Lec9_08BIEB102

Lec9_08BIEB102 - BIEB Lecture 9: Age-structured population...

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BIEB Lecture 9: Age-structured population I. Geometric growth II. The importance of age structure III. Factors contributing to extinction a. small population size b. habitat destruction and fragmentation c. overexploitation d. introduced species
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Some organisms (e.g., humans, bacteria) reproduce continuously. But many other organisms exhibit discrete reproductive periods. These populations increase by geometric growth. Ricklefs Figure 14.4 I. Geometric growth
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I. Geometric growth Modeling geometric population growth 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 . . . .
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I. Geometric growth Modeling geometric population growth 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 . . . . t
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I. Geometric growth Exponential and geometric growth can describe the same data. Geometric and exponential growth are related: λ = e r and ln λ = r Ricklefs Figure 14.6
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II. The importance of age structure An assumption of models discussed so far … … birth and death rates do not vary with age . When birth and death rates vary with age, their contributions to population growth must be calculated separately. Populations with different age structures *, but identical birth and death rates at corresponding ages, grow at different rates - at least for awhile. Life tables can be constructed to calculate the growth rate of populations in which birth and death rates vary with age. * age structure = proportion of individuals in each age class
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Environmental variation affects age structure of populations. Changes in environmental conditions can affect yearly level of recruitment. e.g., 1944 whitefish cohort in Lake Erie Population growth depends: (1) on past conditions, which determine age structure Ricklefs Figure 15.7 II. The importance of age structure
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Environmental variation affects age structure of populations. e.g., age distribution of trees harvested in Pennsylvania in 1928 Ricklefs Figure 15.8 Shade tolerant Shade intolerant II. The importance of age structure
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A hypothetical example for an organism with discrete generations and for which birth and death rates vary with age s x = survival = probability of surviving from one breeding period to the next b x = fecundity = number of offspring produced by each age class n x = number of individuals in each age class II. The importance of age structure
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Birth & death schedule can be used to project population into future Number surviving to next breeding season: n x (t) = n x-1 (t-1) s x Number of newborns: n o (t) = Σ n x (t) b x II. The importance of age structure
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II. The importance of age structure Geometric rate of population growth: λ = N(t+1) / N(t) If age-specific birth and death rates remain unchanged, the population assumes a stable-age distribution .
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Geometric growth rate fluctuates erratically, but converges on a specific
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Lec9_08BIEB102 - BIEB Lecture 9: Age-structured population...

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