By Robert Hazen, George Mason University
Humans can affect the environment by eliminating species; many large animals have been hunted to extinction. It appears that we may be in the middle of a mass-extinction event, especially of larger mammals and other large animals, as a result of human activity. It is important to remember that with our actions, we can change ecosystems in dramatic ways that aren’t predictable.
Elimination of Species
These are things to be worried and concerned about, if in fact we do eliminate certain species. While it may seem improbable to some that this can happen, a fate of this kind befell the passenger pigeon.
These North American birds numbered in the billions. It is described that when they migrated, people would see bands of birds blackening the sky as far as one could see, to the right and left, front to back. Hunters would take their shotguns and point them straight up at these bands of birds and just fire shot after shot, and the birds would fall from the sky by the hundreds. Eventually, these billions of birds were wiped out by overzealous hunters; the last of the passenger pigeons died sometime in the 19th century.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
Impact of Pollution
Human activities also result in a wide variety of air, water and soil pollution, which may degrade ecosystems on a regional or on a global scale.
For example, twenty years ago, the Chesapeake Bay, which is the largest estuary in the United States, boasted abundant water plants and birds; it teemed with commercially valuable crabs and oysters and fish. Today, those populations have been devastated, largely by chemical runoff from farms and factories upstream, as well as overfishing.
Naturalist Jane Goodall has made a sobering point about these human influences on world ecosystems:
We love to point fingers when we try to deal with difficult problems such as the environment, to lay the blame on industry or science or politicians. And there is no question that industrialization has polluted our surroundings. But who buys the products? We do; you and I.
Experimental Fieldwork
One hope for understanding the behavior of ecosystems is experimental fieldwork. The usual protocol is to isolate a small system, such as a lake, or a stream, or a small patch of land. Researchers then remove one species, or they alter one variable, for a long enough time period to compare any changes to those on a similar, unperturbed system, which is nearby, and that serves as a control.
The first of these studies took place in 1961, off the rocky Scottish coast. Biologist Joseph Connell manipulated and distributed a species of barnacle called Balanus, and observed complementary changes in another species of barnacle, called Chthalamus. As simple an experiment as this was in concept, the idea of establishing a clear cause-and-effect relationship between one population and another was revolutionary in ecology, and it set off a whole new kind of ecological study, in experimental field ecology.
In 1966, American biologist Robert Payne followed Connell’s lead and induced dramatic changes in an ecosystem off the Washington coast, by removing one species of starfish; it was the dominant carnivore from that area. Within a year, the common California mussel had overwhelmed that ecosystem, crowding out most other invertebrates and greatly reducing the local diversity of local species. By removing one species, many other species also disappeared from that ecosystem.
Modifying Ecosystems
These pioneering efforts guide many of today’s ecologists, who modify ecosystems one variable at a time to see how they’re affected. Researchers, for example, have changed the acidity of entire lakes. They’ve added iron or other nutrients to patches of soil; they’ve introduced or removed species in enclosed areas.
Some plant and animal species can be added or removed and nothing much happens, while changes in other species can cause drastic effects, altering the entire ecological balance. This simple strategy of altering one variable of a complex system at a time pervades modern biological research, from genetics to brain science.
It’s a neat and clean surgical approach, but ecosystems are not quite that simple, because all the components are complexly interconnected. Controlled experiments do indeed hold the prospect of revealing general principles about ecosystem behavior, and they certainly point out the severe unintended consequences that can result from the addition or the removal of a single species; but these experiments can’t reveal the intricate interplay of all the different factors that work simultaneously. Complex ecosystems may behave chaotically when something goes wrong.
Common Questions about Ecosystems and Effects of Human Activities
One hope for understanding the behavior of ecosystems is experimental fieldwork. The usual protocol is to isolate a small system, such as a lake, or a stream, or a small patch of land. Researchers then remove one species, or they alter one variable, for a long enough time period to compare any changes to those on a similar, unperturbed system, which is nearby, and that serves as a control.
In 1961, biologist Joseph Connell manipulated and distributed a species of barnacle called Balanus, and observed complementary changes in another species of barnacle, called Chthalamus. As simple an experiment as this was in concept, the idea of establishing a clear cause-and-effect relationship between one population and another was revolutionary in ecology, and it set off a whole new kind of ecological study, in experimental field ecology.
Many of today’s ecologists modify ecosystems one variable at a time to see how they’re affected. Some plant and animal species can be added or removed and nothing much happens, while changes in other species can cause drastic effects, altering the entire ecological balance. This simple strategy of altering one variable of a complex system at a time pervades modern biological research, from genetics to brain science.
