Testing fundamental hypotheses of colonization success in the ferns

Non-native species are now ubiquitous members of regional floras. The factors that lead to establishment and dominance of non-native species are continuously debated. Fundamental hypotheses about drivers of invasion success include the role of phylogeny, polyploidy, genome size, and rapid niche evolution. These hypotheses have been tested in the seed plants, but ferns, the second largest group of vascular plants, have rarely been considered in these analyses, despite making up a non-trivial portion of non-native floras.

We compiled a dataset of global non-native ferns and categorized them along the invasion spectrum using descriptions from the literature and natural history collections. Using this dataset, we assessed I) the taxonomic diversity and phylogenetic clustering of non-native ferns, II) the geographic distribution of fern introductions, testing for shifts in climatic niches, and III) test for the association of 'invader' traits across the invasion continuum, including smaller genome sizes and higher ploidal levels.

We generated a dataset that includes 93 taxa; of these, we classified 19 as casual, 43 as naturalized (but not invasive), and 31 as invasive. Using this dataset, we found I) weak or no phylogenetic clustering of non-native ferns, II) some regions are overrepresented as sources and recipients of documented introductions, III) in a set of well-documented invasive taxa, climatic niches are often conserved between native and introduced ranges, but can differ between introductions, IV) naturalized ferns may have smaller genomes, and V) invaders may have higher ploidal levels, though the analyses in IV and V are sensitive to cytotype treatment.

We integrated regional floras, occurrence and climate data, phylogeny, and cytology to test fundamental hypotheses regarding the colonization success of ferns. This study provides insights into the ecological, genomic, and phylogenetic features associated with the colonization of new habitats by non-native ferns, a largely overlooked portion of non-native plant taxa.