organism population community ecosystem biosphere Population Ecology AP

organism population community ecosystem biosphere Population Ecology AP Biology

Why Population Ecology? § Scientific goal u understanding the factors that influence the size of populations § general principles § specific cases § Practical goal u management of populations § increase population size w endangered species § decrease population size w pests § maintain population size w fisheries management n AP Biology maintain & maximize sustained yield

Life takes place in populations § Population u 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

Factors that affect Population Size § Abiotic factors u u u sunlight & temperature precipitation / water soil / nutrients § Biotic factors u other living organisms § prey (food) § competitors § predators, parasites, disease § Intrinsic factors u AP Biology adaptations

Characterizing a Population § Describing a population range u pattern of Dispersion u Density of population u u #individuals per unit area 1970 1966 1964 1960 1965 1961 Equator 1958 1951 1943 1937 1956 1970 Immigration from Africa ~1900 range AP Biology

Population Range § Geographical limitations u abiotic & biotic factors § temperature, rainfall, food, predators, etc. u habitat adaptations to polar biome AP Biology adaptations to rainforest biome

Population Dispersion § Spacing patterns within a population Provides insight into the environmental associations & social interactions of individuals in population clumped Why clump? random Why uniform? AP Biology uniform Why random?

Population Size § Changes to population size can occur by: AP Biology

Population Growth Rates § Factors affecting population growth rate u sex ratio § how many females vs. males? u generation time § at what age do females reproduce? u age structure § #females at reproductive age in cohort? AP Biology

Why do teenage boys pay high car insurance rates? Demography § Study of a populations vital statistics and how they change over time § Life tables, Age Structure Diagrams and Survivorship Graphs females AP Biology males What adaptations have led to this difference in male vs. female mortality?

Age structure § Relative number of individuals of each age What do these 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) 100 1 0 AP Biology 25 I. High death rate in post-reproductive years II. Constant mortality rate throughout life span Oyster (type III) 10 What do these graphs tell about survival & strategy of a species? 50 75 Percent of maximum life span 100 III. Very high early mortality but the few survivors then live long (stay reproductive)

Trade-offs: survival vs. reproduction § The cost of reproduction u To increase reproduction may decrease survival: (think about…) § age at first reproduction § investment per offspring § number of reproductive cycles per lifetime § parents not equally invested Natural selection § offspring mutations favors a life history § Life History determined by costs that maximizes lifetime and benefits of all adaptations. reproductive success AP Biology

Reproductive strategies § K-selected u u u late reproduction few offspring invest a lot in raising offspring § primates § coconut § r-selected u u u K-selected early reproduction many offspring little parental care § insects § many plants AP Biology r-selected

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. ”

Survivorship Curves with Reproductive Strategy 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

Population Growth Rate Models § Exponential growth Rapid growth u No constraints u § Logistic growth Environmental constraints u Limited growth u AP Biology

Population Growth Math § Change in population = Births – Deaths § § § Per capita birth rate = b Per capita death rate = d # of individuals = N Rate of population growth (r) = b – d Survivorship = % surviving Ex: If there are 50 deer in a population, 13 die and 27 are born the next month. What is the population size the following month? u (Answer: 27 -13 = 14, so new population is 64) Ex: What is the birth rate for the deer? #Births/N = b w Answer: 27/50 =. 54 w Death rate (d) = 13/50 =. 26 Ex: What is the rate of growth for the deer? r =. 54 -. 26 =. 28 AP Biology

Exponential Growth (ideal conditions) § No environmental barriers § Growth is at maximum rate d. N/dt = rmax. N N = # individuals Rmax = growth rate AP Biology

Exponential Growth § Characteristic of populations without limiting factors u introduced to a new environment or rebounding from a catastrophe Whooping crane coming back from near extinction AP Biology African elephant protected from hunting

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

Logistic Growth Equation d. N/dt = rmax. N(K-N)/K K = carrying capacity of population Ex: If a population has a carrying capacity of 900 and the r max is 1, what is the population growth when the population is 435? 1 x 435 (900 -435)/900 = 224 What if the population is at 850? What if it is at 1010? Explain the results of each problem. AP Biology

u varies with changes in resources What’s going on with the plankton? AP Biology 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 10 8 6 4 2 0 1915 1925 1935 Time (years) 1945 500 400 300 200 100 0 0 10 20 30 40 Time (days) 50 60

Changes in Carrying Capacity § Population cycles u predator – prey interactions K K AP Biology

Regulation of population size marking territory = competition § Limiting factors u density dependent § competition: food, mates, nesting sites § predators, parasites, pathogens u density independent § abiotic factors w sunlight (energy) w temperature w rainfall APcompetition Biology for nesting sites swarming locusts

Introduced species § Non-native species (INVASIVE) u u transplanted populations grow exponentially in new area out-compete native species reduce diversity examples § African honeybee § gypsy moth AP Biology kudzu

Zebra mussel ~2 months u u AP Biology ecological & economic damage u reduces diversity loss of food & nesting sites for animals economic damage

Purple loosestrife 1968 1978 u u AP Biology reduces diversity loss of food & nesting sites for animals

Any Questions? AP Biology 2007 -2008