The Effects of Topographic Variation on Seed Dispersal and Dispersal Limitation

Dispersal limitation has been widely recognized as an important mechanism to maintain species diversity, thus lead to significant consequences at the population, community and ecosystems levels. Despite the importance and prevalence of dispersal limitation, few studies have evaluated how dispersal limitation may be altered by abiotic and biotic factors. The objective of this study was to quantify the effect of one abiotic factor, topographic variation, on seed dispersal and its consequences on dispersal limitation. The study was carried out in the Kenting Forest Dynamics Plots in the Southern Taiwan. Seventy two seed traps along four transects were established to collect reproductive parts of woody plants weekly from August 2006 to April 2010. A modified inverse modeling was applied to develop four alternative dispersal models that simulated various effects of topographic variation on seed dispersal. A set of models were developed for each of the study species, including Aglaia formosana, Bischofia javanica, Dendrocnide meyeniana, Lagerstroemia subcostata, Macaranga tanarius, and Radermachia sinica. The degree of dispersal limitation at homogeneous and heterogeneous environments was evaluated by semivariograms. The results indicated that topographic variation exerted significant effects on seed dispersal. Topographic variation could influence seed dispersal via both source and path effects for all of the study species. Furthermore, dispersal limitation was stronger in a heterogeneous habitat than homogeneous habitat. The prediction of heterogeneous model could be improved by accurately describing the topography and more long-term data of Kenting plot.