Biodiversity and ConservationClass 12 Biology NCERT Solutions

Genetic diversity: This refers to the variation of genes within a single species. For example, the text mentions that the medicinal plant Rauwolfia vomitoria shows genetic variation in the potency and concentration of the chemical reserpine across different Himalayan ranges. Similarly, India has over 50,000 genetically different strains of rice and 1,000 varieties of mango.

Species diversity: This refers to the variety of different species (species richness) within a region. For example, the Western Ghats have a greater diversity of amphibian species than the Eastern Ghats.

Ecological diversity: This refers to the variety of ecosystems in a region. For instance, India, with its diverse ecosystems like deserts, rain forests, mangroves, coral reefs, wetlands, and alpine meadows, has a greater ecological diversity than a Scandinavian country like Norway.

Select a well-studied group: Biologists choose an exhaustively studied group of organisms, such as insects, for which species numbers are well-documented in both temperate and tropical regions.

Determine the ratio: They make a statistical comparison of the species richness of this group between the temperate and tropical areas, establishing a ratio. For example, if there are 5 insect species in a temperate area for every 50 in a comparable tropical area, the ratio is 1:10.

Extrapolate the ratio: This ratio is then extrapolated to other, less-studied groups of plants and animals. By applying this ratio to the known number of species in other groups in temperate regions, they can estimate the probable number of species in the tropics.

Longer Evolutionary Time: Tropical latitudes have remained relatively undisturbed by frequent glaciations for millions of years, unlike temperate regions. This long period of environmental stability has provided more evolutionary time for species diversification to occur.

Constant and Predictable Environment: Tropical environments are less seasonal and more constant and predictable compared to temperate zones. Such stable conditions promote niche specialisation, allowing many different species to coexist without competing, which leads to greater species diversity.

Higher Solar Energy and Productivity: The tropics receive more solar energy, which contributes to higher productivity. This high availability of energy and resources in the food web can support a larger number of species and more complex food webs, indirectly contributing to greater biodiversity.

Habitat loss and fragmentation: This is the most significant cause of species extinction. It involves the destruction of natural habitats, such as the clearing of tropical rain forests for agriculture or urban development. When large habitats are broken into smaller, isolated fragments, it badly affects animals with large territories and migratory habits, leading to population declines.

Over-exploitation: When humans harvest natural resources like plants and animals at a rate faster than they can replenish, it leads to their extinction. The extinctions of the Steller's sea cow and passenger pigeon were due to over-exploitation. Many marine fish populations are currently over-harvested.

Alien species invasions: When non-native (alien) species are introduced into an ecosystem, either intentionally or unintentionally, they can become invasive. They may outcompete native species for resources or prey on them, leading to the decline or extinction of indigenous species. An example is the introduction of Nile perch into Lake Victoria, which led to the extinction of over 200 species of cichlid fish.

Co-extinctions: When one species becomes extinct, other species that are dependent on it in an obligatory way also face extinction. For example, if a host fish species becomes extinct, its unique parasites also perish. Similarly, in a co-evolved plant-pollinator relationship, the extinction of one species will inevitably lead to the extinction of the other.

Stability: Ecologists believe that communities with more species tend to be more stable. A stable community does not show excessive variations in productivity from year to year. It is more resistant to occasional disturbances (natural or man-made) and to invasions by alien species. David Tilman's long-term experiments showed that plots with more species exhibited less year-to-year variation in total biomass.

Productivity: Increased biodiversity contributes to higher overall productivity of an ecosystem. Tilman's experiments also demonstrated that plots with a greater diversity of species had higher total biomass.

Ecosystem Health: The 'rivet popper hypothesis' by Paul Ehrlich explains that each species in an ecosystem is like a rivet in an airplane. While losing a few 'rivets' (species) might not initially affect the 'flight' (ecosystem functioning), the loss of too many, especially 'key' rivets (keystone species), can weaken the ecosystem dangerously, eventually leading to its collapse.

Refuge for Rare and Threatened Species: They serve as safe havens for a large number of native species, including those that are rare, threatened, or endemic. For example, in Meghalaya, sacred groves are the last refuges for many rare plants.

Preservation of Genetic Diversity: By protecting a wide array of plants and animals in their natural habitat, these groves help in conserving the rich genetic diversity of the region.

Repository of Indigenous Knowledge: They are centers of traditional knowledge and cultural practices related to nature conservation.

Mobility: Most animals are mobile, whereas plants are largely sessile. Mobility allows animals to disperse to new areas, colonize diverse habitats, and avoid competition more effectively. This can lead to geographic isolation of populations, a key driver for the formation of new species (speciation).

Complex Nervous and Sensory Systems: Animals possess complex nervous and sensory systems, which facilitate intricate behaviors related to foraging, avoiding predators, and mating. Complex mate recognition systems and sexual selection can lead to rapid reproductive isolation and speciation.

Diverse Feeding Strategies: Animals have evolved a vast array of feeding mechanisms (predation, herbivory, parasitism, etc.), leading to specialized adaptations and co-evolutionary arms races (e.g., between predator and prey). This constant evolutionary pressure promotes diversification.

Structural and Developmental Flexibility: The animal body plan has shown greater flexibility in evolving different forms for locomotion, feeding, and reproduction compared to the more constrained body plan of plants (roots, stem, leaves), which is primarily adapted for photosynthesis. This has allowed animals to exploit a wider range of ecological niches.

Alleviation of Immense Suffering: The smallpox virus caused millions of deaths and left many others disfigured or blind. Its eradication has saved countless lives and eliminated immense human suffering.

Lack of Ecological Role: The virus is an obligate human parasite. It cannot survive outside a human host and plays no constructive role in any natural ecosystem. Therefore, its removal does not cause negative ecological consequences, unlike the extinction of a keystone species in a food web.

Net Benefit to Humanity: The benefits of eradicating such a harmful species—in terms of lives saved, suffering prevented, and economic costs of treatment and control eliminated—are considered to vastly outweigh the intrinsic value of the pathogen's existence.