Species Extinction and
Species are currently going extinct at a faster rate than at any time in the past with the exception of cataclysmic encoders with extraterrestrial objects. A good proxy for the rate of extinction is the rate of growth in energy used by the human population. In other words, extinction rates are increasing in step with the product of population growth times the growth in affluence.
- Graph is based on a mathematical model linking species to
habitat loss developed by Edward O. Wilson and others.
- Assumptions: Total number of species = 10 million
Background extinction rate from fossil records is one extinction
per million species per year; estimated total number of species
10 million - background rate = 10 species per year.
- Extinction Rates:
- 1. Edward Wilson estimates 27,000 species are currently lost
per year. By 2022, 22% of all species will be extinct if no action
- 2. Niles Eldridge estimates 30,000 per year currently.
- 3. Georgina M. Mace using a different methodology based on
extrapolations from the current lists of endangered species arrives
at a figure of 14-22% loss of species and subspecies over the
next 100 years.
- 4. Paul Ehrlich, using another approach based on total energy
use estimates extinction rates at 7,000 to 13,000 times the background
rate, (70,000 to 130,000 species per year) which he says is higher
than figures based on data for higher orders of animal indicates,
but we have little data on insects and micro flora and fauna.
Species extinctions are very difficult to quantify. In the past the man caused extinctions have been primarily due to hunting. As man crossed over from Asia and entered the North American Continent, a series of extinctions occurred caused in part by man's predation of slow moving species like the mammoth and other mega-herbivores and perhaps, according to a new hypothesis, by the introduction of new diseases by man or his domesticated animals. The loss of these species caused other dependent species to go extinct like the giant vultures and the long nosed bear. A similar wave of extinctions happened as the Polynesians colonized the pacific islands. This time it was the flightless birds that were defenseless against the new predators. The Moa was the largest, but on many islands there is evidence that up to 50% of all species of birds were hunted to extinction including such remarkable species as the Hawaiian Eagle.
- The cascade of current extinctions, however, is related mostly
to destruction of habitat, and displacement by introduced species.
Chemical pollutants, over harvesting and hybridization have played
smaller but still significant role. While the actual extinction
rate is difficult to pin down, there is no doubt that the planet
is in the midst of a mass extinction of major proportions. The
most conservative estimates place the extinction rate at 1000
times the background rate. These numbers are more easily accepted
when placed in the context of habitat destruction.
- Habitat Loss:
- African Nations: average 68% with Gambia suffering the most
at 91% loss.
- Asian Nations: 69% average with a range of 34% to 96% (excluding
- Mexico 66%
- US 26% (data WRI 1990)
- Habitat destruction can also be estimated in terms of the
product of population times affluence times a factor for technology,
all of which can be summed up by total energy use. Pre-agricultural
revolution energy use is estimated at .001 to .002 terawatts
for a population of 5-10 million. World consumption in 1990 was
13 terawatts or 7,000 to 13,000 times higher.
- In the future, the rapid increase in temperature will become an increasing threat to species. A tree species, for instance, can only migrate at a rate much slower than the rate at which its climactic zone will shift toward the poles.
- "Biodiversity is our most valuable but least appreciated resource. We need to reclassify environmental problems in a way that more accurately reflects reality. There are two major environmental problems, and only two. One is the alteration of the physical environment to a state uncongnial to life, the now familiar syndrome of toxic pollution, loss of the ozone layer, climactic warming... all accelerated by the continued growth of human populations.
- The second category is the loss of biological diversity. ...Merely the attempt to solve the biodiversity crisis offers great benefits never before enjoyed, for to save species is to study them closely, and to learn them is to exploit their characteristics in novel ways.*
The benefits of species diversity can be approached from two
angles, one is the Cost Benefit approach of our monetary based
value system, and the other is the Safe Minimum Standard which
holds each species as irreplaceable and worthy of preservation
for its own sake. The cost benefit analysis would be quite adequate
if all the costs and benefits were included, but many benefits
are not known and the potential benefits cannot be known. For
example, in 1970 Grassy Stunt devastated rice crops in India and
Indonesia. Severe famine was averted by the development of a resistant
strain. After testing 6,273 varieties, the resistant gene was
found in only one variety discovered in 1966.
- The full valuation of species diversity must include but
is not limited to:
- 1. The value of the products obtained from the species. In
addition to potential medicinal values, many species have great
potential as agricultural and livestock that offer benefits of
greater efficiency and less destruction of the environment. 7000
species are grown and collected for food, but 50% of our food
comes from 3 plants, wheat, maze, and rice. The same is true
of commercially raised animals, especially cattle which are ill
suited and destructive to many of the environments they are raised
in. For example a study shows that the green iguana, a delicacy
of the rainforest could produce up to 10 times the yield per
acre of cattle, and the forest would be left in tact to provide
- 2. The present and future value of the genetic material held
in the species. The potential for utilizing genetic material
in beneficial ways is expanding so rapidly that to put a value
on the material from any species would be impossible. There are
many examples like the rice disease mentioned above where the
benefits of a single gene only recently discovered has had incalculable
- 3. Stability of the ecosystem. "In a world created by
natural selection, homogeneity means vulnerability."* Diversity
gives the natural system the ability to resist and adapt to disease,
severe weather, and climactic change. Disease striking a society
dependent on monoculture has been a major factor in many famines,
the Irish Potato Famine being the most infamous, mostly because
of the ability of plant geneticists to invent new resistant variety
as fast as the diseases arise.
- 4. Maximizing the efficiency of the ecosystem. Many studies
have shown that a diversity of species is better able to utilize
the inputs of water, sun and nutrients than a single or small
number of species which leads to greater biomass and less soil
erosion and nutrient loss. This is especially true of rainforests,
but also applies to temperate forests and grasslands.
Recovery time: Berkeley environmental scientist James
W. Kirchner and paleontologist Anne Weil released a report on
3/9/2000 that the recovery time for mass extinction is around
10 million years. This is significantly longer than previously
thought, and seems to hold true for any level of extinctions from
major extinctions of 75% of to minor ones of 25%. http://www.urel.berkeley.edu/urel_1/CampusNews/PressReleases/releases/03-09-2000.html
- Resources: Listed in order of usefulness and readability
- Web Sites
- 1) Wilson, Edward O. The diversity of Life, The Belknap Press
of Harvard university press, Cambridge, Mass.1992. A classic
- 2) Baskin, Yvonne, The Work of Nature, Island Press, 1998.
A very fascinating account of the interrelationships that make
an ecosystem work.
- 3) Eldredge, Niles, Life in the Ballance humanity and the
Biodiversity Crisis Princeton university Press, princeton 1998
- 4) Lawton, John H. & May, Robert M., Editors, Extinction Rates, Oxford University Press, 1995. An academic treatment of the techniques of population estimating.
- There are far too many to list here, but any of these works
will list 100 more references.