沖縄島西方諸島の留鳥種数と留鳥相
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概要
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沖縄島西海岸の沖に位置する慶良問諸島,久米島,粟国島,伊是名島,伊平屋島における留鳥の鳥類相の特徴を知るため,これらの島の面積と種数との関係を求めた｡得られた回帰直線に基づく種数の期待値と観測値とを比べたところ,渡嘉敷島と久米島での種数は期待値よりも小さかった｡渡嘉敷島での観測値が少ない理由は,観察が十分なされていないことによるほか,森林の樹種の単純さなどによるためと考えられる。逆に,伊是名島と粟国島では,種数の実測値は期待値よりも多かった｡これらの島には,他の島には生息していない種が1-3種見られたが,それらの中でコウライキジPhasianus colchicus karpowi(伊是名島)やシロガシラPycnonotus sinensis(粟国島)など導入・侵入種の存在が大きな役割を果たしていた｡慶良間諸島とそれ以外の島との留鳥相を比較したところ,慶良間諸島ではバンGallinula chloropus indicaなどの沼沢地を生息場所とする種が欠けていた｡これは,慶良間諸島では島の大部分が森林で覆われていて川や池がほとんどないためである｡このことは,環境の多様性が鳥類相の豊富さをもたらしていることを示している｡In order to know the characteristics of resident bird fauna in five islands from Kerama Islands and in four of Kume, Aguni, Izena and Iheya Islands off the western coast of Okinawa Island, we could obtain a linear relationship between the number of bird species in the islands and the area of these islands. Comparison of the actual number of species with the expected number based on the species-area relationship showed that the numbers of species in Tokashiki Is., Kerama Islands and Kumejima Is, were smaller than the expected one. Smaller number in Tokashiki Is. was thought to be due to the scarce survey frequencies and to a simple flora of forests at this island. On the contrary, the numbers of species in Izena Is. and Aguni Is. were larger than the expected. In these islands the introduced or invaded species, such as the pheasant, Phasianus colchicus karpowi (in Izena Is.) or the light-vented bulbul, Pycnonotus sinensis (in Aguni Is.), increased the actual number of species. Comparison of bird fauna between the islands in Kerama Islands and the other islands showed that bird species inhabiting rivers, ponds and swamps were few in the former. This is because the islands in Kerama have a large area of the forest but few of rivers and swamps, showing that diversified topography and land use result in the diversified bird fauna.
- 2008-03-31
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