Understanding what drives non-native species naturalization (the establishment of a self-sustainable population outside its native range) is a central question in invasion science. Plants’ capacity for long distance dispersal (LDD) is likely to influence the spread and naturalization of non-native species differently according to their introduction pathways. These pathways include intentional introductions (for economic use, e.g. for agriculture), unintentional introductions (e.g. seed contaminants), plant dispersal via human infrastructures (e.g. roads), and plant spread from an adjacent region where the species was previously introduced. Herein, we tested the relationship between sets of LDD traits (syndromes) of 10,308 European plant species and their global naturalization incidence (i.e. whether a species has become naturalized or not) and extent (i.e. the number of regions where a species has become naturalized) using the most comprehensive database of naturalized plants worldwide (GloNAF). Diaspore traits allowed the identification of four traditional LDD syndromes, namely those with specializations for dispersal by: wind (anemochorous), animal ingestion (endozoochorous), attached to animals (epizoochorous), and sea currents (thalassochorous). These evolutionary specializations have been historically interpreted by biologists even though actual dispersal is not always related to diaspore syndromes. We found that while epizoochorous and thalassochorous traits are positively associated with global plant naturalization incidence, anemochorous and endozoochorous traits show a negative relationship. Species´ residence time outside their native range, their economic use and presence of epizoochorous traits (such as hooks, hairs and adhesive substances) are positively associated with global naturalization extent. Furthermore, we found that plants’ economic use reduces the influence of LDD syndromes on the naturalization incidence of intentionally introduced plants. While the success of non-native plants is influenced by a broad array of species- and context-specific factors, LDD syndromes play an important role in this context depending on the economic use of plants.

We used information on LDD syndromes from a comprehensive database of European Spermatophytes (Heleno & Vargas, 2015), which includes 10,308 species from 137 families native to Europe. Here, each species was assigned LDD syndromes based on diaspore (typically seeds and fruits) morphology, including five classes (Table 1). Diaspores with wings or pappus (plumose hairs), which facilitate dispersal by wind, were considered anemochorous. Diaspores with fleshy and nutritive tissues, which favor animal ingestion, were considered endozoochorous. Diaspores with hooks or sticky substances, which promote the external adhesion to animals, were considered epizoochorous. Diaspores with corky tissues or air chambers, which favor floatability and protection in saltwater, were considered thalassochorous. Finally, diaspores with no specialized dispersal structures for LDD were considered unspecialized (Heleno & Vargas, 2015). Since some plants show heterocarpy (production of different kinds of diaspores) and others show diaspore traits that facilitate LDD through more than one dispersal vector, we included both species with one and species with multiple LDD syndromes, following Heleno and Vargas (2015). In this way, we acknowledge the fact that some plants might take advantage of more than one LDD strategy. However, for comparison purposes we built a second LDD syndrome database where we considered only plants with a single LDD syndrome, discarding all plants with multiple LDD syndromes. Dispersal syndromes that favor short distance (local) dispersal, such as myrmecochory and autochory, were assigned to the unspecialized category because they are not relevant for LDD (Heleno & Vargas, 2015).

We obtained distributional data of naturalized vascular plants from the GloNAF database v. 1.2, which includes information of 13,939 taxa and 1,029 regions, based on 210 data sources (van Kleunen et al., 2019). A region is defined here as the smallest geographic area for which a list of non-native plants is available (mostly countries, or distinct sub-national regions such as federal states or islands), including 648 mainland regions and 381 island regions. Species names in the GloNAF database have been standardized according to The Plant List (www.theplantlist.org). For merging the database on LDD syndromes with the GloNAF database, we also standardized species names to The Plant List by using the “TPL” function from the “taxonstand” package (Cayuela et al., 2012). We used two complementary proxies for naturalization success: naturalization incidence and naturalization extent (Razanajatovo et al., 2016). Naturalization incidence is a binary response variable (yes or no) that considers if a species has been recorded as naturalized outside its native range. For a given LDD syndrome the naturalization incidence is an indicator of the likelihood that a species with a particular LDD syndrome has naturalized outside its native range. From the 10,308 species in the LDD syndrome database, 2416 (23.44 %) were recorded as naturalized in at least one region according to the GloNAF database. For these 2416 species we estimated the naturalization extent: the number of GloNAF regions where each species is reported to be naturalized. This metric is an indicator of the capability to spread across large regions for a species with a particular LDD syndrome.

A recent study (van Kleunen et al., 2020) has shown that economic use of plants increases their global naturalization success, likely because economic use of plants increases propagule pressure, particularly for intentional introductions (e.g. for horticulture). We propose that species with economic use and species without economic use are mostly under the influence of different introduction pathways (as defined by Hulme et al. (2008) and CBD (2014)) (Figure 1). Species with economic use are mostly introduced intentionally, and then either intentionally released in nature (e.g. for erosion control or landscaping) or escape cultivation (mainly through seed dispersal) (Hulme et al., 2008; Harrower et al., 2018). Species without any economic use can be introduced accidentally by human vectors such as a contaminant of a commodity (e.g. as seed contaminant) or attached to (or within) a transport vector (e.g. in ships ballast water) (Hulme et al., 2008; Harrower et al., 2018). Alternatively, these species without economic use can disperse using human infrastructure that connects previously unconnected regions, or can colonize a region through unassisted dispersal from adjacent regions, where they were previously introduced (Hulme et al., 2008; Harrower et al., 2018). To test for the effect of the economic use of plants on naturalization incidence and extent, we used the dataset by van Kleunen et al. (2020) and assigned the 10,308 species from our LDD syndrome database, with which we estimated naturalization incidence and extent using GloNAF, into two groups – i.e. plants with and without economic use. We acknowledge that this is not a perfect proxy for introduction effort: some variation of introduction effort will not be explained by the economic use of plants. Further, the economic use of plants does not account for their accidental introductions by humans. In this regard, variations in propagule pressure (not explained by economic use) among species (Pyšek et al., 2015), for which we don’t have further data, may also influence naturalization patterns.

To account for species’ residence time outside their native range, a key driver that favors plant naturalization (Pyšek et al., 2015; Fristoe et al. 2021), we used data on the date of first record for each species. We expected that plant species with earlier first record date would show higher naturalization extent because they had more residence time outside their native range. To estimate species´ minimum residence time outside their native range we used a global database of first record dates for non-native species compiled by Seebens et al. (2017) and updated by Seebens et al. (2018). This database includes first record dates for 11,450 non-native vascular plants around the world. To test for the effect of the first record date on naturalization extent, we used the dataset by Seebens et al. (2017, 2018) and assigned the 2416 species from our LDD syndrome database, with which we estimated naturalization extent using GloNAF, their earliest first record date outside their native range. In other words, for each naturalized species we used its earliest record date anywhere in the world to account for its residence time outside its native range. We acknowledge that this approach has its limitations. First, data on first record are only available for a subset of regions around the world. Second, there may be a time lag between the introduction of a new species and its first record. Third, data on first record is only available for a subset of naturalized species around the world. Out of the 2416 naturalized species in our LDD syndrome database we obtained data on their first record for 1986 species (83.23 %), so we restricted our dataset for analyses of naturalization extent to these 1986 species.

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The files included are simple spreadsheets and no specific software is required to open them.