15. Biodiversity , Conservation and environmental issues

15. Biodiversity , Conservation and Environment Environmental issues

Biodiversity: Variety of life on Earth.

● Includes a vast range of organisms: Microorganisms, viruses, algae, fungi, Plants and animals.

● Found in terrestrial and aquatic habitats, along with the ecological complexes they form.

Basis of Biodiversity

Biodiversity refers to variations among organisms in:

● Size: Microscopic to macroscopic.

● Shape, colour and form.

● Mode of nutrition.

● Type of habitat.

● Reproduction and motility (ability to move).

● Life-cycle duration.

How Does Biodiversity Develop?

Organisms face different environmental conditions and adapt for survival and perpetuation (continuation of their species).

Environmental factors include:

• Climatic: Temperature, rainfall, etc.

• Edaphic: Soil-related factors.

• Topographic: Land features and elevation.

• Geographic: Location and distribution.

Adaptations develop distinct features in organisms.These differences contribute to biodiversity.

Definition of Biodiversity

Biodiversity: Total variety of genes, species and ecosystems in a particular region.

Includes three levels:

1. Genetic diversity: Differences in genes among individuals of the same species.

2. Species diversity: Variety and richness of plant and animal species at local, national and global levels.

3. Ecosystem diversity: Variety of terrestrial and aquatic ecosystems within a defined area.

Origin of the Term

Walter Rosen (1982): Coined the term Biodiversity.

Edward Wilson: Popularised the term to describe diversity at all levels of biological organisation.

Evolution of Biodiversity

Present-day biodiversity is the result of over 3.5 billion years of evolutionary history.

Mainly influenced by:

● Natural processes.

● Human activities, particularly in recent times.

15.1 Levels of Biodiversity

Biodiversity exists at different levels, from molecular to ecosystem level.

Three major, hierarchical and interrelated levels:

1. Genetic diversity

2. Species diversity

3. Ecological (ecosystem) diversity

A. Genetic Diversity

Intraspecific diversity: Variation within the same species.

Includes differences in:

Number and types of genes and chromosomes.

Genes and their alleles (alternative forms of a gene).

Individuals within a population and between different populations.

Helps organisms adapt to local environmental conditions.

Genetic variations:

Produce individual differences.

Provide raw material for evolution.

Increase chances of survival in changing environments.

Examples:

India has about 1,000 varieties of mangoes and 50,000 varieties of rice or wheat.

Rauwolfia serpentina (medicinal plant) shows variation in the potency and concentration of its active chemical reserpine across different Himalayan regions.

Existence of subspecies and races.

Importance: Genetic variability is essential for a healthy breeding population and long-term survival of a species.

B. Species Diversity

Interspecific diversity: Diversity between different species.

Refers to the variety and number of plant and animal species in a region.

Two components:

Species richness: Number of different species.

Species evenness: Relative number of individuals belonging to different species.

Examples:

Amphibian diversity is greater in the Western Ghats than in the Eastern Ghats.

Natural, undisturbed tropical forests have greater species richness than monoculture timber plantations.

India is among the 15 nations rich in species diversity.

C. Ecological (Ecosystem) Diversity

Refers to the variety of ecosystems and habitats within a geographical region.

Each ecosystem has its own distinctive, interlinked species.

Depends on differences in habitats and environmental conditions.

Examples:

India has high ecosystem diversity: deserts, rainforests, deciduous forests, estuaries, wetlands and grasslands.

Western Ghats show high ecosystem diversity.

Norway has relatively low ecosystem diversity.

Ladakh and Rann of Kutch show less ecosystem variation than the Western Ghats.

15.2 Patterns of Biodiversity

Biodiversity shows two major patterns:

1. Latitudinal and altitudinal gradients

2. Species–area relationship

A. Latitudinal and Altitudinal Gradients

1. Latitudinal Gradient

Latitudinal gradient: Variation in species richness from the equator towards the poles.

Species richness is maximum at lower latitudes (tropics) and gradually decreases towards the poles.

This pattern is observed in many plants and animals, except in certain arid, semiarid and aquatic habitats.

Why are tropical regions richer in species?

Long-term climatic stability: Fewer drastic climatic changes over millions of years favoured speciation.

Less disturbance: Tropical regions experienced fewer periodic glaciations than polar regions.

Reduced migration: Less migration may have reduced gene flow between isolated populations, favouring speciation.

Favourable conditions: More intense sunlight, warmer temperatures and higher annual rainfall.

Abundant resources: Stable climate and food availability support more species.

Example:

Tropical rainforests have maximum species richness.

Amazon rainforest:

40,000 plant species.

1,300 bird species.

427 mammal species.

3,000 other species

2. Altitudinal Gradient

Altitudinal gradient: Variation in species diversity with increasing height above Mean Sea Level (MSL).

Species diversity is higher at lower altitudes and decreases at higher altitudes.

Reasons:

Greater climatic changes.

Drastic seasonal variations at higher altitudes.

B. Species–Area Relationship

Describes the relationship between species richness and the area of a habitat.

Alexander von Humboldt (German naturalist) observed that species richness increases with increasing area, but only up to a certain limit.

Larger areas generally provide more resources and habitats for species.

For many species, the relationship forms a rectangular hyperbola.

Equation:

log S = log C + Z log A

Where:

S = Species richness.

A = Area under study.

C = Y-intercept.

Z = Slope of the line.

Important observations:

On a logarithmic scale, the relationship becomes a straight line.

For smaller areas, Z = 0.1–0.2, irrespective of the species or region.

For very large areas (e.g. entire continents), the slope becomes steeper (closer to the vertical axis).

This indicates that species richness increases more rapidly with area in very large regions.

PYQs from 2024

Q. (x) Observe the graph and select the correct option:

(a) Line 'A' represents S = CA².

(b) Line 'B' represents log C = log A + Z log S.

(c) Line 'A' represents S = CAᶻ.

(d) Line 'B' represents log S = log Z + C log A.

Importance of Species Diversity to the Ecosystem

1. Stability of an Ecosystem

A stable ecological community has:

Constant productivity: Average biomass production remains fairly constant over time.

Resistance: Ability to withstand disturbances.

Recovery: Ability to recover quickly after disturbances.

Resistance to invasive species: Prevents establishment of unwanted species.

2. Productivity–Stability Hypothesis

David Tillman conducted field experiments and showed that greater species richness helps maintain ecosystem stability.

Higher species diversity leads to less variation in biomass production over time.

This concept is called the Productivity–Stability Hypothesis.

3. Rivet Popper Hypothesis

Proposed by Paul Ehrlich, an ecologist from Stanford.

Explains the importance of species diversity using an analogy:

Aeroplane = Ecosystem

Rivets = Species

Rivets hold different parts of an aeroplane together, just as species maintain ecosystem functioning.

Removal of a few rivets may initially cause little noticeable effect.

As more rivets are removed, the aeroplane becomes unsafe.

Similarly, extinction of species may not immediately disturb an ecosystem, but continuous species loss creates serious threats.

Removal of key rivets (species at critical positions, like those joining wings to the body) can cause serious damage even sooner.

4. Effects of Species Loss

Loss of important species can disturb:

Food chains and food webs.

Energy flow.

Natural nutrient cycles.

Overall ecosystem balance.

PYQs from 2023

Q. (v) Rivet Popper Hypothesis is an analogy to explain the significance of ______.

(a) Biodiversity

(b) Natality

(c) Sex-ratio

(d) Age distribution ratio

15.3 Biodiversity: Current Scenario

1. Global Biodiversity

Exact number of species on Earth is not known.

According to IUCN data (2004), over 1.5 million species have been documented.

Many species are still undiscovered, especially in tropical rainforests.

Most biodiversity studies have been conducted in temperate regions.

Estimates of total global species:

Some estimates: 20–50 million species.

Robert May: Approximately 7 million species (more convincing estimate).

2. Why Are Many Species Still Undiscovered?

Tropical rainforests, major biodiversity hotspots, are not fully explored.

Many prokaryotic (Moneran) species cannot be cultured under laboratory conditions.

Conventional taxonomic methods are unsuitable for identifying many prokaryotic species.

Speciation (formation of new species) may still be continuing.

3. India's Biodiversity

India is one of the 12 megadiversity countries.

Contains approximately 8.1% of global biodiversity.

Covers only 2.4% of the world's total land area.

Recorded species:

Around 45,000 plant species.

Nearly 90,000 animal species (almost double the number of plants).

According to Robert May's estimate, only 22% of India's natural wealth has been recorded.

4. Need for Biodiversity Exploration and Conservation

More taxonomists are needed to identify and study biodiversity.

Major concern: Species may become extinct before being discovered.

Threatening human activities:

Reclamation: Converting wetlands or other natural areas into land for human use.

Deforestation: Large-scale removal of forests.

Revision: 

Documented globally: 1.5 million+

Robert May's global estimate: 7 million

India's share: 8.1%

India's land area: 2.4%

Recorded plants in India: 45,000

Recorded animals in India: Nearly 90,000

Recorded natural wealth: 22%

15.4 Loss of Biodiversity

1. Meaning and Effects

Biodiversity loss: Decline or disappearance of species from an ecosystem.

Major consequence: Ecosystem imbalance.

Can cause:

Decline in plant production.

Reduced ability to recover from disturbances (e.g. floods).

Changes in disease cycles and environmental processes.

Changes in plant productivity.

2. Types of Extinction

1. Natural extinction: Occurs due to natural processes.

2. Mass extinction: Large-scale extinction of many plant and animal groups.

3. Anthropogenic extinction: Extinction caused by human activities.

3. Causes of Biodiversity Damage

Natural causes:

Forest fires.

Earthquakes.

Volcanic eruptions.

Human-made causes:

Habitat destruction.

Hunting.

Human settlements.

Overexploitation.

Reclamation of mangrove lands.

4. Mass Extinctions

Earth has experienced six major mass extinction events in its geological history ex. ice age.

Present biodiversity loss is considered the 7th extinction.

Current extinction rate is estimated to be 100–1,000 times faster than pre-human times.

Ecologists identify human interference with natural habitats as a major cause.

If the trend continues, approximately 50% of biodiversity may be lost.

The Evil Quartet: Four Major Causes of Biodiversity Loss

1. Habitat Loss and Fragmentation

Prime cause of biodiversity loss.

Natural habitats are destroyed or divided into smaller, isolated patches.

Pollution also causes local habitat degradation.

Threatens:

Migratory birds.

Animals requiring large territories.

Tropical rainforest cover has decreased from 14% to 6% over time.

2. Overexploitation

Excessive use of biological resources beyond their ability to recover.

Human tendency to accumulate resources beyond basic needs leads to overexploitation.

Example: Decline in fish populations due to excessive fishing.

Extinct species due to overexploitation:

Dodo.

Steller's sea cow.

Passenger pigeon.

3. Alien Species Invasion

Introduction of a non-native species, accidentally or intentionally, into a new ecosystem.

If it harms native species and threatens their survival, it is called an invasive alien species.

Examples:Carrot grass (Parthenium).

Lantana

Water hyacinth (Eichhornia).

Nile perch introduced into Lake Victoria → caused decline of about 200 native Cichlid fish species.

African catfish (Clarias gariepinus) introduced for aquaculture in India → threatens native catfish varieties.

Major reason: Lack of natural predators in the introduced habitat.

4. Co-extinctions

Occur when two or more species are closely and obligatorily associated.

Extinction of one species leads to extinction of its dependent partner.

Examples:

Extinction of a host fish → extinction of its unique parasites.

Co-evolved plant and pollinator species may face the same threat.

5. Extinct vs Endangered Species

Extinct: A species that has been completely eliminated from Earth.

Example: Dinosaurs.

Endangered: A species whose population has declined greatly and faces a high risk of extinction.

6. IUCN Red Data Book / Red List

Maintained by the International Union for Conservation of Nature and Natural Resources (IUCN).

Records the conservation status of plant and animal species.

7. Example: Great Indian Bustard (Maldhok)

A critically endangered grassland bird.

Considered a flagship species of grasslands.

Last Maldhok in Maharashtra was lost in 2018, according to the textbook.

Now found mainly in Rajasthan and Gujarat.

Example of local extinction due to habitat loss and hunting.

IUCN Categories of Conservation Status

After evaluation, species are classified into the following 9 categories:

1. Extinct (EX)

Last individual has died or no longer exists.

Example: Dodo.

2. Extinct in the Wild (EW)

Species survives only in captivity or outside its natural habitat.

3. Critically Endangered (CR)

Extremely high risk of extinction.

Very few individuals survive.

4. Endangered (EN)

Very high risk of extinction.

Rapid population decline of 50% to over 70% in the previous 10 years or three generations.

5. Vulnerable (VU)

High risk of extinction.

Population decline of 30% to over 50% in the previous 10 years or three generations.

6. Near Threatened (NT)

Close to qualifying as a threatened species.

May become threatened in the near future.

7. Least Concern (LC)

Species are widespread and abundant after assessment.

8. Data Deficient (DD)

Insufficient information is available to assess the risk of extinction.

9. Not Evaluated (NE)

Species have not yet been assessed by the IUCN.