In regards to population change Natural Factors are those that will occur naturally to a population and cannot be changed much by human actions. For example, birth and death are considered natural factors affecting population change. This is because every single individual in a population has been born and will eventually die in one way or another. Another natural factor would be natural disasters caused by weather which lead to the death of a certain percentage of the population.
Artificial Factors are the complete opposite. These are factors that are mainly swayed by the choices of the individuals in the population. One such major factor would be migration. When individuals choose to pick up their stuff and move to another geographic location they are ultimately reducing the population in one area and increasing another area's population. This is a choice that was made which affected the population size.
Therefore, natural and artificial factors exist in every single population and can drastically affect the size of the population. Natural factors cannot be swayed by humans while Artificial ones can
Natural factors of population change can't be swayed by humans. So for an example of a natural factor take an Earthquake. As of right now we can only predict when Earthquakes will. Inevitably some things will still get damaged and that just can't be helped. An Artificial factor for population change is something specifically made by humans. For an example take a genocide. If some guy decides he wants to go on a killing spree, well all I can say is that is Definitely not natural. Hope that helped.