Humboldt’s Enigma

General Studies Paper -3

Context: Humboldt’s enigma is one of many puzzles of mountain biodiversity.

• The world’s tropical areas receive more energy from the Sun and have greater primary productivity, which facilitates greater biological diversity.
• Alexander von Humboldt, has observed that mountains contribute disproportionately to the terrestrial biodiversity of Earth, especially in the tropics, where they host hotspots of extraordinary and puzzling richness.

What is Humboldt’s enigma?

• Humboldt’s enigma held that the earth’s tropical areas don’t contain all the biodiverse regions. There are many areas outside the tropics that are highly biodiverse. These places are mountains.
• There is a relationship between temperature, altitude, and humidity on one hand and the occurrence patterns of species (or their biodiversity) on the other.

Indian Scenario

• In the case of India the biodiversity in tropical areas, south of the Tropic of Cancer are supposed to be the most diverse in the country.
• The Western Ghats and Sri Lanka biodiversity hotspot lies in this zone.
• However, the Eastern Himalayas are much more diverse. The area is often considered the second-most diverse area of perching birds in the world.

Reasons of high biodiversity in mountain range

• Geological processes, like uplifts, result in new habitats where new species arise, so the habitats are ‘cradles’.
• Species on some climatologically stable mountains persist there for a long time, so these spots are ‘museums’ that accumulate many such species over time.
• The more heterogeneous the geological composition of mountains is, the more biodiverse they are.

Examples of Humboldt’s enigma

• Coastal tropical sky islands (mountains surrounded by lowlands), like the Shola Sky Islands in the Western Ghats.
• Here, old lineages have persisted on the mountain tops as climates and habitats fluctuated around them in the lower elevations.
• The oldest bird species in the Western Ghats, such as the Sholicola and the Montecincla, are housed on the Shola Sky Islands.
• The northern Andes range in South America is considered the most biodiverse place in the world.
• Different temperatures and rainfall levels support tropical evergreen biomes in the lower elevation to the alpine and tundra biomes near the top.