Ecology Drives the Worldwide Distribution of Human Diseases

TLDR

The latitudinal diversity gradient is a key ecological pattern whose drivers remain unclear, and most research has focused on free‑living organisms, overlooking parasitic and infectious disease species. The study investigates how environmental factors shape the global diversity and spatial distribution of human pathogens. The authors applied generalized linear multivariate models and Monte Carlo simulations to compare human pathogen patterns with those of other taxonomic groups. They found that human pathogen richness declines with latitude, follows a nested spatial pattern, and is mainly driven by climate, supporting the view that biotic interactions largely generate the latitudinal diversity gradient and that including parasites and pathogens could raise total species diversity estimates by more than an order of magnitude.

Abstract

Identifying the factors underlying the origin and maintenance of the latitudinal diversity gradient is a central problem in ecology, but no consensus has emerged on which processes might generate this broad pattern. Interestingly, the vast majority of studies exploring the gradient have focused on free-living organisms, ignoring parasitic and infectious disease (PID) species. Here, we address the influence of environmental factors on the biological diversity of human pathogens and their global spatial organization. Using generalized linear multivariate models and Monte Carlo simulations, we conducted a series of comparative analyses to test the hypothesis that human PIDs exhibit the same global patterns of distribution as other taxonomic groups. We found a significant negative relationship between latitude and PID species richness, and a nested spatial organization, i.e., the accumulation of PID species with latitude, over large spatial scales. Additionally, our results show that climatic factors are of primary importance in explaining the link between latitude and the spatial pattern of human pathogens. Based on our findings, we propose that the global latitudinal species diversity gradient might be generated in large part by biotic interactions, providing strong support for the idea that current estimates of species diversity are substantially underestimated. When parasites and pathogens are included, estimates of total species diversity may increase by more than an order of magnitude.