Q.Define habitat fragmentation, and explain why it is especially damaging to species that need a large, continuous territory to survive.

Parthenium hysterophorus (congress grass/carrot grass) is a well-known invasive alien plant species in India.

Parthenium hysterophorus, commonly called congress grass or carrot grass, is a notorious invasive alien plant species introduced accidentally into India, which has spread aggressively, displacing native vegetation, reducing biodiversity and crop yields, and causing allergic health problems in humans and livestock. Gloriosa (glory lily) and Michelia (champa) are ornamental/native plant species valued for their flowers, and Sansevieria is a commonly cultivated ornamental succulent — none of these three is classified as an invasive species in this context, unlike Parthenium.

Because amphibians depend on both water and land habitats and have thin, permeable skin that is highly sensitive to environmental disturbance, they are considered the vertebrate group most vulnerable to extinction from habitat destruction.

Amphibians (frogs, toads, salamanders and caecilians) occupy a unique ecological position, typically requiring an aquatic environment for egg-laying and larval development (e.g., tadpoles) and a terrestrial environment for their adult life -- making them dependent on the health and continuity of two distinct habitat types simultaneously. Their thin, moist, highly permeable skin, which they use for cutaneous respiration and water balance, also makes them extremely sensitive to changes in habitat quality, such as pollution, desiccation of wetlands, temperature change, and loss of either their breeding water bodies or their terrestrial habitat. Because of this dual habitat dependency and physiological sensitivity, amphibians as a group show disproportionately high rates of population decline and extinction risk whenever habitats are destroyed or fragmented, which is also why they are widely used as bio-indicator species to monitor overall ecosystem health. Mammals, birds and echinoderms, while also affected by habitat loss, are not considered as uniformly or acutely vulnerable as amphibians as a whole group.

The Dodo, Passenger pigeon and Steller's sea cow became extinct mainly because of direct over-exploitation (excessive hunting) by humans.

These are classic textbook examples of species driven to extinction by over-exploitation: the flightless Dodo of Mauritius was hunted to extinction by sailors and introduced animals; the Passenger pigeon, once numbering in the billions in North America, was hunted so intensively for food and sport that it went extinct by the early 20th century; and Steller's sea cow, a large marine mammal, was hunted to extinction within about 27 years of its discovery by fur traders and sailors for meat and oil. Option (a) Habitat loss and (d) Habitat fragmentation refer to destruction or breaking up of natural habitats (e.g., deforestation, dam building), which is the leading cause of extinction generally but not the specific cause for these three species. Option (c) Shifting cultivation is a form of traditional agriculture that can degrade forest habitat, again not the direct cause in these classic cases.

Amphibians are considered the animal group at greatest risk of extinction from habitat destruction because their life cycle depends on both water and land habitats remaining intact.

Amphibians (frogs, toads, salamanders) have a biphasic life cycle -- aquatic larval stages (e.g. tadpoles) that need clean water bodies, and terrestrial adult stages that need suitable land habitat -- so destruction of either habitat, or the corridor between them, disrupts their life cycle. Their thin, permeable, glandular skin (used for cutaneous respiration) also makes them highly sensitive to habitat degradation, pollution and desiccation. Mammals (b), echinoderms (c) and birds (d) certainly suffer from habitat loss too, but are comparatively more mobile or ecologically flexible and are not considered the single most vulnerable group; amphibians are repeatedly cited as the most threatened vertebrate class worldwide due to habitat destruction.