Jens Christian Svenning_Megafauna ecology | Carlsbergfondet
Til projektoversigt

Megafauna Ecosystem Ecology from the Deep Prehistory to a Human-Dominated Future (MegaPast2Future)

Semper Ardens forskningsprojekt | 28/07/2016

Evidence is emerging that megafaunas may be crucial for ecosystem function and may even affect Earth’s climate and large-scale nutrient cycling. Reflecting this, it is increasingly, but controversially argued that megafaunas should be reintroduced to restore their ecological functions to promote self-regulating biodiverse ecosystems (trophic rewilding).

By Professor Jens-Christian Svenning, Aarhus University

Prior to the global expansion of Homo sapiens, ecosystems across the world teemed with large animals (megafauna). Elephants, for example, occurred from Patagonia to the British Isles and the Cape until just ~10,000 years ago. Since then megafaunas have declined dramatically, a decline that continues today, driven by unsustainable hunting and loss of natural habitats. In some regions, however, declines have been replaced by comebacks, e.g. re-expansion of wolves and other large animals in Europe. 

Evidence is emerging that megafaunas may be crucial for ecosystem function and may even affect Earth’s climate and large-scale nutrient cycling. Reflecting this, it is increasingly, but controversially argued that megafaunas should be reintroduced to restore their ecological functions to promote self-regulating biodiverse ecosystems (trophic rewilding). Given the intensifying human impact on Earth’s environment, we are now at a crossroads for Earth’s megafauna.

What is megafauna?

Megafauna simply refers to large-bodied animals. A classical definition defines megafauna as species with a body mass of ≥45 kg. Megaherbivores are defined as herbivores weighing ≥1 tonnes, and are functionally important, notably because they are generally too big to be regulated by predators (except humans).

Do we let it become lost or do we attempt to restore it and its functional importance? The MegaPast2Future project addresses this major societal challenge. It aims to strongly improve the scientific basis for acting in this critical situation by developing our theoretical and empirical understanding of the role of megafauna in ecosystems and by developing the scientific basis for megafauna conservation and restoration.

Giants Used to Be Common

66 million years ago, a giant asteroid crashed into Earth and killed off all dinosaurs (except some birds) and most other large-size animals, as well as numerous other organisms. Following this mass extinction event, mammals started diversifying into the megafauna niche space. By 40 million years ago, there were large-sized mammals on all continents, and across the following tens of millions of years rich megafaunas were the norm from tropical to polar ecosystems. This continued until within the last 50,000 years, where megafaunas around the world have been decimated.

“Today most people view rich megafaunas such as those of the Maasai Mara-Serengeti ecosystem or the Yellowstone National Park as unusual. But, from an evolutionary perspective it is really ecosystems where the largest animal is a deer, a wild pig, a fox, or a kangaroo that are unusual,” explains Jens-Christian Svenning.

Where Have all the Mammoths Gone?

It is still much discussed what is the reason for this selective loss of the biggest and fiercest animals, with very few extinctions among other organisms. One of the two main hypotheses puts the blame on the big climate changes during or at the end of the last ice age. The other suggests that the extinctions were caused by hunting by modern humans (Homo sapiens), which spread out of Africa and around the world during this period. In the latter scenario, modern humans are seen as analogous to an invasive species, with the most severe impacts on faunas, which did not have any previous experience with more primitive humans.

“My group’s research has strongly supported this explanation, finding a strong global tendency for severe extinctions where modern humans were the first humans and much lower extinctions where humans have evolved over millions of years, and with severe extinctions in the former area irrespective of the severity of climate changes,” says Professor Svenning.

Impacts of Megafauna on Ecosystems

Small megafauna on islands

Islands naturally harbour smaller animals than mainlands, and their functional megafauna and megaherbivores (e.g. giant tortoises) often weigh less than the standard size limits.

In the last decade, there has been increasing interest in understanding the role of large animals in ecosystems. Traditionally, there has been a strong tendency to understand ecosystems as being controlled bottom-up, i.e. via climate, soil etc. and their impacts on the plants. However, it is becoming apparent that top-down control, where ecosystems are controlled by the consumers higher up in the food web can also be important, with large-bodied species often having disproportionally strong effects.

“The ecosystem importance of megafauna is exactly the overall focus of the MegaPast2Future,” explains Jens-Christian Svenning.

There is little ecological theory for understanding the importance of megafauna in ecosystems. The MegaPast2Future project will focus on developing theory for (1) understanding the importance of having a diversity of ecological strategies in a megafauna community, and (2) predicting how megafaunas of different functional types assemble and what the ecosystem consequences will be.

“I see this as crucial for being able to guide the design of restored megafaunas, which may involve novel species combinations, e.g. due to extinctions of native species,” comments Jens-Christian Svenning.

Build-Up of Megafaunas Over Millions of Years

We only have a rudimentary understanding of the factors that have driven the functional build-up of megafaunas worldwide over the last 40 million years and their ecological impacts. MegaPast2Future will address this issue, integrating modern-day and paleobiological data to assess how functional complexity in megafaunas has built up and what the ecosystem consequences have been. In combination with the theoretical work, this will provide another important component to the scientific basis for restoring megafaunas.

“Given an immensely varied past climate, sometimes causing strong faunal changes, I expect our findings to be important for predicting impacts of future climate change on megafaunas,” adds Jens-Christian Svenning.

Testing Megafauna Theory on the Savanna

The project will also have a strong field-based component, testing key hypotheses on the ecosystem impacts of megafauna. With this component, the project wants to achieve an empirically based understanding of the carrying capacity for megafaunas and test for the importance of megafauna structure for ecosystem processes and biodiversity. A key facet of this work will involve studies in some of the most complete remaining megafaunas (Maasai Mara, Kenya; Pantanal, Brazil) as well as in relation to reintroduction projects in Denmark and elsewhere.

Trophic rewilding

Trophic rewilding is defined as species introductions to restore top-down food web effects to promote self-regulating biodiverse ecosystems. It is often focused on large-bodied animals given their ecological importance and the particularly strong human-caused extirpations in this group.

Megafauna Conservation, Comebacks, and Restoration

Megafaunas across the world have been decimated and many of the remaining megafauna species are undergoing strong decline due to uncontrolled hunting and loss of natural habitats. This is dramatically illustrated by the current poaching crisis for rhinos, and represents a major loss of biodiversity, with negative consequences for ecosystems and negatively impacting livelihoods and cultures in many areas. Avoiding and reversing these losses constitute a big societal challenge, as human populations and resource needs are forecasted to exhibit strong growth across the 21st century.

“With MegaPast2Future, I am committed to improving the scope for maintaining and restoring megafaunas in a world moving towards 11 billion people and strong climate changes,” says Jens-Christian Svenning.

A key focus will be the development of economic and technical methods for facilitating human-megafauna coexistence. The project thus emphasises Scientific Social Responsibility (SSR), directly addressing one of the United Nations’ 17 Sustainable Development Goals (SDGs) for Sustainable Development, namely its goal 15 “Sustainably manage forests, combat desertification, halt and reverse land degradation, halt biodiversity loss”.

Key Megafauna Papers by Jens-Christian Svenning

Svenning, J.-C., Pedersen, P.B.M., Donlan, C.J., Ejrnæs, R., Faurby, S., Galetti, M., Hansen, D.M., Sandel, B., Sandom, C.J., Terborgh, J.W. & Vera, F.W.M. 2016. Science for a wilder Anthropocene: Synthesis and future directions for trophic rewilding research. Proceedings of the National Academy of Science USA 113:898-906.

Bakker, E.S., Gill, J., Johnson, C.N., Vera, F.W.M., Sandom, C.J., Asner, G.P. & Svenning, J.-C. 2016. Combining paleo-data and modern exclosure experiments to assess the impact of megafauna extinctions on woody vegetation. Proceedings of the National Academy of Science USA 113:847–855.  

Doughty, C.E., Roman, J., Faurby, S., Wolf, A., Haque, A., Bakker, E.S., Malhi, Y., Dunning, J. & Svenning, J.-C. 2016. Global nutrient transport in a world of giants. Proceedings of the National Academy of Science USA 113:868–873.

Faurby, S. & Svenning, J.-C. 2015. Historic and prehistoric human-driven extinctions have reshaped global mammal diversity patterns. Diversity & Distributions 21:1155-1166.

Sandom, C., Faurby, S., Sandel, B. & Svenning, J.-C. 2014. Global late Quaternary megafauna extinctions linked to humans, not climate change. Proceedings of the Royal Society B: Biological Sciences 281:20133254.

Sandom, C., Ejrnæs, R., Hansen, M.D.D. & Svenning, J.-C. 2014. High herbivore density associated with vegetation diversity in interglacial ecosystems. Proceedings of the National Academy of Science USA 111:4162-4167.

Other Relevant Literature

Recent (2016) special issue in Proceedings of the National Academy of Science USA on “Megafauna and Ecosystem Function: From the Pleistocene to the Anthropocene

Recent (2016) megafauna special issue in Ecography

Popular science paper on the late-Quaternary megafauna extinction