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
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
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
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
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
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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