Question

how could adiverse population be more restistant to predation and diseases

Answer 1

A diverse population would be more resistant to these factors because, the organism number of species in a population can accommodate for losses by predators, resistant to disease because of the high tolerance range each member possesses, different immunity to different diseases and a more diverse population tend to out-compete other invasive species gaining dominance

Answer 2

A more diverse gene pool increases the chance that there will be beneficial mutation and thus protects the entire population against extinction due to diseases due to lack of a certain immunity factor, i.e. a greater T-cell number or the ability to produce a certain antibody.