Populations

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Populations

• Developed by Adam F Sprague

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We are the most important species, and we are in
charge of the rest of nature.
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Population

• A population is an interbreeding group of
  individuals.
• Defining characteristics
• Populations have various defining characteristics
  including
• species of organism
• time (historical)
• place where they live
• their number (size)
• their density
• their distribution in space (dispersion)
• age structure/demographics
• niche

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Living sustainably

• Sustainable system survives and functions over a
  specified time.
• Sustainable society manages its economy and
  population size without exceeding all or part of
  the planets ability to absorb environmental
  problems, replenish resources, and sustain life.

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Exponential Growth and Resource Usage

• Exponential growth, in general, is not understood
  by the lay public. If exponential use of a
  resource is not accounted for in planning -
  disaster can happen.
• Its not too great of simplification to state that
  the failure to understand the concept of
  exponential growth by planners and/or
  legislators, is the single biggest problem in all
  of Resource Management.

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Introduction

• Exponential growth is a process that occurs all
  around us in real life. If you put money in a
  bank account, it grows exponentially. Cancer
  cells grow exponentially. The population of the
  world grows exponentially. Anything that grows at
  a fixed percent is growing exponentially

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Biotic potential

• Each population has a has a characteristic
  reproductive potential. This is the rate at which
  a population could grow if it had an unlimited
  amount of resource. Result would be growth
  exponentially.

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An example

• A survey of Boulder Colorado residents about the
  optimal size for growth returned a result that
  most residents thought that a growth in
  population at the rate of 10 per year was
  desireable.

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Example Cont.

• Well 10 a year may not seem innocuous but let's
  see how these numbers would add up?
• Year 1 60,000
• Year 2 66,000
• year 3 72,600
• Year 4 79860
• Year 5 87846
• Year 6 96630
• year 7 106294
• Year 8 116923
• So in 7 years (year 2--7) the population has
  doubled and by then 10,000 new residents per year
  are moving to boulder!

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The difference between linear growth and
exponential growth is astonishing.
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What kinds of things grow exponentially?

• Population Energy resource use Number of shopping
  malls Number of automobiles on the freeway Your
  tuition (up to a limit) Number of Xerox Machines
  Number of cows McDonalds uses each year Number of
  hospital patients Number of prisoners Number of
  Web Pages
• any resource that people use will grow
  exponentially

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Rule of 72

• How long will it take for a population to double?

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Assignment1

• 1. Read Chapter 1, Answer Critical thinking
  question 5
• 2. Determine doubling time for country of your
  choice. Present in class. Everyone will have a
  different country.

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Factors determining Pop. Growth

• It produces many offspring each time it
  reproduces
• It has a long reproductive life
• It starts reproducing early in life.
• Bacteriainsects(reproduce only once but start
  early in life) vs Oaks(reproduce several times
  but late in life)

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Population forecasts

• What factors determine how fast a population
  grows?

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Birth Rate Death Rate are not the only factors

• Migration movement from one place to another
• Emigration movement of people out of a country
  or particular population.
• (US vs. Australia)
• Immigration movement of people into a country or
  population (US vs. Mexico)

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Important

• Change in population size(birthsimmigration)-(de
  athsemigration)
• can also determine if population is growing or
  shrinking

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Dependency Ratio

• The ratio of people over 65 and under 15 years
  old.
• People in these ranges contribute very little to
  the economy they must be supported by the people
  within the age group.

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Life expectancy

• The average number of years that a newborn baby
  can be expected to survive.

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Zero pop. growth

• ZPG population size remains stable

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Infant mortality rate

• the number of babies out of 1000 born each year
  that die before their first birthday

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Factors affecting birth and fertility rate

• Average level of education
• Importance of children in labor force
• Urbanization
• Cost of raising a child
• Educational and employment opportunities for
  women
• Infant mortality rate
• Average age at marriage
• Pension programs
• Abortion
• Birth control
• Religious beliefs

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Fertility Rates

• General Fertility Rate number of babies born
  each year to 1000 women of reproductive age.
• Age specific fertility rate the number of births
  per year per 1000 women of each age group.
• Total fertility rate the number of children that
  an average women bears during her lifetime.
• Replacement level fertility the number of
  children each couple must have to replace
  themselves

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Reduce Births

• Family planning
• Using economic rewards or penalties
• Empowering women

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Population-Age Pyramids

• While fertility rates are obviously useful, the
  demographics of the existing population are also
  important and can provide key information to
  predict future growth rates

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Demographic Transition

• The demographic transition model seeks to explain
  the transformation of countries from having high
  birth and death rates to low birth and death
  rates. In developed countries this transition
  began in the eighteenth century and continues
  today. Less developed countries began the
  transition later and are still in the midst of
  earlier stages of the model.

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CBR CDR

• The model is based on the change in crude birth
  rate (CBR) and crude death rate (CDR) over time.
  Each is expressed per thousand population.

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Stage I

• Prior to the Industrial Revolution, countries in
  Western Europe had a high CBR and CDR. Births
  were high because more children meant more
  workers on the farm and with the high death rate,
  families needed more children to ensure survival
  of the family. Death rates were high due to
  disease and a lack of hygiene. The high CBR and
  CDR were somewhat stable and meant slow growth of
  a population. Occasional epidemics would
  dramatically increase the CDR for a few years
  (represented by the "waves" in Stage I of the
  model.

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Stage II

• In the mid-18th century, the death rate in
  Western European countries dropped due to
  improvement in sanitation and medicine. Out of
  tradition and practice, the birth rate remained
  high. This dropping death rate but stable birth
  rate in the beginning of Stage II contributed to
  skyrocketing population growth rates. Over time,
  children became an added expense and were less
  able to contribute to the wealth of a family. For
  this reason, along with advances in birth
  control, the CBR was reduced through the 20th
  century in developed countries. Populations still
  grew rapidly but this growth began to slow down.

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Stage III

• In the late 20th century, the CBR and CDR in
  developed countries both leveled off at a low
  rate. In some cases the CBR is slightly higher
  than the CDR (as in the U.S. 14 versus 9) while
  in other countries the CBR is less than the CDR
  (as in Germany, 9 versus 11). (You can obtain
  current CBR and CDR data for all countries
  through the Census Bureau's). Immigration from
  less developed countries now accounts for much of
  the population growth in developed countries that
  are in Stage III of the transition. Countries
  like China, South Korea, Singapore, and Cuba are
  rapidly approaching Stage III.

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Assignment 2

• Read Chapter 9 Critical Thinking Questions 1,3,5
• Determine Population Age Structure, and of your
  country CBR and CDR http//www.census.gov/ipc/www/
  idbpyr.html will help

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Some more ecology

• Community groups of populations that interact
  with each other in a specific area
• Habitat where an organism lives (its address)
• Niche an organisms relationship to food and
  enemies (its job)

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Carrying capacity

• The number of individuals in a certain species
  that the environment can support.
• Show Growth chart Ex rabbits in Australia
• Species reaches its carrying capacity ina
  particular ecosystem when it starts using the
  natural resources as fast as the ecosystem can
  produce them.
• Populations that exceed the carrying capacity
  degrade the environment. (Humans have probably
  exceeded their carrying capacity)

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How density affects population regulation

• Small populations grow fast
• larger populations grow slowly
• larger populations get smaller
• Why?

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Density Dependent Regulation

• Density determined factors kill a higher
  proportion of a crowded population than a sparse
  one
• Why? Predation, parasitism, and disease cause
  high death rates in dense populations.
• A disease causing oragnism or a preadtor is more
  likely to find its prey or host if there are more
  in an area.

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Density Independent Factors

• Bad weather or natural disasters could be an
  example.
• Drought may kill vegetation. Hard for a large pop
  to find food
• Bad winter hard for a large pop to find shelter.

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Survivorship

• The ages for which death occurs are given by the
  survivorship data for the population.
• This shows how long people are living.
• Ex. Cemetery study

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survivorship

• Type I
• Type II
• TypeIII

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Type I survivorship

• Type I survivorship starts out with simple
  exponential decline but shows bimodal kinetics
  whereby post-reproductive individuals display
  much more rapid exponential decline (a
  consequence of physiological limits on life
  span).
• Such limits actually may represent an
  optimization of type II survivorship whereby
  replicative potential early in life (when
  survivorship is relatively high) is optimized at
  the expense of long-term physiological robustness
  (when survivorship declines anyway due to random
  effects).
• K strategists which display physiological limits
  on reproductive capacity (e.g., humans) tend
  toward Type I survivorship.

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Type II survivorship

• Organisms displaying type II survivorship show
  simple exponential decline from day one There is
  no enhanced mortality at any age, nor any
  significant decline in reproductive potential
  with age.

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Type III survivorship

• Type III survivorship combines low
  pre-replicative survival with a reduced rate of
  exponential decline following the achievement of
  reproductive maturity (i.e., such organisms
  display bimodal survivorship curves).
• Organisms displaying type III survivorship
  typically produce large numbers of offspring few
  of which survive.
• Long lived fecundity
• Once established in a stable environment,
  however, individuals from populations displaying
  type III survivorship show little decline in
  reproductive potential over time.
• Longer term survival thus leads directly to
  increased progeny production creating benefits
  for the long lived and therefore selecting
  against premature death.
• Premature death be accident and predation
  nevertheless occurs thus accounting for the
  gradual decline in survivorship.
• Sea turtles, with their extremely high
  post-hatching mortality, but long lives, given
  survival to adulthood, show type III
  survivorship.
• example oak trees

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r strategist

• Adapted to exponential increases
• An organism which is particularly well adapted to
  an exponential increase in population size is
  know as an r strategist (the r coming from the
  differential equation described above).
• r strategists are characterized by great rapidity
  in their developmental programs combined with an
  ability to produce large numbers of offspring.
• No organism is a pure r strategist. Most show at
  least some capacity to survive at equilibrium,
  i.e., in carrying capacity situations.

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r strategist

• Pioneer species
• r strategists tend to be particularly good at
  finding disturbed environments and then rapidly
  producing large numbers of progeny in such
  environments.
• Often those offspring are ill-equipped for
  survival except under optimal conditions because
  of the small amount of parental resource put into
  their survival. However, the large numbers
  produced tend to both make up for low
  survivorship as well as allow for great
  dispersal.

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K strategist

• Adapted to limitation
• In contrast to r strategists, many organisms show
  extreme potential to survive and prosper at or
  near carrying capacity, though often at the
  expense of their ability to display rapid
  population increases under most circumstance
  (i.e., their intrinsic rate of population growth
  is small). Such organisms are called K
  strategists.
• The variable K refers to carrying capacity (i.e.,
  they display a bias in their adaptations toward
  maximizing carrying capacity).
• K strategists tend to be very good at surviving
  in mature (climaxed) ecosystems.
• K strategists also tend to put a great deal of
  resource into raising only a few young.
• A gorilla is a K strategist.

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Genetics Population
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Selection

• Types of selection
• Stabilizing
• Directional
• Disruptive

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Directional selection

• A population may find itself in circumstances
  where individuals occupying one extreme in the
  range of phenotypes are favored over the others.
• example can be found in the breeding of the
  greyhound dog. Early breeders were interested in
  dog with the greatest speed. They carefully
  selected from a group of hounds those who ran the
  fastest. From their offspring, the greyhound
  breeders again selected those dogs who ran the
  fastest.

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Stabilizing selection

• Natural selection often works to weed out
  individuals at both extremes of a range of
  phenotypes resulting in the reproductive success
  of those near the mean. In such cases, the result
  is to maintain the status quo. It is not always
  easy to see why both extremes should be
  handicapped perhaps sexual selection or
  liability to predation is at work. In any case,
  stabilizing selection is common. In humans, for
  example, the incidence of infant mortality is
  higher for very heavy as well as for very light
  babies.

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Disruptive selection

• Disruptive selection, like directional selection,
  favors the extremes traits in a population.
  Disruptive selection differs in that sudden
  changes in the environment creates a sudden
  forces favoring that extreme.
• meteor crashed into Earth 65mya

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Evidence for directional selection in nature
Industrial melanism in the peppered moth (Biston
betularia)
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Evidence for directional selection in
natureEvolution of pesticide and antibiotic
resistance
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Evidence for directional selection in nature
Evolution of heavy-metal tolerance in plants
Agrostis tenuis growing on a copper mine in
Britain
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Examples of stabilizing selection
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Population size

• Population size has a direct effect on the
  magnitude with which genetic drift can affect
  populations. Particularly, smaller populations
  are more affected by random occurrences than are
  larger populations.

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Genetics

• Small effective population size can result in a
  high occurrence of inbreeding, or mating between
  close relatives.
• One of the effects of inbreeding is a decrease in
  the heterozygosity (increase in homozygosity)
• This effect places individuals and the population
  at a greater risk from homozygous recessive
  diseases that result from inheriting a copy of
  the same recessive allele from both parents.

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Phenotypic variation in populations
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Genetic variation in populations

• Allele frequencies
• allele frequency the proportion of a certain
  allele within a population.
• Fact allele frequency gene frequency gametic
  frequency
• gene pool the set of all alleles at all loci in
  a population

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The Hardy-Weinberg genetic equilibrium

• The allele and genotypic frequencies remain the
  same from generation to generation in a
  population in which there is
• no mutation no genetic drift (i. e. the
  population size is infinitely large)
• no migration.
• random mating
• no selection.

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Balanced polymorphism through heterozygote
advantage

• Maintenance of high frequencies of harmful or
  deleterious alleles is usually due to balancing
  selection through heterozygote advantage (i.e.
  heterozygotes have the highest relative fitness).

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EFFECTS OF INBREEDING

• Inbreeding was very common among the royal
  families of Europe, and it has been linked as the
  cause of the widespread number of cases of
  hemophilia in the families.
• The presence of hemophilia in the royalty of
  Europe started with Queen Victoria of England.
  Victoria is thought to be the original carrier
  for the recessive X-linked hemophilia gene, which
  lead to over twenty members of royal families
  inheriting the disease in just over 100 years.
• The disease was spread throughout Europe,
  because Queen Victoria's children and
  grandchildren married into many different royal
  houses in Europe to create political alliances.
• Females can only been carriers for the rare blood
  clotting disease if one of there X chromosomes
  contains the deleterious recessive allele.
• Moreover, males inherit the disease if there X
  chromosome carries the gene for hemophilia.

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COEVOLUTION

• coevolution is a change in the genetic
  composition of one species (or group) in response
  to a genetic change in another
• For example, predation by birds largely drives
  the coevolution of model and mimetic butterflies.
  Some butterflies have evolved the ability to
  store poisonous chemicals from the food plants
  they eat as caterpillars, thus becoming
  distasteful. This reduces their chances of being
  eaten, since birds, once they have tried to
  devour such butterflies, will avoid attacking
  them in the future. Other butterflies have
  gradually evolved color patterns that mimic those
  of the distasteful butterflies (called "models").

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Extinction

• Population size 0
• A population whose size has been reduced to zero
  is said to have gone extinct.
• A population size of zero is unique among
  population sizes in that subsequent recovery
  (increase in size) is not possible.
• Limits
• Limits and extinction often go hand in hand.
• Thus, limits on population size, range,
  availability of nutrients, or abiotic
  requirements (e.g., as a consequence of
  over-specialization) can all result in an
  increased likelihood that a population will
  become extinct.

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Higher likelihood extinction

• Starting with a population consisting of 100
  individuals ("large" population) and a second
  population consisting of 10 individuals ("small"
  population), a decline of 10 or more will bring
  the large population down to 90 or so
  individuals, but will bring the small population
  down to 0.
• Individual alleles are also likely to be lost
  from small populations with much higher
  likelihood (and for much the same reason) than
  from large populations.
• Another was of saying this is that large
  populations are able to sustain genetic
  variability (genetic polymorphisms, lot's of
  alleles) much more readily than small
  populations.
• Loss of genetic variability leads to a lack of
  evolutionary flexibility which in turn leads to a
  higher likelihood of extinction.

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Sexual Selection

• differences in mating opportunity among
  individuals due to male contest and female
  choice.
• Fact Sexual selection results in dimorphism
  (pronounced phenotypic differences) between the
  sexes in many instances.

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Why are females so choosy? Several hypotheses
have been put forward

• 1./ females have some innate preference toward
  more ornamented or colorful males, i.e. they just
  happen to be choosy (Fisher's runaway hypothesis)
  
• 2./ females choose males that carry superior
  genes (the "good genes" hypothesis)
• 3./ females choose males that are healthier (the
  Hamilton-Zuk hypothesis)
• 4./ females prefer ornamented or colorful males
  because their male offspring will be attractive
  again leading eventually to higher fitness (the
  "sexy son" hypothesis)

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Male and female sugarbird
Females choose from among the cocks in the
junglefowl
Elephant seal bulls are much larger than females.
Bulls fighting for females.