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BIO120H1 (305)

BIO120 Online Readings #2

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Paul Thompson

Survivorship Curves 10 Introduction • Survivorship curves describe survivorship in a given cohort • Can be affected by both biotic and abiotic factors; competition and temperature Idealized survivorship curves - type 1 " high survivorship throughout the life cycle • Type II - constant proportion dying overtime • Type III - high mortality at young age • Must be done on a log scale not a linear scale Human Survivorship Patterns • Demography: study of characteristics of human populations • Developed like type I 11 Semelparity and Iteroparity Semelparity • Death after first reproduction, iteroparity is reproducing again and again • monocarpy or polycarpy -> same thing and sp and ip Dilemma and Cost of Reproduction • semelparous species produce more in one offspring than similar organisms do • this is a fecundity advantage • "Under what conditions does the increase in fecundity associated with semelparity more than compensate for the loss of potential subsequent reproductive episodes?" Theoretical Approaches 1.Demographic models: when adult survival is lower than juvenile survival; favour sp 2.Bet hedging models: when adult survival is highly variable; ip 3.Non linear pattern models: costs of reproduction happen at low levels of reproductive effort Empirical Evidence • All show semelparity is more likely in species where adult survivorship is low Synchronous Semelparity - Species " Approaching" Semelparity - Semelparity in Grain Crops 12 Causes and Consequence
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