This is the Causal Loop Diagram for the model Deer Population - Overshoot and Collapse.
An increase in the Deer Population causes an increase in consumption of the resource / vegetation resulting in reduction of the resources. A reduction of resources in turn causes higher than normal death rate within the population resulting in lowering of the Deer Population.
Therefore, essentially this resource constraint balances deer population. Hence this loop is called a Balancing Loop.
Essentially a balancing loop should maintain a population. But in certain cases where the net growth rate of population is different from that of resources, there can be an overshoot of the population (above the carrying capacity) leading subsequently to a rapid collapse in the population.