Changes to Populations
4 factors that effect
the size of a population
• Increase Population
– 1) Birth
– 2) Immigration (entering a population)
• Decrease Population
– 3) Death
– 4) Emigration (leaving a population)
Is the population
increasing or decreasing?
• When Immigration + Births are greater
than Death + Emigration:
• Populations Increase
• When Immigration + Births are equal to
Death + Emigration:
• Population remains stable
• When Immigration + Births are less than
Death + Emigration:
• Populations Decrease
Limiting Factor
• Something that prevents the growth
of a population
• What would happen without limiting
factors?
Reflection
• Think of an example where an organism
does not have enough limiting factors.
• What is the organism, how does this affect
the habitat around that organism?
Carrying Capacity (k)
• the maximum population a species can
maintain in a certain area without
damaging the ecosystem
Population can stabilize at K
Populations can crash if #s go
above K
• 29 introduced in 1944
• More than 6,000 by 1963
• Down to 42
Seasonal Fluctuations
Limiting Factor #1:
Space
• Territorial Animals need a large
amount of space
• Loss of Habitat causes the decline of
many species
Bluebirds
• Loss of trees/wooden posts caused a
huge decline
• Between 1935-1985 numbers declined by
90%
Limiting Factor #2
Food and Water
• Leads to death via dehydration,
starvation
• Some animals will emigrate
• Organisms that rely on one type of
food are severely affected
Darwin’s Finches
• Drought caused a loss in seed numbers
• Finch numbers declined from 1400 to 200
Snowshoe Hare and Lynx
Limiting Factor #3:
Climate and Weather
• Temperature changes can affect
plants and animals
• Floods and storms can cause
death/destruction of habitat
Mosquito Populations
• Mosquitoes breed in
standing water
• Rainfall creates puddles
of standing water
• Culex tarsalis-WNV
Coffee Habitat
Impact of Temperature Rise on Robusta Coffee in Uganda. Developing countries,
whose economies often rely heavily on one or two agricultural products, are
especially vulnerable to climate change. This graphic shows that with an increase of
only 2 degrees Celsius, there would be a dramatic decrease in the amount of land
suitable for growing Robusta coffee in Uganda.
Limiting Factor #4:
Cover
• Protection from predators
• Protection from weather
Limiting Factor #5:
Increase Predation
• An increase in the number of
predators to an area
House Cats!
• Predicted that in one year
house cats kill 1 billion
songbirds!
Limiting Factor #6:
Disease
• Spread quickly through high density
populations
• Can devastate populations with low
genetic diversity
West Nile Virus
• Mosquito born disease
• 5,697 crows reported dead in NYS in 1999
Limiting Factor #7:
Light
• Plants that cannot tolerate too much
or too little light can be affected
Tree Growth and Shade
• Aspen Pine Poplar = intolerant,
will dominate young forests
• Beech, fir, hemlock, maple =
tolerant will dominate older forests
Limiting Factor #8:
Human Presence
• Close proximity to humans causes
some species to emigrate
• Other species thrive
Competition
• Limiting factors lead to competition
among organisms for available
resources
• A loss in a limiting factor can
contribute to a decline in populations
• Increased due to exotic species
Exotic Species-Introduced species not
native or endemic to the area in question
(alien species).