Latitudinal Gradients in Biodiversity and Biotic Interactions

Patterns of species diversity and the strength of ecological interactions often vary predictably with latitude, forming one of ecology’s most enduring observations: the latitudinal diversity gradient, whereby species richness peaks in the tropics and declines towards the poles. Underlying this gradient are multiple interacting drivers, including climatic stability, evolutionary history, habitat heterogeneity and energy availability. In terrestrial ecosystems, warmer temperatures and higher primary productivity near the equator tend to support greater numbers of species, while historical refugia and speciation rates contribute to regional endemicity. In marine realms, factors such as ocean currents, depth regimes and salinity gradients overlay thermal effects, producing complex diversity patterns that sometimes diverge from the classic tropical peak. Biotic interactions—including predation, herbivory and parasitism—are hypothesised to intensify at lower latitudes, potentially stabilising high tropical diversity through niche partitioning, mutualism and coevolutionary dynamics. Yet empirical tests reveal that interaction strengths can vary idiosyncratically with taxonomic group, ecosystem type and methodological approach. Contemporary research combines large‐scale species databases, standardised field experiments and meta‐analytical methods to disentangle the relative importance of abiotic drivers and biotic processes across latitudes. This integrated view highlights the global significance of latitudinal patterns for conservation planning, as shifting climates and human impacts reshape both species distributions and the interactions that maintain ecosystem function.

Research from Nature Portfolio

Analyses of global marine biogeographic realms have revealed 30 distinct zones of species assemblages, each with high levels of endemicity, demonstrating how depth, salinity barriers and historical isolation shape large‐scale diversity patterns. A complementary study uncovered a pronounced deficit of marine species records at equatorial latitudes, attributing the apparent dip in tropical richness largely to reduced sampling effort rather than genuine absence. These findings reinforce the need for targeted surveys in data‐poor regions to clarify the true shape of marine diversity gradients. In the open ocean, long‐term fisheries data have shown that predation by large pelagic fish is unexpectedly stronger in temperate waters and inversely related to local species richness, challenging the notion that biotic interactions uniformly intensify towards the equator.

Latitudinal Gradients in Biodiversity and Biotic Interactions publication trend

The graph below shows the total number of articles in latitudinal gradients in biodiversity and biotic interactions across all publications each year (not limited to Nature Index journals).

Technical terms

Latitudinal diversity gradient: The pattern of decreasing species richness from equatorial to polar regions across the globe.

Biotic interactions: Ecological processes such as predation, herbivory, competition and mutualism that occur between living organisms.

Species richness: The count of distinct species present in a defined area or community.

Endemicity: The state of species being unique to a specific geographic region, often due to historical isolation.

References

1. Marine biogeographic realms and species endemicity. Nature Communications (2017).
2. Mapping knowledge gaps in marine diversity reveals a latitudinal gradient of missing species richness. Nature Communications (2018).
3. Pelagic fish predation is stronger at temperate latitudes than near the equator. Nature Communications (2020).
4. Global distribution and richness of terrestrial mammals in tidal marshes. Diversity and Distributions (2023).
5. Latitudinal gradient in the intensity of biotic interactions in terrestrial ecosystems: Sources of variation and differences from the diversity gradient revealed by meta‐analysis. Ecology Letters (2021).