Biology Chapter 4- Population Biology

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Biology Chapter 4- Population Biology

• Population
• Limiting factor
• Exponential growth
• Carrying capacity
• Life-history patterns
• Density
• R strategy
• K strategy
• Competition

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More Vocabulary

• Stress
• Crowding
• Demography
• Birthrate
• Deathrate
• Doubling time
• Age structure

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Population Growth

• J Curve
• http//cauchy.math.colostate.edu/Applets/Exponenti
  alGrowth/exponentialgrowth.htm
• Limits to growth (Limiting Factors yall)
• Biotic and abiotic
• Carrying Capacity
• Exponential growth
• Page 94 growth graph and explaination

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More graphing

• Add carrying capacity
• http//cauchy.math.colostate.edu/Applets/LogisticG
  rowth/logisticgrowth.htm

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Life History patterns

• Rapid Life history
• Slow life history
• K reproduction strategy (but intrinsic, not
  conscious)
• R reproduction strategy
• http//www.sumanasinc.com/webcontent/animations/co
  ntent/tradeoffs.html

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Population Density

• Patterns
• Random
• Clumped
• Uniform
• Limiting Factors
• Density-dependent
• Disease
• Competition
• Density-independent
• Usually abiotic

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Organism interactions

• Predation
• Graph p 98
• Interspecies competition
• Intraspecies competition
• Effects of crowding

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Addendum

• An S shaped curve is logistic growth
• This is the more common representation of
  population growth

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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.

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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.

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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
• Populations reproduce only at certain times.

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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.
• When there is a delay such that population growth
  depends on past population sizes, the population
  may cycle or have chaotic dynamics.

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Dynamics of Lagged Logistic Growth Models

• As growth rate increases, populations overshoot
  carrying capacity (K).
• Further increases cause the population to cycle.

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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 human
  population growth to slow, but global human
  carrying capacity is not known.

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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.
• Disease outbreaks and starvation are two factors
  that may increase with population density.

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r-selected Reproductive Strategy

• r-selected Species
• have high reproductive rates
• tend to occur in unpredictable environments
• typically have type III survivorship curves

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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 curves.

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Populations

• Groups of organisms of the same species that live
  within a given area
• Key characteristics
• Dispersion patterns
• Population density
• Growth rate

Ostriches are nomadic, wandering in small groups.
Aspen trees are quick to pioneer areas that have
been disturbed by fire.
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Dispersion Patterns Within Populations

• Three common patterns of population distribution
  are

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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.
• Population size can be measured by several
  sampling techniques.

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Population Growth

• Exponential vs. Logistical Growth
  

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Survivorship in Populations
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Reproductive Strategies

• r- Selected (maximum growth rate, below carrying
  capacity)
• Early reproduction
• Short life span
• High mortality rate
• Little or no parental care
• Large investment in producing large numbers of
  offspring
• Below carrying capacity
• Examples
• Bony fish
• Grasshoppers

• K-Selected (maximizes population size near
  carrying capacity)
• Late reproduction
• Long life span
• Low mortality rate
• Extensive parental care
• Greater investment in maintenance and survival of
  adults
• At or near carrying capacity
• Examples
• Sharks
• Elephants

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Limits on Population Growth

• Density Dependent Limits
• Food
• Water
• Shelter
• Disease
• Density Independent Limits
• Weather
• Climate

Water and shelter are critical limiting factors
in the desert.
Fire is an example of a Density independent
Limiting factor.