Africa’s biggest animals may be rare, in part, because there isn’t enough salt, according to a new study.
In research led by Northern Arizona University (NAU), scientists discovered that the availability of salt may limit the number of mega-herbivores – such as elephants, rhinos and giraffes – in West and Central Africa.
“We found that salt plays an important role in shaping the density and distribution of large mammals across Africa,” lead author Dr Andrew Abraham, now a research associate at City University of New York, told BBC Science Focus.
Abraham’s team generated high-resolution maps which displayed the saltiness of plants in different areas. Then, they tested animal dung for signs of salt deficiency.
Together with data on animal populations, this revealed that there were fewer large herbivores in areas where there was less salt.
“While all animals need salt to think, move and survive, sodium is not important for most plants,” explained Abraham. “Therefore, the concentrations of salt in plant leaves vary considerably depending on the saltiness of the environment that plant grows in.”
For example, plants might contain more salt if they’re growing near the sea, or in saltier soils.
“We found that across Africa, the least salty plants have a thousand times less sodium than the saltiest plants,” Abraham continued.
In areas with much less salt, herbivores may struggle to get enough sodium in their diets to survive – especially the largest species, such as elephants.
But the study also suggested that low salt availability could put these animals at risk in other ways, by forcing them to engage in risky behaviours for the sake of salt.
“Just like humans, animals have a specific taste for salt and will go to great lengths to satisfy their salt cravings when they are running short,” said Abraham. “From gorillas chewing on salty wood stumps in Uganda to elephants mining salt from the insides of caves in Kenya – animals are inventive when it comes to getting enough salt.”
These salt-seeking behaviours can make the animals vulnerable by putting them into the paths of predators.
Conversely, in the saltiest environments, large herbivores need a lot of water to flush the mineral out of their system, which Abraham said could also limit their numbers.
For the future, the study concluded that salt should be a consideration for those trying to protect these large herbivores, as human activity and climate change both alter its availability.
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