What is the amount by which a populations size changes in a given time

answer; i believe its echoic memory,it is believed to last three to four seconds; good luck

i am going to guess that it is co2.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).