Elevational diversity gradient
Elevational diversity gradient (EDG) is an ecological pattern where biodiversity changes with elevation. The EDG states that species richness tends to decrease as elevation increases, up to a certain point, creating a "diversity bulge" at middle elevations. There have been multiple hypotheses proposed for explaining the EDG, none of which accurately describe the phenomenon in full. A similar pattern, known as the latitudinal diversity gradient, describes an increase in biodiversity from the poles to the equator. While the EDG generally follows the LDG (i.e., high elevations in tropical regions have greater biodiversity than high elevations in temperate regions), the LDG does not account for elevational changes. Origin The first recorded observation of the elevational diversity gradient was by Carl Linnaeus in his treatise On the growth of the habitable Earth. In this document, Linnaeus based his predictions on flood geology, assuming most of the world was at one point inundated, leaving only the highest elevations available for terrestrial life. Since, by Linnaeus’ hypothesis, all life was concentrated at high elevations, a higher species diversity would be observed there even as life re-populated lower elevations. In 1799, Alexander von Humboldt and Aimé Bonpland described elevational changes along the Andean slopes, noting