COS 22-7
The strength of evolutionary priority effects changes along environmental gradients in forest communities
The order in which species colonize a community can influence community structure, with priority effects over both ecological and evolutionary timescales often resulting in communities dominated by early colonizers. However, the strength of priority effects in plant communities varies across environmental gradients, at least in some ecosystems. Previous work demonstrated that evolutionary priority effects, or the age of plant lineages, contribute to community dominance at both landscape and local scales in New Zealand’s alpine grasslands. This relationship between lineage age and dominance can vary across environmental stress gradients, however, suggesting that the strength of priority effects depends on the relative role of competition in structuring plant communities. To assess the generality of evolutionary priority effects across ecosystems, we related the age of plant lineages (i.e. estimated time of divergence from closest relative outside New Zealand) in a forest ecosystem to dominance of those lineages in local plant communities (i.e. relative diversity and abundance in plots). To determine if environmental conditions consistently alter the strength of priority effects, we analyzed the interaction between lineage age and two environmental gradients, elevation and precipitation. We used linear models fit within a Bayesian framework to incorporate uncertainty in lineage age estimates into our analysis.
Results/Conclusions
As in alpine grasslands, forest community dominance tended to increase with lineage age at both landscape and local scales, especially for relative diversity (using 32 of 131 total genera observed in 340 sampled plots). The lack of a strong relationship between relative abundance and lineage age may be due to differences in growth form and maximum size among focal genera (e.g. canopy trees vs. understorey herbs). Within plots, lineage age interacted with environmental gradients such that the relationship between lineage age and relative diversity became weaker with increasing elevation and decreasing precipitation. Thus, evolutionary priority effects seem to weaken with increasing environmental stress, when abiotic filtering is likely to be a more important driver than competition in community assembly. Our findings are consistent with observations from alpine systems, suggesting that evolutionary priority effects shape communities in multiple biomes in New Zealand.