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 Population size Time Population size Time Positive Negative Population size Time 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

Succession Succession- changing of plant communities Primary 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-forest Pioneer community- first community (ex: moss,grass) Climax community- ending community (ex: forest) Secondary Succession