Biodiversity and ConservationNEET Botany · Class 12 · NCERT Chapter 6

Biodiversity and Conservation typically contributes 2 to 4 questions per NEET paper. High-yield topics include: types of biodiversity (genetic, species, ecosystem), biodiversity hotspots (criteria, Indian hotspots), in situ vs ex situ conservation methods, threats (HIPPO), species-area relationship (equation and Z values), and the rivet-popper hypothesis. NEET 2022 had 3 questions from this chapter.

A region qualifies as a biodiversity hotspot if it meets two criteria: (1) it must have at least 1,500 endemic vascular plant species (endemic means found nowhere else in the world), AND (2) it must have already lost more than 70% of its original habitat. There are 34 biodiversity hotspots globally. India has 4 hotspots: Eastern Himalayas (Indo-Burma), Western Ghats + Sri Lanka, Sundaland (includes Andaman-Nicobar Islands), and Indo-Burma (partially overlapping).

The species-area relationship (described by Alexander von Humboldt, formulated by McArthur and Wilson) states that species richness increases with area in a predictable way. The equation is: log S = log C + Z log A, where S = species richness, A = area, Z = slope of the regression line (regression coefficient), and C = Y-intercept. Z values: 0.1 to 0.2 for small areas (like islands within a continent), 0.6 to 1.2 for very large areas or separate continents. The slope Z is steeper for larger, more isolated areas because larger regions support more habitat types and more species can speciate.

In situ conservation (on-site) means protecting species in their natural habitat. Examples: National parks (no human activity allowed), Wildlife sanctuaries (limited human activity allowed), Biosphere reserves (have a core zone, buffer zone, and transition zone), Sacred groves (community-protected forest patches). Ex situ conservation (off-site) means protecting species outside their natural habitat. Examples: Zoological parks (animals), Botanical gardens (plants), Seed banks (dried seeds, e.g. NBPGR in New Delhi), Gene banks, Cryopreservation (gametes and embryos in liquid nitrogen at -196°C). Both approaches are complementary and needed.

HIPPO is an acronym for the major threats to biodiversity: H = Habitat loss and fragmentation (most critical threat globally; tropical deforestation causes most species loss), I = Invasive species introduction (alien species that outcompete native species; examples: Nile perch in Lake Victoria causing extinction of 200 cichlid fish species; water hyacinth, Parthenium, Lantana in India), P = Pollution (air, water, soil pollution kills organisms), P = Population growth (human overpopulation drives all other threats), O = Overexploitation (hunting, poaching, overfishing). Co-extinctions (also mentioned in NCERT) are when the loss of one species leads to extinction of another dependent species (e.g. fig wasp when fig tree goes extinct).

Multiple hypotheses explain the latitudinal biodiversity gradient: (1) Tropics have undisturbed stable climate for millions of years, allowing time for greater speciation. (2) Tropical environments are constant and predictable (no harsh winters), allowing highly specialised niche differentiation. (3) Greater solar energy input to tropics allows greater primary productivity, which supports more complex food webs and more species. (4) The tropics have been free from glaciation disturbances that reset species composition in temperate and polar regions. Tropical rainforests cover only 2% of Earth's land but harbour 50% of all species.