Moving beyond species diversity metrics: a global synthesis of plant invasion impacts on phylogenetic and functional diversity

AimBiological invasions, being one of the major drivers of global environmental change, are currently driving a worldwide decline of biodiversity. To date, several meta-analyses have synthesised impacts of biological invasions on species diversity – the most common metric for measuring biodiversity. However, an empirical synthesis of invasion impacts on functional and phylogenetic diversity – recently emerging dimensions of biodiversity measurement – remains unexplored. Here, we conducted a meta-analysis of 605 effect sizes to synthesise global plant invasion impacts on the functional and phylogenetic diversity.LocationGlobalTime Period2015-2023Major Taxa StudiedInvasive plant speciesMethodsWe employed a novel meta-analytical framework by integrating, hitherto largely ignored, deviational effects with traditional directional effects. The framework, besides quantifying the relative changes in response variables (i.e., directional effects), allowed us to measure the absolute changes in response variables from the reference values (i.e., deviational effects).ResultsOur findings show that, in terms of directional effects, invasion impacts on community-weighted functional trait and phylogenetic distance metrics are largely non-significant. Conversely, in terms of deviational effects, the invasion impacts were significant on the key functional metrics: richness, dispersion, Rao’s Q, and overall phylogenetic diversity. We also found the invasion impacts to be context-specific, with directional effects observed only in wastelands but those of deviational effects in forests, grasslands and wastelands.Main ConclusionsThese findings provide empirical evidence to posit that plant invasion impacts increase variability within communities rather than shift trait means, underscoring urgency of quantifying both directional and deviational effects in meta-analysis. By moving beyond the simple metric of species diversity, our study calls for integrating trait- and lineage-based metrics in invasion impact studies, with immense implications in measuring and managing invasion impacts on biodiversity. Leveraging on the insights gained from this global synthesis, we identify existing knowledge gaps and directions for future research.