A new meta-analysis across six continents shows that large wild herbivores influence ecosystems in important ways, from soils and vegetation to small animals, and contribute to ecosystem variability.Various large herbivores, or megafauna, have impacted terrestrial ecosystems for millions of years. These include elephants in Europe, giant wombats in Australia and ground sloths in South America.
However, as humans expanded across the world, these animals experienced a wave of extinctions, resulting in dramatic changes in ecosystems that are still not fully understood. Even animals that have survived these extinctions have seen their populations decline dramatically, and many animals are now on the verge of extinction.
While there are many case studies and theories on the effects of large animals, formal attempts to quantitatively synthesize their effects and establish generalizability have been lacking.
A new study published in the journal Nature Ecology & Evolution by an international team of researchers led by researchers from Aarhus University and the University of Göttingen collected a large number of case studies and analyzed the results. The findings suggest that large animals have a variety of pervasive impacts - impacts that are likely missing from most ecosystems today.
Impact of large animals on ecosystems
Identified general impacts of large wild herbivores include:
Changes in soil and plant nutrients
Promote open and semi-open vegetation
Regulate the population of small animals
Furthermore, one of the main findings of these studies is that megafauna contribute to ecosystem diversity by increasing the structural variability of vegetation.
"Given that environmental heterogeneity is a well-known universal driver of biodiversity, its positive impact on vegetation structural variability is particularly noteworthy. Although our study focused primarily on the effects of megafauna at small scales, our results show that megafauna can contribute to biodiversity even at the landscape level," says Jonas Trepel, a PhD student at Aarhus University who led the study.
Large herbivores alter vegetation structure by consuming biomass, breaking off woody plants and trampling smaller plants—an effect that is hypothesized to depend on the animal's size. Given that the dataset analyzed spanned two body size classes (45-4500 kg), the researchers were able to specifically examine how this important trait affects large animals. For example, they found that megafauna communities composed of large herbivores tended to have a positive impact on local plant diversity, while communities composed of small species (for example, weighing less than 100 kilograms) tended to reduce local plant diversity.
Erick Lundgren, one of the study's senior authors, explained: "Large herbivores can eat lower-quality food such as branches and stems, which may have a proportionally greater impact on dominant plant species, giving less competitive plants a better chance of competing for sunlight and space."
Assistant Professor Elizabeth Roux, also a senior author, added:
"These findings support the expectation that many small herbivores cannot fully compensate for the loss of a few large herbivores."
This study is part of what's called a meta-analysis. This means the researchers analyzed data from all existing studies on the topic to find general patterns. The conclusions of meta-analyses are particularly powerful because they draw on large pools of data, making it possible to draw conclusions beyond the local scope.
While many recent ecological studies have shown or hypothesized the importance of large animals in ecosystems, according to senior author Jens-Christian Svenning, this meta-analytic study, which synthesizes direct experimental and quasi-experimental evidence from around the world to provide a quantitative assessment of the prevalence of these effects, is an important step forward.
"This global meta-analysis shows that large herbivores have important general effects on ecosystems and their biodiversity," Professor Jens-Christian Svening continues to explain: "Importantly, our analysis shows that these effects span a range of important ecological phenomena, from soil conditions to vegetation structure to plant and animal species composition, affecting not only their overall status, but also how they change across different landscapes."
Jens-Christian Svenning is director of the Center for Ecodynamics of Novel Biospheres (ECONOVO), a center of excellence established by the Danish National Research Foundation at Aarhus University.
How did the researchers arrive at these results?An important aspect of these 297 studies, which included 5,990 individual data points, was that the researchers compared adjacent areas where megafauna communities differed significantly for known reasons (i.e., the presence or absence of megafauna). The vast majority of studies in the data set are so-called fencing studies, where fences are placed in certain parts of a field site to prevent the entry of large animals. By comparing different plots inside and outside the enclosure, researchers were able to assess how the megafauna affected the ecosystem.
The widespread importance of large herbivores to ecosystem functioning is well established, meaning that important ecosystem functions are being lost due to the disappearance of wild megafauna. This could impact approaches to nature conservation and ecosystem restoration.
"Most protected areas today lack large animals and therefore a range of important functions. So even areas that we think of as pristine ecosystems may not be as natural as we thought," says Jonas-Trepel. "Reintroducing large animals could be a key way to make these areas more vibrant and resilient to disturbance: by increasing the ecosystem's Structural variability allows large animals to provide refuge, for example during extreme weather events, while also opening up more space for other species to survive. This prevents one or a few species from dominating, allowing species with similar ecological properties to coexist - which in turn could make ecosystems more resilient to the consequences of global change."
Given the important functions of megafauna for ecosystems and their biodiversity, the researchers concluded that it is crucial not only to protect the few remaining megafauna species but also to rebuild megafauna populations as part of recovery efforts in order to achieve positive outcomes for Earth's biosphere, especially under increasingly unprecedented global environmental conditions.
Compiled source: ScitechDaily