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What do humans, bacteria and the American plains bison (Bison bison bison) have in common? Not very much, on the surface, but if you plot graphs of population growth in these wildly different organisms, you may start to see similarities.
Nature Education 2012, all rights reserved
We’re probably most familiar with our own growth pattern. The human population has undergone a population explosion over the last 10,000 years, increasing from less than 10 million to more than 7 billion. The increase has been so rapid for humans that we tend to plot it on a graph using a logarithmic scale, which allows us to get to the bigger numbers quicker and spread out the points. A graph of the American plains bison population in northern Yellowstone Park between 1900 and 1916 looks quite similar. Both are exponential growth patterns, in which the number of individuals added each year increases as the population grows in size. When we plot a graph of bacterial growth, it also looks sort of similar, except that it starts to level off at the top.
This is because, at some point, the population gets so big that it becomes limited by resources like food and space: it reaches its carrying capacity. It’s been speculated that the same will happen to the human population.
Can you work out how many bacteria would grow in a day, starting with a population of one and doubling every hour? What happens if you try to plot a graph of the population size over 24 hours? Can you adapt your graph to make it clearer? We had a go – take a look at our table and graph. Is that how you would do it? Share your version with us at email@example.com.
‘Big Picture: Populations’ (2014)