The Biodiversity Crisis:

Is There a Biodiversity Crisis? If So, Are Humans Responsible?

By Mark Schneider, Daniel Weiner, and Jiayue Yuan | This page last updated on: October 30, 2009

What is biodiversity?

According to GreenFacts, biodiversity simply means having a variety of "living organisms." This comprises of organisms "within species (genetic diversity), between species (species diversity), and between ecosystems (ecosystem diversity).”

What effect does extinction have on biodiversity?

Extinctions decrease the variety of species in a given environment. Therefore, there is a direct relationship between extinction and biodiversity. Extinctions can also occur in a pattern much like the domino effect. For example, if a keystone species, such as a grizzly bear, goes extinct, many other species that depended on the grizzly bear will go extinct as well. However, some scientists have argued that mass extinctions have no effect on biodiversity.

What is the difference between mass and background extinction?

Extinction – the total loss of one or more species
- Limiting factors such as environmental changes, competition, predation and pure chance control extinctions
Background extinction
- Automatic extinction of species due to constant environmental changes or other limiting factors
- The species that go extinct are often replaced by other similar species to fill their niche through evolution
- The rate of background extinction is much lower than that of mass extinctions despite the fact that it occurs continually
Mass extinction
- Rapid extinctions of large groups of animals from causes completely different from the causes of background extinction,1.gif,1.gif
Themes in mass extinction
1) The causes of extinction tend to occur on both land and sea simultaneously
2) Plants seem to be relatively resistant to extinctions
3) Tropical life forms are favored for extinction (Ex. Extinction of marine life at the end of the Cretaceous Period)
4) Extinction is inclined to affect some groups more than others
Extinction in the Status Quo
- In the 20th Century, extinction rates have become 1000 times higher than the background rate of extinction
- At this rate, more than 33-66% of the species now will be lost by the end of the next century
- The rate of species extinction is far more rapid than the rate at which new species appear; consequently, there is a net loss of biodiversity

What kind of world do we want?
(Ehrlich, & Ehrlich, 1981)
(Stanley, 1987)

Are humans responsible for the loss of biodiversity?
- An article in the Environment News Service points to human activity as a leading cause for the loss of biodiversity. Dr. Lubchenco specifically cites the burning of fossil fuels and overuse of fertilizer as main causes for the many “dead zones” in the ocean.
- Dr. Peter Raven believes that human activities such as deforestation will lead to a faster mass extinction rate. He also notes that only about 1.6 species are known, so there are actually a lot more species going extinct than can be calculated.
- Dr. Raven proposed a seven point plan to deal with plant extinction (which often leads to animal extinction). All of his points required some change in the way humans act and treat the earth. Dr. Raven also touched on the economic aspect of the crisis, saying that providing technology to poorer countries was another way to improve our use of resources (e.g. storing information on the Internet would help slow deforestation).

Why do we care if humans are responsible?

- Humans naturally have curiosity for the living organisms around them and they feel compassion towards endangered species
- Animals are esthetically pleasing
- Biodiversity offer resources that economically benefit humans
o Biological resources make up 40% of the world’s economy and offer 80% of the necessities to those in poverty
o Biological resources allow for medicinal research as well as other economic developments

- Ecosystem is a network of interconnected animals that depend on each other for survival; disturbing one aspect of the ecosystem might endanger the other inhabitants in the same habitat
- Humans depend on biodiversity for environmental services to maintain the ecosystem; Some examples include:
o Water resource purification
o Nutrient storage and recycling
o Formation of soils
o Contribution to climate stability
- Such environmental services are very costly to substitute (if they can be replaced at all)

(Ehrlich, & Ehrlich, 1981)
(Stanley, 1987)

Mathematically, how can we tell if we are effecting biodiversity?

Even though it is not a direct relationship, human population does seem to have an effect on the number of extinctions:
It is very hard to find a specific number for a rate of extinction because new species are being discovered all the time. Without a known number of species, scientists have a hard time deciding if the number of extinction has actually increased.
However, scientist have come up with several models to detect if humans have had an effect on extinction rates. An example of an equation is:
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This equation shows what fraction of species is left after the habitat has been destroyed.
Scientists have used math to see if the extinction rate is increasing:
After calculating the recent extinctions vs. historically documented extinction, it has been decided that the current rate of extinction is around 7,000 times the background rate of extinction.
The current estimated rate of extinctions is around 27,000 extinctions per year.

Are we in a mass extinction right now?

The Facts
- According to The Times, there has been a 35% decrease in biodiversity in the last 35 years
- 25% more natural resources are being used up than the Earth can replace
- Last 400 years: 89 mammalian extinctions, 45% higher than what scientists predicted
The Answer?
There is really no way to be sure. However, many scientists agree there is a possibility that a 6th mass extinction could be underway by pointing to facts such as the ones listed above. One thing is for certain: the emergence of humans didn't help the environment. Major concerns today include a rising human population (which means destroying habitats in order to clear land) and unhealthy human activity such as burning fossil fuels, using too much fertilizer, using up resources too quickly (faster than can be replaced), and causing more pollution (the world is much more industrialized today).

(1999, August 2). "Human Impact Triggers Massive Extinctions." Environment News Service. Retrived October 29, 2009 from

Ehrlich, P, & Ehrlich, A. (1981). Extinction: the causes and consequences of the disappearance of species. New York, New York: Random House.

Eldredge, Niles. (2005). "The Sixth Extinction." American Institute of Biological Sciences. Retrived from

GreenFacts. (2009, September 10). Scientific facts on biodiversity & human well-being. Retrieved from

Shah, A. (2009, July 12). Loss of biodiversity and extinctions. Retrieved from

Shah, A. (2009, April 26). Why Is Biodiversity Important?. Retrieved from

Stanley, S. (1987). Extinction. New York, New York: Scientific American Library.

(2001). "The Current Mass Extinction." Evolution Library. Retrived from

Warren, Georgia. (2008, October 26). "Humans 'drive biggest mass extinction since dinosaurs'." The Times. Retrived October 29, 2009 from