• The only remaining major wildebeest migration is the ‘Great Migration’ in the Serengeti-Mara.
• Wildebeests that can no longer migrate have lower genetic diversity, are more genetically isolated and are more inbred.
Image: FILE
The savanna ungulates (large mammals with hooves) are facing genetic problems due to fences, roads, farms and settlements, a new study shows.
A scientific article published in the Nature Communications journal shows that wildebeest migration hurdles not only hamper their natural movement but also lead to genetic decay in those herds that are confined and no longer able to roam freely.
The only remaining major wildebeest migration is the ‘Great Migration’ in the Serengeti-Mara.
Approximately 1.3 million wildebeest, accompanied by about 200,000 zebras and 400,000 gazelles, cover up to 3,000 kilometres annually in a clockwise cycle that follows seasonal rainfall patterns.
But only the wildebeest and zebra from the Serengeti cross the Mara River into Maasai Mara.
The study says due to limited source material on African wildlife populations prior to the mid-1800s, the number of historical wildebeest migrations is uncertain.
However, it is known that migrations comparable to those of the Serengeti-Maasai Mara population have been lost.
The study says an example of this relates to two wildebeest subspecies known as the white-bearded wildebeest: the Western white-bearded wildebeest, which makes up the Serengeti-Mara population, and the Eastern white-bearded wildebeest, whose migration is centered around Kajiado county.
“From early European explorers and the first big game hunters, we know that both of these subspecies migrated a great deal historically. And they had very large populations, presumably of approximately similar size," it says.
The study shows that while the Western white-bearded wildebeest was protected in the Serengeti-Mara from the early 1950s, increased human presence and activities dating back to the early 1900s put mounting pressure on the Eastern white-bearded subspecies.
"Today, only 6,000-8,000 Eastern white-bearded wildebeests remain and are divided into many, small and isolated populations,” it says.
Epic migration has become a rare sight in Africa as humans continue to interrupt their historic migratory routes with roads, oil and gas pipelines, railway lines, fences, cities, livestock and farmland.
“The annual migration of 1.3 million wildebeest through Tanzania’s Serengeti and Kenya’s Maasai Mara attracts hundreds of thousands of tourists, and the phenomenon has put the Serengeti on Unesco’s list of World Heritage Sites. Besides its majestic sight, the migration of this emblematic species is important for the ecological functioning of ecosystems,” the study says.
Epic annual migrations of this scale are only found in a few places in Africa.
In some areas, roads, fences, farms and urban sprawl have fractured the historic migratory routes of wildebeest herds and prevented them from roaming far and wide in search of fresh grass and water.
The new study, led by researchers from the University of Copenhagen, shows that the genetic health of wildebeest has suffered as a consequence.
“No one ever knew that this affected the genetics of wildebeest. But our results clearly show that wildebeest populations, which no longer migrate, but have historically done so are simply less genetically healthy than those that continue to migrate. And this weakens their chances of long-term survival,” says Rasmus Heller, an associate professor at the department of biology and one of the new study’s lead authors.
The results demonstrate that the genetic decline of non-migratory populations is reflected in several of the parameters by which genetic health is measured in nature conservation.
“Wildebeests that can no longer migrate have lower genetic diversity, are more genetically isolated and are more inbred. We expect this to lead to lower survival, reduced fertility and other negative effects on fitness,” says Xiaodong Liu, one of the study’s first authors and a postdoc at the department of biology.
Overall, this iconic savanna grazer is not currently threatened. But in the long term, wildebeest herds that can no longer migrate will likely be worse off in the face of climate change.
“The long-term consequence is that populations with low genetic diversity are less equipped to cope with the effects of environmental changes. Their evolutionary potential is reduced," Heller says.
"So, if climatic changes continue to occur, there isn’t as much genetic variation for them to work with to adapt, which could ultimately threaten their survival.”
Researchers analysed the whole genomes of 121 wildebeest from their entire range, which spans from South Africa to Kenya.
This is the first time that scientific researchers have studied the genetic effect of migration in wildebeest.
The researchers say that since they studied the genomes of many wildebeests from virtually their entire range, they have been able to make a general genetic comparison of migratory versus non-migratory populations.
“And because we witness a consistent difference across multiple locations, the conclusion is clear. Indeed, we can say the overall negative effect is evident in those wildebeests that have been prevented from migrating, regardless of where they live on the continent,” Xiaodong Liu says.
Around 150 years ago, many wildebeest populations made great migrations but 40 years ago, only two large wildebeest migrations remained in Africa. They were the Great Migration of the Serengeti-Mara and one in the Kalahari Desert of southern Africa.
Joseph Ogutu, a co-author of the study and a senior statistician in the biostatistics unit at the University of Hohenheim, says wildebeests are dependent on migrations to support their large numbers.
He says they can survive in resident, non-migratory populations, but their numbers simply shrink when they cannot migrate.
“For example, we see this in the populations in the other parts of Kenya and Tanzania that have been prevented from migrating and whose numbers have decreased as a result,” Ogutu says.
He says the migrations of wildebeest make them a keystone species in ecosystems, as their grazing keeps vegetation healthy, transports and distributes nutrients, while they themselves serve as prey for predators and carrion for scavengers.
“Therefore, it isn’t just the iconic animal that we threaten when we prevent them from migrating, but many other species as well. And to that, we might add the enormous amount of tourism revenue that benefits governments and local communities,” Ogutu adds.