Overexploitation

People sometimes take too much from nature.

This is called overexploitation. It happens when we take things faster than they can grow back.

It can happen to fish in the sea.

It can happen to trees in the woods. It can even happen to grass used by cows.

If we take too much, the resource can be lost. Some animals have even gone away forever. This is called extinction.

Taking too much can hurt the whole world. It can change how many animals live in one place. We must learn to take only what we need.

Overexploitation happens when we take too much from nature.

This means we take things faster than they can grow back. It can happen to fish, trees, or even grass. If we take too much, the resource might be lost forever. This can lead to extinction. Extinction is when a whole group of animals dies out.

This is not a new problem. Long ago, people hunted the moa. These were giant birds in New Zealand.

Because the moa were gone, the Haast's eagle also died out. This happened because the eagle had no more food to eat.

In the ocean, we see this with fish.

If we catch fish too fast, the population can collapse. A collapse means the number of fish drops very low. For example, Atlantic cod stocks collapsed in 1992. This happened after too much fishing in the 1970s and 1980s. We can avoid this by using a steady way to harvest. This is called a sustainable yield. It means we take only what nature can replace.

Overexploitation happens when we use a natural resource too much.

This can include things like fish, forests, or even water in the ground. It also applies to wild plants and grazing pastures. When we take these things faster than they can grow back, we face diminishing returns. This means it becomes harder to get what we need. If we keep going, the resource might be destroyed completely. This can lead to extinction for many living things.

To understand how this works, think about a fish population.

Fish reproduce to replace the ones that are caught. For a fishery to be sustainable, the rate of catching must balance the rate of reproduction. If people catch too many, the total amount of fish, called biomass, starts to drop. There is a point called the maximum sustainable yield. This is the most amount we can take without hurting the future supply. Usually, this happens when only 30% of the original biomass is left. If the biomass drops by more than 95%, the fishery is said to collapse.

This is not a new problem in human history.

Long ago, the Māori people in New Zealand hunted giant moa birds. These birds were large and could not fly, which made them easy targets. By 1500 AD, only 200 years after people arrived, ten species of moa were extinct. This loss also affected other animals, like the giant Haast's eagle. Because the eagle preyed on the moa, it also became extinct. In Hawaii, making one ceremonial cloak required feathers from 70,000 mamo birds. This huge demand helped drive those birds to extinction.

Scientists have studied these patterns for a long time.

In 1916, Edward Winslow Gifford suggested humans caused changes in marine life in San Francisco Bay. A 2018 study showed large mammals in Africa began going extinct 125,000 years ago due to hunting. This was 90,000 years earlier than experts once thought. In the ocean, Atlantic cod stocks were overexploited during the 1970s and 1980s. This led to an abrupt collapse of the cod in 1992. Even after fishing stopped, the cod have not recovered.

We can use a story to understand why this happens.

This is called the tragedy of the commons. Imagine herders sharing a piece of land to graze their cows. Each herder wants to add more cows to make more money. They get all the benefit from the new cow, but the damage to the land is shared by everyone. Eventually, everyone adds too many cows and the land is ruined. To avoid this, we can use rules to regulate how we use shared resources. This helps keep our world in a healthy balance.

Overexploitation, also known as overharvesting or ecological overshoot, occurs when a renewable resource is harvested at an unsustainable rate.

This process happens when the rate of extraction exceeds the natural capacity of a population to replenish itself through reproduction. In ecology, overexploitation is recognized as one of the five primary activities threatening global biodiversity. It can lead to the destruction of a resource or even the extinction of entire species. While the term is often used in conservation biology to describe human economic activity, it can also apply to non-human actors. For example, introduced predators or herbivores can overexploit native flora and fauna in an ecosystem.

To understand the mechanism of overexploitation, consider how a fish stock functions.

A population maintains its biomass, which is the total weight of the living organisms, through reproduction. For a fishery to remain sustainable, the rate of harvesting must be balanced by the rate of reproduction. When humans increase the harvest rate beyond this balance, the total biomass begins to decrease. There is a specific threshold known as the maximum sustainable yield. This is the highest amount of a resource that can be harvested without causing a long-term decline. In practice, this point often occurs when a fishery is reduced to about 30% of its original biomass.

If harvesting continues past the maximum sustainable yield, the consequences become severe. A fishery is officially considered to have "collapsed" if its biomass declines by more than 95% of its maximum historical levels.

This collapse can be abrupt and difficult to reverse. A famous example is the Atlantic cod stocks. These populations were severely overexploited during the 1970s and 1980s. This led to a sudden collapse in 1992. Even after fishing activities ceased, the cod stocks have failed to recover. This shows how removing an apex predator can permanently alter an ecosystem.

Overexploitation manifests in many different sectors of natural resource management. In fisheries, it is often called overfishing. In forest management, the term is overlogging.

When managing livestock, it is referred to as overgrazing.

In hydrology, the term for taking too much water from aquifers is overdrafting. Even when a resource is not completely destroyed, overexploitation can reduce its quality. For instance, the footstool palm in Southeast Asia has seen its leaf size decrease due to overharvesting for food wrapping and thatching.

Historical evidence shows that overexploitation is not a purely modern phenomenon. It has been documented for millennia across various human societies.

In New Zealand, the Māori people hunted the giant, flightless moa birds for food and resources. By 1500 AD, only 200 years after human settlement, ten species of moa had gone extinct. This rapid loss also caused the extinction of the Haast's eagle, which preyed on the moa. Similarly, in Hawaii, the demand for mamo bird feathers for ceremonial cloaks was immense. Crafting just one cloak required the feathers of approximately 70,000 adult mamo birds, contributing to their extinction.

Scientific research has provided deeper insights into the timing and scale of these events. The "overkill hypothesis" suggests that human migration and population growth drove the rapid extinction of megafauna.

In North America, about 80% of large mammal species became extinct within 1,000 years of human arrival. A 2018 study also found that large mammals in Africa began facing extinction from human hunting at least 125,000 years ago. This is 90,000 years earlier than previous estimates. Other studies suggest that extinction rates in large carnivores correlate with increased hominin brain size and changes in vegetation.

One way to conceptualize the social drivers of overexploitation is through the "tragedy of the commons." This concept was popularized by Garrett Hardin in 1968, based on an 1833 parable by William Forster Lloyd.

Imagine a group of herders sharing a common piece of land for grazing. Each individual herder acts in their own self-interest by adding more cows to the land to increase their own profit. However, the benefit of each new cow goes to the individual, while the damage to the shared land is shared by everyone. Eventually, every herder makes the same rational decision, and the land is destroyed. Hardin noted that this tragedy occurs in unregulated commons, such as oceans, rivers, and the atmosphere. To prevent this ruin, these shared resources must be appropriately regulated.