在競爭資源的行為中，資源價值與動物的打鬥能力會是影響其決定是否投入打鬥的重要依據，資源價值可使個體評估打鬥獲得的好處，而打鬥能力則會影響個體評估打鬥中需付出的代價。資源擁有狀態的差異也可提供擁有資源的個體競爭上的優勢，因為資源擁有者通常攻擊性較強，較容易在打鬥中獲勝，此稱為擁有者優勢（ownership advantage）。擁有者優勢可能受到打鬥中其他因子的影響，如打鬥能力和/或打鬥經驗，導致不同打鬥能力的擁有者有不同的表現。在使用遮蔽物作為資源的物種中，不同個體可能因對遮蔽物評估的價值不同而影響使用遮蔽物的傾向，對遮蔽物的偏好會影響競爭的強度。本研究之目的為了解打鬥能力與遮蔽物使用程度如何影響擁有者優勢的展現。本研究使用北美紅樹林鱂魚（Kryptolebias marmoratus）作為實驗物種，提供遮蔽物作為資源，設計了四個實驗處理組：A. 雙方皆打鬥能力較好，僅目標個體（隨機決定）有遮蔽物、B. 雙方皆打鬥能力較差，僅目標個體（隨機決定）有遮蔽物、C. 目標個體打鬥能力較差且擁有遮蔽物，其對手打鬥能力較好但無遮蔽物、D. 目標個體打鬥能力較差，其對手打鬥能力較好，雙方皆無遮蔽物。我以雙方打鬥能力相同的A、B處理組檢測配對雙方的打鬥能力與遮蔽物使用程度對擁有者優勢與配對雙方打鬥意願之影響，以雙方打鬥能力不同的C、D處理組檢測打鬥能力較差的個體有無遮蔽物與遮蔽物使用程度對其獲勝率與雙方打鬥意願之影響。實驗結果發現雙方打鬥能力相同（A、B處理組）時，配對雙方的打鬥能力對擁有者優勢沒有影響，在雙方打鬥能力皆較差（B處理組）時有偵測到顯著的擁有者優勢，而雙方打鬥能力皆較好（A處理組）時其擁有者優勢則是接近顯著。而雙方打鬥能力不同（C、D處理組）時，打鬥能力較差的擁有者因為擁有遮蔽物，獲勝率得以提升，但仍低於打鬥能力較好的對手，顯示擁有者優勢無法彌補打鬥能力的劣勢。個體使用遮蔽物的程度只在雙方打鬥能力相同時有影響：入侵者越傾向使用遮蔽物，其打鬥意願越高；而擁有者越傾向使用遮蔽物，則越能展現擁有者優勢。

When animals compete for resources, the resource value and the animal's fighting ability will be important factors in deciding whether to engage in fighting. The resource value lets individuals know the benefit that can be gained from fighting, while an individual's fighting ability will affect the assessment of the cost of fighting. Differences in resource ownership status can also provide resource owners with a competitive advantage because resource owners are usually more aggressive and are easier to win in fights. This is called the owner advantage. The owner's advantage may be affected by other factors in fighting, such as fighting ability and/or fighting experience, causing owners with different fighting abilities to perform differently. In species that use shelter as a resource, individuals may assess the value of shelter differently, which may affect the tendency to use shelter and continuously affect the intensity of the contest. The aim of this study is to understand how fighting ability and sheltering tendency influence owner advantage. The experiment species for this study is Kryptolebias marmoratus. I designed 4 treatments to answer the questions: A. Both contestants have better fighting ability; only the focal individual (randomly assigned) has a shelter; B. Both contestants have worse fighting ability; only the focal individual (randomly assigned) has a shelter; C. The focal individual has worse fighting ability and shelter, and its opponent has better fighting ability but has no shelter; D. Both contestants have no resources. The focal individual has worse fighting ability, and its opponent has better fighting ability. I used treatment A and B to test how fighting ability and sheltering tendency influence owner advantage and the willingness of both contestants to fight. The treatment C and D were used to detect whether the individual has a shelter and sheltering tendency affects the winning probability and the willingness of both contestants to fight. The results show that in treatment A and B, the fighting ability doesn't impact the owner advantage. When both individuals have worse fighting abilities (treatment B), a significant owner advantage is detected; and when both individuals have better fighting abilities (treatment A), the owner advantage is close to significant. In treatment C and D, the owner with worse fighting ability has an improved winning probability because it has a shelter. But it’s still lower than the opponent with better fighting ability. This indicates the owner advantage can’t offset the disadvantage of fighting ability. The sheltering tendency of an individual only has an influence when the fighting ability of both individuals is the same: the more the intruder tends to use shelter, the higher its willingness to fight; and the more the owner tends to use shelter, the more owner advantage can be detected.

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