Invasion trajectory of alien trees: the role of introduction pathway and planting history

Abstract

Global change is driving a massive rearrangement of the world's biota. Trajectories of distributional shifts are shaped by species traits, the recipient environment and driving forces with many of the driving forces directly due to human activities. The relative importance of each in determining the distributions of introduced species is poorly understood. We consider 11 Australian Acacia species introduced to South Africa for different reasons (commercial forestry, dune stabilization and ornamentation) to determine how features of the introduction pathway have shaped their invasion history. Projections from species distribution models (SDMs) were developed to assess how the reason for introduction influences the similarity between climatic envelopes in native and alien ranges. A lattice model for an idealized invasion was developed to assess the relative contribution of intrinsic traits and introduction dynamics on the abundance and extent over the course of simulated invasions. SDMs show that alien populations of ornamental species in South Africa occupy substantially different climate space from their native ranges, whereas species introduced for forestry occupy a similar climate space in native and introduced ranges. This may partly explain the slow spread rates observed for some alien ornamental plants. Such mismatches are likely to become less pronounced with the current drive towards 'eco gardens' resulting in more introductions of ornamental species with a close climate match between native and newly introduced regions. The results from the lattice model showed that the conditions associated with the introduction pathway (especially introduction pressure) dominate early invasion dynamics. The placement of introduction foci in urban areas limited the extent and abundance of invasive populations. Features of introduction events appear to initially mask the influence of intrinsic species traits on invasions and help to explain the relative success of species introduced for different purposes. Introduction dynamics therefore can have long-lasting influences on the outcomes of species redistributions, and must be explicitly considered in management plans.

Climatic niche shift of aquatic plant invaders between native and invasive ranges: a test using 10 species across different biomes on a global scale

“…For example, Mainali et al (2015) reported improved prediction performance of ENMs of Parthenium hysterophorus L. (Asteraceae) with the distribution occurrences from both native and invasive ranges. Therefore, it is important to obtain a large volume of occurrences to generate accurate predictions with ENMs (Donaldson et al, 2014;Mainali et al, 2015). Additionally, our study may provide an important theoretical basis for the future prediction of APIs in invasive ranges based on ENMs and aid further studies that study invasion mechanism(s) of APIs on a global scale.…”

“…2). Human activities are the main driving force for plant invasion; e.g., human introduction has been reported to disperse invasive plant species over long distances either on footwear or water sports equipment (Brinson and Malvárez, 2002;Donaldson et al, 2014;Callen and Miller, 2015). Furthermore, hydrological processes of catchments may affect the habitat distribution of species in freshwater biomes (Abell et al, 2008).…”

Transatlantic invasion routes and adaptive potential in North American populations of the invasive glossy buckthorn,Frangula alnus

“…The high genetic diversity in urban areas near ports indicates that genetic founder effects have been circumvented. Strong founder effects during ornamental plant invasion can indeed be avoided if the shipped seeds harbour most of the alleles of the source population, and this relatively rich gene pool is used for cultivation and subsequent plantation (Tracy et al, 2011;Donaldson et al, 2014). It remains unclear, however, whether the introductions involved single large seed-shipping events or multiple small seed-trade episodes from the same European area for each of the trade routes.…”

“…parks and public gardens). These urban populations may serve as bridgehead populations (sensu Lombaert et al, 2010;Estoup and Guillemaud, 2010), enabling regular secondary migration to natural areas (Donaldson et al, 2014). The success rate of secondary spread can be expected to further increase if the planted populations originate from genetically distinct native sources, a scenario that is not unlikely in the ornamental plant trade, given that larger trait variation provides a wider basis for artificial selection towards cultivars.…”

“…Third, due to higher levels of genetic differentiation, especially in species with high gene flow, functional SNPs are more suitable for discriminating among genetically differentiated populations compared with neutral SNPs (see also Freamo et al, 2011;Gagnaire et al, 2015). Although the use of loci potentially subjected to natural selection may affect the reliability of demographic inferences, the nurture of F. alnus shrubs in parks protects these populations from environmental stochasticity, hence largely exempting park populations, which represent the focal sites of introduction, as targets of natural selection (see also Donaldson et al, 2014).…”