Each of the following is a condition necessary for natural selection to occur EXCEPT A. population size is very large.
B. more offspring are born than can survive.
C. fitness varies among individuals.
d. there is heritable variation among members of the population

the right option is; decreased genetic variation  

decreased genetic variation describes the effect of this environmental change.

genetic variation is the naturally occurring genetic diversities or differences between organisms of the same species in a population. genetic variation allows the survival and adaptability of a species when they encounter changing environmental conditions. when an endangered species reduces, it loses genetic variation which may not be restored even if the species rebound and will only be recovered through the gradual collection of mutations over many years.