Neutral biodiversity models make the simplifying assumption that all species are the same. These models have been used extensively over the last two decades to understand real biodiversity patterns. One failing of neutral models is that they predict species ages that are far too long. For example, for Amazon trees standard neutral models predict species ages that exceed the age of the angiosperms (~140 million years). In a new paper led by Tak, we explore a mechanism that can fix species ages in these models without breaking neutrality: allowing community size to change over time in a non-equilibrium situation. We develop new mathematical formulas for the species abundance distribution and species ages in a neutral model with changing community size. We show that if this model is parameterised to represent changes in the size of the Amazon since a meteor impact obliterated much of the vegetation 66 million years ago, it can produce species ages and a species abundance distribution that are both consistent with reality. The results suggest that a neutral explanation for Amazon tree diversity cannot be completely ruled out.

Fung, T., and R. A. Chisholm. 2022. Improving the realism of neutral ecological models by incorporating transient dynamics with temporal changes in community size. Theoretical Population Biology (in press)