臺灣木本植物物種豐富度沿海拔梯度變化—模式與機制

Woody species richness along elevation in Taiwan: patterns and mechanisms

林柏佑(Po-Yu Lin)

指導教授 ： 澤大衛

國立臺灣大學/生命科學院/生態學與演化生物學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202101126

摘要

在不同物種分類群中，數種物種豐富度與海拔梯度關係模式被提出，其中駝峰狀物種豐富度沿海拔梯度模式最為常見，此外多種解釋此駝峰狀模式的機制也被提出，如中間區域效應 (mid-domain effect)、生產力效應 (effect of productivity)、陸地面積效應 (effect of land area)、環境異質性效應 (effect of environmental heterogeneity) 及過渡帶效應 (ecotone effect)。然而，當沿環境梯度描述物種豐富度模式時，梯度間不同區域的不均勻採樣可能會誤導所描述之模式。本研究中，我們使用臺灣國家植被數據庫中的植被樣區來描述臺灣木本植物物種豐富度沿海拔梯度變化的模式，並比較以樣區數量或取樣完整性為基準的物種豐富度標準化之差異，最後我們檢定不同機制用以解釋物種豐富度沿海拔變化之關係。
　　首先，將臺灣自海平面至最高峰劃分為十七個海拔帶，對每個海拔帶的物種豐富度以樣區數量或取樣完整性為基準進行標準化，接著描述標準化後物種豐富度沿海拔梯度變化模式。以簡單線性回歸檢定不同機制對物種豐富度沿海拔梯度變化模式的解釋量，其中，中間區域效應以假設模型 (null model) 表示，陸地面積效應以面積的平方根表示，環境異質性效應以地形崎嶇指數表示，生產力效應以潛在蒸發散量表示，並藉由不同變數的乘積檢定不同效應間的交互作用對此模式的解釋量。而過渡帶效應，則以每個海拔帶內物種分佈的平均海拔標準差量化。
　　結果發現，物種豐富度沿海拔梯度變化模式呈駝峰狀，物種豐富度最大值落在中低海拔 (約1000公尺)，而模式形狀並未因標準化基準不同而有所差異。陸地面積效應和環境異質性效應的交互作用有最大的解釋量，而中間區域效應本身並不顯著地解釋物種豐富度沿海拔梯度變化模式，但當與陸地面積效應或生產力效應交互作用時，中間區域效應則開始表現其顯著性。而過渡帶效應，標準差沿海拔梯度變化模式有兩個峰值，這兩個峰值都位於兩個不同森林植被的邊界上，提供了過渡帶效應存在的證據。

關鍵字

物種豐富度與海拔梯度關係 ； 標準化 ； 陸地面積 ； 環境異質性 ； 生產力 ； 中間區域效應 ； 過渡帶效應

並列摘要

Several patterns of richness-elevation relationship were reported in different taxa. Among them, the hump-shaped richness-elevation relationship is the most common. Several mechanisms were also proposed to explain hump-shaped richness-elevation relationship, such as mid-domain effect (MDE), effect of productivity, effect of land area, effect of environmental heterogeneity, and ecotone effect. However, when describing richness patterns along environmental gradients, uneven sampling effort in different parts of the gradient may mislead the described patterns. In this study, we used vegetation plots from the National Vegetation Database of Taiwan to describe the pattern of woody species richness along elevation in Taiwan and compare plot-based and completeness-based standardization. Then, we tested alternative mechanisms explaining the richness-elevation relationship.
Firstly, we divided elevation of Taiwan into 17 elevation bands, and pooled vegetation plots into each elevation band. We standardized richness of elevation bands based on fixed number of plots and fixed completeness and used the standardized values to describe pattern of woody species richness along elevation. Simple linear regression was performed to test how much different mechanisms can explain the observed richness-elevation pattern. MDE was represented by null model, effect of area by square-rooted sizes of area, effect of heterogeneity by topographic ruggedness index, and effect of productivity by potential evapotranspiration. We also tested the regression of richness to the interaction between each two mechanisms by multiplying the values of the variables they are represented by. For ecotone effect, we analyzed the standard deviation of mean elevations of species distribution.
The results show that the patterns of woody species richness along elevation are hump-shaped, with the species maxima are at lower middle elevation (around 1000 m a.s.l.), and both standardization bases did not make the pattern different. Interaction of effects of land area and heterogeneity can explain the most variation in species richness. MDE by itself is not significant, but becomes significant when interacting with the effect of land area or productivity. For ecotone effect, the pattern of standard deviations along elevation has two peaks. Both peaks are on the boundaries of lower and higher forest vegetations, which provides evidence that ecotone effect is present.

並列關鍵字

richness-elevation relationship ； standardization ； land area ； environmental heterogeneity ； productivity ； mid-domain effect ； ecotone effect

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