Relationship between wing form and dispersal distance in the fruits of Carpinus (Betulaceae) and Pterocarya (Juglandaceae)

Background/Question/Methods

Dispersal of organisms is one of the most important determinants in the establishment of spatial patterns in ecosystems. But because flowering plants are immobile organisms, their dispersal almost solely depends on the utilization of the movement of wind, water, and animals to carry their offspring into new localities. Effectiveness of this strategy depends on modifications to fruit form specific to the type force being exploited. The most common type of modification for wind dispersal, and the type with the highest morphological diversity, is the winged seed. Within Fagales, and over angiosperms as a whole, very similar wing structures have evolved independently. This repeated evolution suggests significant evolutionary pressures for certain morphologies, but the exact relationship between fruit form and dispersal patterns in winged seeds remains unresolved. Previous experiments measuring the descent rate in other angiosperm groups have identified potentially important morphological characters for dispersal, but the importance of these characters during natural dispersal events is unclear. To elucidate this relationship, I performed field experiments using three isolated trees from the genera Carpinus (Betulaceae) and Pterocarya (Juglandaceae). For each tree, seed litter was collected from transects on the North and South sides of the tree. The morphology of these collected fruits was then analyzed.

Results/Conclusions

From these collections, the seed distributions were identified.  The patterns of these distributions were similar to previous observations in other wind dispersed groups, but differences in seed distributions on the North and South side of each tree were detected. These differences suggest that one species may have different migration capabilities depending on the direction of migration. Knowledge of this kind of differential migration ability could become even more important when predicting the migration patterns in the face of rapid climate change. Results from morphological analyses suggest that the same morphological character found to be important in experimental seed drops, wing loading, is also important in natural dispersal events, but only at a certain distance away from the parent tree. Because of the potential far-reaching effects of spatial patterning on ecological processes, an understanding of dispersal patterns and morphological effects on dispersal is essential towards understanding those mechanisms macroecological and macroevolutionary patterns of clades.