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Lecture 6

Biology Lecture 6 Article 3.docx

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Scott Browning

BIOLOGY LECTURE #6: Survivorship Curves - Ecologists use survivorship curves to visualize how # of individuals in pop drops off with time - Choose cohort, collect data on when each person dies in pop - Cohort: group of individuals of same species in same pop born @ same time - Compares generations, populations, different species - Describe survivorship in a cohort: if cohort similar thru time, considered to describe survivorship of pop - Besides constraints of general life history strategy, shape is affected by biotic + abiotic factors (competition and temp) Plot # survivors per 1000 individuals on a log scale, 3 basic patterns emerge: TYPE 1: high survivorship through life cycle TYPE 2: constant proportion of individuals die over time TYPE 3: high mortality at young ages Most real pops mix of 3 types Ex) Juveniles for some species Type 3, followed by type 2 for long lived adults HAVE TO BE ON LOG, WILL LOOK DIFF ON LINEAR - log = per capita effects instead of actual # - Ex) type 2 = constant @ dying each period: start with 1000 ppl, first period 40% live, so 400 left, second, 40% of 400 live, so 160 left : LINEAR = NOT A STRAIGHT LINE, big drop when 60
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