Abstract

In this paper, we examined the breeding bird species richness along an elevational gradient in northern Taiwan. These data obtained from 144 sites were used to test the mid-domain model. We compared the species richness with expectations from the mid-domain models, and identified elevational ranges at which the species richness was excessive or depauperate in species, relative to expectations. In addition, we compared the observed spatial distributions of geographic ranges with those predicted by mid-domain models to explore how species richness deviations were produced. Along the entire elevational gradient, observed species richness in most sites obviously deviated from those predicted by mid-domain models. We hypothesize that asymmetrical hump-shaped curve of the species richness may come from the combination of the favorableness hypothesis, the productivity hypothesis, and the mid-domain effect. Comparisons between observed and predicted spatial distributions of geographic ranges indicated that the nonrandomness of the distributions of endpoints or midpoints was highly congruent with vegetation transitions along the elevational gradient. The time hypothesis may account for the nonrandomness below 500 m.

中文摘要

本報告係調查臺灣北部海拔梯度上的繁殖鳥類種豐富度。我們用調查所得144 筆資 料來檢驗其是否支持中間區域模式。首先我們比較鳥種豐富度的觀察值與中間區域模式的預測值，並且指出觀察值多於或少於預測值的海拔區段。再比較鳥種海拔分布範圍的所在位置，其觀察值與預測值的差異，以探究鳥種豐富度觀察值偏離預測值的原因。結果發現大部份的鳥種豐富度觀察值明顯偏離中間區域模式的預測值，並且觀察值在海拔梯度上呈現出不對稱駝型分布，可能是由喜好假說、生產力假說及中間區域效應的合成效應所產生。鳥種海拔分布範圍之上下限及中點，其觀察值偏離預測值之所在，與海拔梯度上的植被變換帶有高度的一致性。海拔分布範圍較小的鳥種多聚集於海拔500 公尺以下，則可能歸因於歷史因素。

Keyword: Bird species richness, Elevational gradient, Mid-domain effect, Taiwan.