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?
Compare these snapshots of typical ecosystems found in the tropics to those found in polar regions. There are lots of species in the tropical photos and far fewer in the polar pictures.
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?