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organism population community ecosystem biosphere Population Ecology AP Biology Life takes place in populations Population group of individuals of same species in same area at same time rely on same resources interact interbreed AP Biology Ecology: What factors affect a population? Population Characterizing a Population Describing a population population range pattern of spacing density size of population 1970 1966 1964 1960 1965 1961 Equator 1958 1951 1943 1937 1956 1970 Immigration from Africa ~1900 range AP Biology density Population Range Geographical limitations biotic & abiotic factors food, predators, temperature, rainfall, etc. habitat adapted to polar region AP Biology adapted to rainforest Population Spacing Dispersal patterns within a population Provides insight into the environmental associations & social interactions of individuals in population clumped random AP Biology uniform Clumped Pattern AP Biology (most common) Uniform May result from direct interactions Clumped patterns between individuals in the population territoriality AP Biology Population Size Changes to population size adding & removing individuals from a population birth death immigration emigration AP Biology Population growth rates Factors affecting population growth rate sex ratio how many females vs. males? generation time at what age do females reproduce? age structure how females at reproductive age in cohort? AP Biology Age structure Relative number of individuals of each age What do the data imply about population growth in these countries? AP Biology Survivorship curves Graphic representation of life table The relatively straight lines of the plots indicate relatively constant rates of death; however, males have a lower survival rate overall than females. Belding ground squirrel AP Biology Survivorship curves Generalized strategies Survival per thousand 1000 Human (type I) Hydra (type II) What do these graphs tell about survival & strategy of a species? I. High death rate in post-reproductive years 100 II. Constant mortality rate throughout life span Oyster (type III) 10 1 0 25 50 75 Percent of maximum life span AP Biology 100 III. Very high early mortality but the few survivors then live long (stay reproductive) Trade-offs: survival vs. reproduction The cost of reproduction increase reproduction may decrease survival investment per offspring reproductive events per lifetime age at first reproduction AP Biology Natural selection favors a life history that maximizes lifetime reproductive success Trade offs Number & size of offspring vs. Survival of offspring or parent r-selected K-selected “Of course, long before you mature, AP Biology most of you will be eaten.” Life strategies & survivorship curves K-selection Survival per thousand 1000 Human (type I) Hydra (type II) 100 Oyster (type III) 10 r-selection 1 0 25 50 75 Percent of maximum life span AP Biology 100 Exponential growth rate Characteristic of populations without limiting factors introduced to a new environment or rebounding from a catastrophe Whooping crane coming back from near extinction AP Biology African elephant protected from hunting Regulation of population size Limiting factors density dependent food supply, competition predators disease density independent abiotic factors sunlight temperature rainfall AP Biology Introduced species Non-native species transplanted populations grow exponentially in new area out-compete native species loss of natural controls lack of predators, parasites, competitors reduce diversity examples African honeybee gypsy moth gypsy moth zebra mussel purple loosestrife AP Biology kudzu Zebra mussel ~2 months AP Biology ecological & economic damage Purple loosestrife 1968 1978 AP Biology reduces diversity loss of food & nesting sites for animals Logistic rate of growth Can populations continue to grow exponentially? Of course not! no natural controls K= Carrying capacity What happens as N approaches K? AP Biology effect of natural controls varies with changes in resources What’s going on with the plankton? AP Biology 10 8 6 4 2 0 1915 1925 1935 1945 Time (years) Number of cladocerans (per 200 ml) population size that environment can support with no degradation of habitat Number of breeding male fur seals (thousands) Carrying capacity Maximum 500 400 300 200 100 0 0 10 20 30 40 Time (days) 50 60 K-selection density dependent selection for traits such as competitive ability and efficient resource utilization late reproduction few offspring but invest a lot in raising offspring primates coconut r-selection density independent selection for traits that maximize population growth such as increased fecundity (fertility) and early maturity early reproduction many offspring but little parental care insects many plants AP Biology Changes in Carrying Capacity Population cycles AP Biology predator – prey interactions