Biomass pyramids do not translate into diversity pyramids, a global study shows.
The new research also finds a strikingly uniform ratio of herbivores and predators across the planet’s land animals, challenging classic ideas about how biodiversity is organised
A new global analysis of more than one million terrestrial animal species has revealed that, contrary to textbook diagrams, biodiversity across trophic levels is not generally organised as a pyramid of many herbivores supported by fewer predators. Instead, the overall pattern of species richness across food structures is closer to a “square”, with comparable numbers of species at lower and higher trophic levels, and remarkably constant predator–prey ratios across the globe.
The study, by Luis F. Camacho and Miguel B. Araújo and published today in Proceedings of the Royal Society B, brings together diet information for virtually all known terrestrial tetrapods (mammals, birds, reptiles and amphibians) and more than a million terrestrial arthropods — a sample that represents over 90% of described land animals.
Key findings
- Across all terrestrial tetrapods and arthropods combined, roughly 46% of species are primary consumers (feeding on plants), about 43% are higher-level consumers (feeding on other consumers), and around 11% are mixed feeders that regularly use both plant and animal resources.
- Tetrapods alone show an inverted pyramid of diversity: nearly 70% of species are higher-level consumers, with herbivores in the minority. This pattern is especially strong in reptiles and amphibians.
- Terrestrial arthropods, thanks to their enormous diversity, flatten the global pattern into a near-square, with similar numbers of plant-eaters and predators.
- When the authors mapped terrestrial tetrapods worldwide, the relative proportions of herbivores, predators and mixed feeders remained strikingly stable across six very different “trophic biomes”, from boreal forests to humid tropical regions, despite large differences in climate, productivity and total species richness.
- For birds and mammals, even when the researchers looked not only at how many species occur at each trophic level, but at the composition of their diets, the proportion of plant-based versus animal-based food in whole communities was again extremely consistent across regions.
“Energy is pyramidal. Species richness is not.”
Ecology textbooks typically depict ecosystems as pyramids: abundant plant biomass at the base, fewer herbivores above, and even fewer predators at the top. That shape is rooted in thermodynamics: energy is inevitably lost when it flows from one trophic level to the next.
The new study shows that species richness does not necessarily follow the same rule. “We are used to thinking that more energy at the base means more herbivore species and fewer predators,” says Luis F. Camacho. “What we find instead is that predators and other higher-level consumers can be just as diverse as herbivores, or even more so, while the overall ratios stay surprisingly uniform across the planet.”
According to the authors, this suggests that the distribution of diversity across trophic levels is not dictated directly by energy availability, but emerges from eco-evolutionary processes acting over long time scales.
Why so many predators?
Higher-level consumers typically live at lower population densities and are thought to face higher extinction risks. So how can they match or exceed herbivores in species richness?
The authors propose that greater opportunities for ecological differentiation at higher trophic levels may allow predators and other consumers to diversify more rapidly, offsetting their higher extinction risk. Meat is easier to digest than wood; prey can be mobile or sedentary; and carnivores can exploit multiple trophic levels, creating many axes along which niches can diverge.
“Our results are consistent with the idea that predators may both go extinct and diversify faster, leading to high turnover but also high long-term richness,” explains Miguel B. Araújo. “At the same time, we see a remarkably stable ratio of species across trophic levels, which hints at constraints imposed by the structure and stability of ecological networks themselves.”
The study also notes that trophic omnivores — species feeding heavily across multiple trophic levels — are relatively rare in most groups, suggesting that diversification tends to favour more specialised positions along the trophic hierarchy.
A possible role for selection at the system level
The authors argue that the uniformity of trophic ratios across environments may reflect not only selection on individual organisms, but also a form of selection acting on whole ecological networks. Food webs with unstable or maladaptive configurations may be more likely to collapse or fail to persist over evolutionary time, leaving behind network structures that are dynamically more robust.
This idea resonates with previous work showing that human disturbance can systematically alter food-web topology and species interaction networks, potentially pushing them away from the “typical” configurations revealed in this global analysis.
How the study was done
To build a global picture of trophic structure, the team:
- Compiled diet information from large trait databases, taxonomic revisions and natural history sources for 5237 mammal species, 9271 birds, 8767 reptiles, 2477 amphibians and over 1,075,000 terrestrial arthropods.
- Classified each species according to the proportion of its diet derived from primary production (plants and plant-based resources) versus higher-level consumption (animals, fungi and other consumers), using a strictly energetic definition of trophic levels originating with Raymond Lindeman.
- Mapped all native terrestrial tetrapod species onto a global grid of one-degree cells, and linked these communities to previously defined “community trophic structures” (trophic biomes) based on their guild composition.
- Analysed how the proportions of primary, mixed and higher-level consumers — and the balance of plant versus animal items in birds’ and mammals’ diets — vary across these trophic biomes and across the globe.
Implications for biodiversity research and conservation
By revealing that species richness across trophic levels conforms to simple, highly regular patterns at the global scale, the study opens new avenues for understanding how biodiversity is assembled and maintained over deep time.
The findings imply that:
- Predators and other higher-level consumers are central to global biodiversity, not just functionally but also in terms of species numbers.
- Conservation policies that disproportionately erode higher trophic levels may push ecosystems away from the typical, evolutionarily “filtered” configurations described in the study.
- Theoretical models of ecosystem stability and global change may need to account explicitly for uniform trophic ratios and potential selection at the level of ecological networks, not only at the level of individual species.
“If there are universal constraints shaping how diversity is distributed along food chains, we need to understand them,” says Araújo. “Only then can we anticipate how ecosystems will respond when we selectively remove species from particular trophic levels.”
Article details
Camacho, L. F. & Araújo, M. B. (2025). Global evidence of non-pyramidal and uniform ratios of animal diversity across terrestrial trophic levels. Proceedings of the Royal Society B, 292: 20252335.