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CHAPTER 4
Biodiversity
The variety of the earth’s species, the genes
they contain, the ecosystems where they live
and the energy flow and nutrient cycle that
sustain life.
Is a vital renewable resource.
1.8 million species have been identified.
Thousands of new species are identified each
year.
Typically, higher biodiversity = more stable
system.
Biodiversity
Divided into:
• Genetic diversity - diversity of genes within a
species. There is a genetic variability among
the populations and the individuals of the
same species.
• Species diversity - diversity among species in
an ecosystem. Ex - rainforest
• Ecosystem diversity - the variety of ecosystems
on Earth
• Functional diversity – the variety of processes
occurring in an ecosystem.
• Most species are insects!
Measuring Biodiversity
For a geographic area must consider:
1. Species evenness – count of the number of different
organisms within a species
2. Species richness – the number of different species
We sampled two fields for wildflowers. The first field has 300 daisies,
335 dandelions and 365 buttercups. The second field has 20
daisies, 49 dandelions and 931 buttercups. Both samples have
the same richness (3 species) and the same total number of
individuals (1000). However, the first sample has more evenness
than the second.
•
A community dominated by one or two species is
considered to be less diverse than one in which several
different species have a similar abundance.
Variations in Species Richness and
Species Evenness
Richness
Evenness
Biodiversity is important part of the
earth’s natural capital
• Supplies us with food, wood, fibers, energy
and medicines
• Preserves the quality of air and water and
maintains the quality of soil
• Helps us dispose of wastes and to control pest
populations.
• Biodiversity helps sustain life on earth
Natural Capital: Nature’s Pharmacy
Shannons's diversity index - accounts
for both abundance and evenness of
the species present

H = -Σ Pi(lnPi) where Pi is the proportion of
each species in the sample
H ranges from 0 – 4.6.
0 = every species is the same; no biodiversity
4.6 = evenly distributed species; high biodiversity
Species-Rich Ecosystems Tend to Be
Productive and Sustainable
• Species richness seems to increase
productivity and stability or sustainability
• How much species richness is needed is
debatable
Species Diversity
• Species diversity
– Species richness
– Species evenness
• Diversity varies with geographical location
– Most species-rich communities (highest in the tropics and
less as you move from the equator toward the poles)
•
•
•
•
Tropical rain forests
Coral reefs
Ocean bottom zone
Large tropical lakes
Where Do Species Come From?
• Concept : The scientific theory of evolution explains how
life on earth changes over time through changes in the
genes of populations.
• Concept : Populations evolve when genes mutate and
give some individuals genetic traits that enhance their
abilities to survive and to produce offspring with these
traits (natural selection).
Biological Evolution
• Changes in the genetic makeup of a population of a
species, not an individual, in successive generations.
• Charles Darwin and Alfred Russel Wallace
independently proposed the idea of natural selection
as a mechanism for biological evolution. (1858)
• Darwin gathered and published his
evidence in his book, On the Origin
of Species by Means of Natural
Selection.
• Observed that organisms constantly struggle
to survive.
• Individuals in a population with specific
advantageous traits are more likely to survive,
reproduce and have offspring with similar
survival skills.
• Be sure to see the power point on Darwin on
my website!
• Natural selection occurs when some
individuals of a population have genetically
based traits that enhance their ability to
survive and produce offspring with the same
traits.
• This change in genetic characteristics of a
population from generation to generation is
known as evolution.
Life has evolved into 6 major kingdoms.
The phylogeny of life
The Genetic Makeup of a Population
Can Change
• Populations (not individuals) evolve by
becoming genetically different
• Genetic variations
– First step in biological evolution
– Occurs through mutations in reproductive cells
which involve random changes in the structure or
number of DNA molecules in a cell
Individuals in Populations with Beneficial
Genetic Traits Can Leave More Offspring
• Natural selection: acts on individuals
– Second step in biological evolution
– When individuals of a population have genetically based traits
that enhance their ability to survive
– Adaptations may lead to differential reproduction (those with
the trait leave more offspring than the other members) Ex:
thick fur, chemical tolerance
• When environmental conditions change, populations
– Adapt
– Migrate
– Become extinct
• Natural selection can be attributed to changes
in the gene pool in a population.
• Traits in a species change in response to
selection pressures
– Physiological stress (temp, humidity)
– predation
– Competition
– Chance (mutations)
• The ultimate source of variation in genes is mutations!
Evolution by Natural Selection
Natural selection
Population Genetics
• A population consists of a gene pool – all the
various genes in a species.
• Alleles are different forms of one gene.
• Evolution – change in a gene pool over time,
essentially a change in types of alleles.
4 major evolutionary forces alter population gene pools:
1. Mutations – changes in DNA, slow rate, most
important
2. Emigration/immigration (gene flow) – movement of
genes into or out of the pop.
3. Random genetic drift – unpredictable variations
change the pool
4. Natural selection – one phenotype has more
reproductive success
Phenotype- physical representation of the genotype
(gene)
Adaptation Through Natural Selection
Has Limits
• A change in environmental conditions can lead
to an adaptation only for genetic traits already
in the gene pool.
• A population’s ability to adapt may be limited
by its reproductive capacity.
• Divergent evolution- organisms become less alike
but have a common ancestor (ex: human arm
and dog’s foreleg)
• Convergent evolution – lack a common ancestor,
but are similar (ex: shark and dolphin)
• Vestigial organs- organs that were once useful in
an animal’s evolutionary past, but now has no
apparent nor predictable function (ex: wings on
flightless birds, whales hind leg bones, wisdom
teeth) Observations of vestigial organs helped
Darwin with his theory of natural selection.
Adaptive radiation – development of many species from
a single one.. (ex: Darwin’s finches, Hawaiian silversword
plant- 28 species, came from sunflower)
Why are Humans a Successful Species?
• Strong, opposable thumbs
• An ability to walk upright
• A complex brain