1	DEMOGRAPHY The number of individuals in each age or stage group leads to improved population projection (compared to just knowing N).
2	Reading Read section 52.1 Demography. Box 52.1 on life tables & growth Read p. 1203-06 on age structure. Study Figures 52.11 & 52.15. Life Tables Lab in labbook.
3	Catastrophes Extreme conditions which kill many individuals in a population is an event known as a catastrophe. Typically a catastrophe results in differential (unequal) mortality among age groups (classes). Some populations have not able to recover after dramatic reductions.
4	Age of Individuals Previous models have treated all individuals in the population as equivalent or equal. The probability of reproductive success in real populations is dependent on the age, genotype, geographic location and other characteristics.
5	Age of individuals effects survivorship and fecundity Individuals progress through stages of life (immature to mature) as they age. Knowing the age of an individual is probably the most useful character to predict survival or reproductive status in humans and other mammals. Age is irreversible, that is, one always gets older.
6	Cohort To study change with age we can follow a ‘cohort’ of individuals born at same time from birth to death (longitudinal study). More commonly we study individuals of different ages at one time (crosssectional study)
7	Age These models divide age into intervals given integer values, 0, 1, 2, …. The length of the interval might be 1 year for dogs. For humans it is usually 5 years. The symbol x is used for AGE.
8	S(x) & D(x) S(0) is the number of new borns in the cohort. S(1) is the number of individuals in the cohort that survive to age 1. The difference S(0) –S(1) = number that died between birth and age 1 = D(0) S(x+1) = S(x) – D(x) S(some large age) = 0, all die
9	Proportionate survival =Survivorship Survivorship is the probability of a new born surviving to age X. The symbol for survivorship is l(x). l(x) = S(x)/S(0) where S(0) is the number of new borns in the cohort and S(x) is number of new borns in cohort that survive to age X.
10	Survivorship values l(0) =1 as S(0)/S(0) = 1 l(>>x) =0 as S(>>x)/S(0) = 0 as eventually all individuals die. Mammals have high survivorship at young ages and then steep declines at old age. This is known as a type I curve.
11	Type II survivorship If survivorship declines exponentially with age then survivorship curve is described as type II. Type II survivorship implies that the probability of dying does NOT change with age, ie is constant.
12	Fecundity, age specific The number of female offspring produced by a female of age X in next year is called m(x) = fecundity at age X. m(x) starts out at zero and then increases. In mammals it declines with advanced age. Maturnity is origin of variable name.
13	Net Reproductive Rate R₀ is the symbol for net reproductive rate = average number of female offspring produced by average new born female. R₀ = Σl(x)m(x) from x=0 until age all newborns are dead.
14	R₀and population growth If R₀ is > 1 then population is increasing in size. If R₀ is less than 1 then the population will decrease in toal number of individuals. The model assumes survivorship and fecundity don’t change with time.
15	A life table
16	Population projection 1
17	Population projection 2
18	Population projection 3
19	Population growth is more dependent on numbers in certain age classes than total number
20	Growth rate The growth rate of a population is the increase in number (ΔN) per individual (N) per time period (t), but if only certain age classes reproduce, then the growth rate is artificially lowered by individuals in post-reproductive ages.
21	Number of Humans
22	Life tables can be applied to stages
23	Problem Calculate R₀ for this life table. Is this population increasing or decreasing?
24	Vocabulary Population projection Catastrophe Population recovery Census Age Net Reproductive Rate Attribute l(x), m(x), l(x)•m(x), R₀ Survivorship Fecundity Stage vs age