Plant invasions as a biogeographical assay: Vegetation biomes constrain the distribution of invasive alien species assemblages

Abstract

a b s t r a c t a r t i c l e i n f o Edited by A PottsPlant assemblages define vegetation patterns at different scales, from plant communities at the scale of small plots to broad biomes. Species assemblages are traditionally investigated with a focus on native species, and the spatial patterns and dynamics of alien species assemblages have received much less attention. Here, we explore the biogeography of a subset of invasive alien plants (IAPs) in South Africa and derive several "alien biomes" based on the alien plant assemblages and associated environmental drivers. We propose six hypotheses (the Weed-Shaped Hole; the Biome Decides; Goldilocks; a New World Order; Something In The Way You Move; and Random Tessellation) based on different drivers (disturbance, competition, climate, global change, introduction dynamics, and null respectively) that might explain distribution patterns. In particular, we explore whether invasive plant assemblages are controlled by the same fundamental factors that define native plant assemblages and biomes. A cluster analysis of the spatial distribution of 69 invasive alien plant species revealed five clearly delineated geographic clusters, three of them significantly aligned with the distribution of vegetation biomes (fynbos, grassland and savanna). The major determinants of the distribution of IAP clusters were identified based on a classification tree analysis. We found that broad environmental variables, especially vegetation biomes, explained the distribution of IAP clusters (60% classification accuracy). We could not find a strong relationship with anthropogenic factors, such as land cover or anthromes, even at a finer scale. Our results indicate that vegetation biomes are characterised by hard environmental barriers which also constrain the distribution of IAPs in South Africa. This supports the development of biome-level strategies for the control of alien plant species in South Africa.

Similar compositional turnover but distinct insular environmental and geographical drivers of native and exotic ants in two oceans

“…The fact that the turnover of both native and exotic ants is mostly explained by precipitation, and that the variance explained for these variables is similarly high in the Pacific (Table ; Figures ) suggests that the native and exotic species that compose these communities may have similar abiotic niches. This may be due, for example, to environmental filters forcing exotics to adopt similar traits and distributions as natives (Rouget, Hui, Renteria, Richardson, & Wilson, ). The importance of precipitation (Table ; Figures and ) is consistent with the wide range of precipitation values in the Pacific islands (Figure S2.1).…”

Drivers of species turnover vary with species commonness for native and alien plants with different residence times

“…The fact that turnover in widespread alien species is not driven by the same factors as widespread native species has important implications for the management of vascular plants in Czech nature reserves. Based on the spatial correlation between native and alien biomes, Rouget et al (2015) concluded that management of alien species should be biomespecific. However, our results show that this is only true for relatively rare species.…”

“…Different hypotheses have been advanced for explaining the relationship between alien and native assemblages (Rouget et al 2016); some of these can be tested using such regional assemblages under different residence times. In particular, the correlation between the similarity of alien assemblages and the similarity of native assemblages across communities can be strong, as observed when comparing the South African native and alien biomes (Rouget et al 2015), either due to similar abiotic selection (the "Goldilocks" hypothesis) or because of strong biotic interactions between alien and native species (the "Biome Decides" hypothesis). This correlation can also be weak, either because the distribution of alien species is largely idiosyncratic (the "Random Tessellation" hypothesis) or because the alien distribution predominantly reflects the imprint of particular invasion pathways (the "Something in the Way You Move" hypothesis).…”

“…This is because the distributions of native species should become more influenced by environmental filters than the distributions of co-occurring alien species; this could lead to diminishing the importance of stochastic processes with residence time in structuring communities. Third, if alien species are constrained by the same set of variables as native species in the long term (i.e., the Goldilocks or the Biome Decides hypotheses; Rouget et al 2015), and if such constraints become more apparent with increasing residence time, we would then expect the turnover of native species to better explain the turnover of archaeophytes than the turnover of neophytes. The structure of neophyte communities, and therefore their turnover, should nonetheless be driven primarily by demographic stochasticity (i.e., the Random Tessellation or the Something in the Way You Move hypotheses).…”

Is CRISPR-based gene drive a biocontrol silver bullet or global conservation threat?

“…Given the potential for gene drive approaches for eradicating species, the criticism of elevated risks of indirect effects will be more real for such approaches than has been the case with CBC (14,15). There is increasing awareness, however, that with a growing pool of invasive alien species, many will have considerable niche overlap, such that if one introduced species was to be removed from the community, another would be likely to rapidly take its place (16,17). Hence, the overall effect on ecosystem values may remain unchanged even if one invader is eradicated.…”