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 a survives from one year to the next will largely be a matter of chance. Some pairs may produce in a single year while others may produce none in that same year. Small populations will fluctua enormously because of the random nature of birth and death and these chance fluctuations ca species extinctions even if, on average, the population size should increase. Taking only this ability to reproduce into account, extinction is unlikely if the number of individuals in a populatio about 50 and the population is growing.

B

Small populations cannot avoid a certain amount of inbreeding. This is particularly true if there number of one sex. For example, if there are only 20 individuals of a species and only one is a future individuals in the species must be descended from that one male. For most animal speci individuals are less likely to survive and reproduce. Inbreeding increases the chance of extincti

C

Variation within a species is the raw material upon which natural selection acts. Without genetic species lacks the capacity to evolve and cannot adapt to changes in its environment or to new new diseases. The loss of genetic diversity associated with reductions in population size will co likelihood of extinction.

D

Recent research has shown that other factors need to be considered. Australia’s environment enormously from year to year. These fluctuations add yet another degree of uncertainty to the many species. Catastrophes such as fire, flood, drought or epidemic may reduce population siz fraction of their average level. When allowance is made for these two additional elements of un population size necessary to be confident of persistence for a few hundred years may increase thousand.