What Is Biodiversity and Why Is It Important?

Biodiversity is a term used to describe the astonishing variety and variability of living organisms

What Is Biodiversity and Why Is It Important?
Dr Simone Webber
May 23, 2022

Biodiversity is a term used to describe the astonishing variety and variability of living organisms on planet Earth. From tropical rainforests with jewel-coloured birds to windswept penguins in the Antarctic, diverse communities of bacteria, fungi, plant and animal organisms form ecosystems with their physical environment. The species within these ecosystems interact to produce a complex web of interconnections, with each species affecting others around it. The complexity of these interconnections is the result of millions of years of evolution, leading to the dazzling diversity of life on earth.

Biodiversity is not merely an abstract biological concept, it is essential to humanity because it provides the air that we breathe, medicines to heal us and the food that we eat. The biodiversity of our planet is under serious threat from human activities, however, and we may be causing the sixth mass extinction event in Earth’s history. It is critical that we learn to appreciate and protect the biodiversity of our planet because as Professor of Wildlife Conservation at Oxford University David Macdonald stated, ‘without biodiversity, there is no future for humanity’.  

What is biodiversity and how is it measured?

The extent of our planetary biodiversity is almost beyond comprehension, with an estimated 11 million species on Earth, of which only 13% have been described, and as many as 1 trillion microbial species. The current geological epoch (the Holocene) has been one of the most climatically stable in Earth’s history and until recently life on our planet has thrived. Biodiversity is not distributed evenly across the globe, with latitudinal gradients that culminate in far higher terrestrial diversity in tropical climates. The tropics provide a home to over 75% of known terrestrial and marine species and the Amazon rainforest alone has 1 in 10 of known species, meaning that tropical areas are particularly important for global biodiversity.

Mannion, P. D. 2014. Patterns in Palaeontology: The latitudinal biodiversity gradient. Palaeontology Online, Volume 4, Article 3, 1-8.

Biodiversity can become even more concentrated in hotspots when human activity encroaches on areas with a high number of unique species, such as the Atlantic rainforest in Brazil and the Cape Floristic region in South Africa. The 36 currently defined hotspots are high in endemic species that are unique to that area, and they support nearly 60% of the world’s plant, bird, mammal, reptile and amphibian species.

The study of biodiversity can be considered at three levels, which intertwine with each other to create ecosystem stability: ecosystem biodiversity, species biodiversity and genetic biodiversity.

Ecosystem biodiversity (e.g. a desert, a forest) is the variation in ecosystems either within a geographical area or across the whole planet. It covers all the different geographical features, habitats, biological communities and ecological processes within a defined ecosystem.

Species biodiversity (e.g. mammals, invertebrates) refers to all the different species within an ecosystem but also to the variety within and between different species. Counting the species within an ecosystem is one of the easiest ways of assessing its biodiversity.

Genetic biodiversity is the variety in genes within the species and is essential for healthy populations because low diversity increases extinction risk and reduces the resilience of a species to withstanding environmental changes (stochasticity). A wide variety of genetic characteristics within a population increases the chances that there will be individuals with a morphology that is adapted to the new environment.

The easiest way to measure the biodiversity of an ecosystem is to count the number of species, which gives a metric called the species richness. This can oversimplify the assessment of diversity in an area, however, and does not take into account species evenness, the relative abundance of each species.

Biodiversity indices can help to refine an estimate from an area and take factors such as evenness and phylogenetic components into account, giving a more comprehensive estimate. Biodiversity can also be expressed as a function of the habitat that is being examined and the species that would be expected to use it, such as the DEFRA biodiversity metric. Assessing biodiversity in a systematic way is a useful tool to compare biodiversity between habitats and monitor temporal trends.

The complexity of ecosystems

The extraordinary complexity of the interaction between species within an ecosystem is one of the key reasons that maintaining biodiversity is so important. Every species relies on other species for services such as food, shelter and reproduction, and the local extinction or introduction of any one species can have dramatic consequences for the ecosystem. The intricacy of this web of interactions can be visualised using a food web, where the reliance of individual species on seemingly unrelated organisms lower down the trophic levels can be seen.

The most obvious interactions between species are antagonistic, such as the predator-prey relationship, grazing or parasitism. Species can also interact in ways that benefit each other and exhibit mutualism (e.g. plants and pollinators) or one species can benefit from another without affecting the other species, exhibiting commensalism (e.g. clownfish living in the stinging tentacles of sea anemones). Antagonistic relationships such as the predator-prey one or competition between species for a resource can drive the evolution of defensive mechanisms or avoidance behaviour.

Clownfish (Amphiprioninae sp.) in Wakatobi, Indonesia.

Appreciating the intricacy of these relationships within an ecosystem allows us to understand how the loss or introduction of one species can have extensive repercussions. For example, reintroducing an apex predator, the grey wolf, into Yellowstone National Park has had an unexpected direct and indirect trophic cascade effect that is still being recorded. The wolves reduced elk numbers but also made the elk more vigilant and encouraged them to move around more, reducing grazing pressure on trees and vegetation. This has had an indirect effect of increasing beaver colonies, which will have further significant impacts on species in the park as beavers are regarded as ecosystem engineers.

In contrast, introducing a non-native species can have negative effects on biodiversity, such as the devastation to bird life caused by cats that were introduced into New Zealand by European settlers. Invasive plants can pose particular problems for conservationists as they can be hard to control and dominate landscapes by out-competing native species, such as the non-native fire tree (Myrica faya) and the strawberry guava (Psidium cattleyanum) in Hawaii.

Lyall’s wren (Traversia lyalli), which became extinct after the introduction of cats to Stephens Island, New Zealand.

Why is biodiversity important?

It is exactly this complexity within ecosystems that makes biodiversity so essential as losing one species can have a chain reaction of effects. Higher biodiversity stabilises ecosystems against environmental change, invasive species and disease, and improves resilience to disturbance and potentially climate change. This resilience is driven by the so-called “insurance effect”, where different species can compensate for each other in the event of one being lost due to environmental stochasticity. Increased resilience within an ecosystem makes the provision of ecosystem services such as food, water or flood defence more reliable. Higher biodiversity also increases the productivity of an ecosystem, which has been recorded in zones where Marine Protected Areas have been introduced. Areas where fishing has been banned within an MPA have reported greatly increased marine biodiversity and spillover effects into nearby unprotected areas, increasing fishing yields by five times. Ecosystem services are inextricably linked to biodiversity, and they have been valued at $33 trillion a year globally in a 1997 study, so there are defined financial imperatives to ensuring its preservation.

Road building in the Amazon rainforest

Losing biodiversity may put an ecosystem at risk of ecological collapse, where a combination of extrinsic pressures leads to a tipping point where the vast majority of species cannot continue to exist. For example rapid deforestation and road building in the Amazon is fragmenting the habitat, leading to a cascade of events including loss of biodiversity that could soon turn it into a savannah grassland. The loss of biodiversity and tree cover could have catastrophic consequences for the stability of the global climate as the Amazon is one of the most significant terrestrial stores of carbon.

Threats to biodiversity

The threat that loss of biodiversity poses to the planet and the future of humanity cannot be overstated. Species extinctions are irreversible and we appear to be losing species faster than at any point in the Earth’s history. Ecosystem collapse and massive losses of biodiversity (mass extinctions) have historically occurred as a result of sudden events such as asteroid impacts and volcanic eruptions. However, with animal populations having dropped by 68% since 1970 and a current extinction rate that is 100 to 1000 times higher than background levels, it is human actions that are putting our ecosystems under unbearable pressure. A fifth of countries worldwide are now considered to be at risk of ecosystem collapse, and as the recent Netflix David Attenborough documentary ‘A Life on Our Planet’ makes clear, we need to act and act quickly.

Carolina parakeet (Conuropsis carolinensis) a formerly common parakeet in the United States that became extinct in 1918 following extensive hunting and deforestation. Photo credit: James St. John, https://commons.wikimedia.org

The statistics that demonstrate how much we have affected the planet make for uncomfortable reading. More than one third of the Earth’s land surface and three quarters of freshwater resources are dedicated to agriculture and livestock production. In terms of biomass, 96% of mammal biomass is humans and livestock, and 70% of bird biomass globally is domestic poultry. Simply stated, we are not living sustainably and our way of life is destroying the very biodiversity that we need to survive. Biodiversity is threatened predominantly by habitat loss and deforestation as a result of land use change for agriculture and biofuels, but also by climate change, urbanisation, habitat fragmentation, pollution, over harvesting, poaching and invasive species.

How can we preserve and increase biodiversity?

There is gathering public, business and political awareness of the urgency of tackling the global biodiversity crisis and this current momentum will drive action. The need to preserve biodiversity has been recognised internationally for decades and has been prioritised in global treaties such as the Ramsar Convention to protect wetlands (1971) and the Convention on Biological Diversity (1992). With the introduction of the UN Sustainable Development Goals (2015), biodiversity moved up both the political and business agenda as part of a global movement to prioritise sustainability and reduce biodiversity loss.

Bengal tiger (Panthera tigris tigris) in Ranthambhore Tiger Reserve, India

There are conservation success stories, although many of these are notable by the fact they have tended to focus on large and iconic species such as gorillas and pandas. The traditional approach of focusing on individual species such as pandas can come at the expensive of wider biodiversity, with other mammals such as leopards, snow leopards, wolves and Asian dogs disappearing from many of the panda reserves. There has been further criticism of the top down single species approach to conservation initiatives, such as the hugely successful increase in tiger numbers in India, because it appears that it may come at a high price for indigenous people.

With the right political focus and an ecosystem level approach, however, there can be effective initiatives that provide enormous benefits for biodiversity. Costa Rica is the first tropical country to have stopped and reversed deforestation, with a ban on deforestation and a government funded initiative that pays farmers to preserve natural habitats for biodiversity and climate change mitigation. The results have been very encouraging for global conservation initiatives, increasing forest cover from a low of approximately 38% back up to 60% since 1996.

Arenal volcano, Costa Rica

Biodiversity in the UK

Although the latitudinal gradients mean that biodiversity is not as high in temperate climates as in tropical climates, the diversity of habitats in countries such as the UK is essential to keeping our ecosystems functioning. The state of biodiversity in the UK is poor, however, with the UK failing to meet 14 out of the 20 Aichi biodiversity targets agreed as part of the Convention on Biological Diversity. The 2019 State of Nature report records continuing declines in many UK species, with a 13% decline in average species’ abundance overall since 1970 and 15% of species being threatened with extinction from Great Britain. Although the government committed to increasing the proportion of protected land to 30% by 2030, environmental organisations have highlighted how poorly many of our ‘protected’ areas are managed, with minimal benefits for wildlife. The UK also has one of the lowest levels of forest cover in Europe at only 13%, compared to a European average of 46%.

Cinnabar moth (Tyria jacobaeae). Photo credit: Charles J Sharp (https://en.wikipedia.org)

The UK is also estimated to have lost 50% of its biodiversity, ranking 189 out of 218 countries assessed by the PREDICTS Biological Intactness Index and coming bottom of the G7. There is an incontrovertible need and responsibility to address the loss of biodiversity in the UK urgently. The long-awaited Environment Bill will ensure that construction projects provide a 10% biodiversity net gain, but mitigating for lost habitat is only one of the steps that we need to take. The UK needs to assess the biodiversity and use of our protected areas, encourage debate about how agriculture can be more sustainable and work towards increasing the health of our existing wild ecosystems. The British public care enormously about wildlife, so if we continue to educate ourselves and demand better from the custodians of our landscape, we can play a part in helping tackle the biodiversity crisis.

Yellowhammer (Emberiza citrinella)

One of the cornerstones of the Creating Tomorrow’s Forests approach is that we should increase biodiversity at every one of our UK sites. We want to restore thriving, dynamic, native ecosystems which are resilient to change as well as being an oasis for wildlife and human visitors. We are passionate about British wildlife and ecology and want to enable businesses and individuals to turn the tide and rewild the UK.

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Our biodiversity work is divided into four core projects

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Wetland Nature Reserve

1.4 hectare mosaic of wet woodland, pond, and culm pasture meadow, in the North Devon Biosphere Reserve.

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Freshwater Lake Ecosystem

2.6 hectare freshwater lake with gravel bed and mudflats, wetland and wildflower meadow managed for rare butterflies.

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Seagrass Meadow Restoration

1 hectare of the most spectacular seagrass meadow off the coast of North Wales.

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