Question

While considering the bottleneck effect, why might endangered species be difficult to recover?

Answer 1

Death of several members of a population due to natural calamities leads to genetic drift. The original size of population is then restored by mating among the survivor. The new population may lack the genes of certain traits. This may produce a new species after sometime. The loss of a section of population by death and after sometime a new species is formed that effect is known as bottleneck effect.

And this effect reduces genetic variation in endangered species population, potentially reducing the population's ability to evolve in response to new selective pressures. In endangered populations severe bottleneck may increase inbreeding as survivors are forced to mate with close relatives, resulting in lowered heterozygosity, increased genetic load, and increased expression of deleterious alleles. Inbreeding may yeild significant costs to fitness and decrease population survival, a process called inbreeding depression. That's why endangered species might be difficult to recover after bottleneck effect.