Ecosystem Controls
Changing the level of one species can have a large impact on the rest of the ecosystem. Thus, one species can be considered a control for the ecosystem.
Two Types of Controls
Bottom Up Model
nutrients ➡️ vegetation ➡️ herbivores ➡️ predators
This model assumes that the bottom of the food chain (nutrients) is the control for the rest of the ecosystem. Thus, an increase in nutrients will cause an increase in all other species and vice versa.
Top Down Model
nutrients ⬅️ vegetation ⬅️ herbivores ⬅️ predators
Unlike the bottom up model, a change in the top of the chain does not result in a uniform change in each of the other tiers. If, for example, the predator population increases, the herbivore population will decrease, which will cause the vegetation population to increase, which will cause the nutrient population to decrease.
Try it yourself!
Fill in the population for the bottom or top species, depending on the model, and see how the populations of the other species change.
Bottom Up Model
Top Down Model