Transcript Populations and Communities Population Growth

Populations and Communities
Population Growth
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Population: group of the same species that
live in the same area in a given time.
If living conditions are IDEAL, growth will be
exponential… there is nothing to inhibit growth!
In reality – exponential growth is not
sustainable – there will always be a limiting
factor
– Can you think of an exception to this??
Logistic Growth
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Real growth curves will eventually reach a
steady state = the carrying capacity of the
environment for that species
A population cannot continue to grow forever
because of:
– Lack of food
– Overcrowding (lack of space)
– Competition within the population
Factors that control population
growth
Density-Dependent
Limiting Factors:
Factors that affect
large and/or
overcrowded
populations
DensityIndependent
Limiting Factors:
Weather and natural
occurrences that
have nothing to do
with the density of a
population
Density-Dependent Limiting
Factors
1. Competition (for food, space, water,
sunlight…)
 Remember: if two species compete for the
same niche, one will lose. Natural selection
allows for both species to survive if one
species evolves and adapts to a different
niche
Density-Dependent
Limiting Factors
2. Predation
 Predator-prey relationships keep both
populations in balance
 As prey pop. increases… the predator pop. will
increase… as predator pop. increases, prey
pop. will decrease… as prey pop. decreases,
predator pop. will decrease… this allows prey
pop. to increase… and the cycle begins again
Density-Dependent Limiting
Factors
3. Parasitism
 Parasites: live off host organism without killing it
 Thrive best in large, stressed populations
(stressed populations are susceptible to
disease)
 More easily spread in overcrowded populations
Density-Dependent Limiting
Factors
4. Crowding and Stress
 Smaller area per animal in which to find home
and/or hunt for food
 Crowded populations tend to fight
Interactions within and between
Communities
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Community: all the populations that live
together within an area.
– They live together – therefore they interact
Interactions include:
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Competition
Predator/prey relationship
Symbiosis
Ecosystems are Connected!
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Ecosystems are studied as isolated systems
BUT
All ecosystems are interconnected by
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Proximity
Migratory patterns
Atmosphere (wind patterns)
Hydrology of Earth (groundwater flows, rivers)
THE END!