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Population ecology is concerned with:
- Changes in population size
- Factors that regulate population over time
- Essentially, how and why populations change
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Population
- A group of individuals of a single species that occupy the same general area
- Described by the number and distribution of individuals
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Individuals in a population:
- Rely on the same resources
- Are influenced by the same environmental factors
- Are likely to interact and breed with one another
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Population ecology
The study of how and why populations change
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Cause of variation in population sizes
- A population increases through birth and immigration
- Death and emigration out of an area decrease the population
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Population dynamics
The interactions between biotic and abiotic factors
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Population density
- The number of individuals of a species per unit area or volume
- Ecologists use a variety of sampling techniques to estimate population densities
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Examples of population density:
- The number of oak trees per square kilometer in a forest
- The number of earthworms per cubic meter in forest soil
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Important population variables
Density and dispersion patterns
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Dispersion pattern of a population
Refers to the way individuals are spaced within their area
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Dispersion patterns can be:
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Clumped pattern
Individuals are grouped in patches
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Uniform pattern
Individuals are equally spaced in the environment
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Random pattern
The individuals in a population are spaced in an unpredictable way
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Life tables
Track survivorship over the life span of individuals in a population
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Survivorship curves
- Plot the proportion of individuals alive at each age
- Type 1, Type 2, and Type 3
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Exponential growth model
- The rate of population increases under ideal conditions
- Calculated using the equation G=rN; G is the growth rate, N is the population size, r is the per capita rate of increase
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Logistic growth model
- This growth model takes into account limiting factors
- Limiting factors are environmental factors that restrict population growth
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Boom-and-bust cycles
- Food shortages
- Predator-prey interactions
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Age structure diagram
Reveals a population's growth trends
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US Census Bureau projection
- 8 billion people within the next 20 years
- 9.5 billion by the mid-21st century
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Ecological footprint
Helps understand resource availability and usage
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