Precipitation alters the strength of evolutionary priority effects in forest community assembly of pteridophytes and angiosperms

Abstract

The ecological conditions promoting evolutionary priority effects, where the order and timing of ancestral species arrival into a new habitat influences extant community assembly, are poorly understood. Studies in the New Zealand alpine indicated that early-arriving angiosperm lineages dominated communities via niche pre-emption. Forests have a much longer (>60-myr) evolutionary history in New Zealand than alpine communities (<2-myr) and greater structural complexity. Here we ask whether community effects of arrival order persist in cool temperate forest communities in southern New Zealand that have assembled throughout the Cenozoic. Combining phylogenetically derived clade ages and forest vegetation data from across a mountain range, we compare effects of clade age on relative richness and abundance of two taxonomic groups (pteridophytes and angiosperms) along precipitation gradients. We show that older clades of both groups tended to have greater relative abundance and older angiosperm clades had greater relative richness. Relative richness and abundance also increased with regional clade diversity, independent of clade age. The strength of the clade age effect on community dominance changed differently along precipitation gradients depending on the response and taxonomic group. Clade age had a stronger effect on relative abundance of pteridophytes with increasing elevation and westerliness (i.e. as precipitation increased). In contrast, the effect of clade age on relative abundance of angiosperms decreased with westerliness. Precipitation did not alter the clade age effect on relative richness. Synthesis. We show that evolutionary priority effects persist in communities with a longer evolutionary history than has been investigated to date and across physiologically contrasting taxonomic groups, suggesting priority effects are general drivers of community assembly over macro-evolutionary time-scales. Furthermore, the strength of evolutionary priority effects attenuated along a gradient of decreasing resources, at least for pteridophytes, which improves our ability to predict conditions in which the arrival order of lineages influences community assembly.