge from predation by the scolytid beetle, Coccotrypes rhizophorae, a specialist feeder on Rhizophora propagules and seedlings. Sampling studies demonstrate that each year this herbivore kills nearly all Rhizophora seedlings in the forest understory. When the beetle is experimentally excluded with mesh cages, seedlings survive well in understory environments. This interaction may have a large impact on forest composition. Being shade-tolerant, Rhizophora seedlings that escape or survive beetle attack can persist in the understory for years. However, the high rate of beetle-induced mortality effectively eliminates the contribution of advance regeneration by Rhizophora saplings to gap succession, which may explain why the shade-intolerant, white mangrove, Laguncularia racemosa, is able to co-dominate the canopy in low intertidal forests at our study sites.

Keywords: seed predation, disturbance, insect-plant interactions, mangrove, forest regeneration

This abstract is being presented at: 2:00 PM in session:
Oral Session #18: Mangrove Ecology.