Which characteristic of a geographic region
would have the greatest influence on the type of
ecosystem that forms in that region?
(1) ratio of autotrophs to heterotrophs
(2) concentration of atmospheric oxygen
(3) number of food chains
(4) climatic conditions

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.

i think this picture will you.