Ecology Life Tables
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 bia
It may be worthwhile to research this time period to examine if disease or war may have affected the survival and mortality rates of our cohorts. For example, the 1875-1895 (Figure 2) life table shows that 21 individuals died before the age of 5. This is probably due to either lack of medical care or an outbreak of disease. Nonetheless, both life tables (Figures 1,2) show increasing mortality rates with age. ------------------------------------------------------------------------ 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 that we will see the first type of curve. Begon, M., Harper, J.L., Townsend, C.R. 1996. Ecology : Individuals, Populations, and Communities, 3rd edition. Blackwell Scientific Ltd.: Cambridge, Massachussetts. 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 c
Some common words found in the essay are:
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