翠斑草蜥在晨曦時刻與鳥類掠食風險下之隱蔽效果與行為模式
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2020
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Abstract
最佳逃脫理論（optimal escape theory）指出獵物應該在逃離的損失和獲利中取得平衡，並依此調整逃脫的行為。依據過去相關研究所提出的模型，可計算生物與非生物因子對逃離行為損失和獲利的效應，進而得知這些因子如何影響獵物的逃離決定。本研究以翠斑草蜥（Takydromus viridipunctatus）為對象，探討隱蔽效果（crypsis）、掠食者活動、性別以及溫度如何影響草蜥的逃離行為。草蜥於夜間在草上睡眠並以自身的隱蔽躲避鳥類的掠食。但隨晨曦光環境的漸強，草蜥在草上的隱蔽效果可能下降。因此本研究記錄草蜥與其主要掠食者牛背鷺（Bubulcus ibis）在晨曦時的行為模式，同時記錄光環境的變化與測量草蜥的反射光譜，再以掠食者的視覺模型估算草蜥的隱蔽效果。結果顯示在日出的前後，隨著隱蔽效果的下降與掠食者活動的增強，草蜥離開草的表面並向下移動，以躲避逐漸升高的掠食者風險。另一方面，本研究也發現雌性草蜥在繁殖季比雄性草蜥更早離開草面，這可能是因為雌性草蜥有比雄性草蜥有更高的殘餘生殖價值（residual reproductive value），因此需要更警覺掠食者的風險。同時，隨著溫度越高，草蜥也越晚離開草面。由於草蜥是外溫動物，溫度可能促進生理狀態進而增進逃脫能力，並產生較晚離開草面的行為。隱蔽效應、掠食壓力、性別、溫度這四個因子對草蜥行為的影響與先前解釋最佳逃脫理論的模型預測一致，並支持草蜥最佳化其行為以躲避掠食。總而言之，本研究呈現了獵物如何根據不同因子評估其逃離的損失與獲利，並做出將掠食風險最小化的行為決定。
Optimal escape theory has been studied for decades, which indicates that the prey should adjust its escape behavioral decision to balance the costs of fleeing or not fleeing. Several models have been proposed to explain how biotic and abiotic factors effect on the costs thus influence the escape behavior. Here, I introduce a well-studied species, the green-spotted grass lizard Takydromus viridipunctatus, and investigated how crypsis, predator activity, sex and temperature effect on the behavior of the lizard in twilight environment. This diurnal lizard perches on the surface of the grass at night, which is regarded as crypsis to prevent avian predation from the top. In order to investigate the escape strategy of the lizard under ambient light condition, I recorded the behavior patterns of the lizards and its major predator (the cattle egret, Bubulcus ibis) during twilight period. The reflectance of lizards, the changing of simultaneous ambient light, and visual modeling of the egret were calculated by using spectrum meter and power meter. We found that the lizards left the grass surface to avoid the increasing predation risk of egret since the decreasing of crypsis effectiveness and increasing of predator activity. The female lizards escaped earlier than the males in the breeding season, which could be explained by the higher residual reproductive value than males. The air temperature has a positive correlation with a delayed fleeing timing, which may reveal the temperature effect on the physiology thus influence the ability of escape. These results are consistent with the predictions of crypsis from the models, showing how prey accesses its costs of fleeing or not fleeing according to different circumstances.
Optimal escape theory has been studied for decades, which indicates that the prey should adjust its escape behavioral decision to balance the costs of fleeing or not fleeing. Several models have been proposed to explain how biotic and abiotic factors effect on the costs thus influence the escape behavior. Here, I introduce a well-studied species, the green-spotted grass lizard Takydromus viridipunctatus, and investigated how crypsis, predator activity, sex and temperature effect on the behavior of the lizard in twilight environment. This diurnal lizard perches on the surface of the grass at night, which is regarded as crypsis to prevent avian predation from the top. In order to investigate the escape strategy of the lizard under ambient light condition, I recorded the behavior patterns of the lizards and its major predator (the cattle egret, Bubulcus ibis) during twilight period. The reflectance of lizards, the changing of simultaneous ambient light, and visual modeling of the egret were calculated by using spectrum meter and power meter. We found that the lizards left the grass surface to avoid the increasing predation risk of egret since the decreasing of crypsis effectiveness and increasing of predator activity. The female lizards escaped earlier than the males in the breeding season, which could be explained by the higher residual reproductive value than males. The air temperature has a positive correlation with a delayed fleeing timing, which may reveal the temperature effect on the physiology thus influence the ability of escape. These results are consistent with the predictions of crypsis from the models, showing how prey accesses its costs of fleeing or not fleeing according to different circumstances.
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Keywords
行為決定, 草蜥屬, 鳥類掠食, 最佳逃脫理論, 殘餘生殖價值, 視覺模型, 隱蔽, avian predation, behavioral decision, crypsis, optimal escape theory, residual reproductive value, Takydromus, visual modeling