When we talk about biodiversity, we mean the amazing array of species that live across the earth. When we talk about the biggest five threats to biodiversity, then, we are describing the main factors driving the extinction of plants, animals and fungi, leading to destabilisation of ecosystems, and the growing inability of our world to provide the fundamental services to human existence. In conservation, we are working to try and mitigate the effects of climate change, habitat loss, overexploitation, invasive species, and pollution on fragile habitats. Unfortunately, human-kind is the source of most if not all of these threats to biodiversity, and so it is up to us to halt each threat in its tracks.
This graph shows the measurements of temperature anomaly, or how different temperatures are to what is expected in that year. Before around 1940, most mea
surements were below average (below 0). Once we get to the 1980s however, the rate of temperature increase indicated by a positive value goes through the roof. The increase in global temperatures is real, and the earth’s biodiversity is struggling to keep up.
Interestingly, a lot of research has shown that plants and animals are changing their distributions across the globe, moving to poles, away from the equator, to stay in the temperature that they can survive in. With marine animals, tropical fish are moving to temperate climates, and temperate fish are being found closer and closer the arctic and Antarctic regions of our oceans. As temperatures rise, ecosystems on land are climbing to higher altitudes, and similarly in the sea they are moving away from the equator. On average, species are shifting their distribution by 6.1km per decade towards the poles, and seasons are changing as well with spring events advancing 2.3 days per decade.
This is all very well accepting the movement of animals with climate change, but as I’m sure you can see, animals are eventually going to run out of space. Ecosystems climbing up mountains are shrinking their ranges, as they reach mountain peaks where they become stranded with nowhere else to go, facing almost certain extinction. Likewise, species such as the polar bear, and other polar dwelling species have no colder place to go. Options are incredibly limited, and with some species simply unable to move fast enough with the changing temperatures, it is likely that climate change will be one of the greatest causes of biodiversity loss in the next 50 years if something drastic doesn’t happen very soon.
Deforestation and habitat loss:
Forests, wetland habitats, and other precious ecosystems are being lost at an alarming rate, destroying the ecosystems on which many species depend. It has been estimated that 18 million acres of forest are lost each year, due in part to logging and other human practices, Wetlands and other habit are also suffering, where patches of wetland in Switzerland have shrunk to a fraction of their size, decreasing the amount of habitat available in each wetland, and importantly the ability of animals to move between these patches. Similarly in Dorset in the UK, most of the rough unmanaged grassland and heath areas important for a lot of species have been replaced for lower diversity more strictly managed ecosystems.
The effect of the global habitat loss means ranges available for species is simply not enough: the area available to a lot of the species on the planet is simply not large enough to support large and stable populations. A smaller population is a less stable one, and this means we are pushing animals very close to an edge that would only take a small catastrophic event before numbers can no longer recover, and they become destined for extinction.
Cebu Island, in the Philippines used to contain over 5000km2 of unique Dipterocarp forest. In recent years, however only 15km2 of this special south east Asian habitat remains. Where this forest used to support an incredible number of exotic species, at present it only tells a sorry story. In 1991, a survey only found four species, and a survey the following year only found three more in an unsustainable 2km2 fragment. These species are doomed to extinction, and it is up to us to make sure other forests don’t meet the same end.
Overexploitation means the harvesting of a species from the wild at rates faster than it can naturally recover. Overfishing and overhunting both fall into this category. After hundreds of years of overexploitation leading to species extinctions, we are finally beginning to understand the full effect of our consumptive actions.
Here is perhaps the most iconic image of senseless slaughter at the hands of humankind, depicting an unimaginable mass of Bison skulls. This particular species came close to extinction in the 19th century, following overexploitation, with many shot simply as a means to entertain. Most of the overexploitation occurring in present times, however, resides in the oceans.
Marine and freshwater fish, more than any other group of species, are threatened with extinction by human activities. Industrialised fishing fleets can deplete marine life at a much faster rate than the fish can reproduce. It doesn’t take too much to understand that this leads to rapid population and ecosystem collapse. Fishermen have better technology, and are able to access deeper waters. Nowhere is safe and humans are able to fish faster than ever before – a lethal combination.
Invasive species in the context of threats to biodiversity mostly encompass the process of one species moving and remaining in another habitat, normally resulting from human movement. Normally impacts of invasive species are minor, but occasionally they can have dramatic consequences on the ecosystem being invaded. Generally, impacts of invasive species are unpredictable as to when and where it will be a major problem, making this threat to biodiversity a ticking time bomb, but with no clear warning as to the time of explosion.
The island of Guam in the pacific faced decimation of its endemic bird species, when the arrival of westerners brought the Brown tree snake with them. Before the brown tree snake, the birds faced no ground dwelling predators, and so after its arrival the species on the island faced a similar fate to those on islands that have been invaded in the past few hundred years. Ground dwelling birds were driven to extinction, with eggs stolen by the snake, and no evolved mechanism to prevent such attacks.
Invasions of species are often disastrous on islands, where these communities have remained isolated from the threat of predators. Although often unintentional, the lack of careful human movement between habitats and even continents leads to the introduction of predators, and incredibly destructive consequences for local biodiversity.
Pollution is perhaps one of the most obviously human induced threats to biodiversity, and often one of the most rapid and acute causes of extinction. From oil spills across land and ocean, to the slower destruction of the ozone layer resulting from pesticides and chlorofluorocarbons, humans have frequently and again quite unintentionally caused the destruction of ecosystems around the globe.
One unsung form of pollution that may lead to extensive biodiversity loss is the amount of excess nitrogen released into ecosystems, and confusingly comes in a number of different forms. Nitrogen oxides can be released at power plants, road transport, and other sources, can travel hundreds or thousands of miles, and then can be released onto land and water in the form of acid rain. Ammonia on the other hand primarily results from farm livestock, with bird farms in particular releasing huge amounts of nitrogen into surrounding land and rivers if not carefully regimented.
So why are nitrogen levels so important? In places throughout Europe, Nitrogen levels are four times higher than the levels before the industrial revolution, but in some places this can be further quadrupled to levels sixteen times pre- the industrial era. This is a massive change in the chemical composition of soils and water bodies, and it is changing the structure of many ecosystems.
The UK is the only island home to heathlands, and these ecosystems have evolved to very low levels of nitrogen in their soil. Adding a vast amount of nitrogen into a land previously starved of nitrogen leads to heather being outcompeted by other grasses, and plants requiring this increased nitrogen soil content. If the heather are outcompeted, and can no longer survive in places across the UK, then we can’t expect the species relying on the heather to survive either. Polluting the globe with chemicals that are not even poisonous can lead to vast changes in ecosystem structure, and importantly a wave goodbye to the species struggling to survive.
So, we have unleashed here perhaps one of the hardest hitting messages of our generation. Biodiversity is facing a five-pronged attack, and we’re responsible. Thankfully, due to the work of many unsung heroes, and the organisation and hardship from a large number of conservation bodies, each and every factor threatening the biodiversity across the globe is being attacked right back. It may be easy to sling your hook, and believe it is all over, but that is wrong. So much can be done to retain our precious ecosystems, and next week we will tell the slightly more uplifting and incredibly inspiring ways the five threats to biodiversity are halted. The last Conference on Biodiversity aimed to halt biodiversity loss by 2020, and plans are being made every day to achieve just that.