Population Viability Analysis — IELTS Reading Answers

Scientists are interested in the effect of forestry on native animals.

“One tool for assessing the impact of forestry on the ecosystem is population viability analysis (PVA)”

The passage introduces PVA as a tool for assessing the impact of forestry on the ecosystem, so scientists are interested in that effect.

PVA has been used in Australia for many years.

“It has been successfully used in the United States to provide input into resource exploitation decisions and assist wildlife managers and there is now enormous potential for using population viability to assist wildlife management in Australia’s forests”

PVA has been used successfully in the United States, and the text says there is now enormous potential for using it in Australia, so not for many years there.

A species is said to be extinct when only one individual exists.

“A species becomes extinct when the last individual dies”

A species becomes extinct when the last individual dies, so extinction occurs at zero individuals, not one.

Extinction is a naturally occurring phenomenon.

“A species becomes extinct when the last individual dies. This observation is a useful starting point for any discussion of extinction as it highlights the role of luck and chance in the extinction process”

The passage discusses the role of luck and chance in extinction but never states whether extinction occurs naturally without human cause.

Paragraph A

“Whether an individual survives from one year to the next will largely be a matter of chance. Some pairs may produce several young in a single year while others may produce none in that same year.”

Paragraph A stresses random chance in birth and death, with small populations fluctuating so much that extinction can happen even when average size should grow.

Paragraph B

“Small populations cannot avoid a certain amount of inbreeding. This is particularly true if there is a very small number of one sex. For example, if there are only 20 individuals of a species and only one is a male, all future individuals in the species must be descended from that one male”

Paragraph B explains inbreeding in small populations, particularly when there is a very small number of one sex.

Paragraph C

“Without genetic variability a species lacks the capacity to evolve and cannot adapt to changes in its environment or to new predators and new diseases”

Paragraph C explains that without genetic variability a species cannot evolve or adapt to environmental change, new predators and new diseases.

Paragraph D

“Catastrophes such as fire, flood, drought or epidemic may reduce population sizes to a small fraction of their average level”

Paragraph D describes catastrophes such as fire, flood, drought or epidemic sharply reducing population sizes to a fraction of average.

“Small populations will fluctuate enormously because of the random nature of birth and death and these chance fluctuations can cause species extinctions even if, on average, the population size should increase”

The gap needs what chance fluctuations can cause; the text says they can cause species extinctions even if average population size should increase.

“Besides these processes we need to bear in mind the distribution of a population”

The gap needs what must be borne in mind besides these processes; the text says we need to consider the distribution of a population.

“It is therefore a scientific fact that increasing the area that is logged in any region will increase the probability that forest-dependent animals will become extinct”

The gap needs the activity whose expansion raises extinction probability; the text says increasing the area logged does so for forest-dependent animals.

An alternative heading for the passage could be:

1. AThe protection of native flora and fauna
2. BInfluential factors in assessing survival probabilitycorrect
3. CAn economic rationale for the logging of forests
4. DPreventive measures for the extinction of a species

“This is a tool for predicting the probability that a species will become extinct in a particular region over a specific period To make a prediction about extinction we need to understand the processes that can contribute to it and these fall into four broad categories which are discussed below”

The passage is about predicting extinction probability and the four categories of processes contributing to it, so option B fits.