Carrying capacity

Definition

Another environmental “buzzword” that keeps cropping up in various conversations is “carrying capacity”. As with many environmental terms, it is meaningless without some form of context. So, in the context of an ecosystem or habitat, ‘carrying capacity’ is the maximum number of individuals an environment can sustainably support without depleting resources or causing long-term damage to the habitat. It is further determined by limiting factors like the availability of food, water, and shelter.

In the context of Krantzkloof, it might be the maximum number of hikers that a trail can support before it becomes damaged and subject to erosion and degradation. In the case of a school bus, the context is safety, and it would be the maximum number of scholars that can be safely transported seated in the bus.

Global population

If we look at the global carrying capacity of the human population, things begin to get more complicated. The Earth’s sustainable human carrying capacity is estimated to be roughly 2.5 billion people under comfortable living standards and strict ecological limits. However, with a population nearing 8.3 billion, human consumption exceeds the Earth’s natural capacity to regenerate resources, a situation masked by fossil fuel reliance. While absolute short-term limits might allow up to 12 billion, current high-consumption lifestyles have already put humanity into an unsustainable state of ecological overshoot.

Ecological footprint

One of the ways we can measure our own impact on the Earth is by using the ecological footprint tool. An ecological footprint measures the biologically productive land and water area an individual, population, or organisation requires to produce the resources it consumes and absorb the waste it generates. If you want to measure your personal ecological footprint? Go to: https://www.footprintcalculator.org/home/en

Overcrowded rats

Overcrowded rat populations—whether in a laboratory experiment, an urban infestation, or a pet setup—cause a severe breakdown in social behaviour. John B Calhoun, in his studies on rats in the 1960s, coined the phrase “behavioural sink” and found high density led to the total breakdown of social structures, extreme aggression, and reproductive failure. However, applying these findings directly to humans is inconclusive and largely considered an oversimplification. While high population density can increase stress and antisocial behaviour in humans, humans have higher social flexibility and cognitive coping mechanisms than rats.

Managing elephant populations

A good example of carrying capacity is the fencing in of elephants within game reserves. By restricting the elephant’s ability to range freely, one creates pressure on the ecological resources used and influenced by the elephants within the area. Unless the numbers within the fenced area are contained to within the carrying capacity of the artificially fenced ecosystem, the total quality of the ecosystem will begin to rapidly degrade. While they act as vital “ecosystem engineers” in large, open systems, fencing restricts their natural migration patterns—creating artificial, long-term densities that often exceed the local environment’s carrying capacity.

People overcrowding

This is a more delicate and sensitive topic, which is complicated by culture, varying human behaviours and such imponderables as poverty, inequality, high and low consumption, and religious beliefs.

However, the facts are clear. There are too many people on Earth, and their numbers are clearly affecting the Earth’s ability to function sustainably and to maintain adequate, “clean” resources to serve both human and non-human populations.

What can we do?

Individuals can minimise the adverse effects of carrying capacity overshoot by shrinking their personal ecological footprints. Key actionable steps include transitioning to plant-based diets, reducing energy consumption at home, shifting to sustainable transport (like walking, cycling, or public transport), and practising the circular economy model of reduce, reuse, and repair.

Why move to a more plant-based diet? The water cost of an average T-bone steak, which typically weighs about 500g to 650g, ranges from 13,500 to 17,500 litres of water from farm to table. In our water-deficit country, think what toll our meat-eating habits are having on our water resources…