Populations and Environment

Ecosystems consist of communities of living organisms in which energy is transferred and chemicals cycled. Humans are part of this ecological balance. However, a lack of sustainable management and conservation has had bad environmental consequences.

Human Populations

The growth of the human population over the last 10,000 years has been tremendous. And there are no signs of it slowing down. However, as the population grows more and more limiting factors in different parts of the world will inevitably come into play, for example space. Already there are issues concerning the amount of food available.

Growth isn’t the only issue: the rate of growth has also increased. The population reached one billion in 1802. It took another 125 years to reach two billion then only 33 years to get to three billion. In 1999 it was six billion and only 13 years later it has reached approximately seven billion.

Growth rate can be expressed as:

annual percent change = (population at end of the year – population at start of the year) x 100

population at start of the year

If there’s a decrease in a population then the population change will be negative.

A population structure refers to the age/sex balance in a population. A population pyramid represents the various ages within a population, usually a country or region of the world. The left hand side of the pyramid tends to represents the males and the right hand side the females. When a population is growing, a pyramid shape is formed, hence its name.

The shape of a population pyramid shows the future growth of that population as well as life expectancy:

• If the base is wide then the population growth is fast. If the pyramid has a narrow base then this shows a fall in population number.
• The steeper a pyramid is the longer the life expectancy.

A pyramid with a rectangular shape and a broad tip represents long life expectancy. A pyramid with a wide base which declines rapidly and has a thin tip represents short life expectancy.

Within ecology it can be used to determine the age distribution of a particular population and this information indicates reproductive habits and how likely it is that the population with continue.

Graphs can also be used to represent the number of deaths in a population. A survival curve plots the age in years of a population on the x-axis and the percentage of survival on the y-axis.

Different curves can be plotted onto the same graph so that comparisons can easily be made between human populations. The mean life expectancy can be found by taking the point at 50% survival on the y-axis and dropping a vertical line from where it means the curve to the y-axis.