Right answer is (d) Color of species
Easiest explanation: Decrease in richness of the population affects the microbial population but the color of species is not a relevant factor to consider for affecting microbial population and hence, it really doesn’t matter in a bigger prospective. Resistant population is selected over the original strain, that affects the microbial population, also, reduction in abundance, diversity of species are the other factors that affects the distressing of microbial population.