Download Populations

Populations
Population Genetics
Population Growth
Interactions Among Populations
Ecological Succession
Population Genetics
• A population is a group of individuals of the
same species occupying the same habitat at
the same time
• The gene pool of a population is all of the
different genes that occur within the population
• A deep gene pool results when there is great
variation within a population
• A shallow gene pool results when there is little
diversity in a population
Population Genetics
• For a given trait the frequency of each
phenotype can be calculated
• The frequency of each genotype can
be estimated
• The frequency of each allele can be
estimated
Population Genetics
• The Hardy-Weinberg equilibrium predicts
that allelic frequencies remain constant
over time provided five conditions are met
• A population at equilibrium is not evolving
with respect to the trait
• A population that has its equilibrium
disturbed is evolving with respect to the
trait
Population Genetics
•
Microevolution is the directional change
in frequency of alleles over time
• Change in allele frequencies can occur
due to:
1. Genetic Drift: the reproductive success
or failure of an individual in a small
population
Population Genetics
2. Mutation: new mutations can add new
alleles or change existing alleles that
could be advantageous or
disadvantageous
3. Gene Flow (Migration): Disproportionate
movement of individuals into or out of a
population
Population Genetics
4. Non random mating due to preferences
based on inheritable characteristics
5. The founder effect decreases diversity in the
population of descendents of a small
founding population
6. The bottleneck effect decreases genetic
diversity when a large population is reduced
to a small population by selective pressure
7. Natural Selection is the result of any of the
above factors
Population Genetics
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Change in allelic frequencies can result
in speciation
Speciation can occur if populations of
the same species become
reproductively isolated
Population Growth
• Measures of population growth include
1. Size: determined by census or sampling
2. Density: population size per unit area or
volume
3. Per Capita Growth Rate: the growth of a
population per individual (due to immigration,
emigration, natality and mortality)
4. Growth Rate: the growth of a population over
time
Population Growth
• Characteristics of populations include
1. Distribution (random, uniform or
clumped)
2. Growth Curve : J-shaped (exponential)
or S-shaped (sigmoidal)
3. Ecological Niche: the role played by a
population in an ecosystem
Population Growth
4. Geographic Range: a region where a
population can be found
5. Habitat: the physical conditions that
support a population
6. Population Pyramid (Histogram): a
graph representing the age and gender
distribution of a population
Population Growth
7. Reproductive Strategy: k or r selected
strategies
8. Environmental Resistance: factors that
limit population growth (density
dependent or density independent)
9. Biotic Potential (Fecundity): maximum
reproductive rate under ideal conditions
Population Growth
10. Tolerance Range: the minimum and
maximum levels of an environmental factor
that can support population growth
11. Law of the Minimum: of the number of
essential substances required for growth, the
one with the least concentration is the
controlling factor
12. Open or Closed: an open population is
influenced by immigration, emigration, natality
and mortality (closed has no immigration or
emigration)
Interactions Among Populations
•
All populations exist within a biological community
such that populations must interact
•
Population interactions include:
1. Interspecific Competition: competition between two
different species (-/-)
•
Gause’s Principle: no two species can occupy
the same niche without one being reduced in
numbers or being eliminated
2. Intraspecific Competition: competition among
individuals of the same species(-/-)
Interactions Among Populations
3. Predation: A predator population feeds on a
prey population (+/-)
4. Mimicry
5. Symbiosis: Two different organisms live in
close association with each other
i. Parasitism (+/-)
ii. Commensalism (+/0)
iii. Mutualism (+/+)
Ecological Succession
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Ecological succession is the progessive
replacement of one community by another
during the development of vegetation in an
area
Primary succession refers to the occupation,
by plant life, of an area not previously
covered by vegetation
Secondary Succession refers to an area that
was previously covered
Ecological Succession
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Succession progresses from a pioneer
community, through several seral stages
to a climax community
As succession progresses biomass of
the ecosystem increases
As succession progresses biodiversity
increases and then declines when a
climax community is reached