Multi-hierarchical macroecology at species and genetic levels to discern neutral and non-neutral processes

AimLarge-scale DNA barcoding allows the simultaneous assessment of variation in community composition at species level and below. We here propose that the patterns emerging across multiple hierarchical levels can be used to discern the effects of neutral and non-neutral macroecological processes, which otherwise have proven difficult to separate. LocationIberian Peninsula. MethodsWe performed cox1 barcoding on 20 complete assemblages of leaf beetles for 4533 individuals of 203 species. The neutrality of cox1 sequence evolution was tested using Tajima's test. Haplotypes (n=2020) were grouped into nested n-step networks of up to five intraspecific hierarchical levels. We then assessed whether the spatial variation in assemblage composition at all hierarchical levels from haplotype to species was self-similar (fractal) and predictable from level to level. ResultsTajima's test on a subset of widely sampled species (n=136) was consistent with neutral evolution in 83% of the species, but only 3% of cases exhibited balancing selection. Multiple hierarchical levels representing haplotype genealogies of various ages showed a similar rate of distance decay of assemblage similarity. In addition, we found strong log-log correlations between hierarchical level (lineage age) and number of lineages, lineage range size and assemblage similarity. Similarity at the species level was strongly correlated to similarity at the haplotype level for the whole assemblage (r(2)=0.75) or for within-species haplotype similarity (mean r(2)=0.17, SE=0.03). Main conclusionsThese findings suggest great regularities in the pattern of assemblage variation at all lineage ages that are best explained by the enduring action of stochastic (neutral) processes of mutation and dispersal. The multi-hierarchical analysis therefore bridges predictions of the neutral theory of molecular evolution and the neutral theory of biodiversity. Neutral processes thus emerge as a unifying principle of ecology and evolution, which has deep implications in biodiversity assessment and conservation.