Exotic-to-native affinities and plant invasibility in a tropical dry forest

Abstract

Conflicting hypotheses regarding the factors underlying the invasibility of plant species persist, as portrayed by Darwin’s naturalization conundrum. This is particularly critical in arid and semiarid ecosystems, for which understanding remains elusive. We test how similarities between exotic and native plants in the Brazilian semiarid Caatinga affect the invasion stage and distribution of invasive species. We estimate diversity fields for exotic species, representing the composition of native species that co-occur with each exotic species and calculated phylogenetic metrics of the distance of focal species to its field. We also assess whether changes in stage from exotic to naturalized and from naturalized to invasive are influenced by phylogenetic relatedness and functional traits. We also test whether the observed phylogenetic distance values of the invasive species differ from those expected by chance. Finally, we analyze whether there are functional similarities between the stages of exotic species and native plants. Plants that are phylogenetically closer to the more frequent native species of the Caatinga are more likely to become naturalized and invasive. Among invasive species with a significant pattern of phylogenetic relatedness, those that are closer to native species are more prevalent. Naturalized and invasive plants are shorter and have smaller leaves and seeds than native plants. The observed functional differences suggest that naturalized and invasive species adopt strategies similar to those of competitive native plants, such as seed bank formation and dense populations.