These are feedback loops in which an increase in output leads to an increase in input. These are feedback loops in which an increase in output leads to a decrease in input. Yes, although ecosystems are being displaced from a steady state on a regular basis by ecological disturbance. Ecosystems can change from one steady state to another, giving rise to the ecological concept of multiple stable states. A shift in the communities and ecosystems can occur if the shift is large enough and a new stable state is reached.
Some ecologists think that ecosystems never reach equilibrium because of frequent disturbances.
In such systems, equilibrium may never be reached. The concept of Uniformatarianism suggests that the history of the Earth can be found in fossils trapped in the layers of rocks, with the lowest layers containing the oldest rocks and fossils. It is an example of positive feedback. Doubling time is the time necessary for the quantity of whatever is being measured to double. For populations, this is normally measured in years.