Ecosystem size is known to influence both community structure and ecosystem processes. Less is known about the evolutionary consequences of ecosystem size. A few studies have shown that ecosystem size shapes the evolution of trophic diversity by shaping habitat heterogeneity, but the effects of ecosystem size on antipredator trait evolution have not been explored. Ecosystem size may impact antipredator trait evolution by shaping predator presence (larger ecosystems have longer food chains) and habitat complexity (larger ecosystems may have more diverse habitat structure). We tested these effects using threespine stickleback from bar‐built estuaries along the Central Coast of California. These stickleback populations are polymorphic for Ectodysplasin‐A (Eda), a gene that controls bony lateral plates used as antipredator defense. We inferred Eda genotypes from lateral plate phenotypes and show that the frequency of the complete (C) allele, which is associated with greater number of lateral plates, increases as a function of ecosystem size. Predator presence and habitat complexity are both correlated to ecosystem size. The strongest proximate predictor of Eda allele frequencies was the presence of predatory fishes (steelhead trout and sculpin). Counter to expectations, habitat complexity did not have a strong modifying effect on Eda allele frequencies. Our results point to the importance of ecosystem size for determining predator presence as being the primary pathway to evolutionary effects. Ecosystem size has received much attention in ecology. Our work shows that it may be an important determinant of adaptive evolution in wild populations.

中文翻译：

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生态系统的大小塑造了河口三脊刺棘背动物的反捕食者性状演变

众所周知，生态系统规模会影响社区结构和生态系统过程。人们对生态系统规模的进化后果知之甚少。一些研究表明，生态系统的大小通过塑造栖息地的异质性而塑造了营养多样性的演变，但是尚未探索生态系统的大小对反捕食者性状演变的影响。生态系统的大小可能会通过影响食肉动物的存在（更大的生态系统具有更长的食物链）和栖息地复杂性（更大的生态系统可能具有更多多样的栖息地结构）来影响反捕食者特征的演变。我们使用加利福尼亚州中部海岸的酒吧河口的棘脊棘背刺对这些效应进行了测试。这些棘背类种群对于Ectodysplasin-A（Eda），一种控制骨外侧板的基因，用作抗掠食者的防御。我们从侧板表型推断出Eda基因型，并显示与更大数量的侧板相关的完整（C）等位基因的频率随着生态系统大小的增加而增加。捕食者的存在和栖息地的复杂性都与生态系统的大小有关。Eda等位基因频率最强的最接近预测因子是掠食性鱼类（硬头鳟鱼和鱼）的存在。与预期相反，栖息地的复杂性并未对Eda产生强烈的影响等位基因频率。我们的研究结果表明，生态系统规模对于确定捕食者的存在至关重要，因为这是获得进化影响的主要途径。生态系统的规模在生态学中受到了很多关注。我们的工作表明，它可能是野生种群适应性进化的重要决定因素。