The incorporation of phylogenetic information into biodiversity – ecosystem function research has furthered our understanding of diversity effects on the functioning of ecosystems, bearing promise in unifying evolutionary biology with ecosystem ecology. Although there is general consensus that phylogenetic diversity has overall positive effects on ecosystem function, a few studies have reported negative effects, thus questioning the generality of this premise. Here, we use simulation analyses to emphasize on the importance of the phylogenetic placement of lineages to accurately predict the effects of phylogenetic diversity on ecosystem function. Also, we propose a bootstrapped-based method to quantify the effect of individual lineages in natural communities, where experimental manipulations of biodiversity may not be always feasible. We illustrate our method and findings using survey data from tropical forests and multiple functions measured in natural and human-disturbed sites, respectively. Specifically, we explored the relationships between phylogenetic and taxonomic diversity and multifunctionality.
Results/Conclusions
We found that the direction of phylogenetic diversity – ecosystem function relationships (PDEF) is strongly determined by the interactive effects of tree unbalance and the phylogenetic placement of dominant and ecologically relevant lineages. PDEF relationships are expected to be positive if the lineages that contribute the most to the function occur within long-branched basal clades. In contrast, PDEF relationships would be non-significant or even negative if the relevant lineages represent more derived branches. The effects of biodiversity on multifunctionality were markedly different between natural and disturbed forest habitats. Phylogenetic diversity showed significantly negative effects on multifunctionality, but only in the natural plots. In contrast, taxonomic diversity was positively related with multifunctionality, but only in the disturbed plots. Our bootstrapping method revealed that the negative PDEF relationship observed in the natural plots is largely due to a long-branched basal lineage that contribute little to the function (i.e. Magnoliids). In contrast, the positive relationship between taxonomic diversity and multifunctionality in the disturbed plots was driven by the presence of multiple lineages that specifically maximize ecosystem properties in complementarity. We conclude that predictions on PDEF relationships would be baseless as long as phylogenetic diversity is treated as an evolutionary “black box” where phylogenetic branches are more or less interchangeable, and that detecting the lineages that are significantly associated with the functions should be a preliminary step to form the basis for higher resolution studies in natural ecosystems, where experimental approaches may not be always feasible but biodiversity – ecosystem function research is urgently needed.