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Unformatted text preview: Lecture 14: Population growth II I. Geometric and exponential growth II. Logistic growth III. Density dependence IV. Metapopulations Four processes make up population growth: Births & deaths ➔ Both depend on current population size Immigration & emigration ➔ Movement among populations Four processes make up population growth: Births & deaths ➔ Both depend on current population size Immigration & emigration ➔ Movement among populations Models that we will consider in this lecture focus on births and deaths only ∆ N / ∆ t = (b  d) N b, d = per capita birth and death rates X X I. Geometric and exponential growth Populations either grow continuously or in discrete time intervals Human populations continuously grow; births (and deaths) occur throughout the year. Many organisms have discrete breeding seasons in which new individuals are added to the population seasonally. Modeling geometric population growth ∆ N / ∆ t = (b  d) N, t is a discrete time interval λ = N t+1 / N t ➔ N t+1 = λ N t N(1) = N(0) λ N(2) = N(1) λ = N(0) λ 2 N(3) = N(2) λ = N(0) λ 3 . . . N(t) = N(0) λ t Fifty California Quail were introduced onto Santa Cruz Island in 1950. One year later, there were 70 quail. Assuming this population grew geometrically, how many quail would you expect that there were in 1960? N(t) = N(0) λ t λ = 70/50 = 1.4 N(0) = 50 t = 10 N(10) = 50 (1.4) 10 N(10) = 50 (28.9) = 1445 quail in 1960 Assuming this population continued to grow geometrically, how many quail would you expect that there were in 2010? N(t) = N(0) λ t λ = 70/50 = 1.4 N(0) = 50 t = 60 N(60) = 50 (1.4) 60 = 2.92854664 X 10 10 Modeling exponential population growth ∆ N / ∆ t = (b  d) N, t is instantaneous (bd) = instantaneous rate of increase = r dN/dt = rN b = instantaneous birth rate (births / [(individuals)(time)]) d = instantaneous death rate (deaths / [(individuals)(time)]) r has the units (individuals / [(individuals)(time)]) r expresses population change on a per capita basis r affects how rapidly population size increases; r is constant  not affected by N Modeling exponential population growth To predict the number of individuals at a particular point in time,...
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This note was uploaded on 01/25/2012 for the course BILD 3 taught by Professor Wills during the Spring '07 term at UCSD.
 Spring '07
 Wills

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