Answer:
Maintaining variability in the genetic pool.
Explanation:
In a biodiverse population, there are different alleles in the genetic pool (variability) and not just a single fixed one. In a changing ecosystem it is possible that although not all of these alleles are beneficial to the population's fitness- in the context of change-, one of them is and helps the population survive and adapt to such change.
Biodiversity then helps because if the population does not have multiple alleles, but only one, it would be possible that the only allele in the genetic pool is not appropriate to face the change in the ecosystem.
