A new study published in the journal Diversity and Distributions reveals what the world map of mammals would look like if Homo sapiens had never existed.
The extinct straight-tusked elephant (Palaeoloxodon antiquus) is one of the many large mammals that the new study estimates would have occurred in northern Europe if modern humans had never existed. Image credit: Apotea / CC BY-SA 3.0.
In a previous study, Prof Jens-Christian Svenning of Aarhus University and his colleague, Dr Søren Faurby, showed that the mass extinction of large mammals during the last Ice Age and in subsequent millennia is largely explainable from the expansion of modern man across the world.
In their new study, they investigate what the natural worldwide diversity patterns of mammals would be like in the absence of past and present human impacts. Northern Europe, according to the team, would probably now be home to not only wolves, elk and brown bears, but also large animals such as rhinos and elephants.
“Northern Europe is far from the only place in which humans have reduced the diversity of mammals – it’s a worldwide phenomenon,” Prof Svenning said.
“And, in most places, there’s a very large deficit in mammal diversity relative to what it would naturally have been.”
The current world map of mammal diversity shows that Africa is virtually the only place with a high diversity of large mammals. However, the map constructed by Prof Svenning and Dr Faurby shows far greater distribution of high large-mammal diversity across most of the world, with particularly high levels in North and South America, areas that are currently relatively poor in large mammals.
“Most safaris today take place in Africa, but under natural circumstances, as many or even more large animals would no doubt have existed in other places, e.g. notably parts of the New World such as Texas and neighboring areas and the region around northern Argentina-southern Brazil,” Dr Faurby said.
The reason that many safaris target Africa is not because the continent is naturally abnormally rich in species of mammals.
“Instead it reflects that it’s one of the only places where human activities have not yet wiped out most of the large animals,” said Dr Faurby, who is the lead author on the study.
The existence of Africa’s many species of mammals is thus not due to an optimal climate and environment, but rather because it is the only place where they have not yet been eradicated by humans.
The underlying reason includes evolutionary adaptation of large mammals to humans as well as greater pest pressure on human populations in long-inhabited Africa in the past.
Top: natural diversity of large mammals as it would appear without the impact of Homo sapiens. The figure shows the variation in the number of large mammals (45 kg or larger) that would have occurred per 100 x 100 km grid cell. The numbers on the scale indicate the number of species. Bottom: current diversity of large mammals. It can clearly be seen that large numbers of species virtually only occur in Africa, and that there are generally far fewer species throughout the world than there could have been. Image credit: Søren Faurby.
The current study provides scientists with the first opportunity to analyze the natural patterns in the species diversity and composition of mammals worldwide. Hereby, it can be used to provide a better understanding of the natural factors that determine the biodiversity in a specific area.
Today, there is a particularly large number of mammal species in mountainous areas. This is often interpreted as a consequence of environmental variation, where different species have evolved in deep valleys and high mountains.
According to Prof Svenning and Dr Faurby, however, this trend is much weaker when the natural patterns are considered.
“The current high level of biodiversity in mountainous areas is partly due to the fact that the mountains have acted as a refuge for species in relation to hunting and habitat destruction, rather than being a purely natural pattern,” Dr Faurby said.
“An example in Europe is the brown bear, which now virtually only lives in mountainous regions because it has been exterminated from the more accessible and most often more densely populated lowland areas.”
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S. Faurby & J.-C. Svenning. 2015. Historic and prehistoric human-driven extinctions have reshaped global mammal diversity patterns. Diversity and Distributions, published online August 20, 2015; doi: 10.1111/ddi.12369
