HUMBOLDT'S ENIGMA

• Throughout centuries, explorers and naturalists have posed the question about the factors influencing biodiversity, particularly why certain areas exhibit greater biodiversity than others. Alexander von Humboldt (1769-1859), a versatile scholar with interests spanning geography, geology, meteorology, and biology, delved into this inquiry during his exploration of South America.
• Notably, he documented the distribution of plants on a mountain and observed similarities in climates across mountains worldwide, noting that specific features varied with elevation.
• Humboldt's extensive studies led him to propose a correlation between temperature, altitude, humidity, and the occurrence patterns of species, shaping their biodiversity. He exemplified this relationship using Chimborazo mountain in Ecuador, now a key illustration of mountain diversity.
• In the present day, a group of biogeographers, scientists specializing in exploring the relationship between diversity and geography, employed modern tools to reexamine the drivers of biodiversity. Drawing on their findings, they put forth their interpretation of the connection between biodiversity and mountains, coining it as 'Humboldt’s enigma

3.What is Humboldt’s enigma?

• The Sun's angle of inclination results in higher solar energy reaching the world's tropical regions, leading to increased primary productivity.
• Consequently, the tropics exhibit greater diversity by providing more ecological niches, fostering complex ecosystems, and enhancing biological diversity.
• Supporters of Humboldt's enigma argue that biodiversity is not solely confined to the Earth's tropical areas; many biodiverse regions exist beyond the tropics, particularly in mountainous areas.
• Despite the general expectation of decreasing diversity away from the tropics, mountains represent a notable exception, forming the core of Humboldt's enigma.
• However, gathering scientific evidence to support this idea is challenging, involving intricate analytical methods and extensive datasets across various taxonomic groups, and it remains an ongoing effort.
• To illustrate Humboldt's enigma in the context of India, one can consider the biodiversity in tropical regions south of the Tropic of Cancer, spanning Madhya Pradesh and Chhattisgarh.
• These areas are presumed to be the country's most diverse, housing the Western Ghats plus Sri Lanka biodiversity hotspot.
• Surprisingly, the eastern Himalaya region surpasses them in diversity. Some researchers even propose that this section of the mountain range ranks as the second-most diverse area globally for perching birds, with the highest diversity for river birds

4.What drives biodiversity?

• The diversity of mountains is primarily shaped by the Earth's history, geography, and climate, with variations in biodiversity across locations arising from the intricate interplay of these factors over time and space.
• Mountain ecosystems contribute to biodiversity through two key processes. Firstly, geological activities such as uplifts create new habitats, acting as 'cradles' where new species emerge. Secondly, some mountains serve as 'museums,' hosting species that persist over extended periods due to climatic stability.
• Coastal tropical sky islands, like the Shola Sky Islands in the Western Ghats, exemplify this, where ancient lineages endure on mountain tops amid changing climates and habitats in lower elevations.
• A single mountain can simultaneously function as a cradle for some species and a museum for others, depending on their ecological characteristics.
• The northern Andes range, including Chimborazo, stands out as the world's most biodiverse area. Ascending from the foothills to the summit reveals diverse temperature and rainfall levels, supporting various biomes and contributing to the remarkable biodiversity of mountain regions globally.
• Geological factors play a critical role in biodiversity formation, as the foundation of mountains differs from that of low-elevation regions. Mountains with higher geological heterogeneity tend to be more biodiverse.
• This pattern holds true globally, especially in the tropics. Even within tropical regions, mountains with lower rock diversity may exhibit relatively lower biodiversity.
• The geological composition influences soil type, affecting plant life, creating unique habitat patches, and promoting diversification.
• In the context of the eastern Himalaya, climate dissimilarity remains a crucial factor influencing biodiversity. Observations from Humboldt's study of Chimborazo support this paradigm.
• Additionally, researchers have identified bird groups that evolved elsewhere and dispersed to the Himalaya, contributing to the region's higher diversity

5.Humboldt Enigma Across the World

• Various factors contribute to the diversification and the Humboldt's enigma in different regions worldwide. Scientists have put forth over a hundred hypotheses to explain the variation in diversity across different parts of the world, approaching the enigma in diverse ways. This article aims to provide an overview of the broader context.
• A significant challenge in explaining biodiversity patterns lies in the limited availability of detailed data on species distribution. Currently, birds are the most extensively studied group globally, and their diversity patterns indicate the pivotal role of mountains.
• There is a pressing need for further research, especially in understudied areas within India. Comprehensive understanding of true biodiversity requires the application of modern tools like genetics.
• For instance, the absence of endemic passerine birds in the Eastern Ghats could be attributed to a lack of scientific study, particularly with contemporary methodologies, over the past century.
• National programs such as the National Mission on Himalayan Studies, the National Mission for Sustaining the Himalayan Ecosystem, and the National Mission on Biodiversity and Human Wellbeing aim to address these knowledge gaps.
• However, these initiatives require strengthening, supported by a commitment to fund basic research on diversity.
• Humboldt's enigma represents just one of the numerous puzzles surrounding mountain biodiversity. Our local environments serve as excellent locations for studying these puzzles, offering insights that contribute to addressing global challenges related to climate and landscape change

6.Way forward

Explorers and scientists have long wondered why some areas are more biodiverse than others. The variation in biodiversity among regions, along with the extreme species richness of some tropical mountains, has proven challenging

Source: The Hindu