IAS 2012 Prelims Solved Paper II Aptitude (Part 6 of 18)

Directions for the following, 11 (eleven) items:

Read the following three passages and answer the items that follow each passage. Your answers to these items should be based on the passages only.


Invasions of exotic species into new geographic areas sometimes occur naturally and without human agency. However, human actions have increased this trickle to a flood. Human-caused introductions may occur either accidentally as a consequence of human transport, or intentionally but illegally to serve some private purpose or legitimately to procure some hoped-for public benefit by bringing a pest under control, producing new agricultural products new agricultural products or providing novel recreational opportunities. Many introduced species are assimilated into communities without much obvious effect. However, some have been responsible for dramatic changes to native species and natural communities. For example, the accidental introduction of the brown tree snake Boiga irregularis into Guam, an island in the Pacific, has through nest predation reduced 10 endemic forest bird species to the point of extinction. One of the major reasons for the world's great biodiversity is the occurrence of centers of endemism so that similar habitats in different parts of the world are occupied by different groups of species that happen to have evolved there.

If every species naturally had access to everywhere on the globe, we might expect a relatively small number of successful species to become dominant in each biome. The extent to which this homogenization can happen naturally is restricted by the limited powers of dispersal. By virtue of the transport opportunities offered by humans, these barriers have been breached by an ever-increasing number of exotic species. The effects of introductions have been to convert a hugely diverse range of local community compositions into something much more homogeneous. It would be wrong, however, to conclude that introducing species to a region will inevitably cause a decline in species richness there. For example, there are numerous species of plants, invertebrates and vertebrates found in continental Europe but absent from the British Isles (many because they have so far failed to recolonize after the last glaciations). Their introduction would be likely to significant detrimental effect noted above arises where aggressive species provide a novel challenge to endemic biotas illequipped to deal with them.

  1. With reference to the passage, which of the following statements is correct?

    1. Introduction of exotic species into new geographical areas always leads to reduced biodiversity.

    2. Exotic species introduced by man into new areas have always greatly altered the native ecosystems.

    3. Man is the only reason to convert a hugely diverse range of local community compositions into more homogeneous ones.

    4. None of the statements a, b & c is correct in this context.

    Answer: d

  2. Why does man introduce exotic species into new geographical areas?

    1. To breed exotic species with local varieties.

    2. To increase agricultural productivity.

    3. For beautification and landscaping.

    Which of the above statements is/are correct?

    1. 1 only

    2. 2 and 3 only

    3. 1 and 3 only

    4. 1, 2 and 3

    Answer: b

  3. How is homogenization-prevented under natural conditions?

    1. Evolution of groups of species specific to local habitats.

    2. Presence of oceans and mountain ranges.

    3. Strong adaptation of groups of species to local physical and climatic conditions.

    4. All the statements a, b & c given above are correct in this context.

    Answer: d

  4. How have the human beings influenced the biodiversity?

    1. By smuggling live organisms.

    2. By building highways.

    3. By making ecosystems sensitive so that new species are not allowed.

    4. By ensuring that-now specie? do not have major impact on local species.

    Which of the statements given above are correct?

    1. 1 and 2

    2. 2 and 3

    3. 1 and 3

    4. 2 and 4

    Answer: a

  5. What the impact of invasion of exotic species on an ecosystem?

    1. Erosion of endemic species.

    2. Change in the species composition of the community of the ecosystem.

    Select the correct answer using the codes given below:

    1. 1 only

    2. 2 only

    3. Both 1 and 2

    4. Neither 1 nor 2

    Answer: c