1. Ecosystems and Populations
Boardworks A2 Biology
Ecosystems and Populations

2. Ecosystems and Populations population growth rate
The human population
Boardworks A2 Biology
Ecosystems and Populations
There are currently more than 7 billion people on Earth.
The human population has grown exponentially since the Industrial Revolution, when new technology increased the carrying capacity of the Earth.
population (billions)
The population growth rate can be calculated by subtracting death rate from birth rate, or using the following equation:
population at end of period
population at start of period –
population growth rate = ×
100
population at start of period

3. Ecosystems and Populations
Demography
Boardworks A2 Biology
Ecosystems and Populations
Demography is the study of the size and structure of populations, including a population’s age and sex distribution.
Demographic rates, such as population growth rate, birth rate and death rate can be used to describe how a population, or a subset of a population, changes over time.
births
deaths
population
immigration
emigration
A population’s demographic rates are determined by the environmental conditions. Human populations are greatly affected by their level of economic development. 29

4. Demographic transition model
Boardworks A2 Biology
Ecosystems and Populations
Photo credit (Masai boy): © 2009 Shutterstock, Andrejs Jegorovs
Photo credit (crowded street): © 2009 Jupiterimages Corporation

5. Ecosystems and Populations
Population pyramids
Boardworks A2 Biology
Ecosystems and Populations

6. Survival curves and life expectancy
Boardworks A2 Biology
Ecosystems and Populations
Survival curves measure the life spans of a sample of 10,000 individuals. At each age the number of survivors per 10,000 is plotted.
developing
100
developed
stone age
survivors (%) 50
In general, more developed countries tend to have higher survival rates. This causes their curves to sit further to the right. 50
100
age (years)
Survival curves can also be used to determine average life expectancy. This is the age at which 50 % of the sample population is still alive.

7. Interpreting data on human populations
Boardworks A2 Biology
Ecosystems and Populations