Non-linear thresholds in the effects of island area on functional diversity in woody plant communities

1. Threshold non-linearities in the relationship between island area and species richness can result in dramatic declines in richness with a seemingly small decline in area near the threshold. What is not known, is whether threshold declines in richness are also accompanied by non-linear changes in functional trait space and non-random shifts of trait group composition in response to declining area.

2. Plant species richness was recorded, and four functional diversity (FD) indices calculated based on 12 traits for 76 tree species in 5082 plots (5×5m) on 29 islands in the Thousand Island Lake region, Zhejiang, China. We tested for threshold non-linearities in richness and FD relationships using segmented regression, with randomized resampling using a null model to account for potential sampling artefacts. We clustered tree species into trait groupings based on trait dissimilarity, and used multinomial segmented models to test whether threshold area effects on FD were associated with s...