What is the disadvantage of asexual reproduction

The offspring will be identical to the parent. There is no diversity. If the parent has an illness the offspring will receive it too. The parent and the offspring will be competing for the same nutrients, sunlight and space.

Offspring are genetic clones. A negative mutation can make asexually produced organisms susceptible to disease and can destroy large numbers of offspring. Some methods of asexual reproduction produce offspring that are close together and compete for food and space. Unfavourable conditions such as extreme temperatures can wipe out entire colonies.