I. What is biological diversity?
A. Scales of organization
Across globe, there is a marked pattern of species diversity being much higher at the equator and less at the poles. Many species groups show this pattern, including small mammals, birds, insects, plants
However, there are always a few exceptions to every rule. Some groups of species which are more diverse pole-ward include shore birds, some groups of butterflies, plants, etc. In all of these cases, the plants and environments needed for their existence are more common toward the poles.
B. Longitudinal (East-West) gradients
No general global patterns in longitudinal diversity exist. However, on each continent, such gradients often exist. For instance, the great majority of plants in the U.S. occur from the Rockies west, with the interior of the continent species-poor.
Similar patterns can be found within states, counties, or smaller regions.
Often species diversity increases as the topography becomes more complex.
Study of the fossil record has shown that diversity is not stable through time. A. Extinction events
The major pattern which emerges from these studies is that the planet has undergone a series of severe extinction events in which up to 95% of the species go extinct.
However, following these extinctions, the survivors rapidly evolve into the 'empty' niches and re-diversity the biosphere
B. Descriptions of major extinction events
I. Background: Through the Paleoecology Looking-Glass
A. At no time has Earth s climate been stable. Variations in temperature and precipitation occur over time scales of days to geological epochs (remember the Milankovitch cycles?).
Because of this, the Earth's biota have always had to adapt to changing conditions.
Paleoecology allows us to study how species have responded to previous episodes of climatic change.
By knowing this, we may be better able to predict how species will respond to current global changes.
B. Response of biomes and communities to rapid global warning 15,000 years ago.
1. The last ice age did not gradually end, but came to a rapid conclusion roughly 15,000 years ago. It took several thousand years for the ice caps to melt, but the climatic warming that caused it may have been much more rapid.
2. This change had catastrophic effects on the biota. Roughly 80% of the large mammals in North America went extinct, and many smaller animals also disappeared. For instance, approximately 25% of eastern North American land snails either went extinct, or had catastrophic reductions in range.
3. Much controversy exists as to the exact cause of these extinctions. Overhunting and disease are often mentioned, but it is unlikely that these would cause both mammoths and pin-head sized snails to disappear.
4. However, loss of habitat could. Paleoecologists have discovered that the plant and animal communities of the ice age are not the same as are found today. The species which disappeared are primarily those which used habitats that vanished.
For instance, mammoths needed open tamarack-sedge tundra, which was absent in North America from10,000 to 2000 years ago. When their habitat disappeared so did the mammoths.
Some of the ice age communities contain species which today live in tundra, prairie, eastern forest, or boreal forest communities.
5. Species migrated back into northeastern North America at different rates and speeds, depending upon their dispersal ability and location of their glacial refuge.
4. However, loss of habitat could. Paleoecologists have discovered that the plant and animal communities of the ice age are not the same as are found today. The species which disappeared are primarily those which used habitats that vanished.
For instance, mammoths needed open tamarack-sedge tundra, which was absent in North America from10,000 to 2000 years ago. When their habitat disappeared so did the mammoths.
Some of the ice age communities contain species which today live in tundra, prairie, eastern forest, or boreal forest communities.
5. Species migrated back into northeastern North America at different rates and speeds, depending upon
their dispersal ability and
location of their glacial refuge.
II. Current Global Changes
A. Because of release of greenhouse gases into the atmosphere, the amount of
heat trapped in the atmosphere will probably increase. This may cause rapid
global climate change similar to that seen at the end of the last ice age.
What effects could these changes have on biodiversity?
B. Obviously, some species may be in trouble if their habitat vanishes.
C. Even if habitats simply move location, this may be a problem, as a
reserves cannot move with their habitats.
D. Migration has become harder since the last great climate change due to
increased fragmentation of the landscape. Thus, the number of extinctions may be
even higher than the last time.
III. What can be done?
A. Create reserves in mountains so that more climate zones can be packed
together
B. Help species migrate to their new homes
C. Hope that global warming won't occur, and do everything we can to keep
down greenhouse gas emissions and lower fragmentation rates.