Large Animals Disappearing at Alarming Rates, Study Warns

Africa is home to some of the most iconic large mammals on Earth, such as elephants, rhinos, giraffes, and hippos.

However, these animals are only a fraction of the diversity and abundance of megafauna that once roamed the continent.

A new study, published in the journal Science, reveals how the size and abundance of living and fossil African large mammals (>15 kg) have changed over the last 10 million years, shedding light on the ecological dynamics behind the decline of these majestic creatures.

The rule of metabolic scaling and its exceptions

(Photo : STR/AFP via Getty Images)

The study, conducted by Faysal Bibi from the Museum für Naturkunde in Berlin and Juan L. Cantalapiedra from the University of Alcalá in Madrid, used measurements of thousands of fossil teeth to reconstruct the size and abundance of African large mammals, as per Phys.org.

They compared the fossil data with the data from living communities, and found a highly similar relationship between an animal's size and its abundance, indicating that fundamental ecological processes governing the structure of living communities are also preserved in the fossil record.

However, they also discovered some surprising patterns and trends that challenge previous assumptions about the causes of megafaunal extinctions in Africa and provide new insights into the restructuring of ecosystems over millions of years.

One of the main findings of the study was that above 45 kg, there was evidence for decreasing abundance with increasing size, both in living and fossil communities.

This pattern aligns with the ecological "rule of metabolic scaling", whereby larger species have lower population densities compared to smaller ones, due to their higher energy requirements and lower reproductive rates.

However, the researchers also found a deviation from this rule: mammals between ~15 and 45 kg were far less numerous than expected, both in living and fossil communities.

They interpreted this as a signature of savanna habitats, where monkeys and small forest-living antelopes are rare.

This suggests that habitat type and availability may also influence the size-abundance distribution of large mammals.

Also Read: Researchers Examine Megafauna Bones From Papua New Guinea Using New Tools to Unlock Their Fascinating History

The loss of giants over time

Another surprising finding was that earlier communities, older than 4 million years ago, had a considerably higher number of large-sized individuals and a greater proportion of total biomass in larger size categories, than did younger communities, as per idw.

The high abundance of large individuals in these fossil African communities - with some individual elephants reaching sizes over 10 tons - is unparalleled in ecosystems today.

Since that time, there has been a gradual loss of large-sized individuals from the fossil record, reflecting the long-term decline of late Pliocene and Pleistocene large mammal diversity, and resulting in the impoverished and "miniaturized" communities we know today.

The study confirms recent work arguing for the deep-time antiquity of African megafaunal losses and challenging the idea that the decline of African megafauna was primarily driven by human activities.

While the spread of humans across the globe during the late Pleistocene and Holocene (the last 100,000 years) coincided with major extinction of many large animals, the research supports the idea that megafaunal losses in Africa began much earlier, around 4 million years ago, and long before humans learned to engage in efficient hunting.

Implications for conservation and restoration

The study has important implications for conservation and restoration efforts in Africa.

It shows that Africa's current megafauna is not representative of its historical diversity and abundance, and that there is potential for restoring some of the lost giants to their former habitats.

However, it also warns that restoring megafauna may not be enough to restore ecosystem functioning, as other factors such as habitat quality, climate change, and human-wildlife interactions may also affect the size-abundance distribution of large mammals.

The study also highlights the value of fossil data for understanding long-term ecological patterns and processes, and for informing conservation decisions.

By combining fossil and living data, the researchers were able to reveal how Africa's megafauna has changed over millions of years, and how it may change in the future.

Related article: North America's Megafauna Likely Went Extinct Because of Climate Change