Extinction

1. The most well understood mass extinction occurred about 65 million years ago; it marked the end of the Cretaceous, and in it the dinosaurs disappeared. The Alvarez hypothesis to explain it is now widely accepted. It suggests a 17km diameter asteroid struck earth in the Gulf of Mexico, just off the Yucatan peninsula. Extinction The fossil record indicates five times in the history of life on earth there have been massive extinctions. Those mass extinction events mark the ends of major geological periods.

2. The ‘nuclear winter’ that resulted deposited exotic elements (Iridium) in a thin layer over the surface of the globe. The impact cloud darkened the earth for months – years. Reduced photosynthesis affected the entire food chain. Reduced temperature affected both aquatic and terrestrial animals. According to very recent evidence, the Permian mass extinction may also have been caused by impact of an asteroid around 250 MYBP. This mass extinction killed 88-96% of marine species, and 30-40% of terrestrial species. The direct causes of other mass extinctions are not yet well understood. Each caused the extinction of a significant fraction of all species alive before the ‘event’. There must have been large scale changes in environmental conditions to drive the pattern of biological change.

3. Here’s a figure for family level extinctions and diversity…

4. At the time of transition from the Permian to the Triassic something else of importance happened… At that time continental drift brought all the major land masses of earth together into a giant supercontinent called Pangaea. Assembly would have changed continental shelves and the climate in many areas then removed from coastlines. Then separation would have caused massive climate changes.

5. And here are indications of when pairs of continents fragmented or became ‘joined’ (at least with respect to dispersal between them).

6. Probably the most important element in explaining the climate change accompanying continental drift is whether polar regions are covered by landmasses (or landlocked seas) or permit free oceanic circulation. The distribution of thermal energy over the surface of the earth is far more even when there is free circulation, and temperate climates extend to near the poles. Without that circulation, polar regions become very cold, and temperate climates reach only far more limited latitudes. As recently as 30 MYBP much of North America had tropical plant communities. Less than 100 MYBP Antarctica had rich temperate communities, and still had connection to Australia with an island-hopping connection to South America. So, climate change has caused many historical extinctions…

7. Extinctions are occurring today at a rate probably unprecedented in the history of life on earth (at a rate comparable to the periods of mass extinction). Some occur naturally, but humans are a major cause through their actions, both direct and indirect. For extinctions occurring in the U.S. (and, by implication, over the rest of the globe), the primary causes are: 1) habitat reduction or modification 2) small population size of endangered species 3) introduction of exotic species, and 4) overexploitation 5) pollution

8. There is a direct parallel (a correlation) between the rate of human population growth since 1600 and the rates of extinction of birds and mammals… We can also consider not just the number of extinctions, but whether they occurred on islands or mainland, and what fraction of the taxonomic group they represent…

10. First, how do the different factors that can cause extinction compare in importance? No assigned cause 56% of recorded extinctions Introduced (exotic) species 17% Habitat destruction 16% Hunting (overexploitation) 10% Other causes 1%

11. How do the factors I listed compare when we look at numbers of species that are endangered (i.e. dangerously close to extinction)?

12. Here are some examples of species we’ve driven extinct: Stellar’s sea cow passenger pigeon dodo Carolina parakeet a and b were hunted to extinction; for c and d habitat loss was also important

13. Habitat reduction and overexploitation are particularly important in developing countries. Why is that important? Because the regions of highest diversity and highest endemism are almost all in the developing world. Norman Myers used endemism, diversity, and population pressure to determine the 25 regions where conservation efforts should be concentrated. These areas have high human population growth rates. They represent only a few percent of land area, yet hold almost half of all plant species and more than one third of terrestrial vertebrate species. Obviously, tropical forest areas are on the list, as are isolated islands with high endemism, but there are others…

15. Massive forest destruction on Madagascar has already driven ~1/2 of lemur and tarsier species extinct. Montaine Central America and the Andes of northern South America have very high habitat diversity, and many parts are severely endangered by development. There is a famous ridge in Ecuador that was cleared for agriculture, causing the extinction of more than 100 endemic species. Edges of major biomes, like the areas around the Mediterranean have much higher diversity than latitude might suggest. The Pacific rainforest of Oregon, Washington, and British Columbia is very diverse, and subject to development pressure (from the forest industry).

16. This last is an excellent example of how knowing too little can be dangerous. The Pacific yew was considered a ‘junk’ tree, until the discovery that Taxis brevifolia produced a secondary chemical called taxol. It is a powerful anti-cancer agent important in the treatment of breast cancer. The yew is now grown in plantations to ‘harvest’/extract taxol. How many other, similarly useful chemicals are being lost with the loss of 2% or so of the total remaining tropical forest per year. I can’t tell you how many extinctions occur with that loss, because we don’t know, haven’t named, or researched the adaptations of most of the species in the areas cut.

17. So, what are we to do? The first, and most important problem is us! There are well over 6 billion of us now, and population projections suggest an increase to 10 billion within about 25 years. The earth cannot sustain that population in the lifestyles we currently enjoy. Reduced (controlled) fecundity must be established verysoon to stabilize the human population at a supportable size. Lifestyles must be modified to increase energy efficiency. The use of energy for heating and cooling needs to be reduced. Our diets need to obtain more of their calories from lower in the food chain (more veggies, less meat).

18. Are either of those minimal necessary changes likely? Population control: In the developed world ‘planned parenthood’ is an established reality, child bearing is occurring later in life, ZPG has largely been achieved. But… In the developing world population growth is still occurring at an alarming rate. The developing countries have larger family size (fertility) and high rates of increase.

19. Here are fertility rates and recent rates of increase for some areas: RegionFertility Rate% rate of increase North America 1.9 0.71 Europe 2.0 0.22 Former USSR 2.3 0.68 Latin America 4.0 1.94 Asia 4.0 1.82 Africa 6.0 3.01 How can we reduce the rate of global population growth? By contraception. In 1992, 70% of couples in developed countries used contraception, while it was only 45% in developing countries. In Africa, it was only 14%!

20. Governments in developing countries need to provide family planning methods, information, and support. Yet there are still 31 developing countries where citizens have virtually no access to family planning. Women in most of those countries want to have fewer children than they actually bear. Only in sub-Saharan Africa do women want family sizes of 5 or more. Elsewhere the desired number is around 2 or even less. Developed countries need to fund and support family planning in the developing world. But that doesn’t provide income to very many corporations in those developed countries, so… Let’s get back to ecology – what can we do to conserve species?

21. Try to conserve species by protecting their habitat. This is particularly important in those ‘hot’ zones with high endemism and high diversity. Which species do we protect? We can’t protect everything. One approach is to choose a species of apparent interest (a ‘warm-furry or feathered’) whose habitat needs encompass the needs of many others. Such a species is termed an umbrella species. How large a population do we need to protect? There is a broad stroke generalization known as the 50-500 rule. Protect a population of at least 500 individuals including at least 50 genetically diverse mating pairs.

22. As a first approximation, use the rules for reserve design drawn from island biogeography. Use any means necessary to keep key species around. For the last wild California condors, that meant bringing them into captivity, incubating and raising their eggs, and eventually releasing young birds back into the wild in areas where their success was more likely. The condor program has been a great success. Instead of extinction, the California condor population now numbers almost 200 individuals.

24. The case of the spotted owl brings up the problems conservation policy faces. The spotted owl lives and breeds successfully only in old growth forests of the northwest U.S. and British Columbia. That is prime timber land. The key question is: How do you balance the rights of the individual (or corporation) with the public good? Strix occidentalis

25. The opposing points of view: Save a logger, Eat an owl. The Timber Industry Save an owl, Ban logging. Environmentalist In the end, conservation begins with an understanding and ‘control’ over human ecology. We cannot continue to ‘rape’ the earth and yet expect it to sustain future generations. Global population growth must soon slow, then stop if we are to live in balance with the earth’s ecological potential. Energy use in the developed world must be brought under control, and a much larger fraction of the energy must come from renewable sources.