Cell Press | 本地和引进物种之间的定量差异

Quantifying Differences Between Native and Introduced Species

地理起源被认为是物种表现的一个重要预测因素，因为与本地物种相比，外来物种通常更丰富，缺乏天敌，具有新的防御机制，并具有独特的进化历史。然而，最近的证据表明，许多外来物种在它们的本地和引入的范围内表现出相似的行为，许多本地物种在不受种群规模限制的情况下可以表现出“入侵”行为。这些结果表明，本地种和外来种可能遵循相似的群落组成规律。我们认为，一旦统计上考虑到性状和进化的相似性，地理起源提供的信息很少，只有社区水平的性能检验提供了入侵假设的充分检验。

从历史上看，外来物种被认为是进化上的新物种，与本地物种“不同”。然而，最近的研究对这些假设提出了质疑，因为促进成功引进的物种和本地物种的特征和因素可能相似。我们提倡一种新的统计框架，利用物种间进化和生态差异的量化指标来检验不同的力量是否控制本地物种和外来物种的成功。在两个案例研究中，我们发现本地物种和外来物种似乎都遵循着同样的“规则”。我们认为，结合物种间性状和进化历史的数量差异，可能在很大程度上解释了许多感知到的地理起源的影响，从而导致对促进生物成功的因素进行更严格和一般的测试。

Figure I. Hypothetical Demonstration of (A) a Sampling Effect that Introduced Species Are Simply More Fecund and (B) Real Differences Between Introduced and Native Species.

Figure I.A Simplified Conceptual Diagram Showing How Our Proposed Framework Assesses Community Assembly Mechanisms. (A) Demonstrates a situation where both native and introduced species undergo environmental filtering. In the left panel, both native and introduced species in the community are phylogenetically clustered compared with the regional community. In the middle panel, the centered trait value declines with increasing relative abundance. The right panel presents the relationship between the absolute value of the centered trait value and the relative abundance. (B) Demonstrates the same situation but only introduced species undergo environmental filtering.

Figure 1.Coefficient Estimates for the Effect of Mean Phylogenetic Distance (MPD), Mean Trait Distance (MTD), Introduced Status (Introduced), and Their Interactions on the Occurrence and Abundance of Species in 25 Forest Stands. Points are colored for significance [white, not significant; grey, marginally significant (80% CI excludes zero); black, significant (95% CI excludes zero)]. (A) MPD had no effect on native species’ occurrence in most forest stands. (B) Functionally dissimilar species were less likely to occur in younger forests. (C) Introduced species were less likely to occur in many older forests. (D) MPD and (E) MTD effects on species’ presence did not differ from those of native species in any forest stand. (F) Phylogenetically and (G) functionally dissimilar native species had lower abundance in almost all forests. (H) Introduced species had higher relative cover than natives in some young forests. (I) The effect of MPD on species’ abundance was similar for native and introduced species in all forests, but (J) introduced species experienced weaker environmental filtering than natives in young forests.

Figure 2.Coefficient Estimates for the Effects of Mean Phylogenetic Distance (MPD), Introduced Status (Introduced), and Their Interactions on the Occurrence and Abundance of Species in Four Grassland Sites. Numbers to the right of each confidence interval indicate the probability that the coefficient is greater than 0, such that either extremely high (>0.95) or extremely low (<0.05) numbers indicate significant effects. (A) Species were less likely to occur at sites with low species richness, but (B) MPD did not affect the probability of occurrence at any site. (C) Introduced species were more likely than natives to occur at the site with 34 species, but (D) were also unaffected by MPD. (F) Native species underwent significant environmental filtering at the most speciose sites where (G) introduced species were relatively more abundant. (F) The lack of significant interactions indicates that MPD affects native and introduced species similarly at all sites.

我们的统计模型的灵活性使研究人员能够调整它来回答许多不同的和重要的问题(见未解决的问题)。例如，这里提出的两个案例研究都跨越了一个相对较小的环境梯度。因此，入侵生物学家可能会问，本地物种和外来物种的群落组装机制如何在大陆尺度的温度、海拔、降水、物种丰富度和群落组成的巨大变化中发生变化。我们的模型还可以通过将年份作为分组变量而不是地点，并将年际环境变量作为预测变量来纳入社区聚集的时间变化。最后，我们的模型可以扩展到考虑多个层次，使研究人员能够研究多个空间尺度上的环境变化如何影响社区聚集。在每个水平都可以纳入相关的预测因子，这样可以同时测试微生境中物种丰富度、土壤氮等的变化，以及站点水平上物种丰富度、降水、温度等的变化是否会影响群落的构建。

尽管几十年来的理论假设都认为外来物种需要独特的生态假说来解释它们的传播和成功，但最近的证据表明，本地物种和外来物种具有相似的演替轨迹、叶片碳捕获性状、化学防御、敌人释放、土壤化感作用和群落构建机制。这些结果表明，外来物种和本地物种可能因非常相似的原因而茁壮成长。在这里，我们提出了一个新的定量框架，使研究人员可以更好地检验相似的组装规则是否控制本地和外来物种的存在/缺失和丰度。与传统的引入和本地测试相比，这种方法为入侵过程提供了更严格和定量的测试，并有助于解决更大的问题，即地理新颖性是否传递了超越物种之间可量化差异的内在优势，包括它们的特征、进化相似性和对关键环境驱动因素的反应。