Answer: The species would decrease in number and eventually die off.
If there is no fertilization in the sexually reproducing species for a longer period of time, then none of the female in the species would be able to give birth to the offspring, because the male and female gamete are not able to meet any more.
Therefore the no of species would ceased and then after some the species would extinct from the population or die off, As there are no any youth to replace the old people.
