The question of why some introduced species become invasive has captivated ecologists for more than 60 years (Elton, 1958). Many factors might contribute to invasiveness, but one of the most long‐standing and persistently compelling hypotheses is that invaders benefit from escaping their enemies (Keane and Crawley, 2002). Human‐mediated species introductions are inherently long‐distance dispersal events, and we know that only some components of a source community are established in new locations. The species that do establish will necessarily experience a novel set of biotic interactions (Mitchell et al., 2006). If these novel interactions result in reduced fitness losses to enemies, then an incipient invader would benefit immediately, and the resulting patterns of selection could also favor evolutionary reallocation of resources away from defenses and into traits that increase reproduction and/or spread, further increasing invasiveness (Fig. 1) (Blossey and Nötzold, 1995; Joshi and Vrieling, 2005).

Whether an evolutionary reduction in defenses has led to an increase in invasiveness has remained an open question in the field of invasion biology, despite many challenges and mixed support. The hypothesis was first articulated as the evolution of increased competitive ability (EICA), which combined enemy escape with optimal defense theory to predict that plant invaders will evolve increased allocation to vegetative growth or reproduction (whichever maximizes fitness in the new environment) in the absence of herbivores in their recipient communities (Blossey and Nötzold, 1995). The EICA hypothesis has since been expanded to include a broader array of enemies and greater complexity of defense interactions, but the core concept of invaders evolving increased competitive ability at the cost of defenses has remained (Joshi and Vrieling, 2005; Mitchell et al., 2006). A number of individual studies have found evidence that supports predictions of EICA, but others have not, and meta‐analyses of these studies have themselves come to different conclusions about the degree of support for EICA (e.g., Chun et al., 2010; Felker‐Quinn et al., 2013; Rotter and Holeski, 2018).

In this essay, we argue that to test the compelling evolutionary hypotheses underlying EICA, we will be better served by reconsidering what we are measuring and how the evolution of defense traits and subsequent trade‐offs can be expected to contribute to invasiveness.

为什么一些引进的物种成为入侵物种的问题已经吸引了生态学家60多年了（Elton，1958年）。许多因素可能会导致入侵，但最长期且持续存在的假说之一是，入侵者从逃避敌人中受益（Keane and Crawley，2002）。人为介导的物种引进本质上是远距离传播事件，我们知道在新的地点仅建立了源社区的某些组成部分。确实建立起来的物种必然会经历一系列新的生物相互作用（Mitchell等，2006）。）。如果这些新颖的相互作用减少了对敌人的适应性损失，那么初期的侵略者将立即受益，并且由此产生的选择模式也可能有利于资源的防御性进化重新分配，而不再是防御，而是转移到可增加繁殖和/或传播的性状上，从而进一步提高入侵性（图1）（Blossey和Nötzold，1995年； Joshi和Vrieling，2005年）。

尽管存在许多挑战和混合支持，但防御性的进化降低是否导致了入侵性的提高仍是入侵生物学领域的一个悬而未决的问题。该假说首先被阐述为增强竞争能力（EICA）的进化，该理论将敌人逃逸与最佳防御理论结合在一起，以预测植物入侵者在缺乏营养的情况下将向营养生长或繁殖（在新环境中最大化适应性）分配更多的分配。接收者社区的食草动物数量（Blossey和Nötzold，1995年））。此后，EICA的假设已扩展到包括更广泛的敌人和更复杂的防御互动，但入侵者以防御为代价发展出增强的竞争能力的核心概念仍然存在（Joshi和Vrieling，2005； Mitchell等，2006）。许多个体研究发现了支持EICA预测的证据，但其他人则没有，对这些研究的荟萃分析本身就对EICA的支持程度得出了不同的结论（例如Chun等人，2010； Felker ‐ Quinn等人，2013年; Rotter和Holeski，2018年）。

在本文中，我们认为，要检验EICA背后令人信服的进化假说，可以通过重新考虑我们正在测量的内容以及如何预期防御性状的演变以及随后的权衡取舍对入侵性的贡献来为我们提供更好的服务。