Biodiversity: levels, hotspots and conservation
Biodiversity: genetic, species and ecosystem levels, alpha-beta-gamma, the Shannon index, hotspots, threats, protected areas and global targets.
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Biodiversity, short for biological diversity, is the variety of life at every level: the genes within a species, the species in a community, and the ecosystems in a landscape. The Convention on Biological Diversity (CBD, 1992) defines it as "the variability among living organisms from all sources … and the ecological complexes of which they are part."
Agriculture depends on biodiversity at every turn. It relies on pollinators and natural enemies of pests, on soil organisms that cycle nutrients, and on the genetic variation that breeders use. Agriculture is also the largest driver of biodiversity loss, through land conversion, pesticides, fertiliser run-off and simplified landscapes. The 2019 global assessment by IPBES estimated that around 1 million species face extinction, many within decades, unless action is taken.
Levels of biodiversity
- Genetic diversity is variation within a species: crop varieties and landraces, livestock breeds, and genetic differences between populations. It is the raw material for adaptation and breeding.
- Species diversity is the number and relative abundance of species in an area.
- Ecosystem diversity is the variety of habitats, communities and ecological processes, such as forests, grasslands, wetlands, mangroves and coral reefs.
Alpha, beta and gamma
R. H. Whittaker distinguished three spatial scales of diversity:
- α (alpha) diversity is diversity within a single site or habitat.
- β (beta) diversity is the turnover of species between sites along a gradient. It is high when sites share few species.
- γ (gamma) diversity is total diversity across a landscape or region.
Measuring species diversity
Species richness (S) simply counts species. Evenness describes how equally individuals are spread among species. Diversity indices combine the two:
Two fields compared
Field 1 has three weed species with 50, 30 and 20 individuals (p = 0.5, 0.3, 0.2). Its Shannon index is H′ = −(0.5 ln 0.5 + 0.3 ln 0.3 + 0.2 ln 0.2) = 0.347 + 0.361 + 0.322 = 1.03, and its evenness J = 1.03 ⁄ ln 3 = 0.94. Field 2 also has three species, but with 90, 5 and 5 individuals. Its H′ = 0.095 + 0.150 + 0.150 = 0.39, and J = 0.36. Both fields have the same richness, but field 1 is more diverse because its species are more evenly represented.
Biodiversity hotspots
Norman Myers (1988) proposed hotspots: regions where conservation can protect the most species per unit of effort. Conservation International's criteria are:
- at least 1,500 endemic vascular plant species, more than 0.5% of the world total; and
- at least 70% of the original habitat lost.
There are now 36 hotspots. They cover about 2.5% of Earth's land surface but hold more than half of all endemic plant species.
India has parts of four hotspots:
- the Himalaya;
- Indo-Burma, covering the north-east;
- the Western Ghats and Sri Lanka;
- Sundaland, which includes the Nicobar Islands.
India is one of the 17 megadiverse countries. With about 2.4% of the world's land, it holds roughly 7–8% of recorded species, including many crop wild relatives and traditional varieties.
Threats
The main drivers of loss are often summarised by the acronym HIPPO:
- Habitat loss and fragmentation, mainly from agriculture, infrastructure and urban growth;
- Invasive species, such as Lantana, Parthenium, Prosopis juliflora and water hyacinth in India;
- Pollution, including pesticides, fertiliser run-off, plastics and air pollution;
- Population growth and consumption;
- Overexploitation: overfishing, hunting and illegal wildlife trade.
Climate change is a fast-growing driver, shifting species ranges and disrupting timing, such as flowering and pollinator activity.
In farming systems, the shift to a few high-yielding varieties has caused genetic erosion of landraces. Larger fields and fewer hedges, trees and fallows have reduced on-farm habitat for pollinators, birds and natural enemies of pests.
Conservation approaches
In situ: in natural habitats
India's protected area network includes:
- national parks, where human activities are strictly limited;
- wildlife sanctuaries, where some activities are allowed;
- conservation reserves and community reserves, managed with local people.
These areas number about 1,000 in total and cover roughly 5% of the country. India also has 18 biosphere reserves, many in UNESCO's Man and the Biosphere network. Each has a strictly protected core, a buffer zone and a transition zone with human use.
Other in situ measures include sacred groves, Ramsar wetlands, gene sanctuaries (such as the citrus sanctuary in the Garo Hills), and species programmes such as Project Tiger (1973) and Project Elephant (1992).
Ex situ: outside habitats
Ex situ methods include zoos, botanical gardens, captive breeding, seed and gene banks (such as NBPGR's National Gene Bank and NBAGR for livestock), field gene banks and cryopreservation.
On farms and in landscapes
- Agrobiodiversity conservation includes community seed banks, recognition of farmer varieties under the PPV&FR Act, and the revival of millets and indigenous breeds.
- Biodiversity-friendly farming uses crop diversification, agroforestry, field margins, hedgerows, reduced pesticide use and integrated pest management.
Law and policy
- Wildlife (Protection) Act, 1972, amended in 2022.
- Biological Diversity Act, 2002, amended in 2023. It set up the National Biodiversity Authority, State Biodiversity Boards and village-level Biodiversity Management Committees, which keep People's Biodiversity Registers.
- CBD (1992), the Nagoya Protocol (2010) on access and benefit sharing, and the Kunming–Montreal Global Biodiversity Framework (2022). The Framework's targets include protecting 30% of land and sea by 2030 ("30 by 30") and reducing the overall risk from pesticides and highly hazardous chemicals by at least half.
Key points
- Biodiversity exists at three levels: genetic, species and ecosystem.
- α is diversity within a site, β is turnover between sites, and γ is diversity across a landscape.
- Shannon H′ = −Σpi ln pi combines richness and evenness; Simpson's D = Σpi2.
- Hotspots need at least 1,500 endemic plants and at least 70% habitat loss. There are 36 worldwide; India has parts of four (Himalaya, Indo-Burma, Western Ghats and Sri Lanka, Sundaland).
- Threats are habitat loss, invasive species, pollution, population and consumption, overexploitation (HIPPO), and climate change.
- Conservation can be in situ (national parks, sanctuaries, biosphere reserves), ex situ (gene banks, zoos) or on-farm. Key frameworks are the WPA 1972, BDA 2002, CBD and the Kunming–Montreal targets.
What the exams ask
- Define biodiversity and its levels; distinguish α, β and γ diversity.
- Calculate the Shannon or Simpson index.
- State the hotspot criteria and name India's hotspots.
- Compare in situ and ex situ conservation, with examples.
- Describe the zones of a biosphere reserve and India's biodiversity laws.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Why does biodiversity matter for farmers?
Pollinators raise yields of fruits, vegetables, oilseeds and pulses. Natural enemies keep many pests below damaging levels for free. Soil organisms build fertility, and diverse crops and varieties spread risk against drought and disease. Losing these services increases costs and risk.
Is a monoculture always bad for biodiversity?
A single field of one variety has low biodiversity, but its effect depends on the surrounding landscape. Monocultures within a mosaic of other crops, trees, field margins and natural habitat support far more life than vast uniform landscapes. Producing more food on existing land can also reduce pressure to clear forests.
What is an endemic species?
An endemic species is found naturally in only one region and nowhere else. Examples are the lion-tailed macaque and many frogs and plants of the Western Ghats. Endemics are especially vulnerable, because losing their limited habitat can mean global extinction.
Sources
- IPBES. Global Assessment Report on Biodiversity and Ecosystem Services. IPBES Secretariat, Bonn, 2019.
- Myers, N., Mittermeier, R. A., Mittermeier, C. G., da Fonseca, G. A. B. and Kent, J. "Biodiversity hotspots for conservation priorities." Nature 403, 853–858 (2000).
- Convention on Biological Diversity. Kunming–Montreal Global Biodiversity Framework. Decision 15/4, 2022.
- Magurran, A. E. Measuring Biological Diversity. Blackwell, 2004.
- Odum, E. P. and Barrett, G. W. Fundamentals of Ecology, 5th edition. Thomson Brooks/Cole, 2005.
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