COS 22-8: Dispersal dynamics affect the distribution, but not the abundance, of tropical trees: A study of tropical tree communities in Amazonian Peru
Kyle G. Dexter, Duke University
The dispersal assembly perspective holds that dispersal dynamics are the primary determinant of the distribution and relative abundance of species. I present patterns in the distribution and relative abundance of tree species in Amazonian Peru and determine if dispersal dynamics can explain these patterns. I censused tree communities in multiple habitat types at 14 locations across a 150 by 200 km area of Madre de Dios, Peru. I focused community censuses, and subsequent dispersal measurements, on the most abundant and diverse tree genus in the area: Inga (Mimosoideae, Fabaceae). To assess levels of seed dispersal across the landscape, I measured gene flow between populations (within species) for a chloropast marker. Of 60 species found in the study area, all are absent from at least one census location. Based on data from soil analyses, some of these absences can be attributed to an unsuitable soil environment for a given species. However, in many cases, a species is absent from locations that have a soil type upon which the species has elsewhere demonstrated an ability to grow and survive. Limited seed dispersal across the landscape could explain why species are absent from these locations. An examination of the relative abundance data gives a different expectation for dispersal levels. Within a habitat type (floodplain or uplands), the relative abundance of species is strongly correlated across the landscape. Common species are consistently common, and rare species are consistently rare. If dispersal were determining the relative abundance of species, there would have to be high rates of dispersal across the landscape to explain this correlation. The chloroplast genetic data indicates that seed dispersal is very limited across the landscape. Thus, dispersal dynamics (i.e. limited dispersal) may be responsible for patterns in the distribution, but not the abundance, of species.