Biodiversity and Conservation Chapter Notes | Biology Class 12 - NEET PDF Download

Introduction

• If an alien from a faraway galaxy were to visit Earth, they would likely be amazed and puzzled by the incredible variety of life on our planet.
• Even for humans, the sheer number of different living organisms is astonishing. For example, there are over 20,000 species of ants, 300,000 species of beetles, 28,000 species of fish, and nearly 20,000 species of orchids.

Understanding Biodiversity

Scientists, such as ecologists and evolutionary biologists, are trying to understand why there are so many different species and how this diversity has come about.

They ask important questions like:

• Why are there so many species?
• Has this diversity always existed throughout Earth's history?
• How did all these different species evolve?
• Why is this diversity important for the biosphere (the global ecosystem)?
• What would happen if there were fewer species?
• How do humans benefit from this diversity of life?

Biodiversity

Biodiversity, a term popularized by sociobiologist Edward Wilson, refers to the combined diversity at all levels of biological organization, from macromolecules within cells to entire biomes.

Levels of Biodiversity

Levels of Biodiversity

(i) Genetic Diversity: This refers to the variation in genetic makeup within a species across different geographical regions. For example, the medicinal plant Rauwolfia vomitoria exhibits genetic differences in the potency and concentration of the active chemical reserpine depending on where it grows. India boasts over 50,000 genetically different strains of rice and 1,000 varieties of mango.

(ii) Species Diversity: This is the variety of species present in a particular area. For instance, the Western Ghats in India have a greater diversity of amphibian species compared to the Eastern Ghats.

(iii) Ecological Diversity: This refers to the variety of ecosystems present in a region. India, with its diverse ecosystems such as deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows, has greater ecological diversity compared to countries like Norway.

Importance of Biodiversity

• Biodiversity is crucial for human survival and well-being. It provides essential services and resources that sustain life on Earth.
• Despite millions of years of evolution to build this rich diversity, we risk losing it all in less than two centuries due to current rates of species loss.
• Biodiversity and its conservation have become vital global issues as more people recognize their critical importance for our future.

How Many Species are there on Earth and How Many in India?

Scientists have recorded and named over 1.5 million species of plants and animals on Earth. However, it's challenging to determine the exact number of species that exist. Estimates of undiscovered species vary widely, with some extreme guesses ranging from 20 to 50 million. A more conservative estimate by Robert May suggests there are about 7 million species globally.

Current Estimates of Species on Earth

• Over 1.5 million species of plants and animals have been described.
• Estimates of total species range from 20 million to 50 million.
• Robert May's estimate: about 7 million species.

Distribution of Species

• More than 70% of recorded species are animals.
• Plants (including algae, fungi, and different types of plants) make up no more than 22% of the total.
• Insects alone account for more than 70% of all animal species.

India's Biodiversity

• India, despite being only 2.4% of the world's land area, holds 8.1% of global species diversity.
• Recorded species in India:45,000 plants and twice as many animals.
• Estimated undiscovered species in India:over 1,00,000 plants and over 3,00,000 animals.

Challenges in Estimating Species

• Many species, especially prokaryotes(like bacteria), are not counted because they are hard to identify and many cannot be grown in labs.
• Estimates for prokaryotes could run into millions if using biochemical or molecular methods.
• India is one of the 12 mega-diversity countries due to its rich variety of species.

Threats to Biodiversity

• A significant number of species are at risk of extinction before they are even discovered.
• The loss of biodiversity is occurring rapidly, with many species disappearing before they can be documented.

Patterns of Biodiversity

(i) Latitudinal gradients

Species diversity is not evenly spread across the globe. One of the most notable patterns is the latitudinal gradient in diversity, where species diversity tends to decrease as we move from the equator towards the poles.

• Tropics vs. Temperate and Polar Regions: Generally, the tropics (23.5° N to 23.5° S) are home to more species than temperate or polar areas.
• Examples: For instance, Colombia, located near the equator, boasts nearly 1,400 species of birds. In contrast, New York at 41° N has 105 species, and Greenland at 71° N has only 56 species. Similarly, India, much of which is in the tropical latitudes, has over 1,200 species of birds.
• Tropical vs. Temperate Forests: A tropical forest in Ecuador can have up to 10 times more species of vascular plants than a temperate forest of the same size, like those in the Midwest of the USA.
• Amazonian Rainforest: The Amazon rainforest, primarily tropical, has the highest biodiversity on Earth, with over 40,000 species of plants, 3,000 species of fish, 1,300 species of birds, 427 species of mammals, 427 species of amphibians, 378 species of reptiles, and more than 125,000 species of invertebrates. Scientists believe there could be at least two million undiscovered insect species in these rainforests.
• Hypotheses for Greater Tropical Diversity: Several hypotheses explain the greater biological diversity in the tropics:
• (a) Speciation and Time: Tropical regions have remained relatively stable and undisturbed for millions of years, unlike temperate regions that have experienced frequent glaciations. This stability has allowed more time for species diversification.
• (b) Environmental Consistency: Tropical environments are less seasonal and more predictable than temperate ones. This consistency promotes niche specialization, leading to greater species diversity.
• (c) Solar Energy and Productivity: The tropics receive more solar energy, which contributes to higher productivity. This increased productivity may indirectly support greater species diversity.

(ii) Species–Area Relationships

• Species richness within a region tends to increase with the area explored, but only up to a certain limit.

• The relationship between species richness and area for various taxa (like plants, birds, bats, and fishes) is depicted as a rectangular hyperbola.
• On a logarithmic scale, this relationship forms a straight line represented by the equation:log S = log C + Z log A
  • S= Species richness
  • A= Area
  • Z = slope of the line (regression coefficient)
  • C = Y-intercept
• Value of Z: The value of Z typically ranges from 0.1 to 0.2, regardless of the taxonomic group or region. This consistency is observed in various studies, whether it’s plants in Britain, birds in California, or molluscs in New York state.
• However, when analyzing species-area relationships across very large areas, such as entire continents, the slope of the line becomes much steeper, with Z values ranging from 0.6 to 1.2.
• Example: For example, the slope for frugivorous birds and mammals in tropical forests across different continents is around 1.15.
• Interpretation of Steeper Slopes: Steeper slopes in species-area relationships for larger areas indicate a stronger positive correlation between area and species richness. This means that, in larger regions, increasing area leads to a more significant increase in the number of species present. The pattern suggests that larger areas can support a greater variety of habitats, resources, and ecological niches, thereby accommodating more species.

Importance of Species Diversity to the Ecosystem

There is a debate among scientists about whether the number of different species in a community is crucial for how well the ecosystem functions. For a long time, ecologists thought that communities with more species are generally more stable than those with fewer species.

Stability in Biological Communities

• Stability in a biological community means that its productivity doesn't change too much from year to year.
• A stable community should be resistant or resilient to disturbances, whether they're natural (like storms) or man-made (like pollution).
• It should also be resistant to invasions by alien species that don't belong there.

Tilman's Experiments

• David Tilman's long-term experiments in outdoor plots have provided some insights into the relationship between species richness and ecosystem stability.
• Tilman found that plots with more species had less year-to-year variation in total biomass.
• He also demonstrated that increased diversity contributed to higher productivity in his experiments.

Biodiversity and Ecosystem Health

• While we may not fully understand how species richness impacts ecosystem health, it is clear that rich biodiversity is essential for the well-being of ecosystems.
• Biodiversity is not just important for ecosystem health; it is also crucial for the survival of the human race on this planet.

Rivet Popper Hypothesis

• When considering the importance of species, ecologist Paul Ehrlich's rivet popper hypothesis provides a useful analogy.
• In an airplane (representing an ecosystem), all parts are held together by thousands of rivets (species).
• If passengers start removing rivets(causing species extinctions), it may not affect the safety of the flight initially.
• However, as more rivets are removed, the airplane becomes increasingly weak over time.
• The specific rivets that are removed also matter; losing rivets on the wings (key species driving major ecosystem functions) is a more serious threat to flight safety than losing a few rivets inside the plane.

Loss of Biodiversity

While it is uncertain whether new species are being added to the planet through speciation, there is a clear and alarming trend of species loss. Our planet's biological wealth is rapidly declining, and human activities are largely to blame. For example, the colonization of tropical Pacific Islands by humans is believed to have caused the extinction of over 2,000 native bird species.

The IUCN Red List (2004) reports that 784 species (including 338 vertebrates, 359 invertebrates, and 87 plants) have gone extinct in the last 500 years. Some recent extinctions include the dodo (Mauritius), quagga (Africa), thylacine (Australia), and Steller’s Sea Cow (Russia). In just the last twenty years, 27 species have disappeared. Extinctions are not random; certain groups, like amphibians, are more vulnerable. Currently, over 15,500 species worldwide are at risk of extinction, including 12% of bird species, 23% of mammal species, 32% of amphibian species, and 31% of gymnosperm species.

Extinct Species

Throughout Earth's history, there have been five mass extinction events, but the current “Sixth Extinction” is different because species are disappearing 100 to 1,000 times faster than before humans existed, primarily due to human actions. If current trends continue, nearly half of all species could be lost within the next 100 years. The loss of biodiversity can lead to a decline in plant production, decreased resistance to environmental changes like drought, and increased variability in ecosystem processes such as plant productivity and pest cycles.

Causes of biodiversity losses

The accelerated rates of species extinctions that the world is facing now are largely due to human activities. There are four major causes (‘ The Evil Quartet’ is the sobriquet used to describe them).

1. Habitat loss and fragmentation

This is the most important cause driving animals and plants to extinction. The most dramatic examples of habitat loss come from tropical rain forests. Once covering more than 14 per cent of the earth’s land surface, these rain forests now cover no more than 6 per cent.

Examples:

• Tropical rain forests are being destroyed rapidly. For instance, the Amazon rain forest, often called the "lungs of the planet," is being cleared for soybean cultivation and beef cattle ranching.
• When large habitats are fragmented into smaller pieces, species that require large territories or have migratory habits struggle to survive. This fragmentation leads to population declines.

2. Over-exploitation

Over-exploitation occurs when humans exploit natural resources out of greed rather than need. Many extinctions in the past 500 years, such as the Steller’s sea cow and passenger pigeon, were due to over-exploitation by humans.

Example: Many marine fish populations around the world are being overharvested, endangering the survival of commercially important species.

3. Alien species invasions

Alien species invasions occur when non-native species are introduced, either intentionally or unintentionally, and some of these species become invasive, causing harm to native species.

Examples:

• The introduction of Nile perch into Lake Victoria in East Africa led to the extinction of over 200 species of native cichlid fish.
• Invasive weed species like carrot grass (Parthenium), Lantana, and water hyacinth (Eichhornia) pose threats to native species.
• The illegal introduction of African catfish (Clarias gariepinus) for aquaculture purposes threatens indigenous catfish species in rivers.

4. Co-extinctions

Co-extinctions occur when the extinction of one species leads to the extinction of other species that are dependent on it.

Examples:

• When a host fish species becomes extinct, its unique assemblage of parasites also becomes extinct.
• In cases of co-evolved plant-pollinator mutualism, the extinction of one species can lead to the extinction of its pollinator.

Biodiversity Conservation

(a) Why Should We Conserve Biodiversity?

Biodiversity is crucial for various reasons, which can be categorized into three main arguments:

(i) Narrowly Utilitarian Argument

• Biodiversity provides direct economic benefits, including food(cereals, pulses, fruits),firewood, fiber, construction materials, industrial products(tannins, lubricants, dyes, resins, perfumes), and medicinal products.
• Over 25% of drugs in the market are derived from plants, with 25,000 species used in traditional medicines.
• There are potentially many more medicinal plants in tropical rainforests waiting to be discovered.
• Bioprospecting involves exploring genetic and species-level diversity for economically important products, benefiting nations rich in biodiversity.

(ii) Broadly Utilitarian Argument

• Biodiversity is essential for ecosystem services such as oxygen production by forests (e.g., the Amazon produces 20% of the Earth’s oxygen).
• Pollination, provided by natural pollinators like bees, birds, and bats, is crucial for plant reproduction and food production.
• There are also intangible benefits from nature, such as the aesthetic pleasure of natural landscapes and sounds.

(iii) Ethical Argument

• Every species has intrinsic value, regardless of its current economic importance.
• We have a moral duty to care for all species and ensure the well-being of future generations by preserving our biological legacy.

(b) How do we conserve Biodiversity?

• When we conserve and protect the whole ecosystem, its biodiversity at all levels is protected - we save the entire forest to save the tiger. This approach is called in situ (on site) conservation. 
• However, when there are situations where an animal or plant is endangered or threatened (organisms facing a very high risk of extinction in the wild in the near future) and needs urgent measures to save it from extinction, ex situ (off site) conservation is the desirable approach.

In- Situ and Ex- Situ Conversation

(i) In situ conservation

Faced with the conflict between development and conservation, many nations find it unrealistic and economically not feasible to conserve all their biological wealth. Invariably, the number of species waiting to be saved from extinction far exceeds the conservation resources available. On a global basis, this problem has been addressed by eminent conservationists. They identified for maximum protection certain biodiversity hotspots regions with very high levels of species richness and high degree of endemism (that is, species confined to that region and not found anywhere else). Initially 25 biodiversity hotspots were identified but subsequently nine more have been added to the list, bringing the total number of biodiversity hotspots in the world to 34. These hotspots are also regions of accelerated habitat loss.

• Three of these hotspots – Western Ghats and Sri Lanka, Indo-Burma, and Himalaya – cover our country’s exceptionally high biodiversity regions.
• Although all the biodiversity hotspots put together cover less than 2 per cent of the earth’s land area, the number of species they collectively harbour is extremely high.
• Strict protection of these hotspots could reduce the ongoing mass extinctions by almost 30 per cent.

• In India, ecologically unique and biodiversity-rich regions are legally protected as biosphere reserves, national parks, and sanctuaries. India now has 14 biosphere reserves, 90 national parks, and 448 wildlife sanctuaries.
• India has also a history of religious and cultural traditions that emphasised protection of nature. In many cultures, tracts of forest were set aside, and all the trees and wildlife within were venerated and given total protection. 
• Such sacred groves are found in Khasi and Jaintia Hills in Meghalaya, Aravalli Hills of Rajasthan, Western Ghat regions of Karnataka and Maharashtra, and the Sarguja, Chanda, and Bastar areas of Madhya Pradesh. In Meghalaya, the sacred groves are the last refuges for a large number of rare and threatened plants.

(ii) Ex situ Conservation

In this approach, threatened animals and plants are taken out from their natural habitat and placed in a special setting where they can be protected and given special care. Zoological parks, botanical gardens, and wildlife safari parks serve this purpose. There are many animals that have become extinct in the wild but continue to be maintained in zoological parks.

• In recent years, ex situ conservation has advanced beyond keeping threatened species in enclosures.
• Now gametes of threatened species can be preserved in viable and fertile condition for long periods using cryopreservation techniques.
• Eggs can be fertilised in vitro, and plants can be propagated using tissue culture methods.
• Seeds of different genetic strains of commercially important plants can be kept for long periods in seed banks.

• Biodiversity knows no political boundaries and its conservation is therefore a collective responsibility of all nations. The historic Convention on Biological Diversity (‘The Earth Summit’) held in Rio de Janeiro in 1992, called upon all nations to take appropriate measures for conservation of biodiversity and sustainable utilisation of its benefits. 
• In a follow-up, the World Summit on Sustainable Development held in 2002 in Johannesburg, South Africa, 190 countries pledged their commitment to achieve by 2010, a significant reduction in the current rate of biodiversity loss at global, regional and local levels.