As an ecologist I am trained to see how different species of plants and animals, as well as creeks, trees, and the rest of the biosphere interact with each other. Most of the time these ecosystems interact in a balanced state of equilibrium because they are closed: plants utilize what they need from soil and water, animals eat what they need, and the sun is always providing a constant source of heat and light. But what happens when too much of the water is utilized by an invasive species? Or, when humans begin to over-fish the stream? What happens when the system is no longer closed?
The book “Thinking in Systems: a primer,” discusses what happens when a closed system, such as a fishery, is suddenly opened. The effects of over-fishing are not immediately noticeable by the casual onlooker, nor by the fish in the fishery (creek). This delay is called inertia and can be seen in almost every system. The fishery can continue to be over-fished at a constant rate for many years before there is any evidence of over fishing. An example that was mentioned in the book “The Sixth Extinction,” by Elizabeth Kolbert was that of the slow extermination of megafauna in the North American Continent. Kolbert’s argument was that even though there was a very small population of humans compared to that of, say a, Mastodon, the Mastodon has no natural predators, and a very slow replacement rate, therefore any level of hunting that might take place would eventually wipe-out the species. Humans would have no sense of the reduction in Mastodon population because the life-span of humans is too short. It would only be in the last few generations of human that someone would notice that the Mastodon was going extinct. (This is depicted in Meadow’s book fig. 41)
As the population of Mastodon, or fish in a creek, begins to decline the system begins to change. To account for the level of hunting the Mastodon is experiencing, it would have to increase its birthrate to maintain its current population. Doing so would, despite being physically impossible, require an increased amount of food and water resources to nourish the young. As the Mastodon begins to require more resources, it will reduce the availability to other mammals who rely on the same resources. This feedback loop will eventually result in displacing other species.
When thinking in systems it is important to remember that every action has a reaction that is not always equal nor opposite. A reduction in rain fall will reduce the available water for all the species. An increase in hunting of a species that is slow-to-reproduce will result in the reduction of that species’ population… and so on. It is also important to note that there is no way to fully account for every possible connection attached to a system. The best we can do is to always keep an eye opened to the inputs and outputs of a system.
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