Biology Class 12 NCERT Solutions: Chapter 15 Biodiversity and Conservation Part 1

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Q.1 Name the three important components of biodiversity.

Answer:

  • Biodiversity is the variety of living forms present in various ecosystems. It includes variability among life forms from all sources including land, air, and water.

  • Three important components of biodiversity are:

  • Genetic diversity

  • Species diversity

  • Ecosystem diversity

Q.2 How do ecologists estimate the total number of species present in the world?

Answer:

  • The diversity of living organisms present on the Earth is very vast. According to an estimate by researchers, it is about seven millions.

  • The total number of species present in the world is calculated by ecologists by statistical comparison between a species richness of a well-studied group of insects of temperate and tropical regions.

  • Then, these ratios are extrapolated with other groups of plants and animals to calculate the total species richness present on the Earth.

Q.3 Give three hypotheses for explaining why tropics show greatest levels of species richness.

Answer:

  • There are three different hypotheses proposed by scientists for explaining species richness in the tropics.

  • Tropical latitudes receive more solar energy than temperate regions, which leads to high productivity and high species diversity.

  • Tropical regions have less seasonal variations and have a more or less constant environment. This promotes the niche specialization and thus, high species richness.

  • Temperate regions were subjected to glaciations during the ice age, while tropical regions remained undisturbed which led to an increase in the species diversity in this region.

Q.4 What is the significance of the slope of regression in a species − area relationship?

Answer:

  • The slope of regression (z) has a great significance in order to find a species-area relationship. It has been found that in smaller areas (where the species-area relationship is analyzed), the value of slopes of regression is similar regardless of the taxonomic group or the region.

  • However, when a similar analysis is done in larger areas, then the slope of regression is much steeper.

Q.5 What are the major causes of species losses in a geographical region?

Answer:

  • Biodiversity is the variety of living forms present in various ecosystems. It includes variability among life forms from all sources including land, air, and water. Biodiversity around the world is declining at a very fast pace.

  • The following are the major causes for the loss of biodiversity around the world.

  1. Habitat loss and fragmentation:

  2. Habitats of various organisms are altered or destroyed by uncontrolled and unsustainable human activities such as deforestation, slash and burn agriculture, mining, and urbanization.

  3. This results in the breaking up of the habitat into small pieces, which effects the movement of migratory animals and also, decreases the genetic exchange between populations leading to a declination of species.

  4. Over-exploitation:

  5. Due to over-hunting and over-exploitation of various plants and animals by humans, many species have become endangered or extinct (such as the tiger and the passenger pigeon).

  6. Alien species Invasions:

  7. Accidental or intentional introduction of non-native species into a habitat has also led to the declination or extinction of indigenous species.

  8. For example, the Nile perch introduced in Lake Victoria in Kenya led to the extinction of more than two hundred species of native fish in the lake.

  9. Co−extinction:

  10. In a native habitat, one species is connected to the other in an intricate network.

  11. The extinction of one species causes the extinction of other species, which is associated with it in an obligatory way.

  12. For example, the extinction of the host will cause the extinction of its parasites.

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