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Life Tables Introduction A life table is a quantified summary of a group of individuals followed over time referred to as a cohort Characteristics of the population including fecundity mortality and survivorship can be quantified Krebs 1989 This allows a researcher to make comparisons between two populations For example one could compare the populations of California and Louisiana during a given time period Then a researcher could analyze what factors such as habitats or resources may have created differences between the two populations A cemetery is a great resource for constructing a life table One can easily gather quite a bit of data about an individual including years of birth and death age and sex Using deceased individuals also eliminates bias created by studying a live population in which certain age groups are harder to study Age determination is difficult for many species and if age is not measured very carefully the resulting life table can be very unreliable Begon et al 1996 Data may also be flawed if a large portion of younger individuals were killed due to inexperience with predation This would cause a majority of samples to be taken from an older age category thus biasing the life table There are many possible causes for population fluctuations A drastic change in climate or competition for resources could potentially alter a given population A new disease or parasite could infect the population and cause a great deal of deaths Social or physiological changes such as overcrowding or aggression may cause changes within a given population A survivorship curve which depicts age-specific mortality will be constructed to examine collected data The first of three types of survivorship curves shows high survival of individuals at early ages but high mortality with old age The second curve shows a constant mortality rate A high mortality rate early in life and few adult individuals characterize the third type of survivorship curve We hypothesize
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