# Global evidence of non-pyramidal and uniform ratios of animal diversity across terrestrial trophic levels

## TL;DR

This study finds that animal diversity is evenly distributed across trophic levels, challenging the expected pyramidal pattern of energy distribution.

## Contribution

The study reveals a non-pyramidal and uniform ratio of species richness across terrestrial trophic levels.

## Key findings

- 46% of terrestrial animal species are primary consumers, 43% are higher-level consumers, and 11% are mixed consumers.
- Species richness ratios across trophic levels are consistent globally, regardless of location or total richness.
- Ecological differentiation at higher trophic levels may offset extinction risks and lead to uniform diversity patterns.

## Abstract

Thermodynamics imposes a well-established pyramidal distribution of energy availability across trophic levels, but whether species richness follows the same pattern remains unclear. In this study, we examined species richness across trophic groups for all known terrestrial tetrapod and arthropod species, representing over 90% of Earth’s terrestrial animal diversity. By categorizing species into fundamental trophic levels, we found that 46% are primary consumers (feeding on plants), 43% are higher-level consumers (feeding on primary consumers) and 11% are mixed consumers (generalists). Further analysis of global community trophic structures in mammals and birds uncovered a consistent ratio of species richness across trophic levels, independent of geographical location or total species richness. We propose that this non-pyramidal distribution of diversity arises from higher ecological differentiation among species at higher trophic levels, which may offset their greater extinction risk associated with smaller populations. This process could generate uniform trophic structures if primarily driven by mechanics intrinsic to trophic positions and their interactions rather than specific environmental characteristics. Such intrinsic mechanisms may ultimately influence diversity across trophic levels and the eco-evolutionary dynamics structuring ecological networks.