BIOTIC POTENTIAL: INTRINSIC GROWTH RATE AND EXAMPLES - BIOLOGY - 2025

The biotic potential is the maximum growth rate of a population in which there are no restrictions. In order for a population to reach its biotic potential, it must have unlimited resources, parasites or other pathogens must not exist, and species must not compete with each other. For these reasons, the value is merely theoretical.

In reality, a population never reaches its biotic potential, since there are a series of factors (biotic and abiotic) that limit the indefinite growth of the population. If we subtract environmental resistance from the biotic potential, we will have the real value of the rate at which said population increases.

Intrinsic growth rate

The biotic potential is also known as the intrinsic growth rate. This parameter is denoted by the letter r and is the rate at which the population of a certain species could grow if it had unlimited resources.

Organisms that have high intrinsic growth rates generally reproduce early in life, have short generation times, can reproduce several times in life, and have high numbers of offspring at each reproduction.

According to these characteristics and life strategies, the species can be classified as prodigal or strategies r and prudent or strategy K. This classification was coined by George Hutchinson.

The r strategies are characterized by giving birth to a high number of offspring, these are small in size, their maturation period is fast and they do not spend time on parental care. Logically, the reproductive strategies r reaches the maximum capacity of the biotic potential in terms of reproduction.

In contrast, the species listed as K have few offspring, which mature slowly and whose body size is large. These species take intensive care of their young to ensure their success.

Factors that affect biotic potential

Biotic potential is influenced by a variety of factors intrinsic to the species. The most relevant are described below:

- The frequency of reproduction and the total number of times in which the organism reproduces. For example, bacteria reproduce by binary fission, a process that can be done every twenty minutes. In contrast, a bear has cubs every three or four. When comparing the biotic potentials of the two, the polar bear has a much lower potential.

- The total descendants that are born in each reproductive cycle. Bacterial populations have very high biotic potentials. If it had unlimited resources and no restrictions, a bacterial species could form a layer 0.3 meters deep that could cover the Earth's surface in just 36 hours.

- The age at which reproduction begins.

- The size of the species. Species with small sizes, such as microorganisms, generally have a higher biotic potential than species with larger body sizes, such as some mammals.

Environmental resistance

The biotic potential of a species is never reached. Factors that prevent unrestricted growth are known as environmental resistance. These include various pressures that limit growth.

Among these resistances are diseases, competition, accumulation of some toxic waste in the environment, unfavorable climatic changes, shortage of food or space and competition between species.

In other words, the exponential growth of a population (which occurs when it does not present any limitation) becomes a logistic growth when the population faces these environmental resistance.

Over time the population stabilizes and reaches its carrying capacity. In this state, the growth curve takes the shape of an S (sigmoidal).

Loading capacity

The environmental resistances together with the biotic potential determine the carrying capacity. This parameter is denoted by the letter K and is defined as the maximum population of a given species that can be maintained in a particular habitat without being degraded. In other words, it is the limit imposed by environmental resistance.

The population growth rate decreases when the population size approaches the value of the carrying capacity of the environment. Depending on the availability of resources, the population size can fluctuate around this value.

If the population exceeds carrying capacity, it is likely to collapse. To avoid this phenomenon, surplus individuals must move to new areas or start exploiting new resources.

Biotic potential in humans

In humans, and other large mammals, the biotic potential can be 2 to 5% each year, in contrast to 100% of the biotic potential of microorganisms every half hour.

Not all biotic potential is reached in human populations. In biological terms, a woman is capable of having more than twenty children throughout her life.

However, this number is almost never reached. Despite this, the human population has grown exponentially since the eighteenth century.

Example

Otters do not reach their biotic potential for a number of reasons. Females reach sexual maturity between 2 and 5 years of age. The first reproduction occurs around the age of 15 years and on average they only have one young.

Regarding the population size, this is fluctuating due to environmental changes. The growth of predators such as orcas, also known as killer whales, decreases the population size of otters.

However, the natural prey of killer whales is not otters. They are sea lions and seals, whose populations are also declining. So to make up for it, the killer whales turn to feeding on the otters.

Parasites are also a crucial factor in the decline of the otter population, specifically parasites that come from companion animals such as cats.

The parasites manage to reach the otters because pet owners flush the waste down the toilets and it contaminates the otter's habitat.

Likewise, human-produced water pollution has also contributed to the decline in the number of otters.

The incidence of each of these factors in reducing the biotic potential of otters could be leading to the extinction of this species.

References

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3. Moore, GS (2007). Living with the earth: concepts in environmental health science. CRC Press.
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5. Starr, C., Evers, C., & Starr, L. (2015). Biology today and tomorrow with physiology. Cengage Learning.
6. Tyler, G. & Spoolman, S. (2011). Living in the environment: principles, connections, and solutions. Sixteenth edition. Cengage Learning