Populations

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Populations

• What influences how populations flourish or
• die out?

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Biotic Potential

• The maximum number of offspring that a species
  could
• reproduce in a life time, if resources were
  unlimited.
• Biotic Potential is determined by
• 1. Birth potential max of offspring per birth
• 2. Capacity for survival of offspring that
  reach
• reproductive age
• 3. Procreation of times a species reproduces
• each year
• 4. Length of reproductive life of years
  species
• can reproduce

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Limiting Factors

• A limiting factor is any factor that places an
  upper limit on the size of a population
• Limiting factors can be biotic or abiotic
• Human influences often act as limiting factors
• What are the limiting factors that might affect a
  population of penguins? How about a suburban
  human population?

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Tolerance Range

• The abiotic conditions within which a species can
  survive
• Species can be successful over a range of
• abiotic conditions
• A population will become stressed and die out if
  conditions exceed their tolerance limits
• See Figure 1, Nelson, p. 52

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Tolerance Range
Use Figure 2, p. 53 (Nelson) to fill in the
following chart

• Cacti Waterlillies
  Bunchberries
• abiotic
• conditions
• that keep
• species
• within
• tolerance
• range
• abiotic conditions
• that put species
• outside of tolerance
• range

- long periods of Drought -full exposure to
sun - long periods of rain (roots cannot
survive damp conditions -low light availability
- water levels minimize exposure of roots to
air -full exposure to sun - if water level
drops exposing roots to air -low light
availability

• shade
• too much light

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Carrying Capacity

• The population remains within the limits that the
  environment can support
• This is the largest population size of a species
  that an ecosystem can support or sustain
• There are several factors that can influence the
  Carrying Capacity of a species
• ? food (think also food chains, webs)
• ? water
• ? shelter
• ? space
• ? climate
• ? susceptibility to disease
• ? predation
• ? competition for many of the above

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Carrying Capacity

• Carrying capacity can be altered through natural
  or human
• Think-Pair-Share Consider a species we
• have discussed or you know about from your
  previous
• personal experience. How was the carrying
  capacity of this species
• affected by either a natural or human action?
  (can be positive or negative)
• Example 1 Irrigation systems in African deserts
  increases the carrying
• capacity of organisms living in a desert
  ecosystem (increased water
• availability)
• Example 2 the removal of wolves by human
  hunters will increase the
• carrying capacity of moose in this ecosystem
  (more space, less predators)
• Example 3 clear-cutting trees will decrease the
  carrying capacity of
• certain bird species that rely on these trees for
  habitat and to maintain
• their nests

8
Population Density

• Is the number of organisms living in a given
  space
• Use a diagram to show a high population density
• vs. low population density and provide a
  specific real example in nature

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Population Density
Density- independent factors
Density-dependent factors

• factors that do not
• depend on the population
• size
• ? weather (storms, cold,
• drought, floods, early
• freezing, heavy snow)
• ? forest fires
• ? comets
• density-independent
• diseases (DDT poisoning)
• ? environmental pollution

• affect
• population size
• can lead to
• species aggression
• and/or panic
• ?can lead to
• extinction
• can help
• populations flourish

• factors that do depend
• on the population size
• food availability
• space (shelter, territories,
• denning sites, nest cavities)
• density-dependent
• diseases (rabies, SARS)
• ? competition
• (intraspecific. vs.
• interspecific)

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Intraspecific vs. Interspecific

• Intraspecific when two organisms from the same
  species are after the same resources or food
• THINK/PAIR/SHARE Give a specific example of
  intra-specific competition.

• Interspecific competition when two organisms
  from different species are after the same
  resources or food
• THINK/PAIR/SHARE Give a specific example of
  inter-specific competition.

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Reaching the Carrying Capacity
In the 1800s, the fur trade led to a Drastic
decline in the fur seal population In 1911 a
treaty was signed to protect the fur seal
population
Exponential Growth
Carrying capacity reached (population size has
reached equilibrium or is in balance)
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Humans and Carrying Capacity
What actions have humans taken to increase the
carrying capacity of our species? - Early on
using fire, making simple tools/weapons -
Improvements in public health, education,
agriculture, medicine,
technology - Exploiting huge amounts of energy
and resources to run complex,
modern societies
What paths might the curve take after this
century? Which path do you think is most likely?
Why?
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• What next?

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Invasive species

• An invasive species is one that can be either
  native and non-native that heavily colonize a
  particular habitat.
• Natural, wild species can be threatened with
  extinction.

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The good ones
Asian Oysters- are better at filtering out water
pollutants than native oysters.
Garlic Mustard- introduced as a means of
erosion control
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Characteristics of Good Invaders

• High rate of reproduction (short generation time)
• Long-lived
• High dispersal rates (produces a lot of seeds)
• Single-parent reproduction
• Tolerant of wide range of conditions
• Habitat generalist
• Broad diet
• Opportunistic (aggressive, out competes)
• Difficult to control and resistant to eradication

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Characteristics of the Community(that make it
susceptible to invaders)

• Invading nonindigenous species tend to be more
  successful when native species do not occupy
  similar ecological niches
• Species that inhabit disturbed environments and
  those with a history of close association with
  humans tend to be successful in invading
  human-modified habitats
• Successful invasion is enhanced by similarity in
  the physical environment between the source and
  target areas
• Absence of predators on invading species
• Absence of native species morphologically (form
  or structure) or ecologically similar to the
  invader

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