Answer:
One population may compete with another population for food. One population may compete with another population for shelter. One population may serve as a food source for another population.
Explanation:
The digestive system is parrallel to the excretory system, but not part of it. The digestive system is where the digestive process of getting energy from food. The excretory is where the blood enters the nephron. It filters out any kind of waste. The excretory is where the urine comes from. The digestive system doesn't produce urine. Urine is transported from the kidneys to the bladder. It does work together for the use of the body like basically everything in your body.
Natural selection is a mechanism of evolution. Organisms that are more adapted to their environment are more likely to survive and pass on the genes that aided their success. This process causes species to change and diverge over time.
