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Survivorship Curves and Semelparity Notes.docx

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Paul Thompson

Survivorship Curves Notes:  Used to visualize how number of individuals in a pop decreases with time o Need to identify a cohort (group of individuals of some species in same pop and born at same time)  Used to compare generations, populations and different species  Describes the survivorship of the cohort (but survivorship can be different in varying environments) o Shape of graph can be affected by abiotic and biotic factors (competition, temp) 3 Basic Patterns: (curves are plotted on a log scale – linear scale will look different)  1. Type I survivorship – high survival throughout entire life cycle; most individuals die of old age (occurs in stable environments with intense competition)  2. Type II – constant mortality rate over time regardless of age (rodents, adult birds, turtles)  3. Type III – high mortality at young ages; after initial period, survival becomes constant; little parental care (fishes, seeds, marine larvae, octopus) Human Survivorship:  Demography – study of characteristics of human pops (births, deaths, growth rates) o Most countries have Type I survival  Affected by diseases and wars or even medicines too Semelparity and Iterparity Notes:  Semelparity – death after reproduction o Includes annual and biennial plants (grain crops, wheat, herbaceous vegetables) and certain invertebrates (spiders)  some marsupial animals too o Annuals produce 2.5x the seeds as iteroparous individuals  Iteroparity – live to reproduce numerous times o Not all perennial plants are iterparous o Side Note – terms monocarpy and polycarpy used in plants – shoots die after reprod
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