What Is the Definition of Carrying Capacity in Biology?

Crowded 5th Avenue in Winter Holiday Season.
Toshi Sasaki / Getty Images

Biological carrying capacity is defined as the maximum number of individuals of a species that can exist in a habitat indefinitely without threatening other species in that habitat. Factors such as available food, water, cover, prey and predator species will affect biological carrying capacity. Unlike cultural carrying capacity, biological carrying capacity cannot be influenced by public education.

When a species exceeds its biological carrying capacity, the species is overpopulated. A topic of much debate in recent years due to the rapidly expanding human populations, some scientists believe that humans have exceeded their biological carrying capacity.

Determining Carrying Capacity

Although the biology term was originally coined to describe how much a species could graze on a portion of land before permanently damaging its food yield, it was expanded later to include the more complex interactions between species such as predator-prey dynamics and the recent impact modern civilization has had on native species.

However, competition for shelter and food aren't the only factors that determine a particular species' carrying capacity, it also depends upon environmental factors not necessarily caused by natural processes — such as pollution and species of prey extinctions caused by mankind.

Now, ecologists and biologists determine the carrying capacity of individual species by weighing all of these factors and use the resultant data to best mitigate species overpopulation — or conversely extinction—which could wreak havoc on their delicate ecosystems and the global food web at large.

Long-term Impact of Overpopulation

When a species exceeds its niche environment's carrying capacity it is referred to as being overpopulated in the area, which oftentimes leads to devastating results if left unchecked. Fortunately, the natural life cycles of and balance between predators and prey typically keep these outbreaks of overpopulation under control, at least in the long term. 

Sometimes, though, a certain species will overpopulate resulting in the devastation of shared resources. If this animal happens to be a predator, it might over-consume the prey population, leading to that species' extinction and the unfettered reproduction of its own kind. Conversely, if a creature of prey is introduced, it might destroy all sources of edible vegetation, resulting in a decrease in other prey species' populations. Typically, it balances out—but when it doesn't, the entire ecosystem risks destruction.

One of the most common examples of how close to the edge some ecosystems are to this destruction is the alleged overpopulation of the human race. Since the end of the Bubonic Plague at the turn of the 15th century, the human population has been steadily and exponentially increasing, most significantly within the last 70 years.

Scientists have determined that the carrying capacity of Earth for humans lies somewhere between four billion and 15 billion persons. The human population of the world as of 2018 was nearly 7.6 billion, and the United Nations Department of Economic and Social Affairs Population Division estimating an additional 3.5 billion population growth by the year 2100.

Humans are in a position where they have to work on their ecological footprint if they hope to survive the next century on this planet.