Ecology Drives the Worldwide Distribution of Human Diseases
Figure 1
The Spatial Organization of Species
Letters represent different PID species. Numbered rectangles represent different countries or areas.
(A) Nested organization of species. Applying Diamond's theory, we here distinguish (1) “high-S” species, like species E, which are exclusively confined to the most species-rich communities; and (2) “tramps,” like species A, which occur mostly in richer communities but also in species-poor communities (e.g., measles, which is found in virtually every country). Thus, this nested pattern implies that some pathogens are restricted to the tropics, while others, more ubiquitous species, are widely and regularly distributed all over the world.
(B) Random distribution of species, where no spatial organization occurs (see also Materials and Methods).