Should humans really be blamed for megafauna mass extinction?

by Nika Shilobod, University of Plymouth

This post is based on the paper: Mann, D. H., P. Groves, M. L. Kunz, R. E. Reanier and B. V. Gaglioti (2013) Ice-age megafauna in Arctic Alaska: extinction, invasion, survival. Quaternary Science Reviews 70: 91-108.

The Anthropocene’s hallmark is human dominance over nature. Some would argue this is a natural process: a result of our own evolution. We have become god-like, with knowledge and ability to manipulate nature to suit our needs and combat existential threats.

With looming pressures of climate change and mass extinctions, we tend to ask questions about where we are headed, rather than where we came from. To get the answers, palaeoecologists turn to the past for examples of similar situations.

Humans have not always been at the centre stage of Earth’s ecology. Megafauna, such as giant sloths, sabretooth tigers and woolly mammoths seem like the stuff of legends, but between 50,000-10,000 years ago they dominated the landscape. Their demise coincided with the end of the last ice age.

One study from the University of Nebraska estimated that the biomass, or total quantity of living organisms, of megafauna in arctic Alaska may have been 30 times greater than in the present. But why did they become extinct? It’s been an unresolved question for scientists since the end of the 18th century.

Popular view assumes that humans were the major cause of the extinction of megafauna, and the idea of hunting mystical beasts has a romantic charm, one must admit. Critics argue that large animals still exist in places like Africa, where they have long coexisted with humans. So, was the cause human invasion or the natural result of a changing climate? Although human impact undoubtedly affected the demise of these large creatures, studies such as this one emphasize the need to look at other factors too.

Glaciers began their retreat about 12,000 years ago and change happened rapidly. Many living things became displaced or were unable to adapt to new and changing conditions.

The arctic is extremely sensitive to climatic changes due to albedo feedback, which is the amount of solar radiation reflected from the Earth’s surface back into the atmosphere with less ice leading to less reflection and more warming. The earliest effects of climatic change can be seen here, often long before temperate regions are affected, making it one of the best places to monitor these changes.

The study on megafaunal extinction in the Alaskan arctic found similar evidence for the driving forces of climate change. Here, fossil evidence from ten thousand years ago suggests that terrestrial ecosystems inhabited by large animals underwent radical restructuring. Steppe bison, horse, and woolly mammoth became extinct; replaced by humans and moose. Muskox and caribou remained, finding refuge in pockets with warmer and moist conditions. The habitats used by the dryland grazing species, such as the mammoth, were transformed by regional flooding, which led to the spread of organic soils and peat over the grassy tundra that they grazed. Additional research also suggests that climate was a major cause of these extinctions.

The youngest mammoth in arctic Alaska has been radiocarbon dated to about 13,800 years ago, while humans arrived 300 years later. It is likely, therefore, that extinction processes were already occurring before hunting could have a large effect. Humans may have finished the job, rather than being the catalyst.

The most important cause of change was moisture availability during this megafaunal extinction event. Dryland specialists could no longer tolerate the wetter and warmer conditions, which also facilitated invasive species, such as humans and moose. It is important to note that these represent local extinctions and this extinction event would have occurred in different ways and times in different places. Results from this study have since been supported by other proxies, such as the analysis of ancient animal DNA.

The end of the last ice age was preceded by a dramatically fluctuating climate. It was not a frozen tundra or Antarctic-like, as imagination may suggest. Periods of short warming increased temperatures by up to 16 degrees Celsius within decades and lasted for periods of hundreds to thousands of years. This instability would fracture plant and animal communities, as their preferred environments could at times have disappeared within a lifetime.

What can we learn from these events to apply to our current crises? Climate change is and will inevitably fracture interconnected networks of plant and animal communities. Human civilization has constricted the ability for many of these species to migrate to seek more favourable habitats, known as refugia. The disappearance of megafauna had rippling effects and still affects present ecosystems, as these large animals were important for spreading nutrients.

Extinction is a natural process and, like all living things, our species will one day die or evolve into something else. We as humans, however, have a long way to go before we are faced with what comes next. Homo sapiens are resilient, exceptional in our numbers and ability to adapt to changing environments, unlike many of our warm-blooded counterparts.

Our uniqueness is simultaneously our biggest advantage and disadvantage. As we continue to further manipulate the world around us, we create new threats, such as nuclear war, pollution and pandemics. The price of new technological advances and cultural development create difficult decisions on what paths to take. By understanding the causes and processes of past major events, such as megafaunal extinction, we may be able to better manage these threats in the future.

Published by mjanebunting

Co-Secretary of the BES Palaeoecology SIG at present Academic (Reader at the University of Hull), palaeoecologist focusing on landcover reconstruction, cultural landscape enthusiast and training to be a mad cat lady

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