Widespread and Diverging Patterns of Change in Local Phylogenetic Diversity

Aim

Ecosystems are witnessing drastic changes in biodiversity worldwide. However, it is still unclear whether changes in phylogenetic diversity—a measure of the evolutionary relationships among species—reflect observed changes in species richness. Specifically, we ask whether changes in local phylogenetic diversity correlate with changes in species richness and examine if major taxonomic groups show diverging trends.

Location

Global.

Methods

We estimate how local phylogenetic diversity has changed compared to species richness and whether there were diverging patterns across taxonomic groups. We use a database of compiled assemblage time series from around the world, BioTIME. We use assemblage total evolutionary history (Faith's phylogenetic diversity; PD) as well as average relatedness (mean pairwise distance and mean nearest taxon distance; MPD and MNTD, respectively) as measures of phylogenetic diversity and report taxon-level and assemblage-level posterior slope estimates from a Bayesian hierarchical model. We report trends in four major taxonomic groups: fish, birds, terrestrial mammals and terrestrial plants.

Results

We found strong evidence of widespread increases in MPD across fish and bird assemblages, reflecting decreases in average relatedness and strong evidence of a decrease of MPD in mammals, indicating the opposite. Conversely, we did not find consistent directional change in MNTD, though null average trends included notable positive and negative trends across studies and regions. We also found moderate evidence that SR and PD were increasing in fish assemblages, while they were decreasing in mammals.

Main Conclusions

Our findings suggest that changes in species composition are significantly altering the evolutionary makeup of assemblages at the local scale and that overall patterns diverge within and across taxonomic groups. We suggest potential drivers of these changes but highlight that our results are more generalisable for fish and birds than for mammals and plants, given the variation in geographical coverage and sample size.