2 - Demography - study of how populations grow Survivorship...

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Demography - study of how populations grow Survivorship - survival schedule in a population 1. What causes mortality? - large fraction of most populations are lost to: - predation - disease - starvation - physical factors (eg. weather) - old age (uncommon) 2. What determines life - span? - organisms have wide range of life-span eg. bacteria - 10 3 sec trees - 10 3 years - life-span of some taxa is size related ? eg. terrestrial mammals - average life - span increases with size - exceptions – bats 3. What is the average life - span of an individual in a population? - few individuals reach maximum life span - maximum possible life - span unimportant
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Survivorship schedule can be studied from survivorship curves Y - axis: logarithm of number or fraction of survivor X - axis: age Type I : death mainly at old age - rare in nature Type II : diagonal - probability of death the same at all ages - found in many birds Type III : mortality high at early age, then drop to low level at old age - most common pattern in nature - found in many invertebrates, plants & marine organisms
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Fecundity is the number of young produced by females of different ages 1) Reproduction has costs Trade-offs : benefit from one process must be bought at the expense of another - females must choose between quantity & quality - reproduction requires energy - female can lay large number of small eggs or a few large eggs - strategy is to leave a many surviving offspring as possible
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Two different reproductive strategies: 1. Prodigal & prudent strategy - species that are often in exponential growth - produce large number of seeds, eggs, or larvae (Prodigal ) - high disperal ability - high mortality among young - high survival rate among individuals that manage to find suitable habitats - Type III survivorship curve - some of these species are Semelparous - ‘semel’= once 2) Prudent strategy - Species living near K - produce few offspring - high energy investment per offspring - high survival rate even at early stages - Type II or Type I survivorship curve - some of these species are Iteroparous - ‘ iterate’= repeat (reproduce several times or repeatedly over entire life)
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Cost of reproduction - increase in current allocation to reproduction may leads to : 2. decrease in future reproduction
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Female red deer on island of Rhum in Scotland - milk hinds (females that raised calves the previous year) have: - lower physical condition - higher mortality especially if old - lower probability of reproducing next year - fecundity is very sensitive to density dependent factors
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Longevity of male fruit-flies is reduced by courtship activity
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Fecundity is age/environment related eg. fecundity of great tits Parus major in Wytham Wood, England - fecundity measured as clutch size - mean fecundity highest among 2-year olds - mean fecundity varies from year to year
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r & K selection - organisms are selected to maximize life-time reproductive output - strategies depend on environment
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This note was uploaded on 09/26/2010 for the course ENG ELT1106 taught by Professor Mei during the Spring '07 term at 한동대학교.

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2 - Demography - study of how populations grow Survivorship...

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