Biological Diversity

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Chapter 5

• Biological Diversity

Big Question Can We Save Endangered Species and
Keep Biological Diversity High?
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Case Study The Shrinking Mississippi Delta
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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

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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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• The word evolution in the term biological
  evolution has a special meaning
• What causes evolution?
• New species arise as a result of
• competition for resources
• the difference among individuals in their
  adaptations to environmental conditions
• Because the environment continually changes,
  which individuals are best adapted changes too

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• Four processes lead to evolution mutation,
  natural selection, migration, and genetic drift

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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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• When a cell divides, the DNA is reproduced and
  each new cell gets a copy
• Sometimes an error in reproduction changes the
  DNA and therefore changes inherited
  characteristics
• When DNA is altered, it is said to have undergone
  mutation

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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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• Migration is an important evolutionary process
  over large areas and long times
• Land bridge between Siberia and Alaska
• Marsupials in Australia

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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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Biological Evolution in Action TodayMosquitoes
and the Malaria Parasite

• About 300400 million people are infected each
  year, and 1.1 million people die.
• Children are especially at risk

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• Malaria is a protozoan disease (Plasmodium),
  transmitted by mosquitoes

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• An anti-malaria campaign was initially
  successful, based on DDT and chloroquine
• However, success was short-lived
• The mosquitoes began to develop a resistance to
  DDT
• The protozoa became resistant to chloroquine.
• The mosquitoes and protozoa developed resistance
  through natural selection.

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• Its either one knockout punch or a continual
  battle to stay ahead
• Mutation often outstrips development of new drugs
  to prevent malaria
• An alternative is to develop a vaccine targeted
  at either the Plasmodia or the mosquitoes

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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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Island Biogeography
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• Isolation on remote islands can lead to adaptive
  radiation
• Hawaiian Honeycreepers

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• Small islands have fewer habitat types and
  greater risk of extinction
• The more distant the island, the less chance of
  reaching it
• Over time, an island tends to maintain a constant
  number of species, because the rate at which
  species are added is about the same as the rate
  at which other species become extinct

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• Species often evolve to a smaller size on islands
  because islands often have a limited supply of
  food, fewer predators, and fewer species
  competing for the same resources
• Examples include island foxes, pygmy mammoths,
  and a dwarf human species Homo floresiensis

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• Island concepts can also be applied to
  ecological islands
• Ecological islands are comparatively small
  habitats separated from a major habitat of the
  same kind
• A small stand of trees within a prairie is a
  forest island

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Basic Conceptsof Biological Diversity

• Genetic diversity is the total number of genetic
  characteristics of a group
• Habitat diversity is the different kinds of
  habitats in a given area
• Species diversity includes
• Species richness - the total number of species
• Species evenness - the relative abundance of
  species
• Species dominance - the most abundant species

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The Number of Species on Earth

• How many species exist today?
• About 1.5 million species have been named, but
  the total number is probably 3 million to 10
  million
• Insects and plants make up most of the known
  species

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Why Are There Many Species inSome Places and Not
in Others?

• The tropics generally have much greater
  biological diversity than other areas
• Biodiversity generally declines with latitude
• Habitat complexity tends to increase biodiversity
• Complex topography also increases biodiversity

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• Disturbances, such as wildfires, can increase
  biodiversity
• Lifes diversity further increases diversity
• Biodiversity changes over time
• People affect biodiversity, usually negatively
• Urbanization can decrease biodiversity
• Change in abundance of a species can occur over
  an area or distance ecological gradient

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Diversity and Elevation
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Diversity and Elevation
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What Can We Do to SaveEndangered Species?

• How many species are threatened with extinction?
• IUCN Red Book of Threatened Species
• 23 of mammals, 12 of birds, 4 of reptiles, 31
  of amphibians, and 3 of fish
• 3 of plants

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• 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?

• What do we really want to save?
• A wild creature in a wild habitat?
• A wild creature in a managed habitat?
• A population in a zoo?
• Genetic material only?

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• Which goals we choose involve not only science
  but also values
• Ecological justification
• Aesthetic and spiritual justification
• Recreational justification
• Utilitarian justification
• Moral justification
• Cultural justification

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• Moral justification has deep roots within human
  culture, religion, and society
• Medicines are one example of the utilitarian
  value of species diversity
• Many species help to control pollution
• Tourism provides yet another utilitarian
  justification, especially in developing countries

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How a Species BecomesEndangered 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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• 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 20,00010,000 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 Extinctionsand Affect
Biological Diversity

• Some ways we cause extinction
• disrupting or eliminating habitats
• introducing exotic species
• hunting or harvesting
• Polluting
• Global climate change

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• When people learned to use fire, they changed
  habitats over large areas
• As people explored new areas, they introduced
  exotic species
• The earliest people probably caused extinctions
  through hunting
• The introduction of thousands of novel chemicals
  into the environment created pollution
• People have caused about 75 of the extinctions
  of birds and mammals since 1600

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The Good News The Statusof Some Species Has
Improved

• Success stories include
• Elephant seals
• Sea otters
• Recovery of bird populations after the ban on DDT
• Blue and gray whales

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Can a Species Be TooAbundant? If So, What Should
We Do?

• Sea lions have become so abundant as to be local
  problems
• Mountain lions have become locally overabundant

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The Kirtlands Warblerand Environmental Change

• Environmental change is necessary for some
  species
• Kirtlands warblers are known to nest only in
  young jack-pine woodlands. Fire is required to
  maintain these woodlands
• Kirtlands warblers require fairly frequent
  change fire every 20-30 years
• Fire suppression reduced nesting habitat
• Managers have now introduced controlled burning

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Ecological Islandsand Endangered Species

• Almost every park is an ecological island for
  some species
• How large must an ecological island be to ensure
  survival of a species?
• Depends on the species