(a) Differentiate among alpha, beta and gamma diversity. Explain various factors which threaten the biodiversity. (20 marks) (b)…

(a) Alpha, beta and gamma diversity and threats to biodiversity (20 marks)

Alpha, beta and gamma diversity. Whittaker (1960, 1972) recognised three levels.

• Alpha (α) diversity is the diversity within a single community or habitat, measured as species richness or by indices such as Shannon's and Simpson's. A tropical forest patch has a high alpha diversity.
• Beta (β) diversity is the change in species composition between habitats or along a gradient (altitude, moisture), or the extent of species turnover. It is measured as β = γ/α, or by similarity indices (Jaccard, Sørensen). It is high when habitats share few species.
• Gamma (γ) diversity is the total diversity of a whole region or landscape made up of several habitats, the product of alpha and beta (γ = α × β), such as the whole of the Western Ghats.

Alpha is local, beta compares habitats, and gamma is regional.

Factors threatening biodiversity.

• Habitat loss, fragmentation and degradation: the greatest threat, from deforestation, agriculture, dams, mining and urbanisation, as in the loss of rainforest and wetlands.
• Overexploitation: hunting, poaching and overfishing, as in the tiger, one-horned rhinoceros, and the extinct passenger pigeon.
• Invasive alien species: Lantana, water hyacinth and Parthenium in India, and the Nile perch in Lake Victoria, which displaced native species.
• Pollution: pesticides such as DDT, which thinned bird eggshells, and diclofenac, which killed vultures in India, with plastics and eutrophication.
• Climate change: coral bleaching, shifts in species ranges and loss of glacier-fed habitats.
• Co-extinction: the loss of a species that depends on another, such as a parasite or a pollinator.

These are often called the "evil quartet" (habitat loss, overexploitation, introduced species and co-extinction), and diseases and human–wildlife conflict add to them.

(b) Instinctive and learned behaviour in animals (15 marks)

Instinctive (innate) behaviour is inherited, stereotyped, species-specific and performed correctly the first time without practice. It is triggered by sign stimuli. Its categories are:

• Taxes, such as the phototaxis of Euglena and fly maggots.
• Kineses, such as the random movement of woodlice that slows in damp air.
• Reflexes, such as withdrawal from a pin prick.
• Fixed action patterns, such as egg-rolling in the greylag goose, web spinning in spiders, and nest building.

Learned behaviour is a change in behaviour with experience. Its types are:

• Habituation: a fading response to a harmless repeated stimulus, as in gill withdrawal in Aplysia.
• Classical conditioning: Pavlov's dogs salivating at a bell.
• Operant conditioning (trial and error): a rat learns to press a lever for food in a Skinner box.
• Imprinting: young animals follow the first moving object in a critical period, as in Lorenz's goslings.
• Latent learning: rats learn a maze without reward and use it later (Tolman).
• Insight learning: Köhler's chimpanzee stacked boxes to reach bananas.
• Observational learning: macaques on Koshima Island learning to wash sweet potatoes.

Interaction. Most behaviour combines both. Instinct gives the basic pattern and learning refines it, as in the bird song of white-crowned sparrows, which have an inherited template but need to hear the adult song. Innate predispositions guide what is learned.

(c) Transgenic animals and their applications (15 marks)

Transgenic animals carry a foreign gene (transgene) stably integrated in their genome and passed through the germ line.

Methods.

• Microinjection of DNA into the male pronucleus of a fertilised egg, which is then implanted in a foster mother (as in the giant mouse with rat growth hormone gene).
• Retrovirus-mediated gene transfer into early embryos.
• Embryonic stem-cell transfer, in which modified cells are injected into a blastocyst, used for knockouts.
• Sperm-mediated transfer, nuclear transfer (cloning) and genome editing by CRISPR–Cas9.

Applications.

• Biomedicine: disease models such as the oncomouse and knockout mice, and testing of vaccines and drugs.
• Pharming: human proteins in the milk of animals, as human α1-antitrypsin in sheep and antithrombin in goats.
• Xenotransplantation: genetically modified pigs to supply organs.
• Livestock: faster growth, leaner meat, disease resistance and improved milk.
• Aquaculture: fast-growing transgenic salmon and fluorescent zebrafish.
• Pest control: transgenic sterile mosquitoes.
• Industry: spider silk protein from goat milk.

Concerns. Animal welfare, ecological risk from escape, biosafety and ethics, so their use is regulated, in India through the GEAC and internationally under the Cartagena Protocol.