I am pretty sure the answer is flower because biotic factors are living things in an ecosystem. Seeing as how fog, soil, and water are not living the answer should be flower.
It demonstrates natural selection since the the bacteria that are resistant are selected for because they are the ones that survive. These resistant bacteria -since they are still living- multiply (thus leaving "offspring") and are able to keep their species in existence which adds to their fitness.
The answer is temperate rain forests
Silica Content have a nice dya