Transcript Biology Chapter 4- Population Biology

Biology Chapter 4- Population
Biology
Population
Limiting factor
Exponential growth
Carrying capacity
Life-history patterns
Density
R strategy
K strategy
Competition
More Vocabulary
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Stress
Crowding
Demography
Birthrate
Deathrate
Doubling time
Age structure
Population Growth
• J Curve
• http://cauchy.math.colostate.edu/Applets/E
xponentialGrowth/exponentialgrowth.htm
• Limits to growth (Limiting Factors y’all)
– Biotic and abiotic
• Carrying Capacity
• Exponential growth
• Page 94 growth graph and explaination
More graphing
• Add carrying capacity
• http://cauchy.math.colostate.edu/Applets/L
ogisticGrowth/logisticgrowth.htm
Life History patterns
• Rapid Life history
• Slow life history
• K reproduction strategy (but intrinsic, not
conscious)
• R reproduction strategy
• http://www.sumanasinc.com/webcontent/a
nimations/content/tradeoffs.html
Population Density
Patterns
– Random
– Clumped
– Uniform
Limiting Factors
• Density-dependent
– Disease
– Competition
• Density-independent
– Usually abiotic
Organism interactions
• Predation
– Graph p 98
• Interspecies competition
• Intraspecies competition
• Effects of crowding
Addendum
• An S shaped curve is logistic growth
• This is the more common representation
of population growth
Basic Characteristics of
Populations
• The suitability of habitats influences the
geographic distribution of a species.
• Insights can be gained by studying the spatial
distributions of populations within habitats.
Population Age Structure
• Differences in environmental conditions and past
history may cause populations to differ in their
age distributions.
• The future growth of a population depends on its
current age distribution.
Density-Independent Population
Growth
• Simple models describe how
idealized populations would
grow in an infinite
environment.
• In these models, populations
increase to infinity or
decrease to zero.
• Continuous Model
– Reproduction occurs in the
population at all times.
• Discrete Model
Density-Dependent Population
Growth
• In density dependent
population growth, the per
capita growth rate
decreases as the
population approaches a
carrying capacity.
• When population growth
rate depends on current
population size, the
population smoothly
approaches carrying
capacity.
Dynamics of Lagged Logistic
Growth Models
• As growth rate increases, populations
overshoot carrying capacity (K).
• Further increases cause the population to cycle.
Human Population Growth
• Human population growth does not
currently show density effects that typically
characterize natural populations.
• In natural populations, per capita
population growth rate decreases with
population size, whereas global human
population growth rate has a positive
relationship.
• Human population growth rate has been
growing more than exponentially.
• Limited resources eventually will cause
Density-Dependent and
Density-Independent Effects on
Populations
• In many habitats, the forces that limit
population sizes are independent of
population density. For example, extreme
weather events may decrease
populations.
• For most species, density-dependent
factors limit birth rates or increase death
rates at least some of the time. This type
of population determination often is
referred to as “regulation.”
r-selected Reproductive
Strategy
• r-selected
Species:
– have high
reproductive
rates
– tend to occur in
unpredictable
environments
– typically have
type III
survivorship
curves
K-selected Reproductive
Strategy
• K-selected
Species:
– occur near
carrying capacity
– experience
effects of
population density
– have low
reproductive
rates, high
parental care
– have type I
survivorship
Populations
• Groups of organisms of the
same species that live within a
given area
• Key characteristics:
Ostriches are nomadic,
wandering in small
groups.
– Dispersion patterns
– Population density
– Growth rate
Aspen trees are quick to
pioneer areas that have
been disturbed by fire.
BioEd Online
Dispersion Patterns Within
Populations
Three common patterns of population
distribution are:
BioEd Online
Population Density
• Population density is total population size
per unit of area.
• Population densities depend on:
– Interactions within the environment
– Quality of habitat
– Density dependent factors
– Density independent factors
• Carrying capacity is the maximum number
of organisms that can be supported in a
given habitat.
BioEd Online
Population Growth
Exponential vs. Logistical Growth
BioEd Online
Survivorship in Populations
BioEd Online
Reproductive Strategies
• r- Selected (maximum
growth rate, below
carrying capacity)
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–
–
–
Early reproduction
Short life span
High mortality rate
Little or no parental
care
– Large investment in
producing large
numbers of offspring
– Below carrying
capacity
BioEd Online
• K-Selected
(maximizes
population size near
carrying capacity)
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–
–
–
Late reproduction
Long life span
Low mortality rate
Extensive parental
care
– Greater investment in
maintenance and
survival of adults
– At or near carrying
capacity
Limits on Population Growth
• Density Dependent Limits
– Food
– Water
– Shelter
– Disease
Water and shelter are
critical limiting factors in
the desert.
• Density Independent Limits
– Weather
– Climate
BioEd Online
Fire is an example of a
Density independent
Limiting factor.