# Population viability analysis: answers and explanations

Cambridge IELTS 1, Test 4, Reading Passage 3

Source: Passage, questions and answer key from Cambridge IELTS 1, Test 4, Reading Passage 3. © Cambridge University Press & Assessment. Used for educational practice. Explanations and evidence notes are written by Testmigo.

## Answer key

| Q | Answer | Proof |
| --- | --- | --- |
| 28 | YES | One tool for assessing the impact of forestry on the ecosystem is population viability analysis (PVA). |
| 29 | NO | there is now enormous potential for using population viability to assist wildlife management in Australia's forests. |
| 30 | NO | A species becomes extinct when the last individual dies. |
| 31 | NOT GIVEN | it highlights the role of luck and chance in the extinction process. |
| 32 | vi | Small populations will fluctuate enormously because of the random nature of birth and death ... Some pairs may produce several young in a single year while others may produce none in that same year. |
| 33 | iii | This is particularly true if there is a very small number of one sex. |
| 34 | i | Without genetic variability a species lacks the capacity to evolve and cannot adapt to changes in its environment |
| 35 | ii | Catastrophes such as fire, flood, drought or epidemic may reduce population sizes to a small fraction of their average level. |
| 36 | will not survive | these chance fluctuations can cause species extinctions even if, on average, the population size should increase. |
| 37 | locality | Besides these processes we need to bear in mind the distribution of a population. ... a species with a single population of 100 individuals in a single locality. |
| 38 | logging takes place | As more forests are logged, animal population sizes will be reduced further. ... will increase the probability that forest-dependent animals will become extinct. |
| 39 | B | To make a prediction about extinction we need to understand the processes that can contribute to it ... This is a tool for predicting the probability that a species will become extinct |

## Why these answers are right

**28. YES.** The statement says scientists care about how forestry affects native animals. The writer describes PVA as a tool for assessing the impact of forestry on the ecosystem and for helping wildlife management in Australia's forests, which shows exactly that interest, so the writer agrees: YES.

**29. NO.** This claims PVA has a long history in Australia. The writer says PVA has been used successfully in the United States, while in Australia there is now enormous potential for using it, which means its use there is only beginning. That contradicts the statement, so NO.

**30. NO.** The statement defines extinction as the moment only one individual is left. Paragraph 2 says a species becomes extinct when the last individual dies, so while one is still alive the species is not yet extinct. The definitions conflict, so the answer is NO.

The why and the trap for questions 31 onwards are free with an account on the [answers page](https://testmigo.com/ielts/reading/population-viability-analysis/answers).

[Practice Population viability analysis](https://testmigo.com/ielts/reading/population-viability-analysis)