All three would decrease the size of the population of the organism. If an organism suddenly has a new predator, the organism's population will decline and it is likely that the members of the prey's population would disperse in an attempt to survive. Disease would just kill off the population in general, maybe the organism's population would distribute itself differently in order to avoid catching the disease. Competition would decrease the amount of food, water, and/or land available to the organism's population causing it to decrease or change habitats in an attempt to find another food source
Bacteria reproduces exponentially so like at first you’d have one, then 2, then 4, then 16... (because each bacteria splits into 2) and eventually a few hours later you’ll have millions
