Age Structure and Life Tables Brook Milligan Department of Biology New Mexico State University Las Cruces, New Mexico 88003 brook@nmsu.edu Fall 2009 Brook Milligan Age Structure and Life Tables
Structured and Unstructured Populaions Simplest model of a population Population characterized by a single number: population size Projections: simply N ( t ) Rate of growth: depends only on current population size Brook Milligan Age Structure and Life Tables
Structured and Unstructured Populaions Simplest model of a population Population characterized by a single number: population size Projections: simply N ( t ) Rate of growth: depends only on current population size Many populations are more complex Rate of growth: depends on age of individuals in population Population characterized by many numbers: e.g., number of individuals of each age N i ( t ) Requires more complex models of population growth Brook Milligan Age Structure and Life Tables
Life Tables A life table is a record of survival and reproductive rates in a population, broken down by age, size, or developmental stage (e.g. egg, hatchling, juvenile, adult). Brook Milligan Age Structure and Life Tables
Life Tables A life table is a record of survival and reproductive rates in a population, broken down by age, size, or developmental stage (e.g. egg, hatchling, juvenile, adult). Life tables are useful in predicting the growth and decline of populations. Brook Milligan Age Structure and Life Tables
Life Tables A life table is a record of survival and reproductive rates in a population, broken down by age, size, or developmental stage (e.g. egg, hatchling, juvenile, adult). Life tables are useful in predicting the growth and decline of populations. For example: The human population of a region depends in part on how many children each person has and the the age at which people die. Brook Milligan Age Structure and Life Tables
Life Tables A life table is a record of survival and reproductive rates in a population, broken down by age, size, or developmental stage (e.g. egg, hatchling, juvenile, adult). Life tables are useful in predicting the growth and decline of populations. For example: The human population of a region depends in part on how many children each person has and the the age at which people die. Perhaps surprisingly, it also depends on the age at which they have their children. Brook Milligan Age Structure and Life Tables
Life Tables A life table is a record of survival and reproductive rates in a population, broken down by age, size, or developmental stage (e.g. egg, hatchling, juvenile, adult). Life tables are useful in predicting the growth and decline of populations. For example: The human population of a region depends in part on how many children each person has and the the age at which people die. Perhaps surprisingly, it also depends on the age at which they have their children. Life tables help organize the effects of population structure on population dynamics. Brook Milligan Age Structure and Life Tables
Types of Life Tables Life tables come in two varieties Brook Milligan Age Structure and Life Tables
Types of Life Tables Life tables come in two varieties: Cohort life tables follow the survival and reproduction of all members of a cohort from birth to death. Brook Milligan Age Structure and Life Tables
Types of Life Tables Life tables come in two varieties: Cohort life tables follow the survival and reproduction of all members of a cohort from birth to death. Here, a cohort is the set of all individuals born, hatched, or recruited into a population during a defined time interval. Brook Milligan Age Structure and Life Tables
Types of Life Tables Life tables come in two varieties: Cohort life tables follow the survival and reproduction of all members of a cohort from birth to death. Here, a cohort is the set of all individuals born, hatched, or recruited into a population during a defined time interval. A static life table records the number of living individuals of each age in a population and their reproductive output. Brook Milligan Age Structure and Life Tables
Age Structured Populations Life tables that classify individuals by age are called age-based life tables . Brook Milligan Age Structure and Life Tables
Age Structured Populations Life tables that classify individuals by age are called age-based life tables . Size-based and stage-based life tables classify individuals by size or developmental stage. Brook Milligan Age Structure and Life Tables
Age Structured Populations Life tables that classify individuals by age are called age-based life tables . Size-based and stage-based life tables classify individuals by size or developmental stage. Such life tables are more useful when organisms are difficult to classify by age or when the vital rates depend on size or stage rather than age. Brook Milligan Age Structure and Life Tables
Cohort Life Tables Suppose we wish to build a cohort life table for humans born in the United States in the 1900s. Brook Milligan Age Structure and Life Tables
Cohort Life Tables Suppose we wish to build a cohort life table for humans born in the United States in the 1900s. We would record Brook Milligan Age Structure and Life Tables
Cohort Life Tables Suppose we wish to build a cohort life table for humans born in the United States in the 1900s. We would record The number of individuals born in the year 1900, and how many survived to the beginning of 1901, 1902, etc. until there were no more survivors. Brook Milligan Age Structure and Life Tables
Cohort Life Tables Suppose we wish to build a cohort life table for humans born in the United States in the 1900s. We would record The number of individuals born in the year 1900, and how many survived to the beginning of 1901, 1902, etc. until there were no more survivors. This record is called the survivorship schedule , denoted S x . Brook Milligan Age Structure and Life Tables
Cohort Life Tables Suppose we wish to build a cohort life table for humans born in the United States in the 1900s. We would record The number of individuals born in the year 1900, and how many survived to the beginning of 1901, 1902, etc. until there were no more survivors. This record is called the survivorship schedule , denoted S x . The number of offspring born to individuals of each age. Brook Milligan Age Structure and Life Tables
Cohort Life Tables Suppose we wish to build a cohort life table for humans born in the United States in the 1900s. We would record The number of individuals born in the year 1900, and how many survived to the beginning of 1901, 1902, etc. until there were no more survivors. This record is called the survivorship schedule , denoted S x . The number of offspring born to individuals of each age. The total number of offspring is usually divided by the number of individuals in the age, giving an average number of offspring per individual of each age. Brook Milligan Age Structure and Life Tables
Cohort Life Tables Suppose we wish to build a cohort life table for humans born in the United States in the 1900s. We would record The number of individuals born in the year 1900, and how many survived to the beginning of 1901, 1902, etc. until there were no more survivors. This record is called the survivorship schedule , denoted S x . The number of offspring born to individuals of each age. The total number of offspring is usually divided by the number of individuals in the age, giving an average number of offspring per individual of each age. This record is called the fecundity schedule , denoted b x . Brook Milligan Age Structure and Life Tables
Quantities in a Life Table Survivorship and fecundity schedules are the raw data of any life table. Brook Milligan Age Structure and Life Tables
Quantities in a Life Table Survivorship and fecundity schedules are the raw data of any life table. We will work with the following example to illustrate the ideas presented here. Brook Milligan Age Structure and Life Tables
Quantities in a Life Table Survivorship and fecundity schedules are the raw data of any life table. We will work with the following example to illustrate the ideas presented here. x S x b x 0 500 0 1 400 2 2 200 3 3 50 1 4 0 0 Brook Milligan Age Structure and Life Tables
Survivorship Curves: Standardized Survival Schedule l x : We standardize all cohorts to S 0 (their initial size at time zero) because we want to compare cohorts of different initial sizes. Brook Milligan Age Structure and Life Tables
Survivorship Curves: Standardized Survival Schedule l x : We standardize all cohorts to S 0 (their initial size at time zero) because we want to compare cohorts of different initial sizes. This proportion is calculated as l x = S x . S 0 Brook Milligan Age Structure and Life Tables
Survivorship Curves: Standardized Survival Schedule l x : We standardize all cohorts to S 0 (their initial size at time zero) because we want to compare cohorts of different initial sizes. This proportion is calculated as l x = S x . S 0 We can think of l x as the probability that an individual survives from birth to the beginning of age x . Brook Milligan Age Structure and Life Tables
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