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Understanding Population Growth Population Ecology •Deals with #’s of indiv. in a species •How and why their numbers are the way they are Population Density # of indiv. of a species unit of area • A better way to describe size of a pop. Manhattan, New York City 70,595 people per sq. mile Dhaka, Bangladesh: 2 7 million in 59 mi Crowded Much?!? Competition Spread of Disease Lack of Natural Resources Lack of Jobs Populations Change in Size… Dependent on: • Birth rate (b ) • Death rate (d ) • Immigration (i ) • Emigration (e ) Question: How can you get the growth rate of a population to slow down? Give reasonable solutions! Make a list with your partner Growth Rate How fast is pop. growing? Rate of change ( r ) = [birth rate (b)-death rate (d )]/1000 r = 40 - 20 1000 1000 r =0.04 - 0.02 x 100 = 2% per year Growth Rate of a Pop. r = (b - d ) + (i - e ) Total Population (1000) • Use total pop. when given. If prob. states per 1000, use 1000. Population Momentum • Pop. growth that occurs even if levels of childbearing immediately declined to replacement level Older people still have babies Doubling Time • Time for a pop. w/ a stable growth rate to double in size Doubling Time = td = 70 r (%) Practice: With a 2 % growth rate, the world population will double…. Doubling Time Population Reproductive Strategies J-curve (Exponential) = r-selected Reproductive Strategies Exponential Growth= r-selected Reproductive Strategies S-curve (Logistic) = K -selected Reproductive Strategies S-curve (Logistic) = K -selected Carrying Capacity K = carrying capacity (Max. pop. of a particular species that a habitat can support over a given time period. Carrying Capacity • May vary by: – Seasons – Changes in environment (fire, storm, etc.) R Selected vs K Selected • R-selected 1) Many small offspring 2) Little/no care of offspring 3) Most offspring die before reaching reproductive age 4) High population growth rate 5) Generalists • K-selected 1) Fewer, larger offspring 2) High parental care 3) Most offspring reach reproductive age 4) Lower population growth rate 5) Specialists What Advantages do R Selected Species have? What about K? Which would you rather be??? Density-Dependent Controls • Competition for resources due to land issues • Ex: Predation, Parasitism, Disease, Poisoning Density-Independent Controls • Controls on Population not due to space issues • Ex: Natural disasters • Ex: Severe weather Survivorship •Proportion of a pop. to survive to breeding age •Type I= Late loss: K-strategists. •Type II = Constant loss: intermediate reproductive strategists •Type III = Early loss: R-strategists