地形變異對種子傳播及傳播限制之影響

Abstract

種子傳播限制（Dispersal limitation）為維持物種多樣性之重要機制，並影響族群、群聚、生態系統等不同層級。儘管種子傳播限制的重要性經常被討論，但少有文獻探討生物及非生物因素影響傳播限制的程度。本研究之目的為探討地形變異對於種子傳播及傳播限制之影響。研究地點位於墾丁高位珊瑚礁森林10公頃動態樣區，自2006年8月至2010年10月，藉由72個種子網每週收集種子。本研究使用修正型逆向模式分析法發展四種候選模式，分別模擬不同層面的地形變異性對種子傳播之影響。分析物種共六種：紅柴（Aglaia formosana）、茄冬（Bischofia javanica）、咬人狗（Dendrocnide meyeniana）、九芎（Lagerstroemia subcostata）、血桐（Macaranga tanarius）及山菜豆（Radermachia sinica）。本研究以地形凹凸度（Convexity）作為地形變異性之變數。傳播限制之程度以半變異圖模式（Semivariogram model）計算，用以比較異質性與同質性地形對於傳播限制之影響。結果顯示：地形變異的程度顯著影響種子傳播；對於所有物種，地形不僅影響種子產量，也影響傳播過程。此外，異質性環境的傳播限制程度較同質性環境更強。目前地形凹凸度之尺度可能無法反應實際地形之複雜程度，未來若以更詳細之尺度描述地形，並配合長期資料及確認傳播媒介種類，將有助於更瞭解此樣區之種子分布機制。

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.