tailieunhanh - IELTS Academic Reading 1

Nhằm giúp các bạn có thêm tài liệu ôn tập kiến thức, kĩ năng cơ bản, và biết cách vận dụng giải các bài tập một cách nhanh nhất và chính xác. Hãy tham khảo IELTS Academic Reading 1 để tích lũy kinh nghiệm giải đề các bạn nhé! | Reading 001 You should spend about 20 minutes on Questions 28-39 which are based on Reading Passage 1 below Population Viability Analysis Part A To make political decisions about the extent and type of forestry in a region it is important to understand the consequences of those decisions. One tool for assessing the impact of forestry on the ecosystem is population viability analysis PVA . This is a tool for predicting the probability that a species will become extinct in a particular region over a specific period. 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. 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. 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. Part B A Early attempts to predict population viability were based on demographic uncertainty 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. 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. Taking only this uncertainty of ability to reproduce into account extinction is unlikely if the number of individuals in a population is above about 50 and the population is growing. 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

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