Before the industrial revolution, ecology was characterized by stability. Within each habitat, ecosystems had been assembled by long-term evolutionary processes where predators and prey, collaborators and competitors, from microbes to mammals co-existed within complex, inter-connected webs.
Change in biodiversity – the mix of plants, animals, fungi and microscopic organisms living within each habitat – occurred but was largely driven by long-term processes happening over centuries to millennia.
Human activity, such as burning fossil fuels and industrialized farming, have combined to dramatically impact the planet’s biomes and ecosystems. Climate change, deforestation, and pollution have destroyed or damaged habitats, changed where species live and eliminated species at a speed and scale comparable to major extinction events of the past.
Arguably the world is currently undergoing a human-caused major extinction event whose extent and impact we are still only beginning to understand.
Humanity relies on the earth’s natural systems to regulate the environment and maintain a habitable planet.
Terrestrial and marine ecosystems help regulate the earth’s surface temperature by absorbing greenhouse gases and changing the humidity and reflectance of land, and provide products vital for survival such as clean water, food, fuel, fibre, medicines, and shelter.
This article explains how human activity threatens biodiversity, and what actions are needed to address its global decline.
What are threats to biodiversity?
Threats to biodiversity include the burning of fossil fuels and clearing forests and other wild lands for industrialized agriculture. More direct human interventions such as poaching and hunting can also have a serious effect.
Within each ecosystem, the interconnected nature of species’ interactions means even the elimination of a single species, whether an apex predator, a pollinating insect, or a plant can have cascading effects, causing ripple effects which reconfigure the entire ecosystem in ways that are unpredictable and with unexpected consequences.
A famous example is the impact that removal and reintroduction of wolves had in Yellowstone in the US. The US government sought to exterminate wolves in the late 19th and early 20th century, seeing them as a dangerous threat to people and livestock. But with the wolves gone, deer populations exploded, grazing out the vegetation in Yellowstone and rapidly diminishing tree growth. The lack of trees in turn reduced beaver populations, meaning less dams were built, affecting the flooding patterns of Yellowstone’s rivers.
A project to reintroduce wolves has helped stabilize Yellowstone as, to reduce the risk of being eaten, deer now avoid certain areas of the park allowing them to regenerate, and willow and cottonwood trees have returned.
This in turn restored bird populations and beaver colonies. Regenerating river forest also stabilized riverbanks and reduced soil erosion, meaning rivers were more fixed in their courses and flooded in more predictable ways.
The Yellowstone example illustrates how human interventions can dramatically reduce the diversity of species and even change the landscape in ways that are unpredictable and undesirable. These cascading effects are crucial in understanding why threats to biodiversity threaten humanity too.
Climate change threats to biodiversity
Climate change is altering what parts of the planet can accommodate each species as where each species lives is determined by climate either directly – through their ability to cope with heat or cold, dry, or wet conditions – or indirectly through change in the availability of food.
As the world’s climate changes, the ‘envelope’ of suitable climate for each species tends to move towards the planet’s poles. But species respond differently to this change as some can track it quickly and move as the climate changes, but others – with limited dispersal ability – may not track the climate envelope in real time.
As certain species depart ecosystems, seeking cooler climates or spreading into newly warmed areas, animals and plants they interact with changes, meaning the climate change fundamentally ‘rewires’ historical ecosystems.
Animals and plants, pests and diseases may ‘escape’ from their own natural enemies so climate change can lead to outbreaks of new, invasive species or pests – such as locusts – or contribute to diseases jumping to new hosts, including from animals to humans.
A warming world is causing ice and snow to melt and raising sea levels, leading to increased flooding and erosion of vital coastal ecosystems. Increasing global temperatures also raises the probability of fires and drought that destroy natural habitats such as forests and rivers, threatening the survival of more species and driving more climate change.
Wild areas such as forests and peat lands are vital carbon sinks, absorbing carbon dioxide from the atmosphere but, as warming increases and more wild areas are destroyed, more carbon dioxide enters the atmosphere and warming accelerates even more, threatening more destruction of biodiversity.
This creates a vicious circle of heating leading to destruction leading to more heating and more destruction.
Industrialized farming methods have seen the cultivation of single crops, known as ‘monoculture’, and the rearing of livestock on a massive scale. This has been, and still is, justified as essential to feeding the expanding human population and delivering more affordable and safer food supplies.
But industrialized agriculture has enormous impact on biodiversity and human health. Instead of wild animals, a small number of farmed animal species – mainly cows and pigs – now dominate. Together they account for 60 per cent of all mammal species by mass, compared to four per cent for wild mammals and 36 per cent for humans. Farmed chickens now account for 57 per cent of all bird species by mass, whereas wild birds make up 29 per cent of the total.
Wild areas of the planet are being continually cleared to accommodate expanding demand for land to host livestock and for the crops to feed them. This is highly destructive to global biodiversity, reducing wild areas, carving up the territories of large predators, ecologically re-wiring ecosystems, and creating cascading effects.
Pesticides are used on a vast scale to protect crops, wiping out insect populations. When it rains, fertilizers run off the ground and contaminate rivers, impacting the ecology in multiple ways. Nutrient-rich rivers become dominated by fast-growing bacteria and algae, crowding out other wildlife and reducing the oxygen available in the water, creating ‘dead zones’.
Bee populations of all kinds have been declining worldwide due to the use of pesticides in intensive farming and climate change, but they are vital to delivering successful yields of crops, especially nutrient-rich fruit and vegetables.
Even clearing hedgerows has a serious impact as hedges and grassy margins accommodate species of small wasp which provide free natural pest control. Without them more pesticide must be used and insect populations of all kinds continue to decline.
Mass livestock cultivation and the clearing of wild areas to support it also increases the likelihood of humans becoming exposed to new and dangerous pathogens, which can leap from to new host species and then via livestock and ‘bushmeat’ to people. One theory for the origin of COVID-19 is that it spread from bats via pangolins to people via a ‘wet’ market in China.
Antibiotics, used in farming to accelerate the growth of livestock, are also increasing the resistance of microbes, threatening a future where antibiotics are no longer effective for animals or people – and minor injuries and infections kill.