Testing Darwin’s naturalization hypothesis in the Azores

Abstract

Invasive species are a threat for ecosystems worldwide, especially oceanic islands. Predicting the invasive potential of introduced species remains difficult, and only a few studies have found traits correlated to invasiveness. We produced a molecular phylogenetic dataset and an ecological trait database for the entire Azorean flora and find that the phylogenetic nearest neighbour distance (PNND), a measure of evolutionary relatedness, is significantly correlated with invasiveness. We show that introduced plant species are more likely to become invasive in the absence of closely related species in the native flora of the Azores, verifying Darwin's 'naturalization hypothesis'. In addition, we find that some ecological traits (especially life form and seed size) also have predictive power on invasive success in the Azores. Therefore, we suggest a combination of PNND with ecological trait values as a universal predictor of invasiveness that takes into account characteristics of both introduced species and receiving ecosystem.

A test of Darwin's naturalization hypothesis in the thistle tribe shows that close relatives make bad neighbors

“…The phylogenetic scope of this study, encompassing a highly supported clade of 202 species within 64 genera, allows for circumvention of some of the problems that might occur in similar studies aimed at testing Darwin's naturalization hypothesis at lesser or greater taxonomic scales. Examining the relationships between introduced species and native species where the community is composed of taxa classified in multiple families (47) and possibly separated by over a hundred million years of evolution (89), may not be ecologically meaningful, as it becomes difficult to assume ecological similarities between such taxa are the result of shared evolutionary history. Also, at such a large scale, it is difficult to construct well sampled, robust phylogenies of an all-encompassing monophyletic group.…”

“…Previous studies have been equivocal, finding evidence both for (30,31,38,(45)(46)(47)(48)(49)(50), and against (24,32,41,44,(51)(52)(53)(54)(55) Darwin's hypothesis. However, few have used a strict phylogenetic approach based on evolutionary divergence, instead predominantly relying on taxonomic ranks (e.g., refs.…”

“…In instances where phylogenetic trees were used, some have used supertrees compiled from multiple studies (46,60,61), with estimated branch lengths that may not accurately reflect the evolutionary distances between taxa. Other studies have been based on community phylogenetic trees (47,60,62). This approach may be problematic, as communities are not necessarily monophyletic groups, but collections of co-occurring species whatever their evolutionary relationships may be (63), and sampling in such studies is unlikely to include adequate representation of all lineages present, whereas phylogenetic analyses assume monophyly of the ingroup and their accuracy is dependent on sampling that is representative of the diversity within (64,65).…”

Darwin's naturalization hypothesis: scale matters in coastal plant communities

“…Although the issue of spatial scale is clearly important in this context and has been addressed theoretically (Proches et al 2008, Thuiller et al 2010, there are few studies that have investigated the effect of scale on invaders' relatedness patterns using nested resolutions in the field (Cadotte et al 2009, Schaefer et al 2011. While promising evidence comes from an analysis conducted by Diez et al (2008), which however did not include progressively finer sampling resolutions, to our knowledge no empirical study has been able to demonstrate the theoretically predicted spatial turning point from phylogenetic clustering to phylogenetic overdispersion of invaders.…”

Applying an integrated landscape characterization and evaluation tool to small islands (Pico, Azores, Portugal)

“…However, a large number correspond to exotic species resulting from accidental or voluntary introduction after the colonization of the islands. Since the settlement in the 15 th century, vegetation has changed significantly essentially for cereal crops, pasture and forestry, being currently affected by the invasive behavior demonstrated by some of the introduced species (Furtado, 1984;Martins, 1993;Silva & Tavares, 1997;Silva & Smith, 2006;Lourenço et al, 2011;Schaefer et al, 2011;Costa et al, 2012;Gil et al, 2013).…”