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Population: Is a group
of individuals of the
same species that can
mate and produce
offspring.
Gene Pool: Consists of
all the genes and
alleles that are present
in a population.
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Allele frequency: is the number of times an
allele occurs in a gene pool, compared to the
total number of alleles in a gene pool.
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Evolution, in genetic terms, involves a
change in the frequency of alleles in a
population over time.
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The 3 sources for genetic variation
1Mutations
2Genetic Recombination in Sexual Reproduction
3Lateral Gene Transfer
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Organisms provided with ideal conditions for
growth and reproduction will experience a
rapid increase in its population.
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The larger the population the faster it grows
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Populations will grow exponentially if not
threatened by death.
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Most populations go through a number of
growth phases, which can be represented on
a logistic growth curve.
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Limiting Factor: Is a factor that controls the
growth of a population and determine the
carrying capacity of a species.
Population
Size
Natural
Disaster
Competition
Unusual
Weather
Predation
Parasitism
and Disease
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In the distant past most people lived in small tribes that
hunted and gathered plants for food (little effect on the
environment)
Overtime the human population has increased (causing
major effects on the planet)
Many people unaware of their actions and the effect on the
planet
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Many environmental problems loom large and seem urgent
today because of the rapid increase in human population.
The huge number of humans on the Earth are making
enormous demands on the planet.
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Birthrate is greater than the deathrate.
 Birthrate and deathrate vary from one country to another
Life expectancy is longer (advances in medical, food, shelter,
etc)
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As human populations grow, their effects on the
environment grow.
More people = more food = more fields = destroying land
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The lifestyle of a population also contributes to the
extraordinary environmental demands made on the Earth.
 Example: U.S. Although our population growth has
stabilized at a low level, we use more energy and more
natural resources than any other country in the world.
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Density-Dependent Limiting Factors
 Competition
 Predation and Herbivory
 Parasitism and Disease
 Stress From Overcrowding
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Competition: When populations become
crowded, individuals compete for food,
water, space, and other essentials.
Predation and Herbivory: The effects of
predators on prey and herbivores on plants.
 Example: Wolves vs moose or moose on plants
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Parasitism and Disease: Parasites and
disease causing disease and death in a
population.
Stress from Overcrowding: Some species
fight amongst themselves if overcrowded.
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Density-Independent Limiting Factors:
Affect all populations in similar ways,
regardless of population size and density
 Examples: Unusual weather