Density and Dispersion Information

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Density and DispersionInformation

• Any population within a certain area can be
  defined using two key factors, density and
  dispersion. Density is the number of individuals
  per unit area or volume. An example of density
  would be the number of African elephants per
  square mile in Kruger National Park, South
  Africa. Dispersion on the other hand is defined
  as the pattern of spacing among individuals
  within the boundaries of the population. There
  are many different types of spacing under
  dispersion the most common of them is clumped.
  Most of the populations throughout the entire
  world are dispersed as clumped, for example, many
  insects clump together in rotten logs and under
  damp and dark places such as rocks.
• A populations density can be determined in
  several sampling techniques. One way of doing
  this is by actually counting all of the
  individuals within the boundaries of the
  population. For example, one may count the number
  of sea stars in a tide pool to find its density.
  This method is very tedious if populations carry
  great sizes, therefore there are more techniques.
  Another way of determining a populations density
  is by finding the density of a small section in
  the boundaries, the scientist will then
  extrapolate to estimate the density within the
  total area. One of the most common ways of
  determining density is using the mark-recapture
  method. In this method, researchers place traps
  within the boundaries of the population. Captured
  animals are tagged and then released back into
  the wild. The scientists will then return to the
  populations area and then place traps again. The
  animals caught are both tagged and untagged
  individuals. From this data the researchers can
  estimate the total number of individuals in the
  population. This method assumes that each tagged
  individual has the same probability of being
  caught as the untagged individual.
• Interactions between individuals in the
  population can result in the maintaining of
  certain patterns of spacing between these
  individuals, this can also contribute to changes
  in the population density. The clumped pattern of
  dispersion has the individuals aggregated in
  small areas. Examples of species that are clumped
  include plants, fungi, insects, and more. Plants
  are usually found clumped where soil conditions
  and other environmental factors are in favor for
  germination and growth. A uniform or evenly
  spaced pattern of dispersion results from direct
  interactions between the individuals in the
  population. For example, animals show a uniform
  dispersion when aggressive social interactions.
  Territoriality is an example of such aggressive
  social interactions. The last type of dispersion
  is random, random dispersion is not as common in
  nature as clumped or uniform.

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Population Growth Information

• The formal definition for population growth
  starts with the fact that populations increase as
  individuals are born or immigrate into a
  specified location, and decrease as they die or
  emigrate. Rates of population growth, usually
  expressed as a percentage, vary greatly.
  Population growth is a localized group of
  individuals that belong to the same biological
  species and how they increase, decrease, or keep
  their numbers constant with time. Population
  growth is a devise that is used by ecologists to
  study different species reproduction rates, birth
  rates, death rates, immigration rates, emigration
  rates and more. Population growth can be broken
  down into several topics, including exponential
  population growth, zero population growth, and
  logistic population growth.
• Exponential population growth is also known as
  geometric population growth. Population increase
  under conditions such as populations whose
  members all have access to abundant food and are
  free to reproduce at their physiologically
  capacity, is usually referred to as exponential
  population growth. With exponential growth the
  birth rate alone controls how fast (or slow) the
  population grows. Exponential growth causes the
  per capita rate of increase to assume the maximum
  rate for the species, this is also known as the
  intrinsic rate of increase and noted as rmax.
  Exponential growth in a single species in an area
  can upset the entire ecosystem, for example an
  increase in the population of zooplankton will
  result in the decrease in the population of
  phytoplankton.
• Zero population growth is also known as ZPG.
  When the per capita birth rates and per capita
  death rates are both equal, zero population
  growth than occurs. Births and deaths obviously
  still happen in the population, but the births
  and immigration and the deaths and emigration
  actually perfectly balance each other out. The
  next branch of population growth is known as
  logistic population growth. Unlike the
  circumstances in which exponential growth takes
  place, in most real populations, both food and
  disease become important as areas become crowded.
  There is an upper limit to the number of
  individuals the environment can support.
  Ecologists refer to this as the "carrying
  capacity" of the environment. Populations in this
  kind of environment show what is known as
  logistic growth. In the logistic population
  growth model the per capita rate of increase
  decreases as the carrying capacity is reached.

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Global Human Population Information

• The global human population has been increasing
  at alarming rates since the beginning of the
  industrial revolution. The human population has
  sustained so much growth for so long, unlike any
  other large mammal. The human population has
  increased at a slow but steady pace until 1650,
  where the population suddenly doubled to 1
  billion within the next two centuries, then
  doubled again to 2 billion between 18590 and
  1930, and then doubled again by 1975 to more than
  4 billion. In modern times the global human
  population is over 6 billion individuals and is
  still growing, an average 73 million people are
  brought into the population every year.
  Approximately 201,000 people every single day,
  this is the equivalent of adding another city the
  size of Madison, Wisconsin to the population.
• Ecologists have predicted that the global human
  population will reach 7.3-8.4 billion individuals
  by 2050. Although the population is still
  significantly growing, the rate of growth has
  begun to slow since 1650. The rate of growth for
  the global population reached its highest mark in
  1962, a rate of growth at 2.19. This rate has
  declined to 1.16 in 2003. Modern scientists are
  estimating a population growth of just over 0.4
  by 2050. Research indicates that countries like
  Australia, Italy, and Tunisia, among many others,
  have recently shown a decline in human population
  growth. These declines in the rate of growth show
  the population is being effected by fundamental
  changes in population dynamics, specifically
  caused by diseases such as AIDS.

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Density and DispersionAnd DDT

• Density and dispersion are both affected by
  DDT. Density is the number of individuals per
  unit of area or volume. DDT, being toxic to
  living organisms, can lower the density of an
  organism. For example, birds can have a high
  density in an area. After DDT is applied to the
  area where the high density is, DDT enters the
  organism. It is stored in the fatty tissues and
  remains there. It also travels up food chains, as
  one organism will eat an organism affected by
  DDT. Since DDT is toxic, these animals start to
  die. As more and more organisms die, the
  population density decreases. Dispersion is the
  pattern of spacing among individuals within the
  boundaries of the population. DDT also has an
  effect on dispersion. As more and more organisms
  die from DDT, regular dispersion is interfered
  with. For example, uniform dispersion would be
  hard to maintain, especially with the loss of so
  many organisms. Clumped dispersion would also
  become harder, as the diminished numbers of
  organisms would lead to smaller, if any, groups.

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Population Growth And DDT

• Population growth can slow and come to a halt
  with the introduction of DDT. DDT, being toxic,
  poisons organisms and kills them. This causes a
  rise in death rates. If new organisms immigrate
  to an area, they too will be killed by this
  toxin. DDT has also been shown to have an effect
  on the reproductive system, often resulting in
  sterility. If this happens, no new organisms can
  be born. Food and water supplies of an organisms
  population have a good chance of being affected
  by DDT. If this is so, more and more DDT will
  accumulate in the organism until the limit is
  reached, and the organism dies. If the death rate
  exceeds the birth rate, the population growth
  declines. All these factors contribute to how the
  population growth is affected.

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Global Human Population And DDT

• DDT is not only limited to plants and animals.
  DDT can also have an affect on humans. When DDT
  is introduced to the human body it stores itself
  in organs rich in fatty substances such as the
  liver, kidneys, adrenals, thyroid, and testes.
  DDT can be absorbed by humans in several way. One
  is direct exposure to the chemical itself.
  Another is the consumption of food that has been
  exposed to DDT. DDT can also be passed down to
  offspring in the womb and through breast milk.
  Only a certain amount of DDT can be held by the
  human body before its damaging effects are
  realized. DDT has been found to be a chemical
  carcinogen, meaning that it can cause cancer. It
  can cause a range of illnesses, from fevers and
  nausea to fatigue and anxiety. DDT has the power
  to kill a human being. If DDT is applied to an
  area in large amounts, or if DDT has poisoned the
  food supply, the human population will begin to
  drop. Since DDT embeds itself in fatty organs,
  the human testes will become one of its targets.
  Sterility and other birth defects may occur
  because of the harmful effects of DDT. This could
  greatly diminish the number of births. Infant
  mortality would be high, as they will have been
  exposed to DDT in the womb and would now be
  exposed to it through the outside world. They
  would be extremely susceptible to the harms
  caused by DDT. This would mean the life
  expectancy would be low. Eventually, if DDT is
  still in use, the human population will decrease
  dramatically.

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Density and DispersionAnd Modern Environmental
Stress

• At this point in time, global warming has
  become the newest and possibly most destructive
  environmental stress. Global warming affects
  density and dispersion very much. As the Earths
  temperatures rise, the polar ice caps up north
  begin to melt. This threatens many organisms,
  such as polar bears. The polar bears habitat is
  ruined every day because of global warming. As
  the polar bears loose more and more of their
  home, they move to other places where the habitat
  they are used to is still intact. The population
  densities of the certain areas, which have been
  surviving global warming, grow more and more. Now
  there are many more polar bears in certain areas.
  Polar bears are predators, and now the population
  of the animals they prey on becomes lower,
  causing the population of whatever the prey feeds
  on to go higher, and on and on. Unfortunately,
  this isnt only happening with the polar bears,
  but in many other areas.

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Population Growth And Modern Environmental Stress

• Population growth is also affected by global
  warming. When the habitats of certain organisms
  are changing, everything else changes. Global
  warming could cause a lack of food, making the
  death rates higher and the birth rates lower.
  When an animal at the top of the food chain
  begins to die off, its prey multiplies, and the
  population of whatever the prey feeds on
  decreases.

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Global Human Population And Modern Environmental
Stress

• The global human population harmed by the
  contamination of water supplies, because humans
  rely on water as a main resource. Humans drink
  water, use it to bath themselves, clean their
  clothes and dishes, among many others uses. This
  allows many ways for harmful chemicals or
  substances to come in contact with the global
  human population. These pollutants can cause
  people to fall ill and sometimes dies. Another
  stress on the global human population is the
  increasing population. There is only so much
  space on Earth that is inhabitable, and it is
  possible the human race will meet their carrying
  capacity in the near future. Ideally this would
  mean the human population would begin to
  decrease, but this is uncertain. Overpopulation,
  is another issue, and allows for diseases to
  spread easily, and more demand for resources such
  as water, and food.

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Credits

• Timothy Flynn, Sean Coffey, Caroline Kaleda, and
  Pierce Krauland.