玉山地區成熟林之鳥類群聚生態

Abstract

自民國八十一年一月至十月，於玉山山脈西側之沙?仙溪與楠梓仙溪流域之成熟林內進行繁殖季之鳥類群聚生態學研究，共設置五十個取樣站，海拔範圍由1400公尺至3700公尺，由低至高包括常綠闊葉林、針闊葉混合林、雲杉林、鐵杉林、冷杉林及圓柏灌叢等六類主要植群型。以圓圈法估算各取樣站之繁殖季鳥類密度，並量取三十項環境因數，鳥類之食性及覓食行鳥則主要引用其他研究之結果。本研究之目的在於：（一）瞭解不同海拔高度下成熟林內鳥類群聚組成、群聚介量變化。（二）鳥類生態同功群之分類及其分佈。（三）瞭解不同鳥類之海拔分佈及其限制原因、棲息地選擇。 研究期間共記錄到五十九種鳥類。各植群內鳥類群聚組成有明顯差異。以鳥類密度做群集分析，各取樣站分為六類鳥類群聚型式，闊葉林分島上層闊葉林（＞2000m）與下層闊葉林（＜2000m）二類，鐵杉林與冷杉林合併為一類，其餘林型則各自成為一類鳥類群聚型式。鳥類總密度與種數以闊葉林、混合林及雲杉林最高，之後隨海拔遞昇而遞減。鳥類多樣性以闊葉林及混合林最高，之後隨海拔遞昇而遞減。鳥類均勻度以圓柏灌叢最高，之後隨海拔遞降而遞減。鐵杉林與冷杉林內鳥類群聚之相似度最高（0.80），闊葉林與圓柏灌叢最低（0.00），海拔差距愈大，植群間相似度愈低。鳥類多樣性與枝葉結構多樣性及樹木種類多樣性有顯著正相關（r＝0.62，p＜0.01）（r＝0.74，p＜0.01）。由食性、覓食方式及覓食場所，以群集分析將鳥類分成十二個生態同功群：肉食性猛禽（二種）、地面種食者（一種）、地面雜食者（七種）、地面蟲食者（七種）、灌叢蟲食者（十二種）、樹木果食者（一種）、樹木雜食者（十種）、樹木蟲食者（十種）、樹幹覓啄者（一種）、樹幹啄木者（三種）、樹木飛啄者（一種）、空中飛擊者（四種）。闊葉林、混合林與雲杉林擁有較多生態同功群，鐵杉林與冷杉林居中，圓柏灌叢最少。闊葉林以樹木雜食者及灌叢蟲食者最多，混合林以樹木雜食者最多，三類針葉林以樹木蟲食者最多，圓柏灌叢以地面蟲食者佔大多數。59％可解釋之鳥類海拔分佈上下限是因連續梯度變化造成，25％由生態交會帶造成，只有9％由競爭互斥造成。所有結果顯示鳥種間競爭現象並不明顯，鳥類與環境間關係則明顯而強烈。詳細的互動關係與機制，則必須更進一步研究。

I studied avian communities of mature primary forests in Mt. Yushan along 1400-3700m elevational gradients between January and October, 1992. Fifty sample stations along Shalishian Valley and Nantzshian Valley, located at western ridge of Mt. Yushan, were selected. Six major vegetation zones were covered, from lower to higher elevations: broadleaf forests, mixed forests, and conifer forests of Spruce, Hemlock, and Fir, and Juniper shrub. Breeding bird densities were recorded in each station using the circular-plot method. To investigate the relationship between habitat features and bird communities, I measured 30 habitat variables in each sample station. I also collect information on diets and foraging behavior of each bird species observed. The main focuses of this study are: (1) Compositions and parameters of avian communities among these vegetation zones. (2) Classification and distribution of avian guilds. (3) Eelevational distribution and its processes, habitat selection of bird species. Densities of 59 bird species populations were collected in this study. Each forest shows distinct bird compositions. Six bird community types be discerned by cluster analysis based on bird densities observed on each sample station. This classification is associated with vegetation types, with the broadleaf forests be split into two types: higher (> 2000m) and lower (< 2000m), Hemlock and Fir forests being clustered into one type, the others are separately grouped by their vegetation types. Broadleaf forests, mixed forests and Spruce forests have higher total bird density and number of species, then declines with the increase of elevation. Species diversity are higher in broadleaf forests and mixed forests, then declines with the increase of elevation. Hemlock and Fir forests shows highest similarity (0.80), while broadleaf forests and Juniper shrub shows the lowest (0.00). Similarity between forests decline with the increases of their elevational distance. Bird species diversity show significant correlation with foliage height diversity (r=0.62, p<0.01) and tree species diversity (r=0.74, p<0.01). By cluster analysis based on diets, foraging tactics and foraging substrates, I divided each bird species observed into 12 guilds: raptorial carnivores (2 species), ground graminivore (1 species), ground omnivores (7 species), ground insectivores (7 species), bush insectivores (12 species), tree fruitivore (1 species), tree omnivores (10 species), tree insectivores (10 species), bole gleaner (1 species), bole peckers (3 species), tree hover (1 species) and air flycatchers (4 species). Broadleaf forests and mixed forests are dominated by tree omnivores and bush insectivores, three coniferous forest by tree insectivores, and the Juniper shrub by ground insectivores. Broadleaf forests and mixed forests have more guilds than others. I tested the three models that explained the distributions of species along elevational gradients. Continuous gradient changes account 59% for distributional limits, 25% for ecotone, and only 9% for competitive exclusion. The results did not suggest a significant inter-species competition within the bird communities, however, a close relationship between the bird communities and their habitats was detected. The details of interactions and processes need advanced studies.