If the food is limited to the squirrels then that could impact how well they reproduce which could impact their numbers which therefore could impact the food source for the foxes which eat them. Fewer squirrels means the foxes will slow down on their reproductive numbers as well...they are all linked!
In active transport, materials move from an area of high concentration to an area of lower concentration (goes down the concentration gradient) and it requires or uses energy in the form of ATP (adenosine triphosphate)
