Biodiversity And Conservation Class 12 Biology Chapter 13 Notes

Biodiversity and Conservation Class 12 Biology Chapter 13 Notes

Biodiversity and Its Significance

Biodiversity encompasses immense diversity at all levels of biological organization, from macromolecules within cells to entire biomes.
The term “biodiversity” was popularized by sociobiologist Edward Wilson to describe diversity at all levels of biological organization.
The most important levels of biodiversity include:
(i) Genetic diversity: Within a single species, there can be high genetic diversity. For example, the medicinal plant Rauwolfia vomitoria may vary in the potency and concentration of its active chemical (reserpine) across different Himalayan ranges. India boasts more than 50,000 genetically distinct rice strains and 1,000 mango varieties.
(ii) Species diversity: This refers to diversity at the species level. The Western Ghats, for instance, exhibit greater amphibian species diversity compared to the Eastern Ghats.
(iii) Ecological diversity: At the ecosystem level, India showcases a rich array of ecosystems, including deserts, rainforests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows. This diversity surpasses that of Scandinavian countries like Norway.
Accumulating this rich diversity in nature has taken millions of years of evolution.
However, if the current rates of species losses persist, we could lose this wealth in less than two centuries.
Biodiversity conservation has become a vital international environmental concern.
People worldwide are increasingly recognizing the critical importance of biodiversity for our survival and overall well-being on Earth.

The Challenge of Cataloging Earth’s Species

While there are records of all discovered and named species, determining the total number of species on Earth remains a challenging question.
The International Union for Conservation of Nature and Natural Resources (IUCN) reported in 2004 that slightly more than 1.5 million plant and animal species have been described. However, the actual number of undiscovered and undescribed species is uncertain and estimates vary widely.
Biologists face greater difficulties in completing species inventories in tropical regions compared to temperate areas.
Some extreme estimates suggest there could be between 20 to 50 million species globally, but a more conservative estimate by Robert May places the number at around 7 million.
Current species inventories reveal that over 70 percent of recorded species are animals, while plants (including algae, fungi, bryophytes, gymnosperms, and angiosperms) make up less than 22 percent.
Insects are the most species-rich group among animals, constituting over 70 percent of the total animal species.
Fungi species outnumber the combined total of fish, amphibians, reptiles, and mammals.
Prokaryotes, a group that includes bacteria and archaea, pose challenges in estimation due to difficulties in identifying microbial species using conventional taxonomic methods. Their diversity might run into millions if biochemical or molecular criteria are applied.
India, despite occupying only 2.4 percent of the world’s land area, accounts for an impressive 8.1 percent of global species diversity, making it one of the 12 mega-diverse countries.
India has recorded around 45,000 plant species and twice as many animal species, but it is estimated that there are more than 1,00,000 plant species and over 3,00,000 animal species yet to be discovered and described in the country.
Completing the inventory of India’s biological diversity is a challenging task due to the vast number of undiscovered species and the potential threat of extinction before they are cataloged.
The situation is further complicated by the fact that many species face the risk of extinction before scientists have the chance to discover and document them, highlighting the urgency of biodiversity conservation efforts.

Latitudinal Gradients in Biodiversity: Exploring the Tropics’ Richness

Biodiversity across the globe is not evenly distributed but exhibits an uneven pattern, with one of the most prominent phenomena being the latitudinal gradient in diversity.
In general, species diversity tends to decrease as one moves away from the equator toward the poles.
The tropics, which encompass a latitudinal range of 23.5° N to 23.5° S, typically harbor more species than temperate or polar regions.
Notable examples of this gradient include Colombia near the equator, boasting nearly 1,400 bird species, while New York at 41° N has 105 species, and Greenland at 71° N has only 56 species. India, with much of its land area in tropical latitudes, supports over 1,200 bird species.
Tropical forests, such as those in Ecuador, exhibit significantly higher species diversity than temperate forests of equal area, with up to 10 times as many species of vascular plants.
The Amazonian rainforest in South America, a predominantly tropical ecosystem, is the most biodiverse place on Earth, hosting over 40,000 plant species, 3,000 fish species, 1,300 bird species, 427 mammal species, 427 amphibian species, 378 reptile species, and more than 1,25,000 invertebrate species. Additionally, scientists estimate that there might be at least two million insect species yet to be discovered and named in these rainforests.

What makes the tropics so unique, accounting for their extraordinary biological diversity? Several hypotheses have been proposed by ecologists and evolutionary biologists:

Speciation and Evolutionary Time: Speciation, the process by which new species evolve, is often a function of time. Tropical latitudes have remained relatively undisturbed for millions of years, allowing for extended periods of evolutionary time, unlike temperate regions that have experienced frequent glaciations and disturbances in the past.
Stability and Niche Specialization: Tropical environments tend to be less seasonal, relatively constant, and predictable compared to temperate regions. This environmental stability promotes niche specialization among species, leading to a greater overall species diversity.
Solar Energy and Productivity: The tropics receive more solar energy, which contributes to higher levels of productivity in the form of abundant plant growth. This increased productivity can indirectly support a larger number of species at various trophic levels, contributing to greater overall diversity.

Species-Area Relationships: Insights from Alexander von Humboldt’s Observations

Alexander von Humboldt, a renowned German naturalist and geographer, conducted extensive explorations in the South American jungles. During his explorations, he observed that within a region, the richness of species increased as the explored area expanded, but only up to a certain limit.
This relationship between species richness and area is not unique to Humboldt’s observations; it applies to a wide variety of taxa, including angiosperm plants, birds, bats, and freshwater fishes. It is described as a rectangular hyperbola and can be expressed mathematically as: log S = log C + Z log A where:
- S = Species richness
- A = Area
- Z = Slope of the regression line (regression coefficient)
- C = Y-intercept
Ecologists have found that the value of Z, the slope, falls in the range of 0.1 to 0.2 consistently across various taxonomic groups and regions. Whether it’s plants in Britain, birds in California, or molluscs in New York state, the slopes of the regression lines are remarkably similar.
However, when analyzing species-area relationships over very large areas, such as entire continents, the slope of the line becomes much steeper. In these cases, Z values range from 0.6 to 1.2.
For instance, when studying frugivorous (fruit-eating) birds and mammals in the tropical forests of different continents, the slope of the species-area relationship is found to be 1.15.

The Importance of Species Richness in Ecosystems

The question of whether the number of species in a community truly matters for ecosystem functioning is one that ecologists have grappled with without a definitive answer.
Traditionally, ecologists believed that communities with higher species richness tend to be more stable. Stability, in this context, refers to the community’s ability to maintain consistent productivity, resist or recover from disturbances, and withstand invasions by alien species.
Ecologists have identified several attributes related to stability, but the link between these attributes and species richness remains incompletely understood.
Long-term ecosystem experiments conducted by David Tilman have provided some insights. Tilman’s research indicated that plots with more species exhibited less year-to-year variation in total biomass and higher productivity.
While the precise mechanisms connecting species richness to ecosystem health and stability are not fully understood, it is clear that rich biodiversity is crucial for ecosystem well-being and ultimately for human survival on Earth.
The ongoing loss of species at an alarming rate raises questions about the significance of individual species extinctions. Does it matter if a particular tree frog species in the Western Ghats becomes extinct? Is our quality of life affected if we have 15,000 species of ants instead of 20,000?
To gain perspective on this issue, ecologist Paul Ehrlich introduced the “rivet popper hypothesis.” In this analogy, an ecosystem is likened to an airplane held together by thousands of rivets, each representing a species. If passengers (representing human activities) start removing rivets (causing species extinctions), the immediate impact on flight safety (ecosystem functioning) may be minimal. However, as more rivets are removed over time, the plane (ecosystem) becomes increasingly fragile and prone to failure.
Additionally, the specific rivets removed (key species that drive essential ecosystem functions) can have a more profound impact on overall ecosystem stability than the removal of others (less critical species). This analogy highlights the interconnectedness of species and their roles in maintaining the integrity and functioning of ecosystems.

The Accelerating Loss of Earth’s Biodiversity

The Earth’s storehouse of species is facing a critical challenge as the rate of species loss accelerates, primarily due to human activities.
While the addition of new species through speciation is doubtful, there is no doubt that species losses are ongoing and concerning.
Human colonization of tropical Pacific Islands, for example, is linked to the extinction of over 2,000 native bird species.
The IUCN Red List, as of 2004, documents the extinction of 784 species over the past 500 years, including vertebrates, invertebrates, and plants. Some well-known examples of recent extinctions include the dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller’s Sea Cow (Russia), and three subspecies of tigers (Bali, Javan, Caspian).
In the last two decades alone, 27 species have disappeared.
Analysis of extinction records reveals that certain groups, such as amphibians, appear to be particularly vulnerable to extinction.
Adding to the alarming picture, more than 15,500 species worldwide are currently facing the threat of extinction.
Presently, 12 percent of all bird species, 23 percent of all mammal species, 32 percent of all amphibian species, and 31 percent of all gymnosperm species worldwide are under threat.
The history of life on Earth, as seen in fossil records, shows that mass extinctions have occurred even before the emergence of humans. Over the more than 3 billion years since life’s origin, there have been five episodes of mass species extinction.
What sets the current “Sixth Extinction” apart from previous episodes is the pace of species loss. Current extinction rates are estimated to be 100 to 1,000 times faster than in pre-human times, and human activities are primarily responsible for this accelerated rate.
Ecologists warn that if present trends continue, nearly half of all species on Earth could face extinction within the next 100 years.

Causes and Consequences of Biodiversity Loss

Biodiversity Loss Consequences:

The loss of biodiversity in a region can have several detrimental effects:
(a) Decline in plant production
(b) Reduced resistance to environmental disturbances such as drought
(c) Increased variability in ecosystem processes like plant productivity, water use, and pest and disease cycles.

Causes of Biodiversity Loss: The “Evil Quartet” Biodiversity loss is primarily driven by human activities, often referred to as the “Evil Quartet.” These activities include:

(i) Habitat Loss and Fragmentation:

The most significant driver of species extinction.
Tropical rainforests, once covering 14% of the Earth’s land surface, now only cover 6%.
Rainforests are rapidly disappearing due to activities like deforestation for soybean cultivation and cattle grazing.
Habitat degradation through pollution also poses a threat to many species.
Fragmentation of large habitats into smaller pieces affects mammals, birds, and migratory species, leading to population declines.

(ii) Over-exploitation:

Humans have historically relied on nature for food and shelter.
However, when exploitation becomes excessive or driven by greed, it leads to the overharvesting of natural resources.
Historical examples include the extinction of species like Steller’s sea cow and the passenger pigeon.
Presently, many marine fish populations are over-harvested, endangering commercially important species.

(iii) Alien Species Invasions:

The introduction of non-native species, either intentionally or unintentionally, can lead to invasive species that outcompete or harm indigenous species.
For example, the introduction of the Nile perch into Lake Victoria in Africa led to the extinction of over 200 species of cichlid fish.
Invasive weed species like Parthenium, Lantana, and water hyacinth pose environmental threats.
The illegal introduction of the African catfish Clarias gariepinus for aquaculture purposes threatens native catfish species in rivers.

(iv) Co-extinctions:

Co-extinction occurs when a species becomes extinct, leading to the extinction of species closely associated with it.
For instance, when a host fish species becomes extinct, its unique parasites also go extinct.
Coevolved mutualisms, like plant-pollinator relationships, can lead to the extinction of one species when the other is lost.

The Reasons for Conserving Biodiversity: Utilitarian and Ethical Perspectives

Reasons for Conserving Biodiversity: Biodiversity conservation is motivated by a variety of reasons, which can be grouped into three categories: narrowly utilitarian, broadly utilitarian, and ethical.

Narrowly Utilitarian Reasons:

1. Direct Economic Benefits:

Humans derive numerous direct economic benefits from biodiversity, including:
Food sources like cereals, pulses, and fruits.
Resources for daily life, such as firewood, fiber, and construction materials.
Industrial products like tannins, lubricants, dyes, resins, and perfumes.
Medicinal products: Over 25% of drugs sold globally are derived from plants, and native peoples use approximately 25,000 plant species in traditional medicine.
Potential for bioprospecting: Exploring biodiversity for economically valuable products, which can lead to significant economic gains.

2. Broadly Utilitarian Reasons:

Ecosystem Services: Biodiversity plays a crucial role in various ecosystem services provided by nature, such as:
Oxygen production: For instance, the Amazon rainforest, even as it diminishes, contributes approximately 20% of the Earth’s atmospheric oxygen through photosynthesis.
Pollination services: Natural pollinators like bees, bumblebees, birds, and bats are essential for plant reproduction and the production of fruits and seeds.
Aesthetic and cultural value: The aesthetic pleasure derived from nature, including the enjoyment of natural landscapes, seasonal blooms, and the sounds of wildlife, is immeasurable. Ecosystems contribute to human well-being and cultural heritage.
Intangible benefits: There are aspects of nature that are difficult to quantify economically but hold immense value, such as the spiritual and emotional connections humans have with the natural world.

3. Ethical Reasons: Moral Duty: The ethical argument for conserving biodiversity underscores our moral responsibility to protect the millions of plant, animal, and microbial species that coexist with humans on Earth. This perspective asserts that every species has intrinsic value, irrespective of its current or potential economic worth. It emphasizes:

Recognition of the intrinsic worth of all species.
Moral duty to care for the well-being of all species.
The responsibility to preserve our biological legacy for future generations.

Conservation Approaches: In Situ and Ex Situ Conservation

In Situ Conservation:

In situ conservation involves the protection and preservation of entire ecosystems, ensuring the conservation of biodiversity within its natural habitat.
The primary goal is to save species within their native environments, allowing them to continue their ecological roles and natural behaviors.
This approach is applied when conservation resources and efforts are directed toward safeguarding the entire ecosystem.
Biodiversity hotspots are regions with high species richness and endemism. These hotspots have been identified as priority areas for conservation due to accelerated habitat loss.
Initially, 25 biodiversity hotspots were identified globally, and subsequently, nine more were added, bringing the total to 34. These hotspots collectively cover less than 2% of the Earth’s land area but harbor a significant portion of the planet’s biodiversity.
India’s exceptionally biodiverse regions, such as the Western Ghats and Sri Lanka, Indo-Burma, and the Himalaya, fall within these biodiversity hotspots.
India has established biosphere reserves, national parks, and wildlife sanctuaries to protect ecologically unique and biodiverse areas.
Sacred groves in various regions of India, rooted in religious and cultural traditions, have been conserved as well.

Ex Situ Conservation:

Ex situ conservation involves taking threatened animals and plants out of their natural habitat and placing them in controlled settings for protection and care.
Facilities like zoological parks, botanical gardens, and wildlife safari parks play a role in ex situ conservation.
Some animals that have become extinct in the wild are maintained in zoological parks to prevent total extinction.
Advances in ex situ conservation include techniques like cryopreservation for preserving gametes, in vitro fertilization of eggs, and tissue culture methods for plant propagation.
Seed banks are used to store the seeds of different genetic strains of commercially important plants for extended periods.

Global Responsibility and Initiatives:

Biodiversity conservation is a shared responsibility that transcends political boundaries.
The Convention on Biological Diversity, held in Rio de Janeiro in 1992 (Earth Summit), urged all nations to take appropriate measures for biodiversity conservation and sustainable utilization.
The World Summit on Sustainable Development in 2002 in Johannesburg saw 190 countries commit to significant reductions in the rate of global, regional, and local biodiversity loss by 2010.
The conservation of biodiversity is not only a scientific and ecological imperative but also a moral responsibility shared by all nations.