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.
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.
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.
So, if lemmings have such a high biotic potential, why don’t they take over the earth? In the real world, there are environmental factors that constrain the growth of lemmings (and all other populations too). This is called environmental resistance. Environmental resistance includes things such as lack of suitable habitat and space, poor climatic conditions, lack of food or water, predators, and disease.
You can think of environmental resistance as the flip side of biotic potential. The two work to balance a population. As biotic potential INCREASES a population, environmental resistance DECREASES a population.
OK, let’s review. Biotic potential is the maximum growth rate of a population, assuming ideal conditions. It is determined by the reproductive capacity of an organism, which can be broken down into four factors: 1), the age when an organism is first able to reproduce; 2), the number of offspring that survive to sexual maturity; 3), the number of offspring that are produced each time as organism reproduces; 4), the frequency of an organism’s reproductive cycle and the total number of times an organism reproduces during its life.The younger an organism is when it first starts to reproduce, the more often it can reproduce; the greater the number of offspring, the faster a population can grow.
This also means the organism has a higher biotic potential. The flip side of biotic potential is environmental resistance. Environmental resistance constrains a population’s growth and includes things such as lack of suitable habitat, limited food and water, poor climate, predators and disease. Biotic potential and environmental resistance work together to balance population growth.