The 2 things that cause population numbers to change are?

The two factors that increase the size of a population are natality, which is the number of individuals that are added to the population over a period of time due to reproduction, and immigration, which is the migration of an individual into a place.

Explanation:

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.

not only is it colder, it also becomes darker, less salty, and more dense.