One predator-prey relationship that currently exists and how the population of one of the species affect the population of the other

Wolf and Rabbit

Explanation:

If the predator-prey relationship of Wolves and Rabbits goes wrong, it could end in bad consequences for other relationships too. lets say the wolves go missing from the environment. then the Rabbits would over populate and most likely eat most of the berries and other foods that other animals eat. the Wolves keep control of the Rabbit population and without them, it would end badly.