|Rhino is one the species that are threatened with extinction. / Photo by: khunaspix via 123rf|
Thousands of years ago, different kinds of massive mammals roamed across our planet, from mammoths, mastodons, giant elk to marsupial lions, saber-toothed cats, rhinoceros-sized marsupials, and more. However, these and some of the other largest and most fantastic creatures ever to walk the planet are long gone. Unfortunately, the threats to Earth’s remaining large mammal biodiversity have continued up to this day.
A 2015 study of 74 of the largest terrestrial herbivores published in Science Advances showed that the vast majority of these animals are declining in distribution and abundance. About 60 percent of them such as elephants, hippos, and all species of rhino are threatened with extinction. The situation is expected to get worse due to hunting, habitat loss, and competition for food with livestock—the major threats to their existence.
This is not the first time this has happened. Previous studies showed that humans have been initiating extinctions inadvertently for many centuries. For instance, large emu-like terrestrial birds and oversized wombats that roamed Australia between 55,000 and 45,000 years ago became extinct after humans first set foot on the continent. This was because they started setting fires to clear land or flush prey from bushes.
The Conversation, a not-for-profit media outlet that uses content sourced from academics and researchers, reported that today, Southeast Asia has the greatest number of threatened large herbivore species. Reports showed that the continent’s forests are facing “empty forest syndrome” wherein the forests may seem intact, but there are only a few large animals left within them.
Humans are Causing the Extinctions
A 2018 study by researchers from the University of Utah reported that long-term environmental change drove the extinction of large mammals in Africa over the last several million years. They argued that it was mainly due to the falling atmospheric carbon dioxide (CO2) level and not because of our earliest tool-bearing ancestors.
Lead author Tyler Faith, curator of archaeology at the Natural History Museum of Utah, stated this study greatly helped in understanding the depth of anthropogenic impacts on large mammal communities. Science Daily, an American website that aggregates press releases and publishes lightly edited press releases about science, reported that the researchers focused on the very largest species, which are called “megaherbivores.” They compiled a 7-million-year record of herbivore extinctions in eastern Africa and studied when and why these species disappeared.
The researchers examined independent records of climatic and environmental trends and their impacts, including stable carbon isotopes of eastern African fossil herbivore teeth, stable carbon isotope records of vegetation structure, and global atmospheric CO2. They discovered that substantial megaherbivore extinctions have occurred over the last seven million years. At the same time, the massive decline of megaherbivores began roughly 4.6 million years ago, which didn’t change following the appearance of our human ancestors. The global drop of carbon dioxide in the atmosphere during these years caused the expansion of grasslands, which greatly affected the megaherbivores. Many of the woody vegetation, which was their main source of food, became less woody and more open through time.
While the findings were true and justified, a recent paper from the World Economic Forum argued that ancient human ancestors may still have contributed to more recent megaherbivore extinctions. Worst, today’s humans are repeating the pattern. According to the World Economic Forum, an independent international organization committed to improving the state of the world, humans are responsible for causing such profound biodiversity losses. Natural environments of large herbivores are collapsing due to human encroachment and hunting, which can lead to the sixth mass extinction.
Large Animal Extinctions are Changing Global Landscapes
It has been known that large herbivores were major engineers of “landscape openness.” They played a major role in maintaining open landscapes. Thus, extinction of large herbivores such as woolly mammoths, mastodons, and giant ground sloths during the Pleistocene epoch, which spanned from 2,588,000 to 11,700 years ago, altered landscapes across the world. EarthSky, an online site that features daily updates on the cosmos and the world, mentioned that the extinction was driven by climate change and excessive hunting by early humans.
A 2016 study published in the journal Proceedings of the National Academy of Sciences showed that time, the abundance of woody plants increased in many areas that were once open landscapes due to the loss of the large herbivores. Woody plants were able to flourish again since these giant animals went extinct. Also, a recent multi-institutional study explained how the human-influenced mass extinction of giant carnivores and herbivores of North America fundamentally changed the biodiversity and landscape of the continent.
|The abundance of woody plants increased in many areas that were once open landscapes due to the loss of the large herbivores. / Photo by: kampwit via 123rf|
The researchers analyzed how large mammals were distributed across the continent in the Pleistocene and Holocene geological epochs and explored how modern humans have shaped today's ecosystems. The findings of the study showed that there was an ecological transformation across the continent. Large carnivores and the mammoth steppe disappeared and vegetation and fire regimes changed.
“Rather than thinking of humans as separate from ‘natural’ environments, our research has illuminated the major impacts that humans have had on the ecosystem for many thousands of years. The results of this paper and others from our group illuminate the outsized impacts that human-mediated extinction has had in North America,” anthropology assistant professor Amelia Villaseñor said.
Understanding not only the current but also the biodiversity crisis helps us gain a deeper perspective on how our planet is being affected by climate change. This helps us learn to conserve and restore the ecosystems we need for our own survival.