19.4 - Population Size GIS Biology Department Definitions Population: ● a group of organisms of one species, living in the same area, at the same time Community: ● all of the populations of different species in an ecosystem Ecosystem: ● a unit containing the community of organisms and their environment, interacting together 3 Definitions 4 Factors that affect population growth rate 5 Food Supply ● ● An abundant food supply increases population growth as organisms have enough energy and nutrients to survive and reproduce. Limited food supply can cause starvation, reduced reproduction rates, and increased mortality, slowing population growth or causing a decline. Competition ● ● Intraspecific Competition (within the same species): Reduces population growth as individuals compete for limited resources like food, mates, or territory. Interspecific Competition (between different species): Can decrease population growth of one species if it is outcompeted by another for resources. Factors that affect population growth rate cont’d 6 Predation ● ● Predators control prey population sizes by feeding on them, which can reduce prey numbers and slow population growth. If predators are removed, prey populations may grow rapidly, potentially leading to overpopulation and resource depletion. Disease ● Disease outbreaks can reduce population growth by increasing mortality and lowering reproductive success, especially in dense populations where diseases spread more easily. Sigmoid Population Growth Curve 7 Sigmoid Population Growth Curve 8 Explaining the Sigmoid Curve A - Lag phase: ● ● ● ● ● ● ● small starting population organisms not sexually mature limited food supply high incidence of diseases high predation more competition for resources extreme weather conditions B - Log phase: ● ● ● ● ● ● Birth rate greater than Death rate (BR > DR) organisms sexually mature abundant food supply less incidence of diseases low predation less competition for resources 9 Explaining the Sigmoid Curve C - Stationary phase: ● ● ● ● ● ● ● Br = DR Food supply is limiting high incidence of diseases high predation more competition for resources limited space availability accumulation of toxic waste D - Death phase: ● ● ● ● ● ● ● DR > BR Food supply is limiting high incidence of diseases high predation more competition for resources limited space availability accumulation of toxic waste 10 Assessment Assessment Assessment Assessment Assessment Assessment Assessment Assessment Assessment Assessment Assessment Assessment Assessment Assessment
