What criteria should one use in categorising a species as threatened?
The criteria that should be used in categorising a species as threatened are
(i) Number of the members of the species are declining at an alarming rate.
(ii) Their habitat is being modified or destroyed.
(iii) Predator or poacher activities are increasing.
What could be the possible explanation for greater vulnerability of amphibians to extinction as compared to other animal groups?
Amphibians are more vulnerable to extinction
(i) Habitat Modification or Destruction Amphibians generally need aquatic and terrestrial habitats to survive; threats to either habitat can affect populations. Hence, amphibians may be more vulnerable to habitat modification than organisms that require only one habitat type.
(ii) Habitat Fragmentation This means isolation of a few areas by habitat modification. Small populations that survive within such fragments are often susceptible to inbreeding, genetic drift or extinction due to small fluctuations in the environment.
(iii) Large Scale Climate Changes These changes can further modify aquatic habitats, preventing amphibians from spawning.
How do scientists extrapolate the total number of species on earth ?
There are two methods to estimate and extrapolate the number of species on earth
(i) The primary method used by the scientists to extrapolate the number of species on earth is the estimation rate of discovery of new species.
(ii) Total number of species can also be extrapolated by the statistical comparison of the tropical and temperate species richness of exhaustively studied groups of insects. The ratio is then extrapolated with existing species of plants and animals to predict the gross estimate of the number of species on earth.
Humans benefit from diversity of life. Give two examples.
(i) Humans derive numerous economic benefits directly from diversity of organisms.
(a) Food products (cereals, pulses and fruits).
(b) Firewood.
(c) Fibre (cotton, jute from plants and silk, wool from animals).
(d) Construction material (timber for making furniture, houses and sports goods).
(e) Industrial products (tannins, lubricants, dyes, resins and perfumes).
(f) Products of medicinal importance (about 25000 plants are used in traditional medicine).
(ii) There are huge intangible benefits that humans derive from the diversity of life.
(a) Pure oxygen.
(b) Natural pollinators.
(c) Flood and soil erosion control.
(d) Nutrient replenishment.
(e) Waste recycling by microbes and other insects, etc.
(f) Aesthetic pleasure and mental peace.
List any two major causes other than anthropogenic causes of the loss of biodiversity.
The two major causes other than anthropogenic causes of the loss of biodiversity are
(i) Alien Species Invasions When alien species are introduced unintentionally or deliberately in a habitat, some of them can cause decline or extinction of indigenous species.
(ii) Co-extinctions When a species becomes extinct, the plant and animal species associated with it, in an obligatory way, also become extinct.