INTRODUCTION, HISTORY OF LIFE

Biodiversity and Conservation: A Hypertext Book by Peter J. Bryant

Chapter 1: INTRODUCTION, HISTORY OF LIFE

HISTORY OF LIFE ON EARTH
Geological time
Rise of biological diversity

Registered UCI students: view the slide show for this chapter or download it:
http://darwin.bio.uci.edu:80/~sustain/protected/chap1slides.ppt

http://darwin.bio.uci.edu:80/~sustain/protected/chap1slides.pdf

"If today is a typical day on planet Earth, we will lose 116 square miles of rainforest, or about an acre a second. We will lose another 72 square miles to encroaching deserts, as a result of human mismanagement and overpopulation. We will lose 40 to 100 species, and no one knows whether the number is 40 or 100. Today the human population will increase by 250,000. And today we will add 2,700 tons of chlorofluorocarbons to the atmosphere and 15 million tons of carbon. Tonight the Earth will be a little hotter, its waters more acidic, and the fabric of life more threadbare." ...... David Orr (1991), " What is Education For?".

BIODIVERSITY AND CONSERVATION

This hypertext book deals with the problems of trying to preserve biological diversity on the earth. We will discuss the history of life on earth, the reasons for depletion and extinction of animals and plants at various times including the present, the reasons for being concerned about these losses, and what can be done to preserve some of what is left.

Read the Living Planet 2004 Report, by the World Wildlife Fund, to see graphic illustrations of humanity's impact on the natural resources of the planet, and read about a new comprehensive plan to save the planet, drafted by an unprecedented combination of scientists, environmentalists and business leaders in August 2000.

We live at a critical time for the conservation of biological resources on earth. The Living Planet Index, a measure reflecting the state of the world's forests, freshwater and marine ecosystems, fell by 37% between 1970 and 2000 according to the Living Planet 2002 Report.

In the recent past, the level of biological diversity was the highest the world has ever seen. However, the number of species is not known, even to the nearest order of magnitude. The number of described species is about 1.4 million; but the total is estimated at about 5 million. It has taken 3.5 billion years for this biodiversity to evolve, and we are rapidly destroying it. Whereas the natural rate of extinction is estimated at about one species per year, the present rate is estimated at 10,000 times that - about one per hour - and almost all of these losses are caused by human activities. We probably have already lost 1 million species, and several more million will be lost in the first few decades of the 21st century.

Table 1 gives the number of recorded extinctions between 1600 and 1983. Notice that:

- the total number of recorded extinctions is over 700;
- over half of these are vascular plants;
- a very large fraction are island forms, especially with reptiles and birds.

The data are probably most accurate for birds and mammals since these are the most conspicuous of the types of organisms listed. 113 species of birds and 83 species of mammals were definitely lost during this period.

Table 1. Recorded Extinctions, 1600 to 1983
Mainland ^a	Island ^b	Ocean	Total	Approximate Number of species	Percentage of Taxa Extinct Since 1600
Mammals
30	51	2	83	4,000	2.1
Birds
21	92	0	113	9,000	1.3
Reptiles
1	20	0	21	6,300	0.3
Amphibians
2	0	0	2	4,200	0.0
Fish^c
22	1	0	23	19,100	0.1
Invertebrates^c
49	48	1	98	1,000,000+	0.0
Vascular Plants^d
245	139	0	384	250,000	0.2
Total
370	351	3	724
a. Landmasses greater than 1 million square kilometers (the size of Greenland and larger). b. Landmasses less than 1 million square kilometers. c. Totals primarily representative of North America and Hawaii. d. Vascular taxa (includes species, subspecies, and varieties).

Source: Reid and Miller 1989 Keeping Options Alive-The Scientific Basis for Conserving Biodiversity.

Table 2 gives the number of extinct animal species, and also includes counts of the number of animal species considered to be under different degrees of threat. A 1996 study by the World Conservation Union found that 25 percent of mammal and amphibian species, 11 percent of birds, 20 percent of reptiles and 34 percent of fish species are threatened with extinction. About 10 percent of the world's tree species are in danger of extinction.

Table 2. Number of Endangered and Extinct Animal Species compiled from the IUCN's Red List, 1996 From Fact Sheets - Rainforest Action Network
class	critically endangered	endangered	vulnerable	total threatened	extinct
Mammals	169	315	612	1096	89
Birds	168	235	704	1107	108
Reptiles	41	59	153	253	21
Amphibians	18	31	75	124	5
Insects	44	116	377	537	73
Other animals	471	423	1194	2088	343

The number of inconspicuous forms, like insects, that have gone extinct is probably much higher than the number shown on the list. Many of these species are becoming extinct before they are even studied or named by scientists.

More up-to-date data are available for the more conspicuous and well-known types of animals. Species are the best-known categories, but subspecies are also counted in the extinction statistics. Subspecies are distinct groups within a species, and they are important because they would probably evolve into sparate species in the future. The following are known to have gone extinct in historic times, most of them clearly due to human activities:

Birds (worldwide): 42 species and 44 subspecies
Mammals (worldwide): 73 species and 30 subspecies
Amphibians (worldwide): 122 species (since 1980)

In the U.S., where research is probably more intensive than in many other countries, 631 species are known to have been lost since 1642, and the total is probably well over a thousand. Hawaii, Alabama, and California lead the nation in number of extinctions.

The reasons for extinction are changing. In prehistoric times, natural disasters and competition with other species were the main causes. In historic times, overexploitation and exotic species introductions have caused many extinctions. But today, the main problems facing wildlife are destruction of habitat and pollution.

Tropical forest is being destroyed at the rate of 40,000 square miles = an area the size of Ohio, per year. This is mainly due to slash-and-burn agriculture in areas of high population growth, in which small areas are cleared and used for a few years until they become infertile, and then more acreage is cleared. About 44% of the original tropical moist forest on the earth is now gone. It has been estimated that 15-20% of all species will become extinct by the year 2000 because of the destruction of tropical forests. This rate is about 10,000 times as high as the rate prior to the existence of human beings.

Other habitats are also being destroyed - temperate forests, deserts, wetlands, and coral reefs are all being destroyed at alarming rates, either for profit or to make room for housing, agriculture, ports and other human activities. Damming of rivers has depleted salmon populations in the American Pacific Northwest to such an extent that many of the runs are extinct and others have been listed as endangered.

The fundamental reason for the degradation and loss of habitat is the explosive growth of the human population. Since 1900 the world's population has more than tripled. Since 1950 it has more than doubled, to 6 billion. Every year 90 million more people (= 3x the population of California) are added to the planet. All of these people need places to live, work and play, and they all contribute to habitat loss and global pollution.

Our generation is the first one that really became aware of the fact that the human population is causing irreparable damage to the planet - to the air, water and soil of the planet and to its biological resources. Ours is not the first generation to do damage to the planet, but we are the first to realize the extent of the problem.

Ours is the only generation that can prevent a massive loss of biological diversity. Huge losses have already taken place and we will have to make major changes in the way we treat the planet if we are to save it in anything like an intact state.

If we are lucky, ours will be the first generation in which the main principles guiding our governments will not be economic and political systems, but will be learning to live on the planet without destroying it: learning to live, work, grow food, trade, and develop a sustainable way of life that serves the continuing needs of our descendants, and the other species present on earth, as well as ourselves.

How to be expert and active on issues of Biodiversity and Conservation:

	Take this course and sign up for the Interdisciplinary Minor in Global Sustainability
	(UC students) Join CALPIRG (California Public Interest Research Group) and get experience with activism
	Read about Issues and Write Letters about them (here are some tips)
	Read the ideas of one of the main authors on biodiversity: Speciation and Biodiversity, an Interview with Edward O. Wilson
	Subscribe to some of the following information sources:

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Copyright ©2005 Peter J. Bryant (pjbryant@uci.edu), School of Biological Sciences, University of California, Irvine, Irvine, CA 92697, USA. Phone (949) 824-4714 Fax (949) 824-3571 A Project of the Interdisciplinary Minor in Global Sustainability