The world’s tropical areas receive more energy from the Sun because of the earth’s angle of inclination. Consequently, the tropics have greater primary productivity, which then facilitates greater diversity.
Key points
- The proponents of Humboldt’s enigma have held that the earth’s tropical areas by themselves don’t contain all the biodiverse regions, and that many areas outside the tropics are highly biodiverse. These places are mountains.
- Humboldt’s enigma example in India: Biodiversity in India’s tropical areas, south of the Tropic of Cancer passing through Madhya Pradesh and Chhattisgarh, are supposed to be the most diverse in the country. The Western Ghats plus Sri Lanka biodiversity hotspot lies in this zone. However, the eastern Himalayas are much more diverse. Some scientists have even suggested this part of the mountain range is the second-most diverse area of perching birds in the world.
- Modern understanding of Humboldt’s enigma: Scientists have found that the more heterogeneous the geological composition of mountains is, the more biodiverse they are.
- Around the world, all mountains with high biodiversity have high geological heterogeneity as well, especially in the tropics.
- Even in tropical regions, some mountains with a lower variety of rocks are relatively less biodiverse.
