Silent Spring

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Silent Spring Ecology ProjectChapter 52

• By Jacqueline Laurenzano , Judene Mavrikis,
  Samantha Viscovich, and Rebecca Wojfnis

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Density A Dynamic Perspective

• A population is a group of individuals of a
  single species living in the same general area.
  Members of a population rely on the same
  resources, are influenced by similar
  environmental factors, and have a high likelihood
  of interacting and breeding with one another.
• Once a populations boundaries, natural or
  defined by an investigator, are defined a
  population can be described in terms of density
  and dispersion.
• Density- the number of individuals per unit area
  or volume.
• When determining population density it is rare
  to find cases where it is possible to count all
  individuals, in most cases it is impossible to
  count all individuals. So, ecologists use
  sampling techniques, such as the mark-recapture
  method, to estimate densities and total
  population sizes.
• Density is the result of a dynamic interplay
  between two processes
• -Immigration- the incoming of individuals from
  other areas.
• -Emigration- the movement of individuals out of a
  population.

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Patterns of Dispersion

• Dispersion- the pattern of spacing among
  individuals within the boundaries of the
  population.
• Social interactions between members of the
  population, which may maintain patterns of
  spacing between individuals, can contribute to
  variation in population density.
• Three Patterns of Dispersion
• Clumped The most common pattern of dispersion is
  clumped where individuals are aggregated in
  patches. The clumped pattern is associated with
  mating behavior, the uneven distribution of
  resources, and can increase effectiveness of
  certain predators
• Uniform The uniform pattern is not as common as
  clumped and is when individuals are evenly
  spaced. Organisms often exhibit uniform
  dispersion because of antagonistic social
  interactions, such as territoriality
• Random The least common pattern of dispersion is
  random where there is unpredictable spacing, the
  position of each individual is independent of
  other individuals. Random dispersion occurs when
  key physical or chemical factors are relatively
  homogeneous or where there is an absence of
  strong attraction among individuals of a
  population.

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Demography

• Demography is the study of the vital statistics
  of populations and how they change over time
• Life tables, a useful way to summarize some of
  the vital statistics of a population, are
  age-specific summaries of the survival patterns
  of a population. The best way to construct a life
  table is to follow the fate of a cohort, a group
  of individuals of the same age, from birth until
  death
• A graphic way of representing the data in a life
  table is a survivorship curve, a plot of the
  proportion or numbers in a cohort still alive at
  each age.
• Type I Curve low death rate during early and
  middle years and then death rates increase with
  old age
• Type II Curve constant death rate over life span
• Type III Curve high death rates for the young
  then death declines for the survivors
• A reproductive table, or fertility schedule, is
  an age-specific summary of the reproductive rates
  in a population. The best way to construct a
  reproductive table is to measure the reproductive
  output of a cohort from birth until death

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Life History Diversity

• Life Histories are made up of three traits a)
  when reproduction begins, b) how often the
  organism reproduces, and c) how many off-spring
  are produced during each reproductive episode.
• Semelparity or Big Bang Reproduction is a type
  of one-shot reproduction where the female only
  reproduces once in her lifetime.
• Example of Semelparity Pacific Salmon hatch in
  stream, migrate to open waters for 4 years to
  mature, travel back to stream to reproduce and
  then die
• Environments which favor Semelparity
  reproduction Semelparity is favored where the
  survival rate of off-spring is low, in highly
  variable or unpredictable environments, since
  production of large numbers in those environments
  increases the probability that some will survive.
  
• Iteroparity or Repeated Reproduction this is a
  type of repeated reproduction in which the female
  reproduces more than once in her lifetime.
• Example of Iteroparity Reproduction Some lizards
  produce a very large amount of eggs during their
  second year of life, they continue this
  reproductive act annually until death
• Environments which Favor Iteroparity
  Reproduction Iteroparity is favored in
  dependable environments, where competition for
  resources could be intense, since a few
  relatively-large healthy off-spring will have a
  better chance of surviving to reproductive age.

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Per Capita Rate of Increase

• Per Capita Rate of Increase is represented as the
  variable ( r )
• The per capita rate of increase indicates whether
  a given population is growing (r gt 0), declining
  (r lt 0), or remaining constant (r 0)
• You find the Per Capita Rate of Increase by
  subtracting the Per Death rate from the Per
  Capita Birth Rate.
• Per Capita Birth rate is the number of offspring
  produced per unit time by the average member of
  the population It is represented by the variable
  B.
• BbN (Where B is the number of births, b is the
  per capita birth rate, and N is the population
  size)
• Per Capita Death rate allows for calculation of
  the expected number of deaths per unit time in a
  population. It is represented by the variable m
  for mortality.
• The Per Capita rate of Increase equation is r
  b m
• Zero Population Growth occurs when r0, meaning
  the per capita birth and death rates are equal to
  each other.

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Logistic and Exponential Models

• Exponential growth or (geometric population
  growth) is population increase under ideal and
  unlimited conditions.
• Under ideal conditions the per capita rate of
  increase is not restricted and may assume the
  maximum rate of any specific species. This is
  called the intrinsic rate of increase (rmax).
• When graphed it assumes a J shape because even
  though the rate is constant, over time, there
  will be more individuals present per unit time
  when it is large, resulting in increasing
  steepness.
• Characteristic of some populations that are
  introduced into a new or unfilled environment or
  populations whose numbers have been drastically
  reduced and are rebounding.
• The Logistic Model The Logistic Growth Model
  displays exponential growth with limiting
  conditions
• The Logistic Growth Model shows that the per
  capita rate of increase declines as carrying
  capacity is reached.
• It assumes an S-shape because the population
  growth slows dramatically as the population size
  nears carrying capacity.

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The Logistic Model and Real Populations

• The logistic model assumes that populations
  adjust instantaneously to growth and approach
  carrying capacity , usually there is a lag time
  before the negative effects of an increasing
  population are realized in most natural
  populations
• The logistic model also incorporates the idea
  that regardless of population density, each
  individual added to a population has the same
  negative effect on population growth rate.
• however, some populations show an Allee Effect,
  in which individuals may have a more difficult
  time surviving or reproducing if the population
  size is too small
• The logistic model is a useful starting point for
  thinking about how populations grow and for
  constructing more complex models, it is also
  useful in conservation biology for estimating how
  rapidly a particular population might increase in
  numbers after it has been reduced to a small size
  

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The Logistic Model and Life Histories

• The logistic model predicts different per capita
  growth rates for populations of low and high
  density relative to the carrying capacity of the
  environment
• High Densities
• each individual has few resources available, and
  the population grows slowly, if at all.
• selection favors adaptations that enable
  organisms to survive and reproduce with few
  resources
• Low Densities
• per capita resources are relatively abundant, and
  the population can grow rapidly
• selection favors adaptations that promote rapid
  reproduction
• different life histories are favored under each
  condition
• K- selection (density-dependent selection)
  selection for life history traits that are
  sensitive to population density
• tends to maximize population size and operates in
  populations living at a density near the limit
  imposed by their resources ( the carrying
  capacity, K)
• R-selection (density-independent selection)
  selection for life history traits that maximize
  reproductive success in uncrowded environments
• tends to maximize r, the rate of increase, and
  occurs in environments in which population
  densities fluctuate well below carrying capacity
  or individuals are likely to face little
  competition

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Density Dependent Population Regulation

• Density-dependent birth and death rates are
  examples of negative feedback, without some type
  of negative feedback, a population would not stop
  growing. At increased densities birth rates
  decline and/or death rates increase, providing
  the needed negative feedback. The mechanisms
  causing these changes involve many factors.
• Competition for Resources- in crowded
  populations, increasing population density
  intensifies Interspecific competition for
  declining resources, resulting in a lower birth
  rate.
• Territoriality- when territory space becomes the
  resource for which individuals compete. The
  presence of non-breeding individuals is
  indication that territoriality is restricting
  population growth.
• Health- a diseases impact may be density
  dependent, if the transmission rate of a disease
  depends on a certain level of crowding in a
  population
• Predation- if a predator encounters and captures
  more food as the population density of the prey
  increases, then predators may feed only on that
  species, consuming a higher percentage of
  individuals
• Toxic Wastes- the accumulation of toxic wastes
  can contribute to density-dependent regulation
  size. An example would be in laboratory culture
  of small organisms metabolic by-products
  accumulate as the populations grow, poisoning the
  organisms within the environment
• Intrinsic Factors- for some animal species,
  intrinsic (physiological) factors, rather than
  extrinsic (environmental) factors, appear to
  regulate population

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Population Dynamics

• Population dynamics focuses on how the
  interactions between biotic and abiotic factors
  cause variation in population size.
• Populations undergo periods of stability and
  fluctuation
• Large mammals are usually more stable than other
  populations but in some cases this is not always
  true.
• Example Moose from the mainland colonized Isle
  Royale around 1900, being isolated from
  immigration and emigration their population
  should stay stable. Yet because of abiotic
  factors (harsh winters) and biotic factors
  (wolves as predators) the moose population was
  extremely unstable
• While the moose were fluctuating, the Dungess
  crab, a much smaller species, located at Fort
  Bragg varied between 10,000 and hundreds of
  thousand over a 40 yr period
• Severe temperature extremes and cannibalism can
  caused fluctuation in the Dungess Crab
  population.
• A metapopulation is a group of linked populations
• This concept shows the significance of
  immigration and emigration in contrasting
  populations

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Population Cycles

• Some populations follow regular and predictable
  boom and bust cycles.
• While some populations fluctuate at unpredictable
  intervals, some fluctuate with extreme regularity
  and pattern.
• Ex. (voles and lemmings have 3 to 4 years cycles,
  while the ruffed goose has a 9 to 11 year cycle)
• For predators that depend heavily on a single
  prey species, the availability of that prey is
  the major factor influencing their population
  changes
• Some causes of rises and falls in populations can
  be food shortage, excessive predator/prey
  interactions, or both.
• The Hare cycle relies greatly on the predation
  but also partially relies on the food especially
  in the winter

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Global Human Population

• The global population now numbers over 6 billion
  people and is increasing at a rate of about 73
  million each year.
• Zero population growth High birth rate High
  death rate
• or
• Zero population growth Low birth rate Low
  death rate
• Demographic transition - a shift from zero
  population growth in which birth rates and death
  rates are high to zero population growth
  characterized instead by low birth and death
  rates
• reduced family size is the key to the demographic
  transition
• Age Structure is the relative number of
  individuals of each age, is commonly represented
  in pyramids
• age-structure diagrams predict a populations
  growth trend and illuminate social conditions
• Infant Mortality and Life Expectancy
• infant mortality is the number of infant deaths
  per 1,000 live
• life expectancy at birth is the predicted average
  length of life at birth
• these differences reflect the quality of life
  faced by children at birth

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Global Carrying Capacity

• The United Nations estimated that the global
  population IN 2050 WILL BE FROM 7.5-10.3 BILLION
  PEOPLE. Just how many people can our biosphere
  support?
• Estimates of Carrying Capacity Some researchers
  use a logistic curve to predict the future
  maximum of human population. Others predict this
  by looking at existing maximum population
  density and multiplying this by habitable land.
  Still other make prediction based on a simple
  necessary factor such as food.
• Ecological Footprint The ecological footprint
  summarizes the approximate land and water used by
  each nation to produce all the resources it
  consumes and absorbs all the waste it generates.
  How close we are to the maximum carrying
  capacity
• U.S. 8.4 ha per person maximum is 6.32 ha per
  person
• New Zealand 9.8 ha per person maximum 14.3
  ha per
• Perhaps food would be a main factor in limiting
  our growth Perhaps we will be limited by space,
  or we could run out of nonrenewable resources
  such as metal and fossil fuels. Or we may even
  run out of the renewable resource of water

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The Dangers of DDT
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Effects of DDT on Density and Dispersion

• The density and dispersion of different
  populations of species can be very fragile and
  easily disrupted by changes in the environment.
• The web of life and the balance of nature is
  extremely fragile and harmful chemicals such as
  DDT can completely disrupt that balance.
• Certain species are abundant in certain areas
  because of a certain quality, feature, or
  resource that, that environment contains.
• If a needed resource is damaged, destroyed, or
  poisoned by a powerful chemical such as DDT, the
  food chain and eating patterns as well as
  predator/prey relationships are disrupted.
• Other relationships such as Commensalism,
  Competition, Parasitism, Mutualism, etc. can be
  disrupted by the poisoning of the resources in
  the environment.
• The disruption of the food chain and
  interspecific relationships, will eventually
  deplete and destroy the native populations. This
  is because the death and emigration rates will
  increase while birth rates and immigration
  rates will decline.
• In the end result, The use of harmful chemicals
  such as DDT will disrupt the relationships in a
  population and will affect the density and
  dispersion of a population in a given area.

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DDT effects on Density-Dependent Population
Regulation

• DDT that is sprayed filters down from the plants
  or trees that were sprayed, and some of it
  reaches the ground and leeches into the flowing
  streams and ground water.
• Health When DDT has been ingested into an
  animals systems, it will be stored in their fat
  tissue and will greatly harm them. If an animal
  doesnt die immediately it will pass the chemical
  on to whomever it gets eaten by. As DDT moves up
  the food chain its abundance grows immensely.
• Toxic wastes DDT is an extremely toxic and
  harmful waste, as DDT leeches into soil and water
  it will contaminate there reservoirs with toxic
  wastes. Any animal living in or crop produced in
  these reservoirs will become infected and be
  harmed
• Predation Any animal which feeds on smaller
  animals that live in environments which were
  spayed with DDT will not only become infected by
  DDT as well, by will be infected with a larger
  amount of DDT that the animal which was eaten
• Competition for resources When DDT traveling
  through soil and water bodies it either infects
  or kills the life those ecosystems support.
  Herbivores and Carnivores may lose their supply
  of food if that species has been killed off or
  infected by the toxic DDT. This will increase
  competition because there are very limited amount
  of resources.

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DDT affects on Global Carrying Capacity

• The carrying capacity of Earth for humans is
  uncertain. The ecological footprint concept
  summarizes the aggregate land and water
  appropriated by each nation to produce all the
  resources it consumes and to absorb all the waste
  it generates.
• DDT residues are found on the ground and the
  water, affecting all organisms living within, or
  on the ground and the organisms living within the
  waters. These organisms are consumed by humans,
  and the DDT is found in the tissues or humans,
  causing illnesses and may even causing death.
• Through biological magnification, any animal in
  which humans eat that contains toxic chemicals
  such as DDT will harm humans drastically. The
  amount of toxins that animal contains will be
  multiplied in the human body.
• An overall analysis suggests that the world is
  now at or slightly above its carrying capacity.
  We can only speculate about Earths ultimate
  carrying capacity for the human population or
  about what factors will eventually limit our
  growth.
• DDT may cause damage to the factors that could
  potentially limit our growth or limit our
  resources needed for survival, such as water,
  air, and soil. We need water to survive, air to
  breathe, and soil for agriculture. DDT could
  affect all of resources and more

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Acid Precipitation
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Acid Precipitation Effects on Density and
Dispersion

• Acid Precipitation is formed from the excess of
  Carbon Dioxide and Sulfur in the atmosphere which
  combines with water vapor and falls down to the
  earth as acid rain.
• Acid rain damages the ecosystems in which it
  falls, by
• Contaminating water supply
• Contaminating water ecosystems
• Killing animals and plants
• Changing the composition of soil
• Raising the pH levels in water and soil
  ecosystems
• Causing key nutrients to leech out of soil,
  destroying forests
• Causing health problems
• Destroying possible habitats
• All of these effects of Acid Precipitation
  negatively affect density and dispersion
• With less available habitats and less water
  availability competition for resources will
  increase, this will affect the patterns of
  dispersion within an ecosystem. A random
  dispersion ecosystem can be transformed into a
  clumped or uniform patterned ecosystem.
• The density of an ecosystem can be negatively
  affected by acid rain because the rain diminishes
  some of the necessary resources that are required
  by individuals. These individuals will have to
  die off or look elsewhere to survive, lessening
  the density in certain ecosystems.

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Acid Rain effects on Density-Dependent Population
Regulation

• Acid rain has been shown to have immense affects
  on forests, freshwaters and soil ecosystems,
  killing insect and aquatic life forms as well as
  causing damage to buildings and having impacts on
  human health
• Acid precipitation has negative effects on the
  many aspects that regulate the density of a
  population.
• Competition Acid rain contaminates water supply
  and damages aquatic and terrestrial biomes.
  Animals competing for water or for suitable
  habitats will have to compete more for suitable
  water supply and habitats.
• Territoriality Territoriality is affected by
  acid rain, because territoriality comes into
  affect when the density of a population is high
  and there aren't enough suitable habitats. Acid
  Precipitation destroys some of the aquatic and
  terrestrial habitats and therefore lessens the
  amount of suitable habitats.
• Health Small fragments which are mainly formed
  from the same gases which form acid rain, have
  been shown to cause illness and premature deaths
  such as cancer and other diseases
• Toxic wastes Just as garbage is accumulating on
  earth, and carbon dioxide is accumulating in the
  atmosphere, acid precipitation is accumulating in
  the aquatic ecosystems and soil raising the pH
  levels of these ecosystems and killing off their
  inhabitants.

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Acid Precipitation effects on The Global Carrying
Capacity

• Acid Precipitation destroys many of the earths
  resources either by raising the pH level of our
  resources, making our resources unsuitable for
  life, or by destroying the resource all together.
  
• Water Ecologists believe that water could be a
  limiting factor on the Global carrying Capacity.
  When acid precipitation enters lakes, pond, or
  rivers it sometimes raises the pH level to such a
  degree that it is unsafe to consume
• Food Food is also believed to be a possible
  limiting factor. Acid precipitation destroys a
  great deal of plant life when falling to earths
  surface.
• Ecologists have observed severe leaf damage that
  can be attributed to acid rain, the acid rain
  limits the plants ability to sustain itself.
• Acid Precipitation can also raise the pH level or
  change the composition in soil making it
  unsuitable for plant life.
• Many ecosystems, such as forests are destroyed
  because the acid precipitation in the soil causes
  essential nutrients to leech out of the soil
  making it unsuitable to support plant life.
• Acid Precipitation negatively affects many of the
  factors in which ecologists predict will limit
  the Global Carrying Capacity of earth. It is
  imminent that there is an international consensus
  to limit the amount of Carbon Dioxide released
  into the atmosphere.

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Ms. S. AP Bio A Period

• Silent Spring 10962- By Rachael Carson
• AP Edition Biology Campbell Reece