1. Photo Credit: © Frans Lanting/Minden Pictures, Inc.*

2. Characteristics of Populations
Three important characteristics of a population are its:
geographic distribution
population density
growth rate *

3. Population Growth * Three factors can affect population size:
the number of births
the number of deaths
the number of individuals that enter or leave the population
A population can grow when its birthrate is greater than its death rate. *

4. Immigration, the movement of individuals into an area Emigration, the movement of individuals out of an area *

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Under perfect conditions with unlimited resources, a population will grow exponentially.
Exponential Growth
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As resources become less available (no more space, food, water, etc.), the growth of a population slows or stops. Called carrying capacity
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Are humans experiencing exponential or logistic growth?
Do you think humans are close to the Earth’s carrying capacity? Why?
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8. In the context of populations, a limiting factor is a factor that causes population growth to decrease.
Can be:
Density-dependent
Density-independent *

9. Density-Dependent Factors
A limiting factor that depends on population size is called a density-dependent limiting factor.
Density-dependent limiting factors include:
competition
predation
parasitism
Disease
Most impact with larger populations *

10. Competition
When populations become crowded, organisms compete for food, water space, sunlight and other essentials. *

11. Competition can also occur:
between members of same species (intraspecific)
between members of different species (interspecific)
Intraspecific Interspecific *

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Predation
Populations in nature are often controlled by predation. Or Predator – Prey Relationship
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13. Wolf and Moose Populations on Isle Royale
The relationship between moose and wolves on Isle Royale illustrates how predation can affect population growth. In this example, the moose population was also affected by changes in food supply, and the wolf population was also affected by disease.
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14. * Parasitism and Disease
Parasites can limit the growth of a population. *

15. Density-Independent Factors
Density-independent limiting factors affect all populations in similar ways, regardless of the population size.
unusual weather
natural disasters
seasonal cycles
certain human activities—such as damming rivers and clear-cutting forests *