The invasion paradox dissolves when using phylogenetic and temporal perspectives

1. Elton’s prediction that higher biodiversity leads to denser
niche-packing and thus higher community resistance to invasion has long
been studied, with species richness as the predominant measure of
diversity. However, few studies have explored how phylogenetic and
functional diversity, which should represent niche space more faithfully
than taxonomic diversity, influence community invasibility, especially
across longer time frames and over larger spatial extents. 2. We used a
15-year, 150-site grassland dataset to assess relationships between
invasive plant abundance and phylogenetic, functional, and taxonomic
diversity of recipient native plant communities. We analyzed the dataset
both pooled across all surveys and longitudinally, leveraging time-series
data to compare observed patterns in invasion with those predicted by two
community assembly processes: biotic resistance and competitive exclusion.
We expected more phylogenetically and functionally diverse communities to
exhibit greater resistance to invasion. 3. With the pooled dataset, we
found support for the longstanding observation that communities with more
native species have lower abundance of invasive species, and a more novel
finding that more phylogenetically diverse communities had higher
abundance of invasive species. We found no influence of aggregate
(multivariate) functional diversity on invasion, but assemblages with
taller plants, lower variability in plant height, and lower seed mass were
less invaded. Viewed longitudinally, the phylogenetic diversity
relationship was reversed: the most phylogenetically diverse communities
were most resistant to invasion. This apparent discrepancy suggests
invasion dynamics are influenced by both site attributes and biotic
resistance and emphasizes the value in studying invasion across time. 4.
Synthesis: Our results provide insight into the nuances of the
diversity-invasibility relationship: invasion dynamics differed for
different dimensions of diversity and depending on whether the
relationship was evaluated longitudinally. Our findings highlight the
limitations of using single time-point “snapshots” of community
composition to infer invasion mechanisms.