Species from equator to pole.

Species richness falling from equator to poles, anchored on the bird counts (Colombia ~1400, New York 105, Greenland 56), with the three hypotheses as toggles.

Find the latitude band at which bird richness falls below one-tenth of the equatorial value.

Thinking the gradient is uniform or that temperate forests can match tropical ones per area (Ecuador vs US Midwest is ~10×)

• Diversity is spread unevenly over the Earth. A widely known pattern is the latitudinal gradient: species diversity generally falls from the equator towards the poles.
• With very few exceptions, the tropics (23.5° N to 23.5° S) hold more species than temperate or polar regions.
• Birds: Colombia, near the equator, has nearly 1,400 species; New York at 41° N has 105; Greenland at 71° N has only 56. India, mostly tropical, has more than 1,200.
• A tropical forest in Ecuador can hold up to 10 times as many vascular plant species as an equal area of temperate forest in the Midwest of the USA.
• The Amazonian rain forest, largely tropical, holds the greatest biodiversity on Earth. Its counts: plants over 40,000 species, fishes 3,000, birds 1,300, mammals 427, amphibians 427, reptiles 378, and invertebrates over 1,25,000. At least two million insect species there may still await discovery.
• Hypothesis 1: speciation is a function of time. Temperate regions went through frequent glaciations, while the tropics stayed relatively undisturbed for millions of years, giving more time for diversification.
• Hypothesis 2: tropical environments are less seasonal, more constant and predictable, which promotes niche specialisation and so greater species diversity.
• Hypothesis 3: the tropics receive more solar energy, which raises productivity and may indirectly add to diversity.

Teaching this idea? Put the simulation on your own page or LMS with this code.