this is casearia, and it only occurs in this local little area that we' in of about 100 feet by 100 feet. and there are a couple hundred individuals here, t nowhere se in the pl, or very rare in the rest of thet. and so we're trying to understand why this species likes this particular place in the forest. and one idea is that this particular species kehigh-calcium soils and poor-phosphorus soils. and so thi one area that has high calcium and low phosphorus. but other species may not be so particular. in particular, this one -- faraa -- grows everywhere and seems to be indifferent to the variation in soil nutrients. so it's much more common. narrator: unke in temperate forests, re speciesarmber coonpeci. that's not one, but. there you go. over there. this distribution is essential in promoting diversity. on barro colorado island, the common species only account for 15% of the total tree population, compared with around 80% common species in a typical new england forest. one y to investi how this diverseomposition of the rainfores pertued is by studying the seeds and seedlings. dr. davies: