Biodiversity in crisis: Half of earth's species experience alarming declines

A recent study published in Biological Reviews has raised concerns about global wildlife loss, painting a significantly more alarming picture of declining species populations than previously believed. The researchers analyzed more than 70,000 animal species and found that 48 percent of them have declining populations.

The sixth mass extinction

The study's lead author, Daniel Pincheira-Donoso, an evolutionary and climate change biologist at Queen's University Belfast, said the world is currently witnessing the early stages of a mass extinction. Previous conservation estimates focused on determining whether a species is currently at risk of extinction, while this study examines the direction in which species populations are heading. Only three percent of the species tested were found to have increasing populations.

This study adds to growing concern over human-induced mass extinction, aligning with a 2019 United Nations report that warned of the extinction risk facing more than half a million species in the coming decades. Experts emphasize the urgent need to act to reverse this trend and propose effective strategies.

Traditionally, the risk of extinction for wildlife has been measured using "conservation categories" that indicate a species' current level of threat. However, Pincheira-Donoso and his team took a different approach by evaluating broader population trends to determine whether species populations were increasing, declining, stable, or unknown. This perspective provides a temporary view of the state of the species rather than a snapshot.

28% of biodiversity currently threatened

While the research revealed that nearly half of the species examined were in decline, the International Union for Conservation of Nature's Red List classifies only 28 percent of biodiversity as currently threatened. Additionally, the study found that 33 percent of species classified as non-threatened on the Red List were actually experiencing population declines, suggesting future extinction risks.

Among the six animal categories examined (mammals, birds, amphibians, reptiles, fish, and insects), reptiles and fish were found to have the most stable populations, while amphibians experienced the most severe decline.

Christina Davy, assistant professor at Carleton University, highlights the importance of this research in revealing the decline of species despite their conservation categorization. She explains that species can slowly decline without meeting the criteria for threatened, endangered, or vulnerable status.

For more effective biodiversity management, Davy suggests looking at broader population trends. Instead of focusing solely on species on the brink of extinction, attention should also be paid to declining species that cannot yet be considered threatened. By protecting common species, a greater positive impact can be achieved.

Natural landscapes to human-occupied areas

The main driver of biodiversity loss is habitat destruction as a result of the conversion of natural landscapes to human-occupied areas, such as cities, farmland, and roads. Although climate change represents a growing threat to biodiversity, habitat loss remains the number one concern.

David Cooper, the acting executive secretary of the Convention on Biological Diversity, emphasizes the importance of land use in conserving biodiversity. Human activities, agricultural systems and livestock have extensively invaded natural habitats, causing a significant reduction in the abundance of animal species.

Cooper points to the Kunming-Montreal Global Biodiversity Framework as an international agreement that aims to address land use issues and restore ecosystems. The framework sets targets for habitat protection and restoration, climate change mitigation, and combating overexploitation, pollution, and invasive species.

Conservation organizations, such as the Wilder Institute, are taking an ecosystem-focused approach to conservation. Restoring natural habitats and ensuring the release of species into intact ecosystems are critical aspects of their efforts. Habitat restoration benefits not only the target species, but also other species that depend on the same ecosystem.

Threat to biodiversity worldwide

The decline in biodiversity directly affects human dependence on nature, including the vital role of animal pollination for crop production. The decrease in the abundance and diversity of pollinating species affects the productivity of many agricultural crops. Given that humans depend on nature and the diversity of species, it is essential to prioritize.

Human activities currently pose a serious threat to biodiversity worldwide, putting our planet's ecosystems and species at risk of a sixth mass extinction event. Habitat destruction, overexploitation, pollution, invasive species, and climate change are among the key drivers of this crisis. Understanding the seriousness of the situation and taking immediate action to protect biodiversity are of paramount importance to avoid irreparable damage.

Throughout Earth's history, there have been five major mass extinctions, known as the "Big Five." These events involved the rapid loss of a significant part of life on Earth. A mass extinction is generally defined as the loss of around 75% of all species worldwide within a relatively short geological period.

"Big Five" mass extinctions

• Late Ordovician Extinction (around 443 million years ago): This event took place in two peaks separated by hundreds of thousands of years and resulted in the loss of 60-70% of species, mainly marine organisms. It was probably triggered by an ice age and subsequent global cooling.

• Late Devonian extinction (circa 360-375 million years ago): Over millions of years, approximately 75% of all species, particularly marine life, became extinct. The exact cause is not fully understood, but may involve sea level changes and oxygen depletion in the oceans.

• Late Permian extinction or "The Great Dying" (about 252 million years ago): This was the most severe extinction event in Earth's history, wiping out about 95% of all species, both marine and terrestrial . It was probably caused by massive volcanic eruptions in Siberia, causing drastic climate change.

• Late Triassic extinction (about 200 million years ago): About 70-75% of all species perished during this event, which can be attributed to volcanic activity, climate change, and potentially an asteroid impact .

• Late Cretaceous Extinction (around 66 million years ago): This extinction event is famous for ending the reign of the dinosaurs. Approximately 75% of all species disappeared, probably due to the impact of a large asteroid or comet near present-day Mexico.

Scientists are now raising concerns about a possible sixth mass extinction, driven by human activity. Unlike previous extinctions caused by natural events, the current crisis is primarily caused by human factors such as habitat destruction, overexploitation, invasive species, pollution, and climate change.

The current rate of species extinction is estimated to be between 100 and 1,000 times the expected natural rate, exceeding the rate of previous mass extinctions. If left unchecked, widespread species declines could have far-reaching consequences for the stability of ecosystems and human societies.

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