Evolutionary drivers of assembly in NZ forests

Our paper showing an evolutionary legacy of community assembly in New Zealand forests, an evolutionarily older and more structurally complex ecosystem than investigated to date, is now in early view online at the Journal of Ecology. We have shown that evolutionary priority effects — where early-arriving ancestral taxa diversify and preempt niche space, precluding later arrivals from dominating new habitats — shape extant communities of both pteridophytes and angiosperms. These physiologically-contrasting taxonomic groups exhibit different responses to precipitation gradients, however. Evolutionary priority effects in pteridophyte communities become stronger with increasing precipitation, as predicted by the hypothesis that competition has a greater role in structuring communities in benign or resource-rich environments (i.e. the Stress Gradient Hypothesis). Angiosperms show a different pattern, with stronger priority effects in the drier eastern portion of the mountain range we sampled, suggesting that environmental drivers other than precipitation may be more important in structuring angiosperm communities. Our work thus advances current understanding by showing a remarkable consistency of clade age effects on community dominance across different ecological conditions — more structurally complex ecosystems and longer evolutionary timescales, as well as across physiologically-contrasting taxonomic groups.