# The impact of species-neutral stage structure on macroecological patterns

## TL;DR

This study investigates how demographic stage structure within species influences macroecological patterns, finding that while abundance distributions are generally robust, certain life-history traits can cause significant deviations from neutral theory predictions.

## Contribution

The paper introduces a two-stage neutral model incorporating stage-specific fecundity and mortality, revealing effects on species abundance distributions not captured by unstructured models.

## Key findings

- Abundance distributions are mostly robust to stage structure.
- Significant deviations occur with low adult fecundity and mortality.
- The number of births per species remains a power law with exponent 3/2.

## Abstract

Despite its radical assumption of ecological equivalence between species, neutral biodiversity theory can often provide good fits to species abundance distributions observed in nature. Major criticisms of neutral theory have focused on interspecific differences, which are in conflict with ecological equivalence. However, neutrality in nature is also broken by differences between conspecific individuals at different life stages, which in many communities may vastly exceed interspecific differences between individuals at similar stages. These within-species asymmetries have not been fully explored in species-neutral models, and it is not known whether demographic stage structure affects macroecological patterns in neutral theory. Here we present a two-stage neutral model where fecundity and mortality change as an individual transitions from one stage to the other. We explore several qualitatively different scenarios, and compare numerically obtained species abundance distributions to the predictions of unstructured neutral theory. We find that abundance distributions are generally robust to this kind of stage structure, but significant departures from unstructured predictions occur if adults have sufficiently low fecundity and mortality. In addition, we show that the cumulative number of births per species, which is distributed as a power law with a 3/2 exponent, is invariant even when the abundance distribution departs from unstructured model predictions. Our findings potentially explain power law-like abundance distributions in organisms with strong demographic structure, such as eusocial insects and humans, and partially rehabilitate species abundance distributions from past criticisms as to their inability to distinguish between biological mechanisms.