Due to the low population size, banded leaf monkey may not be self-sustaining in the long run.

According to the figure, habitat destruction can severely affect the reproduction of banded leaf monkeys. With each generation, banded leaf monkeys survive to reproduce and pass on their genes. In a population bottleneck, severe reduction in population size can sharply reduce genetic diversity.

Why Genetic Diversity is Important?

A population with high genetic variation suggests that individuals can depend on many different versions of gene to increase their survival rate. On the other hand, low genetic variation poses a risk because it suggests that all individuals are nearly identical. When environmental pressures such as a disease occurs, all individuals within the population may be affected.

Low genetic variation also suggests that the surviving population is no longer genetically representative of the original population. This further increase the chances that surviving individuals may only carry a particular version of gene (allele). Overtime, the random fluctuations in the frequencies of alleles from generation to generation – a process known as genetic drift – may cause some alleles to disappear from the population.

Once gene variants are lost, they cannot be recovered. Only the variants that survive in a particular generation can contribute to species diversity in the following generation. Following a genetic drift, the new population can be genetically distinct from the original population, which can lead to the evolution of new species.