Sustainable management of renewable resources

A renewable resource can be replaced by natural processes, but it can still run out if people remove it too quickly. Its use is sustainable when the rate of removal does not exceed the rate at which the resource is renewed. This allows people to continue using it without exhausting it.

Sustainable management of forests

Trees provide timber, but they need time to grow. For timber use to be sustainable, trees must be able to regrow or be replaced as they are removed. If timber is taken faster than trees can replace it, the forest resource decreases over time.

Sustainable management of fish stocks

A fish stock is a population of fish that can be caught. For fishing to be sustainable, enough fish must remain and reproduce to replace those caught. If fish are removed faster than the population can replace them, the stock declines.

Causes of endangerment and extinction

A species is endangered when its risk of extinction is high. A species is extinct when no individuals of that species remain anywhere.

A population can sustain itself only if enough individuals survive and reproduce. Pressures that reduce survival or reproduction can cause a population to decline. If all populations of a species disappear, the species becomes extinct.

Pressures that cause populations to decline

Climate change can alter temperatures, rainfall and other conditions. If conditions change faster than organisms can tolerate them or move to a suitable habitat, fewer may survive and reproduce.

Habitat destruction removes the places where organisms live and the resources they need, such as food, shelter or breeding sites. With fewer suitable places and resources, fewer individuals can survive and reproduce.

Hunting and overharvesting remove organisms from a population. If individuals are removed faster than the population can replace them through reproduction, the population declines.

Pollution can harm organisms directly or make their habitat unsuitable. This can reduce their survival or their ability to reproduce.

Introduced species are species brought into an area where they do not naturally occur. They can threaten native organisms by competing with them for resources, preying on them or spreading disease.

These pressures can act together. As populations decline, the risk that the whole species will disappear increases.

Protection of endangered species and habitats

An endangered species is at risk of extinction. To conserve it in its natural environment, people need to protect both the organisms and the habitat that supplies what they need to survive and reproduce, such as food, shelter and suitable breeding sites.

Monitoring means regularly checking a species’ population and habitat. A fall in population size may show that the species is under pressure. Checking the habitat can reveal threats, such as damage to breeding sites or loss of food sources. This evidence helps conservationists decide what needs protection.

Protection aims to reduce the threats identified. For example, protecting an area of habitat from damage or disturbance can preserve shelter and breeding sites. Measures may also protect the organisms directly from harm. Protecting the habitat matters because organisms are unlikely to survive and reproduce successfully if the resources they depend on disappear.

Education helps people understand how their actions affect a species or its habitat. For example, people who understand that disturbance can prevent animals from breeding may avoid approaching nesting sites.

These approaches work together: monitoring identifies problems, protection and education reduce the pressures causing them, and continued monitoring helps show whether the actions are working or need to change.

Captive breeding of endangered species

When an animal species has very few individuals left in the wild, it may not produce enough offspring to recover reliably. Continuing threats can make recovery even less likely.

In a captive breeding programme, people manage animals in a controlled environment and breed them to produce offspring. The offspring increase the number of individuals, helping to maintain a population that can support the species’ continued survival.

Captive breeding therefore conserves a species by maintaining and increasing its population when the wild population is too small or threatened to recover reliably on its own.

Seed banks

A seed bank conserves plant species by collecting and storing their seeds. The seeds are kept in conditions that help them remain viable: capable of germinating and growing into new plants later.

If a plant species becomes rare or its wild populations are threatened, stored viable seeds preserve the possibility of growing new plants. Seed banks therefore conserve plant material for future use without requiring every plant to be kept growing continuously.

Forest conservation

Forests can be conserved by controlling how trees are removed and protecting places where they grow. The aim is to prevent forest loss and allow forests to continue growing rather than being cleared faster than they can be replaced.

Protecting forests and managing tree removal

Protected areas restrict activities that damage forests. For example, limiting tree removal in a protected area allows trees to remain and continue growing.

Outside such restrictions, quotas can limit the number of trees that may be removed. This controls the amount of harvesting rather than allowing unlimited removal.

Replanting replaces trees that have been harvested. The new trees need time to grow, so replanting works alongside controls on removal to help the forest persist.

Education for forest conservation

Education helps people understand the effects of forest loss and why forests need protection. This understanding can encourage people to support practices such as restricting damaging activities, following quotas and replanting harvested trees.

Fish stock conservation

A fish stock is a population of fish available for fishing. If too many fish are removed before they reproduce, the population may not replace those caught. Conservation controls fishing so that enough fish survive to reproduce and maintain the stock.

Controlling when, where and how much is caught

Closed seasons prevent fishing during specified periods. They can protect fish at times when they are reproducing. Protected areas restrict fishing in important habitats, giving fish in those areas a chance to survive and reproduce.

Quotas limit the number of fish that may be caught. By reducing the number removed, quotas leave more fish in the population to reproduce.

Controlling which fish are caught

Rules on net types and mesh size affect which fish are captured. A suitable mesh size allows smaller fish to escape through the gaps while larger fish are retained. The smaller fish can then grow and have an opportunity to reproduce before they are caught.

Monitoring and education

Monitoring catches and fish populations helps show whether conservation controls are maintaining stocks. If a stock continues to decline, the controls may need to be changed.

Education helps people understand and follow fishing practices that maintain fish stocks.

Reasons for conservation

Conservation programmes aim to maintain or increase biodiversity: the variety of living organisms and the ecosystems they form. By protecting species and the places where they live, conservation reduces the likelihood that species will become extinct.

An ecosystem contains organisms that interact with one another and with their environment. Protecting a vulnerable ecosystem helps preserve both its organisms and these interactions. For example, a species may depend on other organisms for food; if those organisms disappear, its own survival may be threatened.

Conservation also helps maintain ecosystem functions, such as nutrient cycling. When organisms die or produce waste, decomposers break down the material and return nutrients to the environment, where they can be used again. Protecting the organisms in an ecosystem helps sustain processes like this.

Living organisms also provide resources for humans, including food, drugs, fuel and genes. For example, genes from wild species can provide useful characteristics for crops. Protecting species and ecosystems helps keep these resources available.

These reasons are connected: protecting an ecosystem can protect its species and their interactions, while protecting species helps sustain the ecosystem functions and resources that depend on them.

Assisted reproduction in captive breeding

Captive breeding programmes can use assisted reproduction to produce offspring from selected animals without relying on natural mating. Two methods are artificial insemination and in vitro fertilisation. The main difference between them is where fertilisation—the joining of sperm and egg—occurs.

Artificial insemination

In artificial insemination, sperm is placed in a female’s reproductive tract. If a sperm joins with an egg, fertilisation occurs inside the female’s body. The resulting embryo can then develop there.

In vitro fertilisation

In in vitro fertilisation (IVF), an egg is fertilised with sperm outside the body. The resulting embryo is then placed in a female, where it can develop.

Both methods can help selected captive animals reproduce and increase the number of individuals in an endangered species.

Genetic risks of population decline

When a population becomes small, fewer individuals contribute genes to future generations. Some genetic variants may no longer be passed on, so genetic variation—the differences in genes among individuals—can decrease.

Breeding between relatives

In a small population, individuals are more likely to breed with close relatives. Relatives are more likely to carry the same harmful genetic variants. If both parents pass the same harmful variant to an offspring, the offspring may develop a harmful characteristic. This can reduce its chances of surviving or reproducing.

Reduced variation and survival

Individuals with different genetic variants may respond differently to a disease or an environmental change. When variation is low, there are fewer differences that could help some individuals survive. A threat may therefore affect much of the population.

These genetic risks can cause the population to decline further. As it becomes smaller, variation may decrease further and breeding between relatives may become more likely, increasing the risk of extinction.