Definitions [9]
- The diversity of life forms present on Earth, including plants, animals, and microorganisms, is called biodiversity.
- Biodiversity is the occurrence of different types of genes among the individuals of species, habitats and ecosystems, both terrestrial and aquatic within a defined area.
Define dichotomous key.
It is a tool used to classify organisms based on their similarities and differences.
Define Hotspots.
Hotspot is a biodegradable region that is both a significant reservoir of biodiversity and is threatened with destruction.
Define Eutrophication.
Eutrophication: The process by which a body of water enriched in dissolved nutrients (such as phosphates) that stimulates the growth of aquatic algae usually resulting in the depletion of dissolved oxygen.
Define Ramsar Sites.
Ramsar Sites: It is a wetland site designed of international importance under the Ramsar convention. It is an inter-governmental environmental treaty established in 1971 by UNESCO and coming into force in 1975.
Define Biodiversity.
Biodiversity is defined as the variety of plant and animal life in the world or in a particular habitat, a high level of which is usually considered to be important and desirable
The sum total of species richness, i.e., the number of species of plants, animals and micro-organisms inhabiting in a given habitat, is known as biodiversity.
Give definitions of Extinct species.
Species that completely disappear from the planet are referred to as extinct.
Give definitions of Invasive species.
Species that are not native to a region or locality but are unintentionally or purposefully introduced and cause harm to the native species already present are referred to as invasive species.
Give definitions of Endangered species.
When a species possesses a very high risk of extinction as a result of rapid population decline of 50 to more than 70 per cent over the previous 10 years, it is said to be an endangered species.
Key Points
- Biodiversity is the variety of life on Earth — including microorganisms, fungi, plants and animals in both terrestrial and aquatic habitats.
- Diversity exists in size, shape, colour, nutrition, habitat and reproduction. It arises due to adaptations of organisms to different environmental conditions for survival.
- Biodiversity = totality of genes, species and ecosystems in a region (as per IUCN, UNEP and WRI).
- Term coined by Walter Rosen (1982), popularised by Edward Wilson to describe diversity at all levels of biological organisation.
- Today's biodiversity is the result of 3.5 billion years of evolutionary history, influenced by natural processes and human activities.
- A stable community maintains constant biomass production, withstands disturbances, recovers quickly and resists invasive species.
- David Tilman proved that greater species richness maintains the stability of an ecological community. Rich diversity leads to lesser variation in biomass production — called Productivity Stability Hypothesis.
- Paul Ehrlich (Stanford) proposed the Rivet Popper Hypothesis — an ecosystem compared to an aeroplane and species to rivets. Loss of one species may not cause immediate damage, but gradual loss seriously threatens the ecosystem.
- Loss of key species causes rapid and serious damage, showing that diversity and ecosystem well-being do not share a linear relationship.
- Loss of species disturbs food chains, food webs, energy flow and natural cycles — affecting the entire balance of the ecosystem.
Latitudinal Gradient
- Species richness is high near the equator (tropics: 23.5°N to 23.5°S) and decreases towards the poles. Example: The Amazon rainforest has 40,000 plants, 1300 birds and 427 mammals.
- Tropics have high diversity due to a stable climate, less glaciation, abundant sunlight, higher rainfall and greater niche specialisation.
Altitudinal Gradient
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Species diversity decreases at higher altitudes due to drastic climatic changes and seasonal variations.
Species-Area Relationship
- Observed by Alexander Von Humboldt, species richness increases with area but only up to a limit. For many species, this forms a rectangular hyperbola.
- Expressed as: log S = log C + Z log A, where S = species richness, A = area, Z = slope, C = Y-intercept. On a logarithmic scale, it gives a straight line.
- Z value for smaller areas = 0.1 to 0.2. For larger areas (continents) = 0.6 to 1.2 (steeper slope — species increase faster than area explored).
| Category | Meaning |
|---|---|
| Extinct (EX) | No individuals left alive |
| Extinct in Wild (EW) | Survive only in captivity |
| Critically Endangered (CR) | Extremely high risk (≤ 50 individuals) |
| Endangered (EN) | Very high risk; 50–70% decline (last 10 years) |
| Vulnerable (VU) | High risk; 30–50% decline (last 10 years) |
| Near Threatened (NT) | Likely to become threatened soon |
| Least Concern (LC) | Abundant and widespread species |
| Data Deficient (DD) | Insufficient data available |
| Not Evaluated (NE) | Not assessed by IUCN |
- Loss of biodiversity causes ecosystem imbalance and may lead to extinction of species (natural, mass, and anthropogenic).
- Natural causes include forest fires, earthquakes, and volcanic eruptions, while human causes include habitat destruction, hunting, and overexploitation.
- The present biodiversity loss is considered the 7th mass extinction, occurring 100–1000 times faster due to human activities.
- Loss of biodiversity reduces plant productivity, disturbs environmental processes, and lowers resistance to disturbances.
- The “Evil Quartet” causes biodiversity loss: habitat loss, over-exploitation, alien species invasion, and co-extinction.
- Invasive species can harm or eliminate native species due to a lack of natural predators (e.g., Parthenium, water hyacinth).
- Conservation status is maintained in the IUCN Red Data Book; endangered species have declining populations, while extinct species are completely lost.
