Populations

Population Density• The number of organisms in a population per unit area. • Ex. 5 snakes per square mile• Ex Tigers low density, mosquitoes high density

Growth Rate• Change in population size over time• Positive growth rate- population is increasing• Negative growth rate- population is decreasing• Zero growth rate- population size is not changing

Popu

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Time

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Positive

Negative

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Zero

Exponential Growth• Population will increase exponentially (J-curve)• Not realistic because as population increases

resources become limited. (ex food shortage)

Logistic Growth• Starts out exponential, but levels off at a certain population

size (S-curve)• Carrying Capacity- the maximum population size an

ecosystem can support, leveling off point• Ex. goldfish in a tank

R vs. K• R-selected species- reproduce fast, have many

young, develop quickly. (rabbits)• K-selected species- reproduce steadily, have few

young develop slowly. (kangaroos)

Density Dependant Factors• Factors that have a greater influence on population size as

the population increases• Generally biotic factors• Ex. competition, predation, parasitism, crowding stress

Density Independent Factors• Factors that have an impact on population size regardless of

what the population size is.• Generally abiotic factors• Ex. weather, fires, drought, human activities

SuccessionSuccession- changing of plant communitiesPrimary succession- begins with bare rock from volcanic

activity ex. Rock- moss – grass- shrubs –forest

Secondary succession- begins with soil from a previous community ex. Fire -Soil- grass- shrubs-forestPioneer community- first community (ex: moss,grass)Climax community- ending community (ex: forest)

Secondary Succession