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How Is Biotic Potential Determined?

Instructor: Robin Monegue Keeler

Robin has taught college microbiology and environmental science. She has two master's degrees: one in environmental microbiology and the other in public health.

Biotic potential is the maximum growth rate of a population in ideal conditions. In this lesson, we will review how reproductive capacity determines biotic potential by comparing lemmings and blue whales.

Biotic Potential Definition

What will happen to a wild population of lemmings if they have unlimited food and water, a perfectly suitable habitat, no predators, no sickness, and no disease? In this ideal world, the lemmings will happily reproduce, which will result in more and more lemmings; or, in more technical words, this results in an exponentially increasing lemming population.

A lemming, (Lemming lemus), which lives in the Arctic Circle
Lemming

This maximum growth rate of a population, under ideal conditions, is called biotic potential. However, even under optimal conditions, biotic potential varies for different organisms. For example, assuming ideal conditions, a single E. coli bacterium can double itself every 20 minutes. Incredibly, within about seven hours, nearly one million E. coli cells are produced from one E. coli bacterium! With this many E. coli offspring produced in such a short period of time, we would say that E. coli has a high reproductive capacity. An organism with a high reproductive capacity also has a high biotic potential.

Biotic Potential: Lemmings versus Blue Whales

Now let's look at an organism a lot larger than a bacterium: a blue whale. A blue whale produces one calf about every two to three years. Since a blue whale produces offspring at such a slow rate, we would say a blue whale has a low reproductive capacity and a low biotic potential.

A blue whale, the largest animal on Earth. They can grow to 100 feet long and weigh about 200 tons. Their tongue can weigh as much as an elephant!
blue whale

We can see from the previous examples that biotic potential is determined by the reproductive capacity of an organism. Let's break down this reproductive capacity a little further, into four factors that influence biotic potential:

1. The age at which the organism first reproduces. This is probably the most important factor influencing biotic potential. The younger (earlier) an organism can get busy producing offspring, the faster its population will increase. A lemming is ready to reproduce (is sexually mature) at about three weeks old. In contrast, a blue whale is sexually mature at about ten years old.

2. The number of offspring that survive to sexual maturity/adulthood. The more offspring that survive to an age where they are able to reproduce, the greater a population will increase.

3. The number of offspring produced each time an organism reproduces. A lemming produces about six to eight offspring in one litter. A blue whale only produces one offspring at a time.

4. The frequency of the reproductive cycle/the total number of times an organism reproduces during its life. Lemmings only live about two years, but they can breed year-round. They are able to produce a litter every three to four weeks. In contrast, a blue whale lives for 80-90 years, but it only produces one offspring every two to three years. When we compare the number of potential offspring that can be produced in a lemming's lifetime versus a blue whale's lifetime, the difference is significant. One lemming can produce nearly 200 offspring during its short life, whereas a blue whale can produce about 30-35 offspring in its lifetime.

We see that lemmings have a much higher biotic potential than blue whales. This also means that lemmings can add more members to their population in the same time period as compared to blue whales. The more often an organism can reproduce, the faster its population can grow.

The above examples also demonstrate that smaller organisms have a higher capacity for population growth - they have a higher biotic potential. Larger organisms have a lower capacity for population growth and a lower biotic potential. Organisms with a higher biotic potential are able to respond more quickly to changes in their environment, compared to organisms with a lower biotic potential.

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