Adding stage-structure to a spatial neutral model: implications for explaining local and regional patterns of biodiversity

Theoretical ecologists have analysed a range of neutral models but few including stage structure. Here we introduce a stage-structured neutral model, by extending the standard spatial neutral model to have two-stage classes: a juvenile stage and a reproductive stage. We find that formulas for biodiversity patterns (e.g. species-area relationships and species abundance distributions) of reproductives in the stage-structured model can be obtained from the corresponding standard formulas via a parameter rescaling, which involves calculating an effective speciation rate parameter and an effective dispersal parameter. This is useful because it means existing knowledge about the non-stage-structured model can be transferred to the stage-structured model, providing that applications focus exclusively on the reproductive stage. One surprising implication is that the presence of a juvenile stage can substantially increase the species richness of reproductive individuals: a juvenile stage with a length fraction k that of the reproductive stage increases reproductive species richness by roughly the same factor. We apply our new formulas to a case study of tropical forest trees in Panama and find that while the stage-structured model makes different predictions than the standard model, it does not fix known problems with cross-scale predictions. We speculate that some of our results, in particular the result that the presence of a juvenile stage increases community diversity, likely apply to non-neutral systems as well.

Automated summary

Theoretical ecologists introduced a stage-structured neutral model, showing that the presence of a juvenile stage can significantly increase species richness. A case study on tropical forest trees in Panama revealed that while the stage-structured model made different predictions compared to the standard model, it did not solve known cross-scale prediction issues.