Definition
Carrying capacity is the quantity of organisms that a ecosystem can sustainably support. The carrying capacity of an ecosystem for a given species can be influenced by many factors, such as the ability to regenerate the food, water, atmosphere or other necessities that populations need to survive.
Explanation of carrying capacity
In biology, the concept of carrying capacity relates the number of organisms that can survive with the resources within an ecosystem. Ecosystems cannot exceed their carrying capacity over a long period of time. In situations where the density of population density of a given species exceeds the carrying capacity of the ecosystem, the species will exhaust its source of food, water or other needs. Soon, the population will begin to die out. A population can only grow until it reaches the carrying capacity of the environment. At that point, resources will not be sufficient to allow it to continue to grow in the long term.
The graph above shows the population (N) of a given species over time
Examples of carrying capacity
North American Deer Flourishing
An example of a situation where went too far the The carrying capacity of an environment can be seen in the deer populations of North America.
After the widespread elimination of wolves, the natural predator of North American deer, deer reproduced until their need for food exceeded the environment’s ability to regenerate their food. In many areas, this resulted in large numbers of deer starving to death until the deer population was drastically reduced.
Before Europeans colonised North America, one of its main forest herbivores was deer. Usually existing in small groups, deer populations were kept in check by wolves, the main predator in these forest ecosystems.
Deer, being a fairly large North American herbivore, were capable of eating leaves from trees and shrubs, as well as low-growing plants such as flowers and grasses – and they needed lots of leaves to keep them going, as members of different deer species could weigh anywhere from 50 to 1,500 pounds!
But when European settlers severely depleted the wolf population, which they saw as a danger to human children and livestock, an unexpected consequence followed: the deer began to multiply unchecked, until they exceeded the carrying capacity of their environment.
North American deer decline
As a result, deer began to starve. Plant species also began to suffer, some even becoming endangered. extinctionas hungry deer ate all the green plants they could find.
When humans realised what was happening, and began to affect their own food sources, after wild deer began to invade gardens and farms in search of crops to eat, they began to help nature reduce the deer population.
In modern times, some areas “cull” deer, a practice in which deer are systematically hunted, not just for meat or sport, but to prevent deer starvation and damage to plants. Other areas have even begun to reintroduce wolves and, as a result, these areas have seen healthier ecosystems, gardens and crops.
The story of North America’s wolves and deer has acted as a warning to people who are considering making changes of any kind to their natural environment, which could have unintended consequences.
The Daisyworld model
The hypothetical “Daisyworld” model is a model developed by scientists to study how organisms change their environment and how ecosystems self-regulate.
In the original “Daisyworld” mathematical simulation, there were only two types of life forms: black daisies, which increase the temperature of the environment by absorbing heat from the sun (this is a real property of black materials), and white daisies, which decrease the temperature of the environment by reflecting heat from the sun (this is also a real effect of white materials).
Each species of daisies had to live in a proper balance with the other species. If the white daisies became overpopulated, the world would become too cold. Daisies of both kinds would begin to die out and the world would begin to regain its balance. The same can be said of the black daisies: if they become overpopulated, the world becomes warmer and warmer until the daisies start dying again.
Real-life ecosystems are much more complicated than this, of course.
Each organisation has many needs, and how well the environment can meet those needs may depend on what other organisms it shares the environment with.
Humans change carrying capacity
Humans have become one of the world’s only global species, my technology of domain. Time and again, the human species has overcome a factor, such as the availability of food or the presence of natural predators, that limited our population.
The first great human population explosion occurred after the invention of agriculture, in which humans learned that we could grow large numbers of our most nutritious food plants by saving seeds to plant in the soil. By ensuring that these seeds received sufficient water and were protected from competition from weeds and from being eaten by other animals, we ensured a steady supply of food.
When agriculture was invented, the human population skyrocketed. Scientists believe that without agriculture, between 1 and 15 million humans could live on Earth; today, there are approximately 1 million humans in the city of Chicago alone!
In the Middle Ages, when well-organised agriculture emerged on all continents, there were about 450 million, or about 500 million, human beings on earth.
Putting technology to work
A new revolution in the Earth’s capacity to transport humans began in the 18th and 19th centuries when humans began to apply advanced, automated technology to agriculture. The use of inventions such as the mechanical corn picker and crop rotation, a way of growing different crops in a sequence that enriches the soil and leads to higher yields, allowed humans to produce even more food. As a result, the world’s population tripled from approximately 500 million to 1.5 billion people.
In the 20th century, a third revolution occurred when humans began to learn how to rewrite plant genomes using viruses to insert new genes into seeds directly instead of relying on selective breeding and mutation random mutation to increase crop yields. The result was another dramatic increase in the earth’s ability to produce food for humans.
During the 20th century, the Earth’s human population more than quadrupled, from 1.5 billion to 6.1 billion. We have come a long way since the days before agriculture!
But some scientists worry that we may be on our way to exceeding the earth’s carrying capacity, or have already done so.
What is human carrying capacity?
Although we have greatly expanded the carrying capacity of the human species , our activities are not without consequences. There are several possible limitations on the human species from which not even technology can save us.
Scientists point to the rapid decline in bee populations, which are needed to pollinate some of our crops and which many scientists believe are being destroyed by the pesticides we use to protect those same crops, as evidence that our current food production practices may not be sustainable for much longer.
The proliferation of algae poisonous algae, which can poison our water supplies and which feed on the same fertiliser we use to feed our crops, is another worrying sign that we may be exceeding our carrying capacity, and may start to cause us problems if our population continues to grow.
Some scientists fear that humans may exceed the Earth’s carrying capacity for humans. and encourage the use of contraception to lower birth rates in order to prevent human populations from depleting their sources of food and other vital resources.