Transcript Biogeochemical Cycles - University of Washington

Lesson 5: Biological Diversity
Big Question
Big Question: Can We Save Endangered Species
and Keep Biological Diversity High?
What Is Biological Diversity?
Biological diversity is the wealth of species that live on Earth
Commonly expressed as the number of species or genetic types
in an area
Lesson 5/ ESRM 100 / University of Washington
Biological Evolution
•An important question about biological diversity is "How did it
all come about?"
•In the 19th century, Charles Darwin proposed an explanation
that became known as biological evolution
•It is the change in inherited characteristics of a population from
generation to generation
•Ultimately, it can result in new species
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Mutation
•Deoxyribonucleic acid (DNA) carries inherited information
from one generation of cells to the next
•The chemical information for a single characteristic is a gene
•The genetic makeup of an individual or group is a genotype
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Selection
Change is not always for the better. Mutation can result in a new
species whether or not that species is better adapted to the
environment than its parent species.
Individuals with characteristics making them better able to
survive and reproduce leave more offspring than others; they are
more fit.
This process of increasing the proportion of better-adapted
offspring is natural selection.
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Migration
Geographic isolation can lead to divergent evolution. The two
populations may change so much that they can no longer
reproduce together.
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Genetic Drift
Sometimes changes in genetic makeup of a population occur
simply from chance: drift.
Genetic drift can be a problem for rare or endangered species.
• Lower fitness traits may dominate.
• Small size of the population reduces genetic variability.
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Island Ecology
•Islands have fewer species than continents, and the smaller the
island, the fewer the species, on average.
•Also, the farther away an island is from a continent, the fewer
species it will have.
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Adaptive Radiation
Isolation on remote islands can lead to adaptive radiation. An
example is Hawaiian Honeycreepers.
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Basic Concepts of Biological Diversity
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How many Species on Earth?
See the Wikipedia article on Species.
www.wildlifeinstitute.org/press_gallery.htm
http://www.worldproutassembly.org/
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How many Species on Earth?
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What Can We Do to Save
Endangered Species?
How many species are threatened with extinction? According to
the IUCN Red Book of Threatened Species
• 23% of mammals, 12% of birds, 4% of reptiles, 31% of
amphibians, and 3% of fish; and
• 3% of plants.
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Endangered and Threatened Species
What does it mean to call a species endangered or threatened?
Endangered species means any species which is in danger of
extinction throughout all or a significant portion of its range.
Threatened species means any species which is likely to become
an endangered species within the foreseeable future throughout
all or a significant portion of its range.
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Why Save Endangered Species?
Taken from http://www.fws.gov/endangered/
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How a Species Becomes
Endangered and Extinct
•Extinction is the rule of nature
•Local extinction is when a species disappears from a part of its
range
•Global extinction is when a species can no longer be found
anywhere
•Rates of extinctions have varied greatly over geologic time
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Mass Extinctions
The fossil record suggests that there have been several periods of
mass extinction and other periods of rapid evolution of new
species
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Causes of Mass Extinction
•Six major mass extinctions occurred during the past 550 million
years
•The end of the dinosaurs about 65 million years ago – asteroid
impact?
•Megafauna extinctions 20,000–10,000 years ago at the end of
the last great continental glaciation period
•The rate of extinctions has increased greatly since the Industrial
Revolution
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How People Cause Extinctions
and Affect Biological Diversity
Some ways we cause extinction:
• hunting or harvesting
• disrupting or eliminating habitats
• introducing exotic species
• polluting
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The Good News: The Status
of Some Species Has Improved
Success stories include
• Elephant seals;
• Sea otters;
• Recovery of bird populations after the ban on DDT; and
• Blue and gray whales.
Link: "Living with alligators: A Florida reality"
at http://edis.ifas.ufl.edu/UW230
Lesson 5/ ESRM 100 / University of Washington
Chapter 5: Biological Diversity
Questions? E-mail your TA. [email protected]