1. SBI 4U1 – Population Dynamics
12.2 Demographics
SBI 4U1 – Population Dynamics

2. Learning Goals
To learn the factors that affect population demographics and how they do so

3. Demography Study of population changes
Growth Rate is calculated using:
Natality
Mortality
Immigration
Emigration

4. Life tables Used to summarise demography of a species
Investigates certain cohorts or age groups (Ex. The double cohort that entered universities when OAC was ditched by the government!)

5. Survivorship Curves
Shows the ability of an individual to survive hardships
Types I-III

6. Survivorship Type I Low death rate in early years
High death rate as organism ages
Larger animals with few young Ex. Ram, humans, elephants…
Long gestation period, high infant investment by parents

7. Survivorship type II Constant mortality rate in all cohorts
Ex. Five lined skink, songbirds, small mammals…
Short gestation period

8. Survivorship Type III Newborns die quickly during critical stage
Ex. Plants, insects, invertebrates, fish…
Lots of offspring born– few survive

9. fecundity Ability of an organism to have fertile offspring
Ex. Elephants have lower fecundity than horseshoe crabs that lay thousands of eggs
Depends on environmental conditions
How?

10. fecundity
Larger animals have higher or lower?
lower

11. fecundity
Organisms are pre-reproductive, reproductive, or post-reproductive
Age structure determines how population will grow
Ex. High number of individuals of reproductive age will cause population to increase (Niger has the world’s fastest growing population)

12. fecundity
Affected by generation time (time to complete one generation)
Small body size has short generation time Ex. E. coli
Large size = long generation time Ex. whales

13. fecundity Affected by sex ratio, also
Females have a larger effect on population growth than males
One male can mate with many females Ex. Northern Elephant seals compete for mates—one male may fertilise 100+ females

14. Some organisms mate for life
Male: Female ratio matters more
Ex. Swans, geese