Population-Ecology

Population Characteristics Geographic Distribution/Range- describes area inhabited by population of organisms Population Density- number of individuals per unit area; varies depending on species and its ecosystem Growth rate- change in number of organisms/size of population over time Age structure diagrams

Factors affecting Population size Number of births Number of deaths Emigration-# leaving population Immigration-# entering population

Growth Charts Direct/Linear- rate of population growth constant over time Exponential- (J-shape curve)- Rate of growth increases with time (note: ideal conditions/unlimited resources) Logistic-(S-shaped curve)- realistic way of expressing growth-limiting factors –Carrying capacity- largest number of organisms a given environment can support

Limits to growth Limiting factors- factors causing population growth to decrease –Density-Dependent factors- affect population more strongly as population increases in size –Examples: Competition, Predation, Disease, Famine –Density-Independent- same impact no matter population size –Examples: Unusual weather, Natural disaster, Seasonal cycles, Human activities

Age Structure Diagrams Deals with human population growth Size of human population tends to increase with time; Exponential growth Demography- scientific study of human population; how human population changes with time Birth rates, Death rates and age structure diagrams help predict why some countries have high growth rates and other countries grow more slowly

Age Structure Diagrams Demographic transition- dramatic changes in birth/death rates Countries modernize and advances in nutrition, sanitation and medicine allow more children to survive to adulthood First, graph shows a lowering of the death rate (begin transition)

Age Structure Diagrams Next, birthrates remain high (B>D) and population grows exponentially Countries continue to modernize, families begin to have fewer children and birthrate begins to decrease/population begins to slow down and population growth stops (end of transition)

Age Structure Diagrams Predict future growth How many people of different ages (and genders) make up population U.S.- equal number of people across ages/gender; steady growth/slow Nigeria- far higher number of young vs. old people; foresee large population growth/double over next 30 years