Transcript Population notes.

Populations
Populations = groups of individuals of the
same species living in the same place
• Individuals within a population:
▫ occupy the same general area
▫ rely on the same resources
▫ influenced by the same environmental conditions
Population Dynamics
• Three Key Features of Populations
▫ Size
▫ Density
▫ Dispersion
Three Key Features of Populations
1. Size: number of individuals in an area
Population Size Depends on 4 Factors:
Natality – number of births (increase population)
Mortality – number of deaths (decrease population)
Immigration – number of individuals moving into an area
(increase population).
Emigration – number of individuals moving out of an area
(decrease population).
Population Change
• Population size increases and decreases over
time.
• population change = (natality + immigration)
– (mortality + emigration)
Population Limiting Factors
• Density-dependent factors
▫ Any factor in the environment that depends on the
number of members in a population per unit area
▫ Usually biotic (living) factors
▫ These include





Predation
Disease
Parasites
Competition (for mates, resources)
Food shortage
Population Limiting Factors
• Density-independent factors
▫ Factors that limit population size, regardless of
population density.
▫ These are usually abiotic (non-living) factors
 Natural weather events: Drought, flooding, extreme
heat or cold, tornadoes, hurricanes, fires
 Pesticides
 Destruction of habitat
 Pollution
Three Key Features of Populations
2. Density: measurement of population per
unit area or unit volume
Pop. Density = # of individuals ÷ unit of space
Three Key Features of Populations
3. Dispersion: The pattern
of spacing a population
within an area
▫
3 main types of dispersion



▫
Clumped
Uniform
Random
The primary cause of
dispersion is resource
availability
Clumped Distribution
• Most common pattern in nature.
• Result of unreliable resources.
▫ Individuals of the population will clump around
resources.
▫ Also found among many animals to aid predation
or fend off predators.
Uniform Distribution
• Uniform Distribution = The tendency for
populations to be found evenly distributed about
their habitat.
• Individuals use the resources found immediately
around them, and spread out as to use all of the
available resources
• Happens because of interactions between individuals
in the population.
Random Distribution
• Uncommon in nature.
• Is the tendency for populations to be found randomly
about their habitat.
• This pattern occurs in the absence of strong attraction
or repulsion from another individual.
• Animals
▫ Able to move about their habitat, so that at any given
instance, they can be found anywhere about their
environment.
• Plants
▫ Spores are randomly distributed by the wind
▫ Usually have the ability to live anywhere in a given
habitat.
Carrying Capacity
• Carrying Capacity = the size of a population that
can live indefinitely using the resources available
where that population lives.
Factors that Affect Carrying Capacity
1. Materials and energy – populations are
limited by the amount of usable energy from
the sun and the supply of water, carbon, etc.
2. Food chains – populations are
limited by food supply and their
predators.
3. Competition – each species shares the same
needs. Competition for food, water, mates,
space, etc. can limit population growth.
Intraspecific competition – among members
of the same species
Interspecific competition – between different
species
4. Density – species have differing needs for
space. This determines an organism’s
population density. Overcrowding can
increase stress, promote disease, increase
aggression, neglect of offspring, etc.
Death rates increase and birth rates decrease
so that the population goes down.
Alien and Invasive Species
• Alien species – a species that is accidentally or
deliberately introduced into a new location
• Invasive species – a species that can take over
the habitat of native species
Deer: Predation of Starvation
• Graphing Exercise
Human Population Growth
• http://video.nationalgeographic.com/vid
eo/the-magazine/the-magazinelatest/ngm-7billion/
World population density- 7 billion
http://www.worldometers.info/world-population/
Graphing Question (submit response)
•Does the Human
Population have a
carrying capacity?