Biodiversity: Meaning, Distribution, Types and Importance

Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (genetic variability), species (species diversity), and ecosystem (ecosystem diversity) level.  The first use of the term ‘biological diversity’ was in 1916 in Scientific American by J. Arthur Harris in reference to the flora and fauna diversity of the desert biomes he was studying. The United Nations designated 2011-2020 as the United Nations Decade on Biodiversity.

Distribution of Biodiversity

Biodiversity is not distributed evenly on Earth; it is usually greater in the tropics because of the warm climate and high primary productivity in the region near the equator.

• Tropical forest ecosystems cover less than 10% of earth’s surface and contain about 90% of the world’s species.
• Marine biodiversity is usually higher along coasts in the Western Pacific, where sea surface temperature is highest, and in the mid-latitudinal band in all oceans.
• In the geological history, the Ocean biodiversity was much more than terrestrial as recently as 100 million years ago. During this period, terrestrial biodiversity has expanded dramatically.
• The increase in species richness or biodiversity that occurs from the poles to the tropics, often referred to as the Latitudinal Diversity Gradient (LDG).

Importance of Biodiversity

Biodiversity encompasses the evolutionary, ecological, and cultural processes that sustain life. However, perhaps more importantly, biodiversity plays a fundamental role in maintaining healthy, functioning ecosystems that provide critical “services” behind the scenes.

Biodiversity is essential for human survival and quality of life in many ways. Most directly, biodiversity provides a wide range of food sources, medicines, fuels, and raw materials we harness for our benefit. An estimated 40 per cent of the global economy is based on biological products and processes. Poor people, especially those living in areas of low agricultural productivity, depend especially heavily on the genetic diversity of the environment. There are also non-use values of biodiversity, such as option value (for future use or non-use), bequest value (in passing on a resource to future generations), existence value (value to people irrespective of use or non-use) and intrinsic value (inherent worth, independent of that placed upon it by humans).

Some of the key ecosystem services enabled by biodiversity including

• Formation of Soil
• Fertility of the soil
• Increase in overall crop yield and fodder production
• Increase in soil nutrient remineralisation
• Increases resistance to plant invasion
• Decreases disease prevalence on plants
• Increases soil organic matter

Biodiversity and Soil Formation

Different organisms like bacteria, fungi, insects, and plants all help break down rocks/organic matter and enable soil genesis. Their biodiversity lets them fill specialized niches for decomposition.

Biodiversity and Soil Fertility

Healthy soil depends on biodiversity. Nitrogen fixing bacteria, leaf litter decomposing insects/fungi, and mycorrhizal fungi that shuttle nutrients to roots all enhance plant growth. Their functions are interdependent – losing one species can collapse fertility.

Biodiversity and  Increased Crop Yields

Studies consistently find that higher biodiversity correlates with higher crop yields and quality. More species leads to better nutrient cycling, soil conservation, pollination, and natural pest control. This buffers yields against disease/climate fluctuations.

Types of Biodiversity

Broadly, there are three types of biodiversity as follows:

Genetic Diversity

Genetic Diversity refers to the variation in genes found within a species. For example, not all oak trees are identical – some may be more resistant to disease while others grow faster. This genetic variability allows species to adapt and survive changes. It’s like having a diverse skill set. These key points about genetic diversity are:

• It occurs due to variability in the gene pool of a species
• Conferred by differences in DNA
• Allows populations to adapt to changes (disease resistance)
• Prevents extinction events

Species Diversity

Species diversity means having many different types of species living together, rather than just one or two species dominating an area. For example, a forest with only pine trees has low species diversity compared to a rainforest teaming with thousands of plants and animals. Different species depend on each other in ecosystems. The key points about species diversity are:

• Not just the number of species but their relative abundance
• Considers species’ roles and interactions in the community
• More diversity provides functional redundancy if one species declines
• Keeps ecosystems stable amid population fluctuations

Ecosystem Diversity

Ecosystem diversity is having many different types of ecosystems and habitats in a region. For instance, a landscape with just grassland is less diverse than one with lakes, forests, meadows and deserts. Having this variety of habitats allows more species to thrive and survive disruptions like fires or floods. It provides more options. Important points on Ecosystem diversity are:

• Variability in habitats across geography
• Accounts for biological and non-biological factors
• Creates a mosaic of communities across landscapes
• Buffers ecosystems against regional disturbances like fires or floods
• Allows species to move between intact habitats if one is damaged
• Enables overall species diversity to be maintained at landscape scales

While genetic diversity provides adaptability, species diversity provides stability through redundancy, and ecosystem diversity provides connectivity across space to protect biodiversity when localized disturbances occur. All three facets are important for preserving biodiversity at different scales.

Estimating current biodiversity

Estimating Earth’s total biodiversity is challenging, but best current science suggests there are 8-20 million eukaryotic species globally. Only about 1.5 million species have been formally identified/named so far, indicating there are many yet to be discovered. Calculating total biodiversity requires using multiple methods to estimate numbers across ecosystems and taxa. DNA analysis allows scientists to extrapolate species numbers from limited sampling. Much biodiversity remains undocumented, especially microbial species.

More than 99.9% of all species that ever lived on Earth, amounting to over five billion species, are estimated to be extinct.

Threats to Biodiversity

Since life began on Earth, five major mass extinctions and several minor events have led to large and sudden drops in biodiversity. The period since the emergence of humans has displayed an ongoing biodiversity loss and an accompanying loss of genetic diversity. This process is often referred to as Holocene extinction, or sixth mass extinction. Biodiversity loss is also “one of the most critical manifestations of the Anthropocene” a new proposed geological epoch which is thought to have started around the 1950s. The reduction is caused primarily by human impacts, particularly habitat destruction.