Final answer:
As populations shrink, loss of genetic diversity leads to inbreeding depression and a decreased capacity to adapt to changing environments, due to a phenomenon known as a population bottleneck.
Step-by-step explanation:
As population size becomes small, often due to a phenomenon known as a population bottleneck, there will be a loss of genetic diversity, which will cause a loss of polymorphism. A reduced genetic diversity may lead to inbreeding depression and the fixation of alleles, potentially causing a population to experience difficulties in adapting to new environmental conditions or threats.
This decline in genetic diversity can make a population more vulnerable to the effects of deleterious recessive alleles and to changing environmental conditions. When natural disasters occur or human activities significantly reduce population sizes, the genetic structure of a population can change drastically in an instant, leaving the survivors with a gene pool that may be poorly equipped to handle future challenges. Conservation genetics emphasizes the importance of maintaining genetic variance to ensure populations possess a wide range of alleles, facilitating a better capacity to adapt and survive.