生物體型大小常被外在生態因素所影響，因此要瞭解一個地區的生態，生物體型是一個重要的指標。本研究發現在東沙島之皺紋陸寄居蟹 (Coenobita rugosus) 體型遠大於其它島嶼或生態島的同種類寄居蟹。為了要瞭解造成體型差異的機制為何，本研究驗證了幾個假說 : 1.殼資源是否足夠 2. 寄生蟲影響3.種內或種間競爭 4.天敵因素 5. 食物充裕與否。前四個假說的初步測試皆沒有發現支持的證據，例如東沙的殼資源狀況較其他地方來得差、不論東沙或西子灣僅發現少數個體有體外寄生蟲、各個調查地區的密度變異度均高、年齡群數均同 (在東沙並不是因為年齡大而造成體型大)。由2013與2014東沙島與西子灣之皺紋陸寄居蟹年齡群結果顯示，東沙島在第2013及2014兩年之第二年齡群的皺紋陸寄居蟹成長速率顯著較快於西子灣，因此支持成長速率較快造成東沙島與其它生態島同種類之體型差異。而初步研究發現由肥滿度指標 (Condition index) 支持東沙島皺紋顯著好於其它生態島，間接支持東沙島皺紋陸寄居蟹吃得好的假說。另外在東沙島夏季時發現大量皺紋陸寄居蟹於海草碎屑堆上覓食，相較於其他調查區域並沒有大量海草供食，因此推測是由東沙島提供充足的海草供皺紋陸寄居蟹食用。由食物喜好實驗中，東沙島皺紋陸寄居蟹顯著喜好海草碎屑高於濱海落葉；西子灣皺紋陸寄居蟹對海草碎屑及濱海落葉喜好度並無顯著差異。而餵食實驗顯示東沙島皺紋陸寄居蟹在餵食海草組之成長率顯著快於餵食海濱落葉組；西子灣皺紋陸寄居蟹於餵食海草組及濱海落葉組中，成長率沒有顯著差異。由本實驗支持造成皺紋陸寄居蟹體型差異的原因在於東沙島充沛的海草碎屑使得當地皺紋陸寄居蟹成長較快。

The body size is usually influenced by ecological factors. Reversely, we could study ecology from body sizes of organisms. In this study, we found that the body size of land hermit crabs (Coenobita rugosus) at Dongsha Island, South China Sea was bigger than that in other (eco) islands. To understand the underlying mechanisms, we tested a few hypotheses : (1) shell resource (2) parasites impact (3) competition (4) predation (5) food. We did not find supporting evidence for the first four hypotheses, as shells used by Dongsha were in poorer condition than elsewhere, very few individuals had external parasites at Dongsha or Siziwan, densities were highly variable within sites, and cohort numbers are the same between sites, i.e., Dongsha crabs were not larger due to older ages. The size differences between age 1 and 2, an index of growth rates, in both 2013 and 2014, was greater at Dongsha Island than at Siziwan. The condition index of C. rugosus is also significantly greater at Dongsha Isalnd than at Siziwan. These phenomena suggests that crabs at Dongsha may eat better. There are large amount of seagrass debris accumulated at the shore of Dongsha Island but none at Siziwan, thus we evaluated the possible role of seagrasses as food item of C. rugosus at both sites. Crabs at Dongsha prefer seagrasses to dicot leaves, but no such difference was found in crabs from Siziwan where the latter was the main food source. In feeding experiment, growth increment was faster in crabs from Dongsha feeding on seagrasss than dicot leaves; no such difference was found in Siziwan crabs. The above evidence is compatible with faster growth hypothesis that contributes to the larger size of Dongsha crabs, and abundance of seagrass debris must have played a significant role at Dongsha shores.

目 錄
論文審定書.................................................................................................i
誌謝............................................................................................................ii
中文摘要...................................................................................................iii
英文摘要...................................................................................................iv
前言………………………………………..……………………..............1
材料與方法................................................................................................5
一、調查..................................................................................................5
二、年齡群分析及天敵假說驗證................................................................6
三、殼資源狀況分析.................................................................................6
四、食物豐度分析....................................................................................7
4.1狀況指標測試..............................................................................7
4.2食物喜好實驗..............................................................................7
4.3餵食海草與濱海落葉實驗.............................................................8
五、競爭與否分析....................................................................................9
六、寄生蟲檢視.......................................................................................9
結果..........................................................................................................10
討論..........................................................................................................15
結論..........................................................................................................18
參考文獻……………………………………………………….…….....19

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