IB Biology Review Chapter 52: Population Ecology In

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IB Biology Review

• Chapter 52 Population Ecology

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Population Ecology

• Population
• A group of individuals of the same species
  living in a particular geographic area
• Population Ecology
• Concentrates mainly on the factors that affect
  how many individuals of a particular species live
  in an area

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Exponential Growth Species
Immigration Density Sigmoid/Logistic
Growth Mortality K-Strategy Growth
r-Strategy Growth Demographic
Emigration Carrying Capacity Natality
Life History
Species

• 1. ____________ A group of organisms that can
  interbreed and produce fertile offspring.
• 2. ____________ Number of individuals per unit
  area or volume. Ex. White Oak trees per square
  kilometer in Potter County Pennsylvania
• 3. ____________ The study of the rise and fall of
  population sizes over time
• 4. ____________ Rate of Birth ( of individuals
  in a given period of time)
• 5. ____________ Rate of Death ( of individuals
  in a given period of time)
• 6. ____________ The movement of individuals into
  a population
• 7. ____________ The movement of individuals out
  of a population
• 8. ____________ The maximum population size that
  can be supported by the available resources,
  symbolized by K.
• 9. ___________ The geometric (larger the quantity
  gets, the faster it grows) increase of a
  population as it grows in an ideal, unlimited
  environment
• 10. __________ A model describing population
  growth that levels off as population size
  approaches carrying capacity
• 11. __________ The series of events from birth
  through reproduction and death
• 12. __________ The concept that in certain
  populations, a high reproductive rate is the
  chief determinant of life history and survival
• 13. __________The concept that in certain
  populations, life history is centered around
  producing relatively few offspring that have a
  good chance of survival

Density
Demography
Natality
Mortality
Immigration
Emigration
Carrying Cap.
Exponential.
Sigmoid
Life History
r-Strategy
K-Strategy
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Think back to the Wissahickon Trip. How did we
measure avian biodiversity?

• Simpsons Biodiversity Index

D S(n(n -1) / N(N-1)) 1-D Where D n
N 1-D
Bias corrected form for Simpson Index Number of
individuals of one species Total number of
individuals in community Relative biodiversity
(the closer to 1, the more diverse the
community)
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Simpsons Index Sample ProblemWhich community
is more diverse?

• Community 1
• 3 Chickadees
• 6 Robins
• 9 Carolina Wrens
• 2 Blue Jays
• Total 20

• Community 2
• 3 Downy Woodpeckers
• 2 Robins
• 6 Crows
• 2 Carolina Wrens
• Total 13

(3 (3-1) 6 (6-1) 9 (9-1) 2(2-1))
(20 (20-1)) D 110 / 380
.29 1-D .71
(3 (3-1) 2 (2-1) 6 (6-1) 2(2-1))
(13 (13-1)) D 40 / 156
.26 1-D .74
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Define the term random sample.

• A sample where every member of a population has
  an equal chance of being selected
• Sample selected without bias
• Why is it important to take random samples?
• To ensure the data taken for the biodiversity or
  population size/distribution indices represents
  the whole population

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What is one method for estimating animal
population sizes?

• Lincoln Index/Mark-Recapture Method (hunting
  forks activity)
• Population size n1 x n2
• n3
• Where
• n1 number of individuals initially caught,
  marked, and released
• n2 total number of individuals caught in the
  second sample
• n3 number of marked individuals in the second
  sample

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What is one method for estimating plant
distribution?

• Quadrat Transect Method
• Transects are distributed evenly across the
  entire site so all plants may be sampled
• Each quadrat is spaced evenly along the
  transects, again so all plants have the chance of
  being sampled
• The percent of area covered by each plant species
  is estimated within each quadrat which 1 meter
  squared in size
• Each of these total species percentages is
  divided by the total quadrat percentages (100
  for one quadrat, 200 for two quadrats etc.) to
  get the relative percentage of each plant species

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Calculating the yearly change in population

• Change in population size per year
• births deaths immigration - emigration
• Often, immigration and emigration are said to
  cancel out, so unless otherwise stated, assume
  immigration emigration 0

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MC- 1. A population of ground squirrels has an
annual per capita birth rate of 0.06 and an
annual per capita death rate of 0.02. Estimate
the number of individuals add to or lost from a
population of 1,000 individuals after one year.

• A. 120 individuals added
• B. 40 individuals added
• C. 20 individuals added
• D. 400 individuals added
• E. 20 individuals lost
• Correct answer E (1000 x 1.06) (1000 x 1.02)
  40 individuals

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Population Growth Curves
K

• Exponential Growth
• Unrestricted growth
• Sigmoid/Logistic Growth
• Exponential phasenatality much higher than
  mortality
• Transitional phasenatality higher than
  mortality
• Plateau phasenatality mortality

Plateau
Transitional
Exponential
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MC-2. in a mature forest of oak, maple, and
hickory trees, a disease causes a reduction in
the number of acorns produced by oak trees. Which
of the following would least likely be a direct
result of theis?

• A. There might be fewer squirrels because they
  feed on acorns
• B. There might be fewer mice and seed-eating
  birds because the squirrels would eat more seeds
  and compete with the mice and birds
• C. There might be an increase in the number of
  hickory trees because the competition between
  hickory nuts and acorns or germination sites
  would be reduced or eliminated
• D. There might be fewer owls because they feed
  on baby squirrels, mice, and young seed-eating
  birds, whose population would be reduced
• E. There might be a decrease in the number of
  maple seeds as the disease spreads to other trees
  in the forest.
• Correct answer D

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What is the general ecological feature that
limits population growth?

• Carrying Capacity The maximum number of
  individuals of one species the environment can
  support based on available resources
• These resources are known as density-dependent
  factors
• Means the size of the population is dependent on
  
• these factors.

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MC-3. Which of the following statements correctly
describes the carrying capacity of an environment?

• A. The maximum rate of population growth
  for a species.
• B. The area of land that can support a
  denned population of species.
• C. The minimum population of a species
  that can be sustainably supported by
• a given environment.
• D. The maximum population of a species
  that can be sustainably supported by a
  given environment.
• Correct answer D

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MC-4. As N approaches K for a certain population,
which of the following is predicted by the
logistic equation?

• A. The growth rate will not change.
• B. The growth rate will approach zero.
• C. The population will show an Allee effect.
• D. The population will increase
  exponentially.
• E. The carrying capacity of the
  environment will increase.
• Correct answer B

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Name some density-dependent factors.

• Food supply
• Water supply
• Breeding/nesting sites
• Habitat/shelter
• Predator-prey relationship
• Disease
• Territory

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MC-5. Which of the following can contribute to
density-dependent regulation of populations?

• A. the accumulation of toxic waste
• B. intraspecific competition for nutrients
• C. predation
• D. all of the above
• E. none of the above
• Correct answer D

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r- and K-Strategy Growth

• Only HL kids need to know this in depth
• r-Strategy Growth
• high reproductive rate
• little or no investment in offspring
• short lives
• small size
• can adapt to variable environments
• K-Strategy Growth
• low reproductive rate
• large investment in offspring
• long lives
• large size
• prefer stable environments

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Intrinsic rate of increase and Exponential growth

• The intrinsic rate of increase is the biological
  maximum rate at which a population can grow. In
  other words, many insect species have a higher
  intrinsic rate of increase than humans simply
  because they are biologically able to produce
  more offspring in a shorter period of time.
• However, the same populations may increase at
  different rates through time. In exponential
  growth for example, more individuals are added
  per unit time as population size increases. In
  this case, the intrinsic rate of growth did not
  change, but the size of the population did.

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MC-6. All the following characteristics are
typical of an r-selected population except

• A. occurrence in variable environments
• B. high intrinsic rate of growth
• C. onset of reproduction at an early age
• D. extensive parental care of offspring
• E. occurrence in open habitats
• Correct answer D

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MC-7. A small population of white footed mice has
the same intrinsic rate of increase (r) as a
large population. If everything else is equal,

• A. The large population will add more
  individuals per unit time
• B. The small population will add more
  individuals per unit time
• C. The two populations will add equal numbers
  of individuals per unit time
• D. The J shaped growth curves will look
  identical
• E. The growth trajectories of the two
  populations will proceed in opposite directions

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1. Describe a method, used by ecologists, for
estimating accurately the size of a plant
population.
( 4 marks)
IB Exam Question

• The Quadratic Method
• divide sample area using transects
• use quadrats
• position them randomly
• count the percentage of coverage of the plant
  species in each quadrat
• count as many quadrats as possible
• total (density) total percentage of one species
  / total percentage (per meter squared)

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2. The data shows the number of flowers per
flower head of a random sample from a white
clover (Trifolium repens) population.
Mean 62
Standard deviation 12.5 What statistical
percentage of the population has between 49 and
75 flowers per flower head?
IB Exam Question
36 51 56 62 62 63 65 69 73 83

• A. 5
• B. 32
• C. 68
• D. 95

Correct answer is D. See next slide for
explanation.
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Normal Curves

• When data is distributed in a normal curve (a
  bell shaped curve)
• 68 of the data is within one standard deviation
  of the mean
• 95 of the data is within two standard deviations
  of the mean
• Biological data is usually in a normal curve
  because most organisms have the normal trait
• Mutations are the deviations of the mean

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Normal Curves

• On question 2, they are asking for the
  percentage of the flowers that fall within one
  standard deviation of the mean
• One standard deviation (12.5) of the mean (62)
  is
• the range 49 to 75 (62 12.5 49 , 62
  12.5 75)
• In a normal curve, the percentage of the
  population within one standard deviation of the
  mean is . . .
• 68! So the answer is D.

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3. Describe the use of one technique that
ecologists use to estimate accurately the size of
a population of animals, including details of any
calculations that need to be done.

(6 marks)
IB Exam Question

• One technique is the capture-mark-release method
  (Lincoln Index)
• First, capture a sample of population
• For ex. Bog turtles are captured by probing the
  mud with blunt wooden sticks
• When an animal is captured, it is marked and
  released
• The animals are allowed to settle back into the
  environment until they are randomly dispersed
• Then a second sampling occurs like the first
• In this sample, marked (previously captured) and
  unmarked individuals are counted
• The population size is then estimated by the
  Lincoln Index
• Lincoln Index calculationnumber marked
  originally x recaptured number marked and
  recaptured

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4. Outline the quadratic method of random
sampling and how it could be used to determine
and compare the population size of two plant
species.
IB Exam Question

• A shape (rectangular or circular frame) of known
  area, often one square meter but sometimes larger
• Several transects and distributed evenly through
  each area and quadrats are placed evenly along
  the transects to avoid bias.
• Transecets are placed on mapping prior to site
  visit to avoid human bias
• The number of individual plants or percent aerial
  coverage of the species is estimated in each
  quadrat
• Enough quadrats must be taken to make the sample
  representative of the area
• The size of quadrats is determined by the size of
  distribution of species (trees require larger
  quadrats then herbaceous species)
• Population density is the calculated which is the
  number of plants or relative percent divided by
  total area
• Population density of different species can then
  be compared

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5. Outline the use of a transect to correlate the
distribution of plant or animal species with an
abiotic variable
IB Exam Question

• To correlate plant species with soil moisture
• Several transects are evenly placed through the
  study area from the moist floodplane soil to the
  driest soil on the surrounding hilltops
• Approximately the same number of quadrats are
  placed in each soil moisture type
• The number of individual plants or percent aerial
  coverage of the species is estimated in each
  quadrat
• Enough quadrats must be taken to make the sample
  representative to the area
• The population density of each species is
  determined
• The population densities for each species are
  added up according to soil moisture
• Species which have a higher density in the
  moisture soil types are correlated with moist
  soil and species which have a higher density in
  dryer soil types are correlated with dry soil

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6. Discuss why an index of diversity could be
useful in monitoring environmental change.
(3 marks)
IB Exam Question

• an index of diversity is a measure of species
  diversity
• can be used with plant or animal species
• index diversity of species is a measure of health
  /
• stability / degree of stress of an
  environment
• comparison of two values is a measure of change
  for better or worse
• data can be used for policy decisions regarding
  the environment
• measure of species richness / diversity
• low diversity indicates environmental stress

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7. State three factors that can affect the
distribution of animal species. (1 mark)
IB Exam Question

• temperature
• water
• breeding sites
• food supply
• territory
• predation
• competition

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8. Explain the reasons for the sizes of animal
populations within communities changing and the
reasons for them staying the same. (8 marks)
IB Exam Question

• Increased natality (births) increases population
• But only as long a natality is higher than
  morality
• Abundant food allows increases in population and
  food shortage causes decreases
• Low levels of predation allows increase/ high
  levels causes decrease
• Low level of disease allows increase/ high levels
  causes decrease
• Immigration increases populations
• As long as immigration is higher that emigration
• Populations rise until a plateau is reached
• This is the carrying capacity of the environment
  when the resources of the environment cannot
  support anymore individuals

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9. Describe with the aid of a diagram the phases
of a sigmoid population growth curve. (4
marks)
IB Exam Question
K
2

• Must have a correct S shaped curve
• Must have three phases correctly labeled on
  diagram
• 1(exponential) rapid increase in population
  due to unlimited resources and larger population
  sizes natality much higher then morality
• 2(transitional) slowing of growth resources
  beginning to become limited Natality still
  higher than morality but not as big of a
  difference as an exponential phase
• 3(plateau) leveling off, birth rate death
  rate Population has reached its carrying
  capacity which is the maximum sustainable
  population for that species in that particular
  environment
• Carrying capacity K must be labeled

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10. Distinguish between r strategies and K
strategies (6 marks)
IB Exam Question

• r strategies produce as many offspring as
  possible and often reproduce only one time
• There is little parental care of the offspring of
  r strategies
• This strategy is sometimes called the big bang
  reproduction
• K strategies produce many fewer offspring and
  invest a lot of energy into raising them
• These species live much longer then r strategist
  and there fore reproduce many times.
• Most species have reproductive strategies that
  are intermediate on the continuum between these
  two. Some organisms like Drosophila switch
  strategies depending on the environmental
  conditions

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11. Discuss the environmental conditions that
favor either r strategies or K strategies.
(3 marks)
IB Exam Question

• In predictable environments, it pays to invest
  resources in long term development and long life
  (K strategy).
• In an unsteady environment, it is better to
  produce as many offspring as possible and
  reproduce only one time (r strategy).
• This r strategy is timed to coincide with
  favorable environmental conditions