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Ch 52 Understanding Population Growth Organism POPULATION POPULATION POPULATION Community Ecosystem 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… • Births, deaths, immigrants, and emigrants Question: How can you get the growth rate of a population to slow down? Give reasonable solutions! Make a list with your partner Reproductive Strategies Exponential Growth= r-selected AKA J Curve Occurs when Pops Doubling OverTime 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…. R-selected Species 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 Logistic Growth: K-selected AKA S Curve 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.) 1) 2) 3) 4) 5) K-selected Species Fewer, larger offspring High parental care Most offspring reach reproductive age Lower population growth rate Specialists Density-Dependent Factors • Increasing pop size leads to less available resources limiting pop growth • DD factors: competition, predation, disease, poisoning…all increase when pops grow w/in limited space. Density-Independent Factors • Limits placed on pop growth (not due to space issues) • Ex: Natural disasters or 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