J Plant Ecol ›› 2020, Vol. 13 ›› Issue (5): 601-610.DOI: 10.1093/jpe/rtaa048

• Research Articles • Previous Articles     Next Articles

Scale dependence in the phylogenetic relatedness of alien and native taxa

Chris M. McGrannachan1,2, *, Gillis J. Horner1,3 and Melodie A. McGeoch1   

  1. 1 School of Biological Sciences, Faculty of Science, Monash University, Melbourne 3800, Australia, 2 Manaaki Whenua—Landcare Research, 231 Morrin Rd, St. Johns, Auckland 1072, New Zealand, 3 Greening Australia Ltd, PO Box 470, Flinders Lane, Melbourne 8009, Australia

    *Corresponding author. E-mail: mcgrannachanc@landcareresearch.co.nz
  • Received:2019-10-12 Revised:2020-06-23 Accepted:2020-08-02 Online:2020-08-09 Published:2020-10-01

Abstract:

Aims

Darwin’s naturalization hypothesis proposes that successfully established alien species are less closely related to native species due to differences in their ecological niches. Studies have provided support both for and against this hypothesis. One reason for this is the tendency for phylogenetic clustering between aliens and natives at broad spatial scales with overdispersion at fine scales. However, little is known about how the phylogenetic relatedness of alien species alters the phylogenetic structure of the communities they invade, and at which spatial scales effects may manifest. Here, we examine if invaded understorey plant communities, i.e. containing both native and alien taxa, are phylogenetically clustered or overdispersed, how relatedness changes with spatial scale and how aliens affect phylogenetic patterns in understorey communities.

Methods

Field surveys were conducted in dry forest understorey communities in south-east Australia at five spatial scales (1, 20, 500, 1500 and 4500 m2). Standardized effect sizes of two metrics were used to quantify phylogenetic relatedness between communities and their alien and native subcommunities, and to examine how phylogenetic patterns change with spatial scale: (i) mean pairwise distance and (ii) mean nearest taxon distance (MNTD).

Important Findings

Aliens were closely related to each other, and this relatedness tended to increase with scale. Native species and the full community exhibited either no clear pattern of relatedness with increasing spatial scale or were no different from random. At intermediate spatial scales (20–500 m2), the whole community tended towards random whereas the natives were strongly overdispersed and the alien subcommunity strongly clustered. This suggests that invasion by closely related aliens shifts community phylogenetic structure from overdispersed towards random. Aliens and natives were distantly related across spatial scales, supporting Darwin’s naturalization hypothesis, but only when phylogenetic distance was quantified as MNTD. Phylogenetic dissimilarity between aliens and natives increased with spatial scale, counter to expected patterns. Our findings suggest that the strong phylogenetic clustering of aliens is driven by human-mediated introductions involving closely related taxa that can establish and spread successfully. Unexpected scale-dependent patterns of phylogenetic relatedness may result from stochastic processes such as fire and dispersal events and suggest that competition and habitat filtering do not exclusively dominate phylogenetic relationships at fine and coarse spatial scales, respectively. Distinguishing between metrics that focus on different evolutionary depths is important, as different metrics can exhibit different scale-dependent patterns.

Key words: alien species, community phylogenetics, Darwin’s naturalization hypothesis, spatial scale, phylogenetic beta diversity

摘要:
达尔文的归化假说提出,由于生态位的不同,成功建群的外来物种与本地物种的关系不太密切。先前的研究对这一假设有支持也有反对,其中一个原因是外来物种和本地物种在大的空间尺度上有系统发育聚类的倾向,而在细微尺度上存在过度分散的倾向。然而,对于外来物种的系统发育关系如何改变其入侵群落的系统发育结构,以及在何种空间尺度上可能表现出这种影响,人们知之甚少。在本研究中,我们调查被入侵的森林下层植物群落在系统发育上是聚集的还是或过度分散的,亲缘关系如何随空间尺度变化,以及外来物种如何影响下层群落的系统发育模式。在澳大利亚东南部干旱森林的下层群落进行了5个空间尺度(1, 20, 500, 1500和4500 m2)的实地调查。使用两个指标的标准化效应量[(i)平均成对距离和(ii)平均最近分类单元距离]来量化群落与其外来和本地亚群落之间的系统发育关系,并研究系统发育模 式如何随空间尺度变化。研究结果表明,外来物种之间的亲缘关系非常密切,而且这种亲缘关系会随着尺度的增加而增加。在中等空间尺 度下(20–500 m2), 整个群落呈随机分布趋势,而本地物种高度分散,外来亚群落高度聚集。这说明亲缘关系密切的外来物种入侵使群落系统发育结构由过度分散向随机分布转变。外来物种和本地物种在空间尺度上是远亲,这支持了达尔文的归化假说,但只是在系统发育距离被量化为平均最近分类单元距离时成立。外来物种和本地物种的系统发育差异随着空间尺度的增加而增加,这与预期的模式相反。我们的研究结果表明,外来物种强大的系统发育聚类是由人类干预的引入驱动的,牵涉能够成功建群和传播的密切相关的类群。系统发育相关性的尺度依赖模式可能是由火灾和散布等随机过程引起的,这表明竞争和生境过滤并不是分别在小和大尺度上控制系统发育关系的唯一因素。区分不同进化深度的指标很重要,因为不同的指标可以显示不同的尺度依赖模式。

关键词: 外来物种, 群落系统发育">, 达尔文归化假说">, 空间尺度">, 系统发育β多样性