Biodiversity is measured at different levels of biological organisation. Variation within a species is genetic diversity, variety of species in an area is species diversity, and variety of habitats and ecosystems is ecological diversity.
The three important components of biodiversity are genetic diversity, species diversity and ecological diversity.
Complete inventories are not available for all taxa. Ecologists study groups whose records are relatively complete, compare species richness in temperate and tropical areas, and apply these ratios to other groups to estimate the number of undescribed species. Robert May's conservative estimate places global species diversity at about 7 million.
Ecologists estimate global species richness by using known species inventories and extrapolating from better-studied groups and regions, especially by comparing temperate and tropical species richness.
First, tropical regions were not repeatedly disturbed by glaciations like many temperate regions, so species had more time to diversify. Second, tropical climates are relatively constant, allowing niche specialisation. Third, greater solar energy in the tropics increases productivity, which can support more species.
Tropics show high species richness because they have had long undisturbed evolutionary time, less seasonal and more predictable environments, and greater solar energy that supports high productivity.
On a logarithmic scale the relationship is log S = log C + Z log A. Here Z is the slope. For small or regional areas, Z is usually about 0.1 to 0.2, showing a modest increase in species richness with area. For very large areas such as continents, Z is steeper, about 0.6 to 1.2, meaning species richness increases much more rapidly with area.
The slope of regression, Z, shows the rate at which species richness increases with area in the species-area relationship.
Habitat loss and fragmentation destroy or break up the natural home of species. Over-exploitation occurs when humans harvest organisms beyond sustainable limits. Alien species invasions can outcompete or eliminate native species. Co-extinctions occur when the extinction of one species also causes the extinction of species that depend on it, such as a host and its specific parasite or a plant and its pollinator.
The major causes are habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinctions.
Communities with more species generally show less year-to-year variation in biomass and higher productivity. A diverse ecosystem also contains many interacting species, so the loss or fluctuation of one species is less likely to disrupt the whole system. This idea is illustrated by the rivet popper hypothesis, where each species contributes to ecosystem functioning.
Biodiversity helps ecosystems remain productive, stable, resilient to disturbances and resistant to alien invasions.
In many Indian communities, certain forest tracts are considered sacred and are given total protection. Because cutting trees and harming wildlife are traditionally prohibited, sacred groves act as in situ conservation sites and refuges for rare and threatened species.
Sacred groves are forest patches protected by religious and cultural traditions. They conserve biodiversity by protecting all trees and wildlife within them.
Vegetation cover slows the speed of rainwater and flowing water. Roots hold soil particles together and make the soil more porous. Leaf litter and organic matter improve water absorption. As a result, less soil is washed away and flood peaks are reduced.
Plants and other biotic components control floods and soil erosion by intercepting rainfall, binding soil with roots, improving water infiltration and reducing surface runoff.
Animals can move to new habitats, avoid predators, locate food and mates, and respond rapidly to environmental changes. Their specialised organs and behaviours allow adaptation to many ecological roles such as herbivory, predation, parasitism and pollination. Coevolution with plants and other animals also generated many specialised relationships, increasing speciation and diversity, especially among insects.
Animals achieved greater diversification because their mobility, sensory and nervous systems, behavioural flexibility, varied feeding modes and coevolutionary interactions allowed them to occupy many more niches.
A species may be targeted for extinction when it causes severe disease, death or ecological damage and its removal has a clear public-health or conservation benefit. Such action is justified only after careful assessment, because deliberate extinction can have ecological consequences.
Yes. Humans may deliberately try to eradicate disease-causing organisms or their vectors, such as the smallpox virus or malaria-causing mosquitoes, to protect human health.