Throughout history, humankind has had many impacts on the planet. These impacts have become more noticeable and significant, some even irreversible, since the Industrial Revolution. Concern about the negative effects of human activity on the environment stems from the degradation of ecosystems, the loss of biodiversity , the pollution of air, water, and soil, and the depletion of natural resources.

This concern for the environment is compounded by the existing concern for health and well-being, improving quality of life, and ensuring a good life expectancy. These conditions are affected by human economic and urban development , in which economic activities impact natural resources, flora, and fauna.

Environmental impacts on ecosystems

The need to protect the planet's biodiversity and maintain the functionality of ecosystems as we know them has led to the creation of threat categories for the various species of flora and fauna that are endangered or whose populations are declining. From the moment humans begin to carry out economic activities such as the exploitation of resources (hydrological, mining, agricultural, etc.), certain impacts occur on ecosystems. These impacts affect the flora and fauna existing in these areas, leading to alterations in their way of life. For example, agriculture causes fragmentation in ecosystems, road construction leads to a loss of habitat continuity, and so on.

These impacts prevent flora and fauna from adapting to normal living conditions in the face of new environments. The search for food and water becomes more difficult, new diseases emerge, and movement and finding hiding places from predators become more challenging. All of this means that many species cannot adapt well to these new living conditions caused by human activities, and, unfortunately, they cannot survive, leading to a decline in their populations.

Ecosystems are complex networks of connections between species that exchange energy in a stable way called ecological balance . When this ecological balance is disrupted, populations decline, and the more relationships within the ecosystem, the more vulnerable it is to total degradation. An ecosystem with few species is highly vulnerable to both human and natural impacts. Animal and plant populations that decline below a certain threshold are categorized as "endangered."

Work prior to threat categorization

To discuss threat categories for animal and plant populations, we must first analyze the conservation status of the ecosystem and the species themselves. Conservation status refers to the probability that a species will continue to exist in the present or the near future. This requires analyzing the current population of a given species and its population trends over time. This allows us to predict its population in the near future, provided that the conditions to which it is subjected remain stable. If new predators or other threats (including human impacts) exist that could alter its habitat and living conditions, we must analyze how the species will evolve in response to such situations.

How did the threat categories emerge?

The threat categories for flora and fauna arose from their classification. In the mid-18th century, Linnaeus published a method for classifying all living things. These are the taxonomic categories, and to date, some 1,4 million species have been classified. Vertebrate animals, due to the greater knowledge about them, are used as biological indicators and are generally the focus of the greatest conservation efforts.

Due to the aforementioned ecological balance, the conservation of vertebrates requires studying their trophic requirements and habitat dependencies. Therefore, it is essential to ensure the good conservation status of the ecosystems they inhabit and to conserve the flora and fauna species upon which they depend, in order to maintain the ecological balance that sustains them.

Evaluation criteria for species protection

In order to classify species according to their degree of threat, various tests are carried out on the populations of the taxon under study to assign it the threat category or treat it as not threatened.

• Criterion A it is based on the study of the reduction of the number of mature individuals in a set time.
• Criterion B studies the geographic distribution of populations that are reduced depending on the extent of the presence of the species and the area of ​​occupation that the individuals actually cover.
• Criterion C it is based on the number of mature individuals in continuous decline due to the impacts that are caused on ecosystems.
• Criterion D is the total number of mature individuals that exist in the habitat.
• Criterion E analyzes the probability of extinction in a percentage of individuals per unit of time.

If a species is found to no longer meet the criteria for which it was considered threatened, it should normally be assessed against other criteria and not removed from the list.

Threat categories according to IUCN

There are many ways to classify animals whose populations are declining. The best known are the threat categories established by the International Union for Conservation of Nature (IUCN) . The IUCN compiles species that are threatened in some way in the well-known Red Books and Red Lists.

For a taxon to be threatened, it suffices that it meets only one of the criteria listed above. These are the threat categories according to the IUCN:

– Extinct (EX): There is no doubt about the disappearance of the last individual.

– Extinct in the wild (EW) : Only survives in crops or in seed banks and laboratories.

– Critically Endangered (CR): Extremely high risk of extinction, meeting any criteria after a study of the species and its inclusion on the red list. For a species to be considered critically endangered, it must meet the following criteria:

• Its population is reduced by 80-90% of individuals in 10 years or 3 generations.
• Its total extension is less than 100 km2 or its occupation less than 10 km2.
• The number of mature individuals is less than 50.
• The probability of extinction is 50% in 10 years and 3 generations.

– Endangered (EN): Very high risk of extinction. Today, there are many species worldwide that are endangered. To be considered endangered, a species must meet the following criteria:

• Its population is reduced by 50-70% of individuals in 10 years or 3 generations
• Its extension area is less than 5.000 km2 and its occupation of 500 km2.
• The number of mature individuals is less than 250.
• The probability of its extinction is 20% in 20 years or 5 generations.

– Vulnerable (VU): High risk of extinction. A vulnerable species is not in danger of extinction, but its population is declining due to its situation, way of life, or exposure to various human impacts and activities. For a species to be considered vulnerable, it must meet the following criteria:

• Its population is reduced by 30-50% of individuals in 10 years or 3 generations.
• Its extension area is less than 20.000 km2 and its occupation is less than 2.000 km2.
• The total number of mature individuals is less than 1.000.
• The probability of extinction of the species is 10% in 100 years.

– Near Threatened (NT): Does not meet any of the criteria but is very close to meeting them.

– Least Concern (LC): These are abundant taxa with a relatively wide distribution. They are usually monitored to determine if their populations are declining over time.

– Data Deficient (DD): There is not enough information to assess the species, but it could be threatened. Currently, there are numerous species, especially marine ones, for which there is insufficient data to establish threat categories. They are difficult to study due to their distribution range and the complexity of accessing their habitats.

-Not evaluated (NE): It has not been evaluated but could be threatened.

Threatened species should be evaluated periodically (especially those that are near threatened). The use of these categories on a regional scale is important for larger populations.

For there to be an obligation to protect animal and plant species, there must be binding legislation. In Europe, the Habitats Directive 92/43/EEC has been developed. This directive has created a network of protected natural areas at the European level called the Natura 2000 Network. Its management and conservation objective is to protect the ecosystems where threatened species live. In Spain, Law 42/2007 on natural heritage and biodiversity is responsible for protecting flora and fauna.

As you can see, protecting ecosystems is vital to safeguarding the living conditions of animal and plant species. Thanks to current legislation and the efforts of many environmental organizations, significant progress is being made in protecting endangered species. However, there is still a huge amount of work to be done, as global biodiversity is losing species at an inexorable rate.