Introducing the LDG
The pattern of having lots of species at the equator with diversity dwindling off towards the poles is known as the Latitudinal Diversity Gradient "latitudinal" meaning how far north or south of the equator, "diversity" meaning the number of species, and "gradient" meaning the transition between high and low. We'll just call this mouthful the LDG for short.
Before scientists try to explain a pattern, they need to convince themselves that there is a pattern so the first question we'll try to answer is …
Is the LDG real?
Based on these photos, the LDG sure seems to be real. In science, however, we can't rely on impressions alone. Before we accept an idea, we need carefully collected evidence supporting that idea. What sort of data would it take to convince you that the LDG is real?
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Globe graphic adapted from an original illustration at http://www.flickr.com/photos/ontdesign/ / CC BY-SA 2.0Tundra (Churchill, Manitoba) photo courtesy of Dr. Robert T. and Margaret Orr © California Academy of Sciences; Costa Rica jungle photo courtesy of Lloyd Gomez © California Academy of Sciences; Under Arctic ice photo by Elisabeth Calvert, courtesy of the Hidden Ocean 2005 Expedition: NOAA Office of Ocean Exploration
Understanding Evolution © 2016 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California