Biodiversity lessons from the late Pleistocene megafauna extinctions

Biodiversity; lessons from the late Pleistocene megafauna extinctions. Kevin Olsen April 14, 2004

Important points from Chapter 13 1. Biodiversity oscillates in response to imbalances between the rates of species origin and species extinction. (10 -25 species per year) 2. The number of known species for any geological time period will depend on the accessibility of fossil remains. a. The existence of upper levels in any taxonomic hierarchy is inferred by the prescience of specimens in the lower levels. b. The number of species can be normalized to compensate for the different lengths of the geological periods. 3. The upper levels of the taxonomic hierarchy tend to be more stable over time. In contrast, individual species are subject to constant pressures in a constantly changing environment.

Important points from Chapter 13, Continued 4. Mass extinctions may eliminate large numbers of individual species but the biosphere quickly recovers (at least on a geologic time scale)because new species will arise to fill vacant niches. (Species Biodiversity Limit) 5. It is hard to predict or explain which species will suffer in a given mass extinction event as their effects tend to be non-specific. 6. The largest mass extinction was at the end of the Permian period when 95% of all species became extinct. The best-known mass extinction was the disappearance of the dinosaurs near the end of the Cretaceous.

Copyright 2003, the New Yorker Magazine

Exhuming the Mastodon Rembrandt Peale, 1806

How to spear a mastodon

The Late Pleistocene Extinction in North America • 12, 000 to 9, 000 years BP (Before Present) • Occurring at the end of the Wisconsin Glaciations • 35 to 40 Species of large land animals • Five species of small animals

North America Megafauna • • • • Mastodons Mammoths Sabertooth cats Bison latifrons (long-horned bison) Shruboxen Spectacled Bear (Tremarctos, North America only) Muskoxen Camels (larger species than modern camels) Horses (already in a long term steady decline) Giant Ground Sloths Dire Wolf Giant Beaver (Castoroides, as large as a Black Bear. ) American Lion Giant Short-faced bear.

“Simultaneous” Extinctions • Extinction events also occurred in South America, Africa, and Eurasia but these were spread out over longer time periods. • In the cases of Africa and Eurasia, the events were not as severe. Some 80% of the large African mammals are still extant today. • An extinction occurred in Australia some 10, 000 years earlier.

Proposed causes of the extinction.

But on the other hand…. . • Hunting • Imperfect corroboration with the archaeological record. • Why did large mammals survive in South America? • Many of the species had no known connection to humans.

But on the other hand…. . • Climate Change • Why was this extinction mostly confined to large mammals? • Why were some large animals able to extend their ranges to Central and South America? • Why didn’t previous climate changes cause comparable extinctions?

But on the other hand…. . • Disease • What disease could have infected such a wide range of animal genera? • How would it have spread over such a large geographic area?

But on the other hand…. . • Competition • In some instances, both the invasive and native species had Eurasian origins. Why would a species have an advantage there but not here?

Castoroides vs. Castor

But on the other hand…. . • Astronomical Causes • Why did the duration of this extinction vary from one continent to another?

The Great Escape • • • Spectacled Bears Sloths Stegomaston sp. Llamas Ancestors of today’s South American jungle cats such as the Puma, Ocelot, and Jaguar.

So what did cause the extinctions? • • Environmental insularity? Human hunting? Drought? Climate change? Loss of herbivores? Fire? All of the above?

Burney and Robinson’s Synergistic Scenario: • Human populations increase and so does hunting. • Reduced numbers of herbivores leads to biomass accumulation. • Increased biomass means more frequent and more intense fires. • A combination of human impact and climate change leads to extinction of megafauna.

What evidence supports the synergistic scenario? • Charcoal rises at the same time climate reverses, i. e. more brush and forest fires. • There is a drastic decline in dung fungus spores (a good indicator of large herbivore populations) before humans arrive. • Human associated bones are linked to the appearance of exotic pollens, in other words, humans are changing the landscape. • There is a sudden increase in charcoal, possibly due to fires set as a hunting technique.

Evidence from Madagascar also supports the synergistic theory. 1. Madagascar is an island the size of California. It has been separated from mainland Africa for 165 million years. 2. Humans arrived 2000 years ago 3. Today there are no native terrestrial animals bigger than 25 lbs. A similar pattern was seen on Sardinia, Crete, Hawaii, and the Galapagos

Evidence from Madagascar (continued. ) • Despite a changing climate and shifting vegetation, extinctions on Madagascar were very rare before humans arrived. • BUT. . . Only about a dozen of the extinct animals show associations with humans in the archaeological record.

The Lesson from Madagascar ". . . we can see several negative factors at work. But what comes out of our research is that this is the typical pattern; this extends well back into prehistoric times. What jumps out at you from this research is that each of the negative things that humans do in an environment tends to feed on the other things they do in a synergistic way. ” David Burney

Lessons Learned • If Burney and Robinson are correct, then early humans were able to exert a far greater influence on the environment than previously thought. • Extinction events seldom have a single cause. Often they are created by a number of factors working together. • Biodiversity helps make ecosystems stable. But multiple pressures can start a catastrophic collapse that is impossible to stop.

Topics for Future Research • Use of pollen studies to help ecologists and wildlife biologists in recreating damaged habitats. (Burney) • Expanding our understanding of the synergistic extinction model and how it works in times of climate change. (Burney) • Use of robotic microscopy in paleoenvironmental pollen analysis. (Olsen)

Discussion Questions • Is the current mass extinction unique in that its primary cause appears to be anthropogenic? • We often think of wildlife corridors in terms of migration, do they also play a role as escape routes? • True or false? Biodiversity helps make ecosystems stable. But multiple pressures can start a catastrophic collapse that is impossible to stop. • How important is environmental insularity in causing extinction, for example among Pandas?