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

Characteristics of Populations Three important characteristics of a population are its: geographic distribution population density growth rate http://www.youtube.com/watch?v=RBOsqmBQBQk *

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. *

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

Copyright Pearson Prentice Hall Under perfect conditions with unlimited resources, a population will grow exponentially. Exponential Growth Copyright Pearson Prentice Hall *

Copyright Pearson Prentice Hall As resources become less available (no more space, food, water, etc.), the growth of a population slows or stops. Called carrying capacity Copyright Pearson Prentice Hall *

Copyright Pearson Prentice Hall Are humans experiencing exponential or logistic growth? Do you think humans are close to the Earth’s carrying capacity? Why? Copyright Pearson Prentice Hall

In the context of populations, a limiting factor is a factor that causes population growth to decrease. Can be: Density-dependent Density-independent *

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 *

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

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

Copyright Pearson Prentice Hall Predation Populations in nature are often controlled by predation. Or Predator – Prey Relationship Copyright Pearson Prentice Hall *

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. Copyright Pearson Prentice Hall *

* Parasitism and Disease Parasites can limit the growth of a population. http://www.ted.com/talks/ed_yong_suicidal_wasps_zombie_roaches_and_other_tales_of_parasites *

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 *