Download Lecture Slides on The Power of Exponential Growth | ZOOL 468 and more Study notes Zoology in PDF only on Docsity! 1 Population Growth II. Density Dependence and Regulation The Power of Exponential Growth Tale of the tiny tiny bacterium: Some bacteria (e.g., E. coli) divide (by fission) every 20 minutes in an optimal environment If you started with a single bacterial cell, and it constantly reproduced at this rate, how many bacteria would there be after 2 days? 2 days = 2,880 min = 144 generations N144 = N0λ144 = 1 x 2144 = about 1043 cells How much would all those cells weigh? A single bacterial cell weighs about 10-13 g (1 ten-trillionth of a gram) 1043 cells x 10-13 g per cell = 1030 g So what? The earth weighs about 6x1027 g! This colony of bacteria would weigh 170 times more than the earth! The 2nd Law of Population Growth No population grows exponentially for very long. Population growth must be density dependent Population Dynamics As a population gets large, immigration and/or births go down emigration and/or mortality go up Population Immigration + Births + Emigration - Deaths- Density Dependent Population Growth = birth rate – death rate (per capita) In general, we expect the population will decline if it gets very large. That is: dN/Ndt < 0 for very large N Ndt dNPer capita population growth rate: Density Dependent Population Growth N Per capita growth rate 0 0 + - to infinity >> 2 Density Dependent Population Growth N 0 0 + - to infinity >> Per capita growth rate Johnson County, IL 0 10 20 30 40 50 60 70 80 1975 1980 1985 1990 1995 2000 2005 Time D ee r / S qu ar e M ile -0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0 10 20 30 40 50 60 70 Deer / Square Mile Pe r C ap ita G ro w th R at e Density Dependent Population Growth N 0 0 + - to infinity >>N* equilibrium: population density at which population growth stops Per capita growth rate Density Dependent Population Growth N 0 0 + - to infinity >>N* stable equilibrium: equilibrium that population density will return toward if density is a little bit higher or lower. Population is regulated. Per capita growth rate Density Dependent Population Growth N 0 0 + - to infinity >>N* unstable equilibrium: equilibrium that population density will move away from if it is a little bit higher or lower Per capita growth rate
