以資源防禦理論探討疣尾蝎虎覓食時的種內敵對行為

Abstract

敵對行為(Agonistic behavior)是動物常用於競爭資源的手段，資源防禦理論(Resource defense theory)指出動物展現的攻擊性(Aggressiveness)可能會隨著競爭者數量及資源量的增加而上升、下降或呈現先升後降的變化。疣尾蝎虎(Hemidactylus frenatus)常於夜間聚集捕食牆上趨光的昆蟲，個體之間偶有敵對互動。牠們的種內攻擊性在過往文獻陳述中多有分歧，其是否受競爭者、食物量等因子影響也仍待釐清。本研究透過室內操弄實驗檢視兩個變級的競爭者數量及三個變級的食物量相互組合下疣尾蝎虎展現的敵對行為。結果顯示，疣尾蝎虎在競爭者較多的情況下展現的攻擊性大致較低，包括長距離敵對互動比例較低、碰面發生敵對的比例較低、達中強度敵對行為的比例較低，以及互動時間較短；但同時優勢個體卻會展現更高比例的高強度敵對行為。優勢個體展現高強度敵對行為的比例同時受食物量影響，隨食物增加略呈先升後降的變化；而當非優勢個體碰面時，互動時間亦隨食物量呈先升後降的變化。本研究證實了競爭者數量及食物量皆對疣尾蝎虎覓食時的種內敵對行為有多層面的影響，也進一步發現群內的社會地位會影響這些行為反應，提供了資源防禦理論應用於在爬蟲類行為研究的罕例。

Agonistic behavior is commonly adopted by animals for competing resources. Resource defense theory points out that the aggressiveness of animals is affected by competitor numbers and resource value. As these factors increase, the aggressiveness might increases, decreases, or has a quadratic change. Individuals of Hemidactylus frenatus often aggregate around the lights and compete on insect prey. Results of previous studies on the intraspecific aggressiveness of this species were contradictory, and whether its aggressiveness is affected by abovementioned factors is also unknown. An indoor experiment, manipulating 2 levels of competitor numbers and 3 levels of food abundance, were thus conducted to clarify their effects on the aggressiveness of foraging H. frenatus. The results indicated that the aggressiveness was generally lower when there were more competitors, i.e., lower long-distance agonistic ratio, overall hostility ratio, median intensity ratio, and interaction time. However, dominant geckos tended to show a higher ratio of high intensity behavior at the same time. This ratio was also affected by food abundance and showed a quadratic response along with the increasing food abundance. A quadratic response was also found in the interaction time of encounters between subordinates. The study confirmed that both competitor numbers and food abundance have effects but may act differently on intraspecific agonistic behavior of H. frenatus, and the importance of social status was also revealed. This study provides a rare example of applying resource defense theory on agonistic interaction of reptiles.