穆氏擬態的多樣性：捕食者的最佳取食策略造就多態性的擬態環
photo from Elias Marianne
摘要
The convergent evolution of warning signals in unpalatable species, known as Müllerian mimicry, has been observed in a wide variety of taxonomic groups. This form of mimicry is generally thought to have arisen as a consequence of local frequency-dependent selection imposed by sampling predators. However, despite clear evidence for local selection against rare warning signals, there appears an almost embarrassing amount of polymorphism in natural warning colors, both within and among populations. Because the model of predator cognition widely invoked to explain Mullerian mimicry (Muller’s “fixed nk” model) is highly simplified and has not been empirically supported; here, we explore the dynamical consequences of the optimal strategy for sampling unfamiliar prey. This strategy, based on a classical exploration–exploitation trade-off, not only allows for a variable number of prey sampled, but also accounts for predator neophobia under some conditions. In contrast to Müller’s “fixed nk” sampling rule, the optimal sampling strategy is capable of generating a variety of dynamical outcomes, including mimicry but also regional and local polymorphism. Moreover, the heterogeneity of predator behavior across space and time that a more nuanced foraging strategy allows, can even further facilitate the emergence of both local and regional polymorphism in prey warning color.
在開始前，我們先思考一件事：如果擬態是十分有用的禦敵策略，那麼物種在演化的初期發展出一個紋路後，是否應該其他的物種都加入擴大這個擬態群，讓這個紋路變的廣泛的有用結果大家都長的一樣，更增強這個紋路的作用才對？
但現實中明顯不是這樣，各種不同區域的擬態群各自林立，物種內出現各種不同的多態型，這代表上面那個假設必然出了什麼狀況，才會讓這個假設與實際上差異這麼大。
這篇所使用的方法是大家都頭痛的數理模型，考慮不同的參數後進行模擬，通常這類型的文章考慮的不外乎有幾個因子：防禦/非防禦獵物的比例，捕食者攻擊的頻率，記憶力，一些學習參數等等，而這個研究考量的是「捕食者的最佳取食策略」，也就是透過計算攻擊防禦/非防禦獵物的比率，來達到利益的最大化，然後跟傳統的穆氏擬態的數學模型（捕食者一定要透過攻擊固定數量的獵物才能讓利益最大化）比較。結果顯示這個新的模型比較能夠解釋現實上的狀況，也就是解釋為何擬態中的多態型能夠穩定的存在。捕食者透過挑選防禦/非防禦能讓捕食效益產身變化外，其本身的恐新症（neophobia）在某種情況下也會成為影響挑選獵物的因子之一。
結論上來說，就是用數理的方式告訴大家捕食者如何維持多態型的穩定，不過這個穩定在之前的研究中也有些討論，可能是來自微棲地的分隔所造成。
老話一句，電腦上看起來是這樣，那在自然環境中看起來又是怎樣呢？
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