Class 12 Biology Notes: Biodiversity And Conservation

Key Definitions

Biodiversity

The variety of life on Earth at all its levels, from genes to ecosystems, and the ecological and evolutionary processes that sustain it.

Genetic Diversity

The variation in genes within a single species, allowing populations to adapt to changes in their environment.

Species Diversity

The variety of different species present in a particular region, measured by species richness (number of species) and evenness (relative abundance).

Ecological Diversity

The variety of ecosystems within a region, encompassing different habitats, biotic communities, and ecological processes.

Biodiversity Hotspots

Regions with very high levels of species richness and a high degree of endemism, but also under significant threat of habitat loss.

Endemism

The ecological state of a species being unique to a defined geographic location, such as an island, nation, or other defined zone.

Alien (Exotic) Species

Species introduced intentionally or unintentionally into a habitat where they are not naturally found, often causing harm to native species.

Cryopreservation

A technique of preserving cells, tissues, or organs at very low temperatures (e.g., -196°C in liquid nitrogen) to maintain their viability for future use.

Bioprospecting

Exploring molecular, genetic, and species-level diversity for products of economic importance like medicines, food, fiber, or industrial enzymes.

Patterns of Biodiversity

Biodiversity is not uniformly distributed across the globe; it follows certain patterns. Two significant patterns observed are:

1. Latitudinal Gradients: Generally, species diversity decreases as we move away from the equator towards the poles. Tropical regions (between 23.5° N and 23.5° S latitude) host a greater number of species compared to temperate or polar regions. For example, Colombia, located near the equator, has nearly 1,400 species of birds, while New York (41° N) has 105 species, and Greenland (71° N) has only 56. The reasons for this gradient are complex and debated, but key hypotheses include:

• Stable Climate: Tropical regions have remained relatively undisturbed for millions of years, allowing for longer evolutionary time for species diversification.
• Less Seasonal Variation: More constant and predictable environments in the tropics promote niche specialization and reduce competition.
• Higher Productivity: Greater solar energy availability in the tropics leads to higher primary productivity, which can support a larger and more diverse array of organisms.

1. Species-Area Relationship: German naturalist and geographer Alexander von Humboldt observed that within a region, species richness increases with increasing explored area, but only up to a certain limit. The relationship between species richness (S) and area (A) can be expressed by the equation: log S = log C + Z log A. Here, S = species richness, A = area, Z = slope of the line (regression coefficient), and C = Y-intercept. The value of Z (slope) is usually in the range of 0.1 to 0.2 for small areas, regardless of the taxonomic group or the region. However, for very large areas, like entire continents, the slope of the regression line (Z value) can be much steeper, typically ranging from 0.6 to 1.2. This indicates that larger areas generally support more species due to increased habitat heterogeneity and reduced extinction rates.

Causes of Biodiversity Loss: The Evil Quartet

• Habitat Loss and Fragmentation: The most crucial cause. Destruction of habitats (e.g., rainforests, wetlands) and their division into smaller, isolated patches, leading to reduced populations and increased extinction risk.
• Over-exploitation: Excessive harvesting of resources (plants, animals) beyond their capacity to regenerate, often driven by human greed (e.g., Steller's sea cow, passenger pigeon extinction).
• Alien Species Invasions: Introduction of non-native species into an ecosystem, which can outcompete, prey upon, or introduce diseases to native species, leading to their decline or extinction (e.g., Nile perch into Lake Victoria, Parthenium, Lantana, Eichhornia).
• Co-extinctions: When one species becomes extinct, the species that is obligatorily associated with it (e.g., host fish and its parasites, plant and its pollinator) also faces extinction.
• Amazon Rainforest: Often referred to as the 'lungs of the planet', harboring immense biodiversity, but facing significant deforestation.
• IUCN Red List: A comprehensive inventory of the global conservation status of biological species. It identifies species at risk of extinction.
• Riveting Hypothesis (Paul Ehrlich): Compares ecosystems to an airplane where losing too many rivets (species) can eventually lead to a crash (ecosystem collapse).

In Situ vs. Ex Situ Conservation Strategies

Practical Examples of Biodiversity Conservation

• Biodiversity Hotspots Worldwide, 36 biodiversity hotspots have been identified, covering less than 2% of Earth's land area but harboring over 50% of terrestrial biodiversity. In India, the Western Ghats and Sri Lanka, Indo-Burma, and Himalaya are three major hotspots, characterized by high endemism and threat.
• Sacred Groves Culturally protected forest patches in India (e.g., Khasi and Jaintia Hills in Meghalaya, Aravalli Hills of Rajasthan, Western Ghat regions). These are religious or spiritual sites where cutting trees or hunting is strictly prohibited, thus acting as excellent in situ conservation sites for numerous plants and animals.
• Seed Banks An ex situ conservation method where seeds of different plant species, especially rare and endangered ones, are stored under controlled conditions (low temperature, low humidity) to maintain their viability for long periods. The Svalbard Global Seed Vault is a prominent example.

Exam Tip: Differentiating Conservation Methods

A common mistake students make is confusing in situ and ex situ conservation methods. Remember: In Situ = In place/on site (like national parks, sacred groves where organisms live in their natural environment). Ex Situ = Out of place/off site (like zoos, botanical gardens, seed banks where organisms or their genetic material are preserved outside their natural habitat). Be prepared to provide specific examples for each and explain their advantages/disadvantages. Also, clearly define 'endemism' and 'hotspots' – these are frequently asked terms. Ensure you know 'The Evil Quartet' causes of biodiversity loss thoroughly as it's a very high-yield topic.

Practice Questions with Solutions

• Q: What is the significance of the 'Z' value in the species-area relationship equation? A: The 'Z' value (slope of the regression line) indicates how rapidly species richness increases with increasing area. A higher 'Z' value suggests a greater increase in species richness for a given increase in area.
• Q: Name two major biodiversity hotspots in India. A: The Western Ghats and Sri Lanka, and the Eastern Himalayas (Indo-Burma region is also valid).
• Q: Give one example of an alien species invasion and its impact. A: The introduction of the Nile perch into Lake Victoria led to the extinction of over 200 species of cichlid fish, disrupting the entire ecosystem.
• Q: How do 'sacred groves' contribute to biodiversity conservation? A: Sacred groves are patches of forest protected by local communities on religious grounds, where felling trees or hunting is forbidden. They act as natural sanctuaries for many endemic and threatened species, preserving biodiversity in situ.

Must Remember: Biodiversity Facts & Conservation Efforts

Frequently Asked Questions