[Article] 鼠魚的競爭與親緣關係決定群聚結構
原文標題：Competition and phylogeny determine community structure in Müllerian co-mimics
Until recently, the study of negative and antagonistic interactions (for example, competition and predation) has dominated our understanding of community structure, maintenance and assembly1. Nevertheless, a recent theoretical model suggests that positive interactions (for example, mutualisms) may counterbalance competition, facilitating long-term coexistence even among ecologically undifferentiated species2. Müllerian mimics are mutualists that share the costs of predator education3 and are therefore ideally suited for the investigation of positive and negative interactions in community dynamics. The sole empirical test of this model in a Müllerian mimetic community supports the prediction that positive interactions outweigh the negative effects of spatial overlap4 (without quantifying resource acquisition). Understanding the role of trophic niche partitioning in facilitating the evolution and stability of Müllerian mimetic communities is now of critical importance, but has yet to be formally investigated. Here we show that resource partitioning and phylogeny determine community structure and outweigh the positive effects of Müllerian mimicry in a species-rich group of neotropical catfishes. From multiple, independent reproductively isolated allopatric communities displaying convergently evolved colour patterns, 92% consist of species that do not compete for resources. Significant differences in phylogenetically conserved traits (snout morphology and body size) were consistently linked to trait-specific resource acquisition. Thus, we report the first evidence, to our knowledge, that competition for trophic resources and phylogeny are pivotal factors in the stable evolution of Müllerian mimicry rings. More generally, our work demonstrates that competition for resources is likely to have a dominant role in the structuring of communities that are simultaneously subject to the effects of both positive and negative interactions.
這篇文章有兩個重點，第一個是作者們重建鼠魚亞科 (Corydoradinae) 的親緣關係，並用這個樹推測不同擬態群的斑紋是獨立演化出現，並非因為親緣關係相近導致的遺傳限制；第二個是作者假設一個擬態群包含這麼多種類共棲，從生態上來說，可能會因為利用資源相同導致種間競爭，結果應該是有競爭優勢的物種會排除較弱勢的物種，多樣性應該會降低，但這與觀察到的事實相反，因此作者們推測可能在食物資源的利用上會有區隔，他們利用同位素分析鼠魚腸道內的碳與氮含量，發現在擬態的鼠魚中的確有食物組成上的不同，因此這篇提供一個在共棲擬態生物間，會因為食物利用不同減少競爭的證據。
這篇文章提供一個水中擬態群的證據，文章的角度也從生態共棲的方向切入，的確是篇很好的論文，但其中仍有許多疑問，像是雖然鼠魚可能利用不同的食物，但在人工飼養的環境下，鼠魚沒有食物上的偏好，因此鼠魚的同位素組成有差異是否來自取食偏好或是自身的生理反應所導致仍不清楚。若是以鱗翅目來說，棲位的分割可能來自於不同的飛行高度，或是幼生期的寄主利用不同所導致，因此這個理論的適用性仍需要進一步的討論。
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