By Robert Hazen, George Mason University
Rapid and unexpected changes in ecosystems have led to the idea about the law of unintended consequences. Environmentalists now realize that ecosystems can be disrupted in ways one would never predict. The law states that any change in one part of a complex system may affect other parts of the system, in ways that are often unpredictable.
The Lake Victoria Experiment
Lake Victoria is the largest freshwater lake in Africa. In the 1960s, a large, aggressive predatory fish called the Nile perch was introduced to the lake; this was to make a challenge for sport fishermen. The perch had no natural enemies in Lake Victoria, and it had vast supplies of smaller fish, some of which were called tilapia, the fish that was the main staple of the diet of the African people who lived on the shores of the lake. The populations of these smaller fish plummeted as the Nile perch came in, and the number of Nile perch, of course, increased accordingly.
The smaller fish had provided all sorts of ecological benefits to the lake; one of them was that they had controlled surface algae, which they fed on. With the small fish gone, the algae spread over parts of the lake’s surface. Then the dead algae sunk, and the decaying algae, as it sunk in the deeper parts of the lake, consumed oxygen where other kinds of fish lived, and so deeper-water fish could no longer live in the lake. The tilapia had also controlled populations of snails, which carry parasites harmful to humans. The incidence of parasitic disease increased dramatically since the Nile perch was introduced.
An Invasive Species
The native fishermen now catch Nile perch, but this leads to another unintended consequence. With a small fish, one just lays the fish out in the Sun to dry, and then use them as long-term protein supply. However, with large fish, one has to build large wood fires to dry and preserve them. As a result, forests have been stripped away from the lake’s shoreline, causing extensive soil erosion into the lake, and a further disruption of the ecosystem of Lake Victoria.
Thus, we see that the introduction of a single species of fish into a vast lake ecosystem drastically altered that ecosystem, perhaps for all time—certainly for centuries, if not thousands of years.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
Changes in Populations of Different Species
In many cases, causes of population changes in ecosystems are not nearly so obvious. In the 1980s, naturalists began to notice that evenings near swamps and lakes around the world, from Borneo to Boston, had become much quieter. It turns out that frog populations around the world had been declining at an alarming rate.
There are some ecologists that view this change with a sense of foreboding. They think that the disappearance of frogs is a warning that something desperately wrong is happening to our biosphere. However, there are others who say that there are natural population cycles, or maybe weather is causing the frogs to remain hibernated for longer periods, etc. It’s a debate, and no one’s really sure of the answer.
So, Why Are the Frogs Disappearing?
The trouble is that biologists don’t really know why frogs are disappearing. In the absence of some comprehensive theory of environmental change, any sort of scientific conclusion reflects individual ideologies as much as it does objective truth.
Some observers tend to think of the environment as a fragile thing that’s under assault by opportunistic industry, uncaring government, exploding world population, and so forth. Others believe that the environment is resilient, and that human needs are our first priority, and that almost anything we can do to the Earth, the Earth will bounce right back, and it won’t matter.
Altering the Balance of Matter and Energy
What concerns many scientists is that we can’t predict how the ecosystems are going to change. The law of unintended consequences is constantly coming into play.
We know ecosystems can be affected in dramatic ways; we just can’t predict how, we can’t predict when. One thing is certain: as human population grows, we’re going to alter the balance of matter and energy, and we do this in several different ways.
First, we’re constantly commanding an ever-larger share of water and nutrients, and these are resources that all living things need. Natural processes gradually renew supplies of groundwater, and of course, the nutrients in the soil are also renewed on a gradual basis. But human activities often consume these resources much, much faster than they can be replaced. In addition, humans are eliminating habitats through deforestation, farming, urbanization, and other sorts of endeavors that are common to the growing human population. By limiting the amount of food and energy available for other organisms, these activities can cause large-scale changes in local ecosystems, and they may affect the diversity of animal and plant species as well.
Dramatic Effects of Changes
These changes are gradual, but gradual changes over time can build up. During the past half century, for example, the United States has lost more than half of its wetlands; wetlands that are vital to the migration of birds. More than 90 percent of Brazil’s vast tropical rainforest is now destroyed, and more is being destroyed every day.
At George Mason University, several acres of woodland were cut down. Many squirrels used to live in that woodland, and when the trees were chopped down, they lost their home. These squirrels were then seen fighting and killing each other on campus; squirrels that normally just used to run around and play in the trees and collect their nuts and stuff. They had lost their homes; some of those squirrels had to die, because there was no longer room for them in that ecosystem, and so they changed their behavior entirely.
Common Questions about Law of Unintended Consequences
The law of unintended consequences states the following: any change in one part of a complex system may affect other parts of the system, in ways that are often unpredictable
Humans are constantly commanding an ever-larger share of water and nutrients, and these are resources that all living things need. Moreover, human activities often consume these resources much faster than they can be renewed through natural processes.
Humans are eliminating habitats through deforestation, farming, urbanization, and other sorts of endeavors that are common to the growing human population.
