Abstract
Theories of tropical tree diversity emphasize dispersal limitation as a potential mechanism for separating species in space and reducing competitive exclusion. We compared the dispersal morphologies, fruit sizes, and spatial distributions of 561 tree species within a fully mapped, 50-hectare plot of primary tropical forest in peninsular Malaysia. We demonstrate here that the extent and scale of conspecific spatial aggregation is correlated with the mode of seed dispersal. This relationship holds for saplings as well as for mature trees. Phylogenetically independent contrasts confirm that the relationship between dispersal and spatial pattern is significant even after controlling for common ancestry among species. We found the same qualitative results for a 50-hectare tropical forest plot in Panama. Our results provide broad empirical evidence for the importance of dispersal mode in establishing the long-term community structure of tropical forests.
Highlights
Tropical forest tree communities are among the most species-rich on Earth
The maintenance of diversity remains a central problem in ecology [1], theoretical work has highlighted conspecific aggregation as a mechanism of reducing competitive exclusion and promoting diversity [2,3]
We demonstrate that dispersal morphologies are strongly correlated with spatial distributions for hundreds of tree species, and with the community structure of tropical forests
Summary
Tropical forest tree communities are among the most species-rich on Earth. the maintenance of diversity remains a central problem in ecology [1], theoretical work has highlighted conspecific aggregation as a mechanism of reducing competitive exclusion and promoting diversity [2,3]. Tropical forests exhibit extensive aggregation of conspecific trees at scales ranging from a few meters to a few hundred meters [4,5,6]. We demonstrate that dispersal morphologies are strongly correlated with spatial distributions for hundreds of tree species, and with the community structure of tropical forests. Limited dispersal is known to cause spatial aggregation among seeds and seedlings of pioneer trees [11]. Establishing a link between dispersal mechanisms and spatial patterns at the community level would help close the gap in the ‘‘demographic loop’’ that separates observations of limited seed dispersal from the long-term consequences of dispersal for tree populations [7,12,13]. We hypothesize that trees of a species with limited seed dispersal will be tightly clustered in space, whereas a species with a mechanism for long-distance seed dispersal will exhibit less clustering or even spatial randomness
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