For time immemorial, many wildlife species have survived by undertaking heroic long-distance migrations. But many of these great migrations are collapsing right before our eyes.
Perhaps the biggest peril to migrations is so common that we often fail to notice them: fences. Australia has the longest fences on Earth. The 5,600-kilometre “Dingo Fence” separates southeastern Australia from the rest of the country, whereas the “Rabbit-Proof Fence” stretches for almost 3,300 kilometres across Western Australia.
Both of these enormous fences were intended to repel rabbits and other “vermin” such emus, kangaroos and dingoes that were considered threats to crops or livestock. Built over a century ago, their environmental impacts were poorly understood or disregarded at the time.
Since construction these fences have caused recurring ecosystem catastrophes, such as mass die-offs of emus and other species trying to find food and water in a land notorious for the unpredictability of its rainfall, vegetation growth and fruit production.
The same thing is happening across much of the planet. While a nemesis for larger wildlife, nobody knows how many fences exist today or where they’re located. A study that mapped all the fences in southern Alberta, Canada, found there were 16 times more fences than paved roads.
Scientists are waking up to the peril of fences, realising that from an environmental perspective they’re grossly understudied — “largely overlooked and essentially invisible,” according to a recent global review.
In Africa, home to some of the most spectacular wildlife migrations, scientists found that of 14 large-mammal species known to migrate en masse, five migrations were already extinct. Proliferating fences, along with habitat loss and wildlife poaching, has sent ecosystems such as the Greater Mara in Kenya crashing into ecological turmoil.
And a 2009 audit of Earth’s greatest terrestrial-mammal movements showed that of 24 large species that once migrated in their hundreds to thousands, six migrations have vanished entirely.
Many remaining migrations are mere shards of their former glory. For instance, Indochina once had mass migrations of elephants and other large mammals, big cats, monkeys and birds — often called the “Serengeti of Southeast Asia”.
The thundering herds of American bison – some numbering up to 4 million animals – which once dominated the plains of North America have all but vanished today.
How to save mass migration
There are two main ways to destroy mass migrations: killing the animals outright by hunting and over-harvesting, or stopping the animals from accessing food or water, typically by fencing them out or clearing and fragmenting their habitat.
As the human footprint rapidly expands, scary things for wildlife are happening all over. Research that one of us (Bill Laurance) led revealed that 33 African “development corridors” would, if completed, exceed 50,000 kilometres in length and crisscross the continent, chopping its ecosystems into scores of smaller pieces.
Beyond this, over 2,000 parks and protected areas in Africa would be degraded or cut apart by the massive developments.
Migrations are vulnerable even in the seas. Recent research shows that growing shipping traffic is an increasing danger to migratory great whales, basking sharks, and giant whale-sharks – all highly vulnerable to collisions with fast-moving ships, as well as disruption of their sensitive hearing and vocal communications by shipping noise and sonar, and pollutants from vessels.
But the inspiring news is that, if you remove barriers such as fences, animal migrations can spontaneously resume – like a phoenix rising from the ashes.
In 2004, a fence that had blocked a former zebra migration in Botswana was removed. By 2007 it was one of the longest animal-migration routes in the world.
And a few places on Earth are still free from fencing and fragmentation. The world-famous Seregeti ecosystem of Tanzania is an iconic example. In war-torn South Sudan, a spectacular mass migration of a million antelope — known as white-eared kob — is still intact because there are no fences.
And caribou still migrate in great herds across large expanses of northern Canada and Alaska.
Alarming news for Botswana
Collapsing migrations are a global concern, but right now conservationists are most worried about Botswana.
This mega-diverse nation in southern Africa is considering profoundly changing its wildlife management by expanding fences and cutting off wildlife migrations not considered beneficial to the country’s current priorities.
This would be a shocking decision, because Botswana’s wildlife conservation is almost entirely dependent on its mass migrations.
For wildebeest, zebra, eland, impala, kob, hartebeest, springbok and many other large migrants, isolation is a killer – destroying their capacity to track the shifting patterns of greening vegetation and water availability they need to survive.
And it’s not just grazing and browsing animals that are affected: entire suites of large and small predators, scavengers, commensal and migratory bird species, grazing-adapted plants and other species are integrally tied to these great migrations.
Botswana is already sliced into 17 giant “islands” by fences, erected in colonial times to protect the livestock of European farmers from foot-and-mouth disease.
But foot-and-mouth disease is far more likely to be spread by cattle, not wildlife. Fence-free strategies for managing disease risk also have have great potential.
And nature tourism in Botswana is a large, vibrant, and growing part of the national economy. Ecotourists will continue to favour the nation so long as it maintains untrammelled areas and spectacular animal migrations.
But you can kiss a lot of those tourism revenues goodbye if Botswana shatters its great migrations – killing off the spectacular living panoramas that are a magnet for the world’s nature lovers.
If we can avoid fencing and bulldozing critical parts of the Earth, we could hugely increase the chances that our most vibrant wildlife and ecosystems have a fighting chance to survive.
Bill Laurance, Distinguished Research Professor and Australian Laureate, James Cook University and Penny van Oosterzee, Adjunct Associate Professor James Cook University and University Fellow Charles Darwin University, James Cook University
The global cheetah population is continuing to decline with only about 7000 individuals left in Africa. This is thought to be about half the population that existed 40 years ago. The decline has been caused by the loss and fragmentation of their natural habitats, a decline in their prey base, the illegal trade in wildlife as well as conflict with humans for space.
Cheetahs have disappeared from 91% of their historic range. This is hugely problematic as cheetahs are a wide-ranging species. To be viable a cheetah population needs a contiguous, suitable habitat which covers about 4,000–8,000 km2. But few protected areas in Africa are larger than 4,000 km2.
As a result, most of the cheetahs in the world – 77% – are believed to range outside protected areas. But this isn’t ideal for the animals as, from previous research we conducted using data from GPS satellite collars fitted on cheetahs in the Maasai Mara, we found that cheetahs avoid areas of high human disturbance and prefer protected, wildlife areas.
These results show the importance of wildlife areas for cheetahs, but my most recent research shows that these protected spaces have challenges of their own. We found that the number of cubs a cheetah is able to rear is lower in areas that receive lots of tourists compared with areas that are visited less. This suggests that cheetahs aren’t getting the protection they need, particularly from the impact of growing numbers of tourists.
Famous for its spectacular wildebeest migration, the Maasai Mara is a popular tourist destination. The wildlife areas of the Maasai Mara include the Maasai Mara National Reserve, which is managed by the Narok County Government, and numerous wildlife conservancies, each run by different management companies.
The conservancies are formed through a partnership between Maasai landowners and tourism companies, whereby landowners receive a fixed, monthly payment for leasing their land for wildlife based activities on the condition that they do not live on the land, cultivate or develop it. Combined, the wildlife areas, which are predominantly used for photographic tourism, cover an area of about 2,600 km2 – one-tenth the size of Wales or Belgium.
During the high season about 2,700 people visit the Maasai Mara National Reserve daily. But they are often not adequately managed.
The Mara Reserve – with the exception of a conservancy called the Mara Triangle – doesn’t limit the number of tourists that enter the park per day, and there are no restrictions on the number of tourist vehicles at a predator sighting. It’s therefore not uncommon to see more than 30 tourist vehicles at a sighting.
Ideally, the Mara Reserve should restrict the number of tourists, especially during the peak tourist seasons.
Tourists also affect the landscape of wildlife areas. For example, tourist accommodation is continuing to increase in the Mara Reserve and these facilities are usually built on river banks which are prime habitats for species such as elephants, leopards and breeding raptors.
One crucial element for a healthy cheetah population is cub recruitment, defined as offspring survival to independence.
Cheetahs have relatively big litters, ranging between one to six cubs. But cheetah cubs can succumb to various factors including abandonment, poor health, and fires so the number of cubs that reach independence can be very low, ranging from 5% to 28.9%.
I was interested in finding out if tourism is playing a role in this.
By analysing four years of data on female cheetahs with cubs it became apparent that high numbers of tourists are having a negative effect on the number of cubs that reach independence. More specifically, females in areas with a lot of tourists on average raised one cub (or none survive) per litter to independence compared to more than two cubs in low tourist areas.
There was no hard evidence of direct mortality caused by tourists. But my conclusion from my findings is that tourists are likely to have an indirect effect on cub survival. This could be because they lead to cheetahs changing their behaviour and increase their stress levels by getting too close, overcrowding with too many vehicles, staying at sightings for prolonged periods of time and by making excessive noise.
What can be done?
My study highlights the importance of implementing and enforcing strict wildlife viewing guidelines, especially in areas where tourist numbers are high. The Maasai Mara’s wildlife conservancies are largely getting this right. Tourist numbers are limited to the number of beds per conservancy and only five vehicles are allowed at a sighting at any given time.
Actions that could be taken include:
allowing no more than five vehicles at a cheetah sighting;
ensuring that no tourist vehicles are allowed near a cheetah lair (den);
ensuring that vehicles keep a minimum distance of 30m at a cheetah sighting;
ensuring that noise levels and general disturbance at sightings are kept to a minimum;
ensuring that vehicles do not separate mothers and cubs; and that
cheetahs on a kill are not enclosed by vehicles so that they can’t detect approaching danger.
If tourism is controlled and managed properly, it can play a very positive role in conservation. Money from tourism goes towards the creation and maintenance of protected areas – like the wildlife conservancies – and can help alleviate poverty. It also shows local communities the benefits that predators can bring and can positively influence attitudes.
However if human pressures, like tourism, remain unchecked it risks having a negative impact on wildlife and could mean the loss of some of the biggest attractions – like cheetahs.
Nine of 13 of Africa’s oldest and largest baobab trees have died in the past decade, it has been reported. These trees, aged between 1,100 and 2,500 years, appear to be victims of climate change. Scientists speculate that warming temperatures have either killed the trees directly or have made them weaker and more susceptible to drought, diseases, fire or wind.
Old baobabs are not the only trees which are affected by climatic changes. Ponderosa pine and Pinyon forests in the American West are dying at an increasing rate as the summers get warmer in the region. In Hawaii the famous Ohi’a trees are also dying at faster rates than previously recorded.
There are nine species of baobab trees in the world: one in mainland Africa, Adansonia digitata, (the species that can grow to the largest size and to the oldest age), six in Madagascar, and one in Australia. The mainland African baobab was named after the French botanist Michel Adanson, who described the baobab trees in Senegal.
The African baobab is a remarkable species. Not only because of it’s size and lifespan but also in the special way it grows multiple fused stems. In the space between these stems (called false cavities) bark grows, which is unique to the baobab.
Since baobabs produce only faint growth rings, the researchers used radiocarbon dating to analyse samples taken from different parts of each tree’s trunk and determined that the oldest (which is now dead) was more that 2,500-years-old.
They also have more than 300 uses. The leaves, rich in iron, can be boiled and eaten like spinach. The seeds can be roasted to make a coffee substitute or pressed to make oil for cooking or cosmetics. The fruit pulp has six times more vitamin C than oranges, making it an important nutritional complement in Africa and in the European, US and Canadian markets.
Locally, fruit pulp is made into juice, jam, or fermented to make beer. The young seedlings have a taproot which can be eaten like a carrot. The flowers are also edible. The roots can be used to make red dye, and the bark to make ropes and baskets.
Baobabs also have medicinal properties, and their hollow trunks can be used to store water. Baobab crowns also provide shade, making them an idea place for a market in many rural villages. And of course, the trade in baobab products provides an income for local communities.
Baobab trees are not only useful to humans, they are key ecosystem elements in the dry African savannas. Importantly, baobab trees keep soil conditions humid, favour nutrient recycling and avoid soil erosion. They also act as an important source of food, water and shelter for a wide range of animals, including birds, lizards, monkeys and even elephants – which can eat their bark to provide some moisture when there is no water nearby. The flowers are pollinated by bats, which travel long distances to feed on their nectar. Numerous insects also live on the baobab tree.
Ancient as they are, baobab trees can be cultivated, as some communities in West Africa have done for generations. Some farmers are discouraged by the fact that they can take 15-20 years to fruit – but recent research has shown by grafting the branches of fruiting trees to seedlings they can fruit in five years.
Many “indigenous” trees show great variation in fruit morphological and nutritional properties – and it takes years of research and selection to find the best varieties for cultivation. This process, called domestication, does not refer to genetic engineering, but the selection and cultivation of the best trees of those available in nature. It seems straightforward, but it takes time to find the best trees – meanwhile many of them are dying.
The death of these oldest and largest baobab trees is very sad, but hopefully the news will motivate us to protect the world’s remaining large baobabs and start a process of close monitoring of their health. And, hopefully, if scientists are able to perfect the process of identifying the best trees to cultivate, one day they will become as common in our supermarkets as apples or oranges.
A large crack, stretching several kilometres, made a sudden appearance recently in south-western Kenya. The tear, which continues to grow, caused part of the Nairobi-Narok highway to collapse. Initially, the appearance of the crack was linked to tectonic activity along the East African Rift. But although geologists now think that this feature is most likely an erosional gully, questions remain as to why it has formed in the location that it did and whether its appearance is at all connected to the ongoing East African Rift. For example, the crack could be the result of the erosion of soft soils infilling an old rift-related fault.
The Earth is an ever-changing planet, even though in some respects change might be almost unnoticeable to us. Plate tectonics is a good example of this. But every now and again something dramatic happens and leads to renewed questions about the African continent splitting in two.
The Earth’s lithosphere (formed by the crust and the upper part of the mantle) is broken up into a number of tectonic plates. These plates are not static, but move relative to each other at varying speeds, “gliding” over a viscous asthenosphere. Exactly what mechanism or mechanisms are behind their movement is still debated, but are likely to include convection currents within the asthenosphere and the forces generated at the boundaries between plates.
These forces do not simply move the plates around, they can also cause plates to rupture, forming a rift and potentially leading to the creation of new plate boundaries. The East African Rift system is an example of where this is currently happening.
The East African Rift Valley stretches over 3,000km from the Gulf of Aden in the north towards Zimbabwe in the south, splitting the African plate into two unequal parts: the Somali and Nubian plates. Activity along the eastern branch of the rift valley, running along Ethiopia, Kenya and Tanzania, became evident when the large crack suddenly appeared in south-western Kenya.
Why does rifting happen?
When the lithosphere is subject to a horizontal extensional force it will stretch, becoming thinner. Eventually, it will rupture, leading to the formation of a rift valley.
This process is accompanied by surface manifestations along the rift valley in the form of volcanism and seismic activity. Rifts are the initial stage of a continental break-up and, if successful, can lead to the formation of a new ocean basin. An example of a place on Earth where this has happened is the South Atlantic ocean, which resulted from the break up of South America and Africa around 138m years ago – ever noticed how their coastlines match like pieces of the same puzzle?.
Continental rifting requires the existence of extensional forces great enough to break the lithosphere. The East African Rift is described as an active type of rift, in which the source of these stresses lies in the circulation of the underlying mantle. Beneath this rift, the rise of a large mantle plume is doming the lithosphere upwards, causing it to weaken as a result of the increase in temperature, undergo stretching and breaking by faulting.
Evidence for the existence of this hotter-than-normal mantle plume has been found in geophysical data and is often referred to as the “African Superswell”. This superplume is not only a widely-accepted source of the pull-apart forces that are resulting in the formation of the rift valley but has also been used to explain the anomalously high topography of the Southern and Eastern African Plateaus.
Breaking up isn’t easy
Rifts exhibit a very distinctive topography, characterised by a series of fault-bounded depressions surrounded by higher terrain. In the East African system, a series of aligned rift valleys separated from each other by large bounding faults can be clearly seen from space.
Not all of these fractures formed at the same time, but followed a sequence starting in the Afar region in northern Ethiopia at around 30m years ago and propagating southwards towards Zimbabwe at a mean rate of between 2.5-5cm a year.
Although most of the time rifting is unnoticeable to us, the formation of new faults, fissures and cracks or renewed movement along old faults as the Nubian and Somali plates continue moving apart can result in earthquakes.
However, in East Africa most of this seismicity is spread over a wide zone across the rift valley and is of relatively small magnitude. Volcanism running alongside is a further surface manifestation of the ongoing process of continental break up and the proximity of the hot molten asthenosphere to the surface.
A timeline in action
The East African Rift is unique in that it allows us to observe different stages of rifting along its length. To the south, where the rift is young, extension rates are low and faulting occurs over a wide area. Volcanism and seismicity are limited.
Towards the Afar region, however, the entire rift valley floor is covered with volcanic rocks. This suggests that, in this area, the lithosphere has thinned almost to the point of complete break up. When this happens, a new ocean will begin forming by the solidification of magma in the space created by the broken-up plates. Eventually, over a period of tens of millions of years, seafloor spreading will progress along the entire length of the rift. The ocean will flood in and, as a result, the African continent will become smaller and there will be a large island in the Indian Ocean composed of parts of Ethiopia and Somalia, including the Horn of Africa.
Dramatic events, such as sudden motorway-splitting faults can give continental rifting a sense of urgency. However, rifting is a very slow process that, most of the time, goes about splitting Africa without anybody even noticing.
This article was updated and the headline changed on April 7 to reflect ongoing discussion by geologists about the cause of the large crack that appeared on the East Africa Rift and whether its location is related to the African continent split.