Population

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Population
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Population

• Members of the same species living in a specific
  geographic area.
• Species A group of similar organisms that can
• breed and produce fertile
  offspring
• Factors that effect population size
• Availability of Food
• Weather conditions
• Space
• Breeding Patterns

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Population

• When studying a population boundaries are set to
  limit or make a study easier
• Population Density The number of individuals of
  a
• particular
  species per unit
• area or
  volume
• Can be expressed as a formula
• Individuals / Unit Area
• 1000 Trees / 50 km² 20 Trees/km²
• 20 Trees per km²

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Population

• Sampling Techniques
• Used to estimate the size of the population
• When the numbers are too large or when the
  species moves too much
• Quadrats a marked off area (Boundary) used
• to count species.

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Population

• Indirect Counting A sampling technique for
• organisms that
  move around a
• lot or are
  difficult to see
• Involves counting nest, burrows, or tracks rather
  than organisms themselves

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Population

• Mark Recapture
• Biologist traps animals in the study area and
  mark them with a colored dye.
• Then releases them
• After a period of time the researcher recaptures
  from the population and counts marked and
  unmarked individuals in the 2nd sample

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Limits to Accuracy

• Sampling Techniques are not accurate
• Involves making assumptions

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Limits to Growth Factors

• Exponential Growth Population multiplies by a
• constant
  factor at constant
• time
  intervals
• A populations ability to grow depends partly on
  the rate at which an organism can reproduce.
• Reproduction the formation of new individuals.
• Bacteria reproduce very fast
• Rabbits fast
• Panda S L O W one reason they are critically
  endangered fewer than 1000 in the wild

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Exponential Growth

• Exponential growth is usually represented by a J
  shaped curve

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Limiting Factors

• A condition that can restrict a population growth
• Space
• Normal cells stop dividing when they run out of
  room to grow
• Cancer cells do not they loose this restriction
  and continue to grow beyond available space.

Lung Cancer Cells
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Limiting Factors

• Food
• Disease
• Carrying Capacity The number of organisms in a
• population
  that the environment
• can
  maintain or carry with no net
• increase or
  decrease.
• As you near the Carrying Capacity death rate may
  increase or birth rate may decrease or BOTH
• Continues till about equal

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Carrying Capacity

• It is usually represented by an S shaped curve.

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Factors Affecting Population Growth

• Density Dependent Factors A factor that
  limits
• 
  a population more
• 
  as population
• 
  density increases.
• Availability of food
• Disease that spreads easier among organisms in a
  dense population than one that is less dense.

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Factors Affecting Population Growth

• Density Independent Factors Factors that
  limit
• 
  populations but are
• 
  unrelated to population
• 
  density.
• Extreme Weather Hurricanes, blizzards, droughts
• These conditions have the same effect on
  population regardless of its size
• Fires, floods, habitat changes like deforestation

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Factors Affecting Population Growth

• Growth Cycles
• boom-and-bust Growth Cycles
• A rapid increase in population for a period of
  time followed by a rapid decrease in number
• An uncontrolled growth cause a hormonal secretion
  making animals sterile (rodent)
• A limit to food

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Human Population Birth Rate vs. Death Rate

• History
• As with all other species, the human population
  growth depends on birth and death rates.
• Birth rates go up and death rates go down
  population goes up

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Human Population Immigration Emigration

• Immigration individuals move into an area
• from elsewhere
• Increase the population
• Emigration - individuals move out of the
• population
• Decrease a population

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Human Population

• 10,000 years ago farming replaced hunting and
  gathering
• Provided a consistent food supply
• More food increase population
• Death rates over the last few centuries have
  decreased.

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Predicting Population Growth

• Age Structure the proportion of people in
• different age
  groups
• In the U.S. age groups are balanced
• Some nations (Sweden) have a declining growth
  rate
• Low birth rates and a top heavy age structure

Blue Certified Birth Rates
Swedens Growth Rates
Red Certified Birth Rates
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Predicting Population Growth

• Species interact in Biological Communities
• Populations do not live in isolation they
  interact with other populations
• They do not live in isolation
• In some cases they compete for resources such as
  food, water, or shelter.

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Competition

• Community all inhabitants living in a
  particular area.
• From the organisms in the soil all the way up the
  food chain
• Interspecific Competition competition between
  species
• This competition within a single species limits
  the growth of the population
• This happens when two or more species rely on the
  same limited resource

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Competition

• Competition Exclusion one species succeeding
  over
• another
  when growth of both
• species
  is limited by the same
• resource
• In nature the way we can have Competitive
  Exclusion and still coexist depends on other
  factors in the ecosystem
• A predator may keep competing population below
  levels at which foods would become a limiting
  factor.

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Niches

• A unique living arrangement of an organism
  defined by its habitat, food sources, time of day
  it is most active, and other factors
• A local loss of a species due to competitive
  exclusion is likely to occur if two species have
  niches that are very similar
• Niches are rarely identical

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Predation

• When one organism eats another.
• Predator Organism doing the eating
• Prey The food, the species being eaten

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Predator Adaptation

• Both predators and prey have evolved with
  effective adaptations

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Prey Adaptations
All to avoid being eaten
Mimicry animals that look like dangerous
organisms but are not
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Plants

• Plants have poisonous chemicals and structures
  like spines and thorns.

Poison Ivy
Cactus
Rose
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Disturbances and Communities

• Communities change continuously
• Natural disturbances
• Fires
• Volcanic Eruption
• Floods
• Storms
• Droughts
• Changes not always negative
• Some plants require extremely hot temperatures
  (in a forest fire) to sprout

• Destroy Organisms
• Change resources such as shelter and water

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Disturbances and Communities

• Man made disturbances

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Disturbances and Communities

• Positive man made natural disturbances

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Human Activities / Species Diversity

• Humans have the greatest impact on communities
  world wide
• Land Clearing
• Areas cut down for lumber, planting crops,
  building (homes)

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Human Activities / Species Diversity

• Introduced Species
• Organisms that humans move from the species
  native locations to new geographic areas, either
  intentionally or accidentally

Lionfish
Melaleuca Trees