Understanding Populations

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Chapter 8

• Understanding Populations

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8-1 How Populations Change Size

• Describe the three main properties of a
  population. (slide 3 4)
• Describe exponential population growth. (slide 6,
  7, 11, 12)
• Describe how the reproductive behavior of
  individuals can affect the growth rate of their
  population. (slide 6 7)
• Explain how population sizes in nature are
  regulated. (slide 8)

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What is a population?

• All the members of the same species living in the
  same place at the same time.
• reproductive group or gene pool
• Population refers to the group in general and to
  the size of the group
• Daisies in Ohio, not in Maryland
• Bass in a lake in Iowa
• Properties of populations
• Size
• Density
• Dispersion

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• Size
• Number of individuals in the population
• 250,000 people in Kalamazoo County (2010 census)
• Density
• Individuals per unit of area or volume
• 75 deer per square mile
• Dispersion
• Distribution or arrangement
• Even pine trees in rows in a forest corn
  fields
• Clumped zebras in the savanna deer herds
• Random- dandelions in a field lizards in the
  desert

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Population Growth

• Growth rate is calculated using
• change in births deaths
• population size
• Also included would be immigrants (in) to the
  area and emigrants (out) from the area
• Growth rate can be positive or negative
  numbers with negative numbers equaling a
  decrease in population size

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Growth Curves

• Biotic potential fastest rate at which a
  population can grow. This is also called
  fercundity (max number of offspring that could be
  produced vs fertility which is number actually
  produced).
• Reproductive potential max. number that a
  population can produce.
• Earlier maturity
• Larger numbers of eggs
• Shorter generation time
• Survival rate

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• Sea turtle lay gt2000 eggs, they dont all survive
• A pair of elephants could produce 19 million
  descendants in 750 years.but have one at a time,
  gestate 20 months, nurse 4 years, 15 when
  mature, raise 1 at a time even if live to be
  100 only have a couple kids
• Bacteria and insects have very short generation
  times.
• Average generation time for humans is 20 years

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Limits to population growth

• Resources are never unlimited or constant they
  are either used up or they change.
• A limited resource is something the species needs
  and consumes at the same rate its produced.
• Leads to competition
• Carrying capacity theoretical limit to
  populations size in a given ecosystem.
• Rabbits in Australia
• Islands make good studies because of boundaries
• Regulation
• Density dependent rate of death is worse when
  individuals are closely packed (infection in pine
  trees)
• Density independent rate of death is not
  dependent on numbers of individuals in the area
  storms, crops freezing , etc.

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8-2 How Species Interact with Each Other

• Explain the difference between niche and habitat.
  (slide 17-19)
• Give examples of parts of a niche. (slide 17-19)
• Describe the five major types of interactions
  between species. (slide 14 15)
• Explain the difference between parasitism and
  predation. (slide 14)
• Explain how symbiotic relationships may evolve.

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8.2 Population Dynamics

• Population group of similar individuals that
  are in the same place, at the same time and
  comprise a gene pool
• Species organisms that are similar enough to
  interbreed in nature and produce viable
  offspring.
• Breed, variety, strain, subspecies, etc.
• dynamic means in constant motion, always
  changing, not static.

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• Births increase population
• Deaths decrease population
• If births deaths then population is steady,
  called replacement rate
• If growth is exponential, then population
  increases rapidly. Parents have 2 kids (4) and
  they each have 2 kids (8), and they have 2 kids
  (16).. The sum of population would go like this
  2,4,8,16,32.

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Population Growth patterns

• Logistic steady (S)
• Exponential increasing rapidly (J)
• In a new situation, populations have the
  potential to increase exponentially, but natural
  forces like food/resources, predators and space
  will eventually create a stable level when the
  population reaches Carrying Capacity

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Symbiosis

• In addition to enough food, water, oxygen, sun,
  space, mates and other resources individuals
  have interactions with other species that impact
  their survival and reproductive success.
• Competition (bugs and food)
• Can be direct or indirect
• NOT an example of symbiosis!
• Predator prey (rabbit lynx)
• NOT an example of symbiosis!
• Commensalism (bromeliads like orchids)
• Mutualism (acacia/ants, pollinators/flowering
  plants, intestinal bacteria)
• Parasitism (mosquito, lice, leech, tapeworm)

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Resource Partitioning

• In order to decrease competition some resources
  are allocated or partitioned to specific species
• Common examples include birds that specifically
  live in the upper branches, lower branches, or
  interior of the tree so that one tree can house 3
  species in their own separate zones

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Niche

• An organisms unique role within an ecosystem is
  its NICHE FUNCTION or job grazer,
  pollinator, etc
• Physical space
• Environmental factors
• Interactions
• Realized Niche vs Fundamental Niche
• Where you actually are vs. anywhere you could be
  successful
• HABITAT WHERE you live

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Humans

• The human population is also subject to all of
  the conditions studied in ecology
• Resource availability (coal, Al, transportation,
  Rx)
• Material resources, goods and infrastructure
  including services
• Water, air, food
• Space
• Waste
• Pollution Disease/ immunity
• Genetic impacts Creativity
• Carrying capacity is hard to calculate due to the
  number of variables.

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