Table contentsoAge-specific survivorship oAge-specific fecundity Fecundity just means reproductionVital rates of a populationPredictions from tablesoMean lifespanoAge distribution over timeoFuture population sizeUsed by insurance companies also the IRSHuman tables centuries oldoRecords indicated that the Egyptians were the first to consider life tables – to keep track of the life spans of their slavesoRomans also used life tables to keep track of taxesoPrimary use for taxes and insuranceAnimal/plant tables are scarceAge-specific survivorship (First Half)Survivorships varies with age oLeatherback seaturtles – huge mortality of the hatchlings where the adult seaturtles have a small percentage of death.Basic notation of life tablesox = age interval is specific to the organism studied(time units or stage – minutes/seconds/stages)onx= number alive at start of age xolx= proportion surviving from birth to start of age xEstimating age-specific survivorshipTwo main methods of estimation:Vital Rates
oCohort life table – even aged group of individualsidentify/mark individuals born at same timefollow individuals throughout liferecord births and deathsEx. Desert tarantula -lives 3 years cohort, 100 individuals tables, usually only focuses on females because it is hard with most species to measure male reproduction.oStatic life tableA snapshot in timeRecord age Static life tables use cues to age at death. For human populations it is pretty simple b/c of the cues to age at death (cemetery). As with trees you can verify the age of a tree by the number of rings. You can tell the age of the deer by the age of the teeth. You can get growth rings from antlers on deer and such. You can find out the age of death from those that you can predict.Hypothetical cohort analysisCohort – even aged group of individuals (Just like what’s gonna be on test we would need to fins lx)oDesert tarantulaoLives 3 yearsoCohort of 100 individualsoTables usually focus on females – b/c it is hard to keep track of the reproductive success for malesoAlmost all life tables will start at 1Survivorship curves from life tablesY-axis has to be number of survivors because it has to be numericUsually scales to the 1,000
In type 1 survivorship, juvenile survival is high and most mortality occurs among older individuals.In contrast, individuals in a population with type 2 survivorship die at equal rates, regardless of age. (straight line indicates that no one age is dying quicker than another)Individuals showing type 3 survivorship die at a high rate as juveniles and then at much lower rates later in life.Dall sheep survivorship– studied for many years and a threatened species.oTo all comparisons to other studies, the number of dall sheep surviving and dying within each year of life is converted to numbers per 1000 births.oSubtracting number of deaths from number alive at the beginning of each year gives the number alive at the beginning of the next year.oPlotting age on the x axis and number of survivors on the y axis creates a survivorship curve.
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