From megafauna extinction to the London Underground mosquito: how human activity drives evolution

A tragically extinct bit of megafauna. Image: Hulton Archive/Getty.

When scientists examine the impact of humans on the planet, the focus is mainly on the extinction of species. But increasingly researchers are looking at the idea that humans, through animal domestication, relocation and hunting, have become an evolutionary driving force that has led to new species, new traits and novel ecosystems.

A new paper, recently published in the Proceedings of the Royal Society B, argues that if we are to preserve the biodiversity of life that we value, we need to understand both the nature of this human-driven creation – a process known as speciation – as well as the effects of human-driven extinctions.


A drive to extinction

Look at humans’ effects on Earth’s plant life. Over recent decades, the amount of new plant growth each year across the world appears to have been relatively constant. However, between 25 per cent and 38 per cent of this fresh plant growth is appropriated by humans – for food and other purposes – reducing the amount available for millions of other species.

Thomas Crowther and colleagues at Yale University estimated that before the industrial revolution there were 6bn trees on Earth. There are now only 3bn. This deforestation and the conversion of land to produce food, fuel, fibre and fodder, combined with targeted hunting and harvesting, has resulted in a rate of species extinction some 100 to 1,000 times higher than would have been expected without human intervention. This probably constitutes the beginning of the sixth mass extinction in Earth’s history – an enormous impact on the planet and one reason why many scientists have declared that we have entered the Anthopocene Epoch.

Species removal isn’t a random process: a disproportionate number of those driven to extinction are the larger animals, both on land and at sea. This “megafauna extinction” began 50,000 years ago: unbelievably, half of all large-bodied mammals worldwide, equivalent to 4 per cent of all mammal species, have been lost in that time. And extinctions are not just confined to mammals: since 1500CE there have been 784 documented extinctions, including 79 mammals, 129 birds, 21 reptiles, 34 amphibians, 81 fish, 359 invertebrates and 86 plants.

Domestication and relocation

Humans have also domesticated around 474 animals and 269 plants to meet their needs, and this has led to the emergence of new species. Of the world’s 40 most common agricultural crops, eight can be considered entirely new species, just as animal domestication has created new species of animals such as the dog and domestic pig.

Animal domestication has also led to a major shift in animal distribution. According to Vaclav Smil of the University of Manitoba, of the weight of all the planet’s land mammals, humans make up 30 per cent, domesticated animals make up 67 per cent, and wild mammals just 3 per cent. Organisms have also been transported around the world – including crops, domesticated animals, and pathogens such as viruses and bacteria. This movement has led to a small number of extraordinarily common species such as the brown rat, new hybrid species such as mules, and a general homogenisation of the animal and plant life found on Earth.

There’s more to animal domestication than you’d think. Image: XKCD/creative commons.

This biological relocation started in the 16th century when species from the Old World of Europe and Asia were exchanged with those in the New World (the Americas). This is known as the Colombian Exchange, which led to the globalisation of human food, with New World crops such as maize/corn, potatoes and manioc/cassava swapping places with Old World crops such as sugarcane and wheat. Domesticated animals swapped continents, too.

Many of these plants and animals have since undergone rapid evolution in their new environments, leading to the emergence of new species. Accidental transfers from Europe occurred, too: smallpox, measles and typhus killed over 50m people in South and Central America during the colonisation of the New World. These exchanges continue today, and invasive species have become a major concern on all continents. Mark van Kleunen and colleagues at the University of Konstanz suggest that 4 per cent of plant species have been relocated around the globe, equivalent to all the native plant species in Europe.

These changes are the first of their kind since the supercontinent Pangaea separated about 200m years ago, but in fact the extent of the current epoch’s trans-oceanic exchanges are unprecedented.

Something borrowed, something new

Most ecosystems have been altered by humans, to the extent that the concept of a “natural” biome, completely free from human influence, is obsolete. This has led Erle Ellis at the University of Maryland to suggest that we consider them Anthromes – those ecosystems where most of characteristics have been reshaped by human activity. While many have undergone significant loss of biodiversity, through change they also create environments that allow opportunities for the emergence of new species.

Culex pipiens f. molestus, the mosquito species unique to the London Underground. Image: Walkabout12/creative commons.

An interesting example is that of the common house mosquito (Culex pipiens) which has become adapted to London’s underground railway and established a subterranean population of mosquitoes distinct from any other on Earth. Now called the London Underground mosquito, it has diverged sufficiently from its cousins above ground that it can no longer interbreed with them and exhibits significantly different behaviour.

So through breeding, harvesting and transport of crops and animals, and the impact of higher air and surface temperatures that result from greenhouse gas emissions, humans have, and continue to, alter the evolutionary process of the other species sharing this planet with us.

If we consider also the scientific development of diverse new biological products such as antibiotics, pesticides and novel genetically engineered organisms, humans have indeed become the world’s greatest evolutionary force capable of shaping our world by creating new species and destroying others.

If we are to help preserve the millions of species on Earth, we must consider the impact of humans in terms of these creative and destructive forces.The Conversation

Mark Maslin is professor of Climatology at UCL.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

Green roofs improve cities – so why don’t all buildings have them?

The green roof at the Kennedy Centre, Washington DC. Image: Getty.

Rooftops covered with grass, vegetable gardens and lush foliage are now a common sight in many cities around the world. More and more private companies and city authorities are investing in green roofs, drawn to their wide-ranging benefits which include savings on energy costs, mitigating the risk from floods, creating habitats for urban wildlife, tackling air pollution and urban heat and even producing food.

A recent report in the UK suggested that the green roof market there is expanding at a rate of 17 per cent each year. The world’s largest rooftop farm will open in Paris in 2020, superseding similar schemes in New York City and Chicago. Stuttgart, in Germany, is thought of as “the green roof capital of Europe”, while Singapore is even installing green roofs on buses.

These increasingly radical urban designs can help cities adapt to the monumental challenges they face, such as access to resources and a lack of green space due to development. But buy-in from city authorities, businesses and other institutions is crucial to ensuring their success – as is research investigating different options to suit the variety of rooftop spaces found in cities.

A growing trend

The UK is relatively new to developing green roofs, and governments and institutions are playing a major role in spreading the practice. London is home to much of the UK’s green roof market, mainly due to forward-thinking policies such as the 2008 London Plan, which paved the way to more than double the area of green roofs in the capital.

Although London has led the way, there are now “living labs” at the Universities of Sheffield and Salford which are helping to establish the precedent elsewhere. The IGNITION project – led by the Greater Manchester Combined Authority – involves the development of a living lab at the University of Salford, with the aim of uncovering ways to convince developers and investors to adopt green roofs.

Ongoing research is showcasing how green roofs can integrate with living walls and sustainable drainage systems on the ground, such as street trees, to better manage water and make the built environment more sustainable.

Research is also demonstrating the social value of green roofs. Doctors are increasingly prescribing time spent gardening outdoors for patients dealiong with anxiety and depression. And research has found that access to even the most basic green spaces can provide a better quality of life for dementia sufferers and help prevent obesity.

An edible roof at Fenway Park, stadium of the Boston Red Sox. Image: Michael Hardman/author provided.

In North America, green roofs have become mainstream, with a wide array of expansive, accessible and food-producing roofs installed in buildings. Again, city leaders and authorities have helped push the movement forward – only recently, San Francisco created a policy requiring new buildings to have green roofs. Toronto has policies dating from the 1990s, encouraging the development of urban farms on rooftops.

These countries also benefit from having newer buildings, which make it easier to install green roofs. Being able to store and distribute water right across the rooftop is crucial to maintaining the plants on any green roof – especially on “edible roofs” which farm fruit and vegetables. And it’s much easier to create this capacity in newer buildings, which can typically hold greater weight, than retro-fit old ones. Having a stronger roof also makes it easier to grow a greater variety of plants, since the soil can be deeper.


The new normal?

For green roofs to become the norm for new developments, there needs to be buy-in from public authorities and private actors. Those responsible for maintaining buildings may have to acquire new skills, such as landscaping, and in some cases volunteers may be needed to help out. Other considerations include installing drainage paths, meeting health and safety requirements and perhaps allowing access for the public, as well as planning restrictions and disruption from regular ativities in and around the buildings during installation.

To convince investors and developers that installing green roofs is worthwhile, economic arguments are still the most important. The term “natural capital” has been developed to explain the economic value of nature; for example, measuring the money saved by installing natural solutions to protect against flood damage, adapt to climate change or help people lead healthier and happier lives.

As the expertise about green roofs grows, official standards have been developed to ensure that they are designed, built and maintained properly, and function well. Improvements in the science and technology underpinning green roof development have also led to new variations on the concept.

For example, “blue roofs” increase the capacity of buildings to hold water over longer periods of time, rather than drain away quickly – crucial in times of heavier rainfall. There are also combinations of green roofs with solar panels, and “brown roofs” which are wilder in nature and maximise biodiversity.

If the trend continues, it could create new jobs and a more vibrant and sustainable local food economy – alongside many other benefits. There are still barriers to overcome, but the evidence so far indicates that green roofs have the potential to transform cities and help them function sustainably long into the future. The success stories need to be studied and replicated elsewhere, to make green, blue, brown and food-producing roofs the norm in cities around the world.

Michael Hardman, Senior Lecturer in Urban Geography, University of Salford and Nick Davies, Research Fellow, University of Salford.

This article is republished from The Conversation under a Creative Commons license. Read the original article.