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Populations & Ecological Succession
Chapters 4 & 5
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What is a population? A group of organisms of the same species that live in the same area.
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3 Major Characteristics of Populations
1) Geographic distribution 2) Density 3) Growth Rate
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Geographic Distribution AKA “range”
Where the population is located.
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Density How closely the individuals live to one another.
The lower the density, the more personal space each individual has.
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Growth Rate How quickly the size of the population is changing. Can be
getting bigger or smaller
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What causes changes in population size?
Increase in size Births Immigration (In-migration) Decrease in size Death Emigration (Exit – migration)
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Common Growth Patterns
There are two very common patterns of growth. Exponential Logistic
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Exponential Growth “J-shaped” growth
Growth starts out slowly, then skyrockets. Occurs only in “perfect” conditions: No disease No predators Unlimited space Unlimited food and water
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Logistic Growth “S-shaped” growth
Starts out like exponential growth, but eventually levels out. Growth pattern of most real populations.
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Carrying capacity (K) The maximum number of individuals of a particular species that the environment can support. Determines the point at which a population stops growing.
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Limiting Factors Anything that causes a population to stop growing.
Can be: a shortage of food, water, nutrients or shelter.
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Density-Dependent Factors
Things that only slow/stop population growth when there is a high density. This is because you now have many organisms living close to one another. Disease Predation Parasites Competition (food, water, shelter, mates, etc.)
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Density-Independent Factors
Things that slow any population’s growth, regardless of density. Natural disasters (tornados, hurricanes, earthquakes, etc.) Seasonal changes (winter freeze) Human activity (Pollution, deforestation, global warming, etc.)
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