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Lecture 6

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Department
Biology
Course
BIO120H1
Professor
Scott Browning
Semester
Fall

Description
BIOLOGY LECTURE #6 Semelparity + Iteroparity Iteroparity: - Life histories = LIVING TO REPRO REPEATEDLY - Plants = “polycarpy” Semelparity: - Life histories = D AFTER FIRST R - Plants = “monocarpy”… But term can restrictively describe plants where individual shoots die after reproducing, and not entire plant! - Short lived species: annual + biennial plants (crops) - Annuals live in habitats where S beyond growing seasons is low - Life variety of species live for many years before a single, massive, fatal repro (salmon, bamboo) - While all annuals plants are semelparous, not all perennial plants are iteroparous Dramatic life history diff = adaptive evolution Dillema + Cost of Repro: - Natural selection max’s totally lifetime repro output… SO WHY DIE RIGHT AWAY? - Semelparous species usually make more offspring in their single repro episode than closely related species do in any of theirs - When an org does not need to withhold some resources to ensure future S + R, all available sources put into a single, massive repro episode - New Q! When is semelparity better to compensate for loss of more reproduction? Theoretical Approaches: all assume a tradeoff between R + S 1) DEMOGRAPHIC MODELS: predict that when adult S is low enough (compared to young S) evol should abandon saving resources for a future R that is unlikely… favor semelparity instead! 2) BET-HEDGING MODEL: predict when adult S is highly variable, evol favor iteroparity, because it doesn’t risk putting all R effort into a single R 3) MODELS WITH NON-LINEAR PATTERNTS OF REPRO COSTS + BENEFITS: predict that semelparity should evolve when R costs (decrease in future b/c curren
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