Laboratory 3: Age Structure and Survivorship

Age Structure and Survivorship Populations consist of multiple cohorts which vary greatly in age Populations consist of multiple cohorts which vary greatly in age Demography – the study of the vital statistics of a population Demography – the study of the vital statistics of a population May assign individuals to an age class based upon life history and stage of development May assign individuals to an age class based upon life history and stage of development e.g. juvenile sub-adult adult e.g. juvenile sub-adult adult

How do we age individuals? otolithsscales

Proportions of individuals belonging to age groups are referred to as the age structure or age distribution of a population

Age Structure and Survivorship Cohort – group of individuals of the same age in a population Cohort – group of individuals of the same age in a population

Age Pyramids Can be used to compare population structure among many different sites or the same population at different times of the year or from year to year Can be used to compare population structure among many different sites or the same population at different times of the year or from year to year Tuscaloosa County, AL 2000 Census

Life Tables Compile stats for each age class or cohort Compile stats for each age class or cohort Must first identify the number and type of age interval for the analysis Must first identify the number and type of age interval for the analysis Assign collected individuals to the appropriate age class Assign collected individuals to the appropriate age class xnxlxdxqxLxTxex

Survivorship Curves Type 1 = High survival rate for young, low survivor rate after a particular old age Type 1 = High survival rate for young, low survivor rate after a particular old age Type 2 = A constant rate of mortality occurs at all ages Type 2 = A constant rate of mortality occurs at all ages Type 3 = High juvenile mortality rate with low mortality thereafter Type 3 = High juvenile mortality rate with low mortality thereafter

Point aux Pins Collect young-of-the-year blue crabs from seagrass beds using seines Collect young-of-the-year blue crabs from seagrass beds using seines Collect first 100 crabs Collect first 100 crabs In lab, assign crabs to age classes based on carapace width (p.23) In lab, assign crabs to age classes based on carapace width (p.23) Construct age pyramid, life table, and survivorship curve Construct age pyramid, life table, and survivorship curve

Point aux Pins Seine for first 100 Y-O-Y blue crabs (C. sapidus) and put in bag on ice

Point aux Pins Back in lab, measure carapace width of each crab. Age each crab according to table on p. 23. Record data and make tables and figures.