Ecosystem properties shaping wild megafauna

For millions of years, a variety of large herbivores, or megafauna, have influenced terrestrial ecosystems. Among many others are the elephants of Europe, the giant wombats of Australia, and the ground sloths of South America. However, these animals experienced a wave of extinctions coinciding with humanity’s global expansion, leading to dramatic, but still poorly understood, changes in ecosystems. Even the survivors of these extinctions have declined sharply, and many are currently at risk of extinction.

Although there are numerous case studies as well as theories on the effects of large animals, formal attempts to quantitatively synthesize their effects and establish generalities are lacking.

A new study, carried out by an international team led by researchers from Aarhus University and the University of Göttingen, published in Ecology and evolution of nature, collected numerous individual case studies and analyzed the results. They show that large animals have a variety of generalizable impacts, impacts that are likely absent from most current ecosystems.

The impact of large animals on ecosystems

Among the identified general impacts of large wild herbivores are changes in soil and plant nutrients, promotion of open and semi-open vegetation, and population regulation of smaller animals.

Furthermore, one of the main conclusions of the studies is that megafauna promotes ecosystem diversity by increasing the structural variability of vegetation.

“The positive impact on vegetation structure variability is particularly noteworthy, given that environmental heterogeneity is known as a universal driver of biodiversity. While our study primarily focused on the impact of megafauna at small scale, our results suggest that it promotes biodiversity even at the global landscape level,” says Aarhus University Ph.D. student Jonas Trepel, who led the study.

Large herbivores change the structure of vegetation by consuming biomass, breaking off woody plants, and trampling smaller plants – impacts that are thought to depend on the animal’s body size. Because the dataset analyzed covered two body size magnitudes (45 to 4,500 kg), the researchers were able to specifically test how this important trait shapes the impact of large animals.

They found, for example, that megafauna communities including larger herbivores tend to have positive effects on local plant diversity, while communities composed of smaller species (e.g. <100 kg) tend to reduce local plant diversity.

“Large herbivores may eat lower quality foods, such as branches and stems, which can result in proportionately greater impacts on dominant plant species and thus give less competitive plants a better chance in their fight for sunlight. sun and space,” explains Erick Lundgren, one of the researchers. lead authors of the study.

Assistant Professor Elizabeth le Roux, who is also one of the lead authors, adds: “These results support the hypothesis that many small herbivores cannot fully compensate for the loss of a few large ones.”

The benefits of a meta-analysis

This study is what we call a meta-analysis. This means that researchers analyzed data from all available studies on the subject in order to identify general trends. Meta-analyses are particularly powerful in their conclusions because they draw on massive data pools and allow conclusions to be drawn that go beyond the local context.

While many recent ecological studies have shown or hypothesized the importance of large animals in ecosystems, according to lead author Jens-Christian Svenning, the meta-analytic study represents an important step in synthesizing experimental evidence and direct semi-experimental studies from around the world to quantitatively assess the generality of these effects.

“This global meta-analysis shows that large herbivores have important general effects on ecosystems and their biodiversity,” explains Svenning. “Importantly, our analysis shows that these effects affect a wide range of ecologically important phenomena, from soil conditions to vegetation structure to the composition of plant and animal species, affecting not only their general health but also their variation across landscapes.”

Svenning is the director of the Center for Ecological Dynamics in a New Biosphere (ECONOVO), a center of excellence of the Danish National Research Foundation at Aarhus University.

A key aspect of the 297 studies, comprising 5,990 individual data points, is that researchers compare adjacent areas with clear differences in the megafauna community (i.e. megafauna present or absent) for reasons known. The vast majority of studies in the dataset are so-called exclosure studies, in which parts of a site are fenced off to prevent large animals from entering. By comparing different plots inside and outside the fences, researchers are then able to assess the impact of megafauna on the ecosystem.

Importance of ecosystem biodiversity to respond to global changes

The overall identified importance of large herbivores to ecosystem functioning implies that important functions are missing due to the loss of wild megafauna. This may affect the approach to nature conservation and ecosystem restoration.

“The majority of current protected areas lack large animals, and therefore a significant range of functions. So even areas we consider pristine ecosystems are probably not as natural as we might think. The reintroduction of “Large animals could be a key pathway for these areas are a little more dynamic and used to disturbance,” says Trepel.

He continues: “By increasing the structural variability of an ecosystem, large animals can provide refuges, for example during extreme weather events, but also open up more available niches for other species. This could prevent one or a few species from dominating and allow species to flourish. with similar ecological attributes to coexist, which would make the ecosystem more resilient. Ultimately, this could help them cope with the consequences of global change.

Given the important functions that large animals have on ecosystems and their biodiversity, the researchers conclude that it is crucial not only to protect the few remaining megafauna species, but also to restore megafauna populations as part of the restoration efforts to achieve positive results for the Earth’s biosphere. particularly in increasingly unprecedented global environmental conditions.