Abstract In this study, we explored how the quality of different patches, the costs of traveling between patches, and an individual’s competitive ability might affect their search ability and hence the distribution of eggs laid by the bean weevil (Callosobruchus maculatus). In the low-travel-cost treatment, irregardless of whether one or two females, which would entail competition, were provided, when there was one egg per seed on average, the distribution of eggs laid was concordant with the prediction of ideal free distribution (IFD). In the high-travel-cost treatment, the distribution of eggs laid by one female was not concordant with the prediction of IFD. In addition, the costs of traveling between patches decreased the longevity and fecundity of the female bean weevil. It was also found that in the high-travel-cost treatment, the eggs laid simultaneously by ten females were dispersed as predicted by IFD. Finally, it was found that the number of times of patch leaving had a significant effect on the distribution of eggs laid, while the mechanism of patch leaving was not only due to the pressure of the egg-load but also because the resource quality decreased to a specific threshold level.
摘要 本試驗目的是以理想自由分佈模式（Ideal free distribution, IFD）為理論基礎，透過豆象對資源區中寄主豆的搜尋與利用能力， 探討不均質的資源和資源區間距離的不同， 以及個體間競爭對個體的分佈及資源利用的作用。以四紋豆象（ Callosobruchus maculatus (Fab.)）及紅豆(Vigna angularis) 為材料， 結果發現當紅豆區間的距離很小時， 也就是對四紋豆象而言移動到另一個紅豆區花費能量很低時， 則不論是一隻雌蟲或是兩隻雌蟲競爭情形下，當豆象搜尋過資源區中所有的寄主豆時，其產卵分佈就和IFD 的預測相同，也就是與資源的分佈比一致； 然而當紅豆區間的距離加大時， 對四紋豆象而言移動到另一個紅豆區須花費較多能量，結果一隻雌蟲產卵情形就不符合IFD的預測。同時， 移動的花費還使得四紋豆象的壽命和總產卵量減少； 然而即使有移動的花費，十隻雌蟲競爭資源的結果使得產卵分佈符合IFD。此外，研究也發現轉換資源區次數會影響其產卵分佈； 而豆象離開資源區的機制並非是載卵壓力解除或是環境劣化到達臨界值， 即並非因為豆上卵的化學氣味增加至一定濃度。
| Key words: bean weevil, travel costs, ideal free distribution. | | 關鍵詞: 豆象、移動花費、理想自由分佈 |
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