Abstract
The success of alien plant species can be attributed to differences in functional traits compared to less successful aliens as well as to native species, and thus their adaptation to environmental conditions. Studies have shown that alien (especially invasive) plant species differ from native species in traits such as specific leaf area (SLA), height, seed size or flowering period, where invasive species showed significantly higher values for these traits. Different environmental conditions, though, may promote the success of native or alien species, leading to competitive exclusion due to dissimilarity in traits between the groups. However, native and alien species can also be similar, with environmental conditions selecting for the same set of traits across species. So far, the effect of traits on invasion success has been studied without considering environmental conditions. To understand this interaction we examined the trait–environment relationship within natives, and two groups of alien plant species differing in times of introduction (archaeophytes vs. neophytes). Further, we investigated the difference between non-invasive and invasive neophytes. We analyzed the relationship between functional traits of 1,300 plant species occurring in 1000 randomly selected grid-cells across Germany and across different climatic conditions and land-cover types. Our results show that temperature, precipitation, the proportion of natural habitats, as well as the number of land-cover patches and geological patches affect archaeophytes and neophytes differently, regarding their level of urbanity (in neophytes negative for all non-urban land covers) and self-pollination (mainly positive for archaeophytes). Similar patterns were observed between non-invasive and invasive neophytes, where additionally, SLA, storage organs and the beginning of flowering were strongly related to several environmental factors. Native species did not express any strong relationship between traits and environment, possibly due to a high internal heterogeneity within this group of species. The relationship between trait and environment was more pronounced in neophytes compared to archaeophytes, and most pronounced in invasive plants. The alien species at different stages of the invasion process showed both similarities and differences in terms of the relationship between traits and the environment, showing that the success of introduced species is context-dependent.
Highlights
Invasive alien species (IAS) have a large ecological impact on the diversity and abundance of native plant species (Vilà et al 2010; Pyšek et al 2012)
Individual matrices were generated for five groups of plants: native (976 species), archaeophytes (168 species) and neophytes (156 species), with 1,300 plant species in total; neophytes were further divided into (i) species featured in the German-Austrian Black List Information System of invasive species (GABLIS; Essl et al 2011), with 26 species, and (ii) species not included in GABLIS, with 130 plant species
There was an increase in the number of prominent trait–environment relationships from native species to non-invasive archaeophytes, non-invasive and invasive neophytes (Fig. 1; Suppl. material 1: Tables S2a)
Summary
Invasive alien species (IAS) have a large ecological impact on the diversity and abundance of native plant species (Vilà et al 2010; Pyšek et al 2012). The number of naturalized vascular plant species reaches almost 14,000 with tendencies for further increase (van Kleunen et al 2015, 2019; Pyšek et al 2017; Seebens et al 2019). Much effort has been invested to identify the main causes of invasiveness. Multiple studies have shown that certain functional plant traits promote invasiveness (e.g. Pyšek and Richardson 2007; Küster et al 2008; van Kleunen et al 2010; Tecco et al 2010; Divíšek et al 2018). Propagule pressure and introduction by humans (e.g. cultivation, ornamental purposes) have great effect on invasiveness (Pyšek et al 2015)
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