Chapter 13: Biodiversity and Conservation (Ecology)

• Genetic diversity: diversity of genes within a species (e.g. many strains of rice; variants of Rauwolfia vomitoria in reserpine content).
• Species diversity: variety of species in an area (e.g. the Western Ghats have more amphibian species than the Eastern Ghats).
• Ecological diversity: variety of ecosystems (e.g. India's deserts, rainforests, mangroves, coral reefs, wetlands, estuaries and alpine meadows).

Genetic, species and ecological diversity.

Many species (especially in the tropics and among insects and microbes) are still unknown. Ecologists use statistical comparisons: the ratio of tropical to temperate species is worked out for well-studied groups (such as birds and mammals) and applied to poorly studied groups (such as insects) to extrapolate the total number. Using such estimates, Robert May estimated about 7 million species worldwide (other estimates range from 20 to 50 million).

By extrapolation: the tropical-to-temperate species ratio of well-known groups is applied to less-known groups (about 7 million species, by May).

• Long evolutionary time: tropical regions have remained relatively undisturbed for millions of years (temperate regions were repeatedly glaciated), giving more time for species to diversify.
• Stable environment: tropical environments are less seasonal and more constant and predictable, which promotes niche specialisation and more species.
• More solar energy: the tropics receive more solar energy, which supports higher productivity, which in turn may support greater diversity.

Long undisturbed evolutionary time, a stable less seasonal climate, and more solar energy (higher productivity).

The species–area relationship is $\log S=\log C+Z\log A$, where $Z$ is the slope of the line (the regression coefficient).

• The slope Z shows how quickly species richness increases with the area explored.
• For small areas within a region, Z is about 0.1–0.2, regardless of taxonomic group or region.
• For very large areas such as whole continents, Z is steeper, about 0.6–1.2 (e.g. frugivorous birds and mammals in tropical forests, Z = 1.15).

A steeper slope means species richness rises much faster with area, so larger areas hold far more species.

Z shows how fast species number rises with area: about 0.1–0.2 within regions but 0.6–1.2 for very large areas (continents).

The "evil quartet":

• Habitat loss and fragmentation: the most important cause; e.g. destruction of tropical rainforests (Amazon) for agriculture.
• Over-exploitation: excessive hunting and harvesting, e.g. the extinction of Steller's sea cow and the passenger pigeon.
• Alien species invasions: introduced species that harm native species, e.g. Nile perch in Lake Victoria, Parthenium, Lantana, water hyacinth, African catfish.
• Co-extinctions: when one species becomes extinct, plant and animal species that depend on it also die out (e.g. host fish and its parasites; plants and their pollinators).

Habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinctions.

Communities with more species tend to be more stable: they show less variation in productivity from year to year, are more resistant to occasional disturbance (natural or man-made) and to invasion by alien species. Tilman's experiments showed that plots with more species had less year-to-year variation in total biomass and higher productivity.

The "rivet popper" hypothesis (Paul Ehrlich) compares an ecosystem to an aeroplane held by rivets (species): losing a few rivets may not matter, but losing many, or a key rivet, makes the plane (ecosystem) collapse. Biodiversity thus maintains ecosystem services such as productivity, nutrient cycling and stability.

Higher diversity gives more stable and productive ecosystems that resist disturbance (Tilman's plots; Ehrlich's rivet popper idea).

Sacred groves are forest patches protected by local communities on religious and cultural grounds, where all trees and wildlife are venerated and protected. Examples: the Khasi and Jaintia Hills in Meghalaya, the Aravalli Hills of Rajasthan, the Western Ghats of Karnataka and Maharashtra, and the Sarguja, Chanda and Bastar areas of Madhya Pradesh/Chhattisgarh.

Role: they are refuges for a large number of rare and threatened plants and animals, which would otherwise have disappeared. They are an example of in situ conservation driven by tradition.

Community-protected forest patches with religious significance; they preserve many rare and threatened species (in situ conservation).

• Plant roots hold the soil particles together and prevent soil from being washed or blown away.
• The canopy of trees breaks the force of falling rain, and litter and humus on the forest floor absorb water.
• Vegetation slows down surface runoff, letting more water soak into the soil, which reduces floods and recharges groundwater.
• Soil organisms improve soil structure and its water-holding capacity.

Roots bind the soil; canopy, litter and humus slow rainwater and runoff and let it soak in, reducing erosion and floods.

• Animals are mobile and can move into many different habitats and niches; this has led to many adaptations and new species.
• They show a great variety of feeding habits, behaviours and life cycles.
• Insects in particular (about 70% of animal species) are small, have short life cycles, reproduce rapidly and have exploited countless niches.
• Animals have complex nervous and sensory systems that allow varied responses to the environment.

Mobility and use of many habitats and niches, varied feeding and behaviour, and the huge radiation of small, fast-breeding insects.

Yes: disease-causing organisms (pathogens) and disease-carrying vectors. Examples: the variola virus (smallpox), which has been eradicated in nature; the polio virus; malaria-causing Plasmodium and the mosquitoes that carry it.

Justification: these organisms cause great human suffering and death; removing them protects human health and saves lives and money. (Even so, the possible ecological effects of removing a species should be studied first, and samples may be kept in laboratories for research.)

Pathogens and vectors such as the smallpox and polio viruses or malaria parasites, because they cause disease and death.