material, rather than in large plant size is more beneficial for seedlings at early

developmental stages.

 Next, I described first-year temporal patterns of seedling mortality, susceptibility to

damage agents, and types of damage suffered by seedlings in the forest understory.

Seedling mortality was highest during the first 2 mos (due to vertebrate activity) and

gradually decreased over the remaining 8 mo. Species differed significantly in their

temporal patterns of mortality and in the proportions of seedling surviving at the end of

the study. The three main causes of damage were (in order of severity) vertebrate activity,

disease, and litterfall. The four main types of mechanical damage (in order of severity)

were leaf damage, bent stems, broken stems, and uprooted seedlings. All species suffered

similar levels of mechanical damage but shade-tolerant species (which often had stems

constructed of strong materials) were less likely to die when damaged than light-

demanding species.

 My study provides evidence that, in Barro Colorado Island, physical disturbance is

a major cause of seedling mortality during the first year, and that shade-tolerant species

survive better than light-demanding species after suffering mechanical damage. Higher

survival is potentially influenced by higher carbon investment of shade-tolerant tree

species into structural support of stems at very early developmental stages. However,

greater carbon allocation to structural defense must be accompanied by slower relative

growth rates. Thus, functional diversity in biomechanical properties is an important

aspect of multiple trait associations that lead to the growth-survival trade-offs observed

among coexisting tropical tree species.