Populations Population Density The number of organisms in
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
e v i it s o P Time Ne g ati ve Time Population size 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 • • Growth Rate Zero Time
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- changing of plant communities Primary succession- begins with bare rock from volcanic activity ex. Rock- moss – grass- shrubs –forest
Secondary Succession 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)
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