Transcript Reproductive Patterns and Population Density

Reproductive Patterns
and Population Density
Questions for Today:
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What are the different Reproductive Patterns
found in Nature?
How can Genetic Diversity affect the size of
small Populations?
Compare and Contrast Density-dependent and
Density-independent Population Controls.
What are the different Types of Population
Changes that can occur in Nature?
Review Terms:
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Immigration
Emigration
Biotic Potential
Intrinsic Rate of Increase
Environmental Resistance
Carrying Capacity
Reproductive Patterns
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Species have different Reproductive Patterns
that can help enhance their chance for survival:
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r-selected species *note that the r is not capitalized
K-selected species
r-selected species
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These species are those that have a high
intrinsic rate of increase.
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What are the common traits had by those that have
a high intrinsic rate of increase?
Examples of r-selected species:
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Algae, bacteria, rodents, frogs, turtles, annual plants,
and most insects
r-selected species are opportunists
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When conditions are right they have a boom in
reproduction.
K-selected species
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K-selected species are also called competitor species.
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Reproduce later in life with small number of offspring
Develop inside their mother and are rather large at birth and
mature slowly.
They are cared for by the parent species.
Called K-selected because they live will when the
population is near the Carrying Capacity.
Examples of K-selected species:
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Large Mammals, birds of prey, large-long lived plants.
Genetic Diversity and Population
Size
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The Size of a Population can affect the genetic
diversity in the area.
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Usually in Large population, Genetic diversity is
fairly constant or there is very little change.
There are several factors that can play a role in the
loss of genetic diversity:
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Founder Effect
Demographic Bottleneck
Genetic Drift
Inbreeding
Genetic Diversity and Population
Size
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Founder effect
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Demographic Bottleneck
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When a few individuals survive after a catastrophic event.
Genetic Drift
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Occurs when a few individuals leave the population and
colonize a new area that is geographically isolated from the
main population
Random changes in the gene frequencies in a popuationthat
can lead to unequal reproductive success.
Inbreeding
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Can increase the frequency of defective genes.
Population Density Controls
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Population density is the number of individuals
in a population found in a particular area or
volume.
Two types of controls:
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Density-dependent
Density-independent
Population Controls
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Density-dependent controls limit population
growth as density increases.
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Predation, parasitism, infectious disease, and
competition for resources
Density-independent controls limit population
growth regardless of density.
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Mostly abiotic
Weather phenomenon, geologic processes,
catastrophes
Population Changes
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The are four general patterns of variation in
population size:
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Stable
Irruptive
Cyclic
Irregular
Population Changes
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Stable
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Very little fluctuation around the carrying capacity
of the area
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Species found in the tropical rainforest exhibit stable
population changes because the weather and climate
changes very little from year to year
Irrupt
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When population growth occasionally explode to a
high peak then crash to a more stable lower level.
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Algae and insects
Population Changes
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Cyclic Fluctuations
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Similar to irruptive but the cycle is drawn out
much longer.
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Lemmings populations rise and fall every 3-4 years
Lynx and hare populations rise and fall on a ten year
cycle.
Predator-prey relationships have cyclic fluctuations
Irregular Patterns
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No discernable pattern in population change