Transcript PowerPoint Presentation - Biodiversity and Pleistocene

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?