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Community level patterns of seedling mortality in a tropical tree community.
Comita, Liza*,1, Hubbell, Stephen1, 2, 1 Department of Plant Biology, Athens, GA, USA2 Smithsonian Tropical Research Institute, Balboa, Ancon, Panama
ABSTRACT- Many of the theories proposed to explain the maintenance of diversity in species rich plant communities hinge on mechanisms that shape spatial patterns of seedling survival. The Janzen-Connell hypothesis (Janzen 1970, Connell 1971) posits that successful seedling recruitment in tropical forests may be restricted by natural enemies, namely seed predators, herbivores, and pathogens, that cue in on high densities of seeds and seedlings around reproductive adults. In contrast, the regeneration niche hypothesis (Grubb 1977) suggests that plant species require differing conditions for recruitment, so the progeny of different species will survive and establish in different habitats. In order to fully test these hypotheses, we have established a large-scale community-wide study of seedlings and small saplings in the 50-ha Forest Dynamics Plot (FDP) on Barro Colorado Island, Panama. We have collected data on the abundance and spatial distribution of >60,000 seedlings and small saplings of 344 tropical tree and liana species in approximately twenty thousand 1-m2 plots distributed uniformly over the 50-ha FDP. Using data from two completed censuses of these seedling plots, we examine patterns of seedling mortality in this tropical tree community and compare survival rates among species and among guilds. We look at the effects of seedling size, habitat, and conspecific density on seedling survival and examine the relative importance of these factors in determining spatial patterns of recruitment. We use the results of these analyses to evaluate the relative importance of mechanisms proposed to explain the coexistence of species.
Key words: regeneration niche, seedling survival, Janzen-Connell hypothesis, tropical forest dynamics