Chapter 4: Population Biology

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Chapter 4 Population Biology
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Population

• group of organisms, all of the same species, that
  live in a specific area

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How fast do populations grow?

• Not linear growth so it is not a straight line
• Graph- starts to increase slowly, then resembles
  a J-shaped curve
• Initial increase slow, b/c of organisms that
  reproduce is small
• Increases b/c the total of individuals that can
  reproduce has increased

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Is Growth Limited?

• J-shaped growth curve illustrates exponential
  population growth
• Exponential Growth means that as a population
  get larger, it also grows at a faster rate

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What Can Limit Growth?

• Population growth does have limits
• Limiting Factors food, disease,
• predators, or lack of space will
• Cause population growth to SLOW
• Under these conditions the population may
  stabilize in a S-shape growth curve

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Carrying Capacity

• the number of organisms of one species that an
  environment can support indefinitely
•  Developing population more births than deaths
  and the population increases until the carrying
  capacity is reached or passed
• When a population overshoots the carrying
  capacity, limiting factors come into affect
• Deaths begin to exceed births and the population
  falls below the carrying capacity

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Reproduction Patterns

• Life-History Pattern- organisms reproduction
  pattern
• Slow life-history pattern slow rate of
  reproduction and produce relatively few offspring
•   Ex. Elephant
• Fast life-history pattern reproduce rapidly and
  produce many offspring in a short period of time
• Ex. Mosquito

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Rapid Life- History Patterns

• Common among organisms in changeable or
  unpredictable environments
• Organisms have
• Small body size
• Mature rapidly
• Reproduce early
• Short life span
• reproduction rises rapidly then decline when
  environment becomes unsuitable
• population survives and will reproduce again when
  the environment is favorable

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Slow Life- History Patterns

• large species that live in more stable
  environments
• Elephants, Bears, Whales, Humans, and plants
  (trees)
• reproduce and mature slowly
• long-lived
• maintain population sizes at or near carrying
  capacity

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Density Factors and Population Growth

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• 3 Patterns of Dispersal
• 1. Random
• 2. Clumped
• 3. Uniform

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Density-Dependent Factors

• disease
• competition
• predators
• parasites
• food

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• increasing affect as the population increases
• Example- corn fields
• Crops grow close together
• Disease can spread rapidly and kill off the whole
  crop

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Density-Independent Factors

• can effect most populations regardless of their
  density
• Most are abiotic factors
•   Volcanic eruptions
• Temperature
• Storms
• Floods
• Drought
• Chemical Pesticides
• Major habitat destruction
• Usually affect smaller organisms more
• Example Mosquitoes severe winters kill the
  adults of most species

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Population Size

• limited by abiotic and biotic factors
• controlled by various interactions among
  organisms that share a community
• Predation can effect population size in minor
  and major ways

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• Locusts eat acres of lettuce on a farm
• Brown snake introduced into Guam, there were no
  native predators, and it preyed freely on native
  birds drastic effect on the population size

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• predator- prey relationships are known to
  experience cycles or changes in their numbers
  over periods of time
• prey population increases and there is more food
  for the predator, so the predator population
  increases
• predator population increase and predation
  increase, therefore the prey population
  declines.
• With less food, the predator population decrease.
  
• Cycle starts again

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Competition within a Population

• density dependent factor
• few individuals compete for resources, usually no
  problems
• When population increase and the demand exceeds
  the supply, the population size decreases

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Crowding and Stress

• populations become crowded, individuals exhibit
  stress
• stress symptoms
• Aggression
• decrease in parental care
• decreased fertility
• decreased resistance to disease
• all have negative effects on a population

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Human Population

•  Demography study of human population size
• density and distribution
• movement
• Birth and death rates

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Human Population Growth

• Humans change their environment
• Developed methods for producing
• more food
• infant mortality rate decreased
• clean water
• All enable people to live longer and produce more
  offspring
• Population Grows

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Calculating Growth Rate

• Birthrate number of live births per 1000
  population in a given year
• Death rate number of deaths per 1000 population
  in a given year
• Immigration movement of individuals into a
  population
• Emigration movement of individuals out of a
  population

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Calculate a populations growth rate by

• (Birthrate Immigration Rate) (Death rate
  Emigration Rate) Population Growth Rate
• PGR (B I) (D E)
• Immigration and emigration are not always
  accurate use
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• PGR Birthrate Death rate

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• Positive Growth Rate
• unless the growth rate becomes negative the
  population continues to grow, just slower
• Doubling Time
• time needed for a population to double in size
• Age Structure
• refers to the portions of the population that are
  in the different age levels

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