Humans responsible for extinction of large mammals Growing Evidence

Phys.org reports on the extinction of numerous large mammals, birds, and reptiles over the past 50,000 years, a topic that has sparked considerable debate, according to an article reprinted by Caliber.Az.

The debate has persisted for decades: Were humans or climate change responsible for the extinction of numerous species of large mammals, birds, and reptiles that disappeared from Earth over the last 50,000 years? These "large" animals, classified as megafauna weighing at least 45 kilograms, saw at least 161 mammal species driven to extinction during this period, based on current archaeological evidence.

Among the hardest hit were megaherbivores—land-dwelling herbivores weighing over a ton—of which there were 57 species 50,000 years ago. Today, only 11 of these species remain, although even these have experienced significant population declines.

Researchers from the Danish National Research Foundation's Center for Ecological Dynamics in a Novel Biosphere (ECONOVO) at Aarhus University have concluded that many of these vanished species were hunted to extinction by humans. Their findings, published in the journal Cambridge Prisms: Extinction as a review article synthesizing and analyzing existing research, integrate various fields including direct studies on the extinction of large animals.

They incorporated a broad array of studies to comprehensively analyze the phenomenon, including:

- Timing of species extinctions

- Dietary preferences of the animals

- Climate and habitat requirements

- Genetic estimates of past population sizes

- Evidence indicating human hunting

In addition, they integrated studies from other fields crucial for understanding the context, such as:

- Climate history spanning the past 1–3 million years

- Vegetation history spanning the past 1–3 million years

- Evolutionary trends and dynamics of fauna over the past 66 million years

- Archaeological data detailing human expansion, lifestyle, and dietary preferences

The significant climate changes during the late Pleistocene, spanning from 130,000 to 11,000 years ago, had a profound impact on both large and small animals and plants globally. However, while these changes affected populations and distributions, extinctions were notably concentrated among large animals, especially the largest species.

Interestingly, previous ice ages and interglacials over millions of years did not result in the selective loss of megafauna. Although cold and dry conditions at the onset of glacial periods caused extensive regional extinctions, such as the disappearance of trees in Europe, they did not lead to selective extinctions of large animals.

"The extensive and selective loss of megafauna over the past 50,000 years is unprecedented in the last 66 million years. Historical climate changes did not trigger such specific extinctions, suggesting climate played a minor role in the megafauna extinctions," explains Professor Jens-Christian Svenning, who leads ECONOVO and authored the article.

He further emphasizes, "Another significant observation contradicting a significant role for climate is that recent megafauna extinctions occurred with similar severity in both climatically stable and unstable regions."

Effective hunters and vulnerable giants

Archaeological discoveries include traps designed for large animals, and studies of ancient human bones and spear points' protein residues indicate widespread hunting and consumption of large mammals like mammoths, mastodons, and giant sloths by early modern humans. Professor Jens-Christian Svenning emphasizes that these large animals were particularly vulnerable to overexploitation due to their long gestation periods, low reproductive rates, and slow maturity.

Research indicates that human hunting practices led to the extinction of these large animals at varying times and rates across different regions worldwide. Extinctions occurred after the arrival of modern humans, or in Africa's case, after significant cultural advancements. Species vanished from all continents except Antarctica and from diverse ecosystems, ranging from tropical forests and savannas to Mediterranean and temperate forests, steppes, and arctic regions.

Svenning points out that many extinct species thrived in various environments, suggesting their extinction cannot be solely attributed to climate changes that eliminated specific ecosystem types like the mammoth steppe. In fact, most of these species existed in temperate to tropical conditions and theoretically should have benefited from the warming at the end of the last ice age.

Consequences and recommendations

The researchers underscore that the extinction of megafauna has had far-reaching ecological consequences. These large animals are pivotal in ecosystems as they influence vegetation structure—such as the balance between dense forests and open areas—seed dispersal, and nutrient cycling. Their disappearance has led to substantial alterations in ecosystem dynamics and functions.

"Our findings emphasize the urgency of proactive conservation and restoration initiatives," states Svenning. "Reintroducing large mammals can play a crucial role in reinstating ecological equilibrium and supporting biodiversity, which evolved in ecosystems historically abundant with megafauna."