Taking stock: How animal grazing impacts biodiversity

Study of unprecedented scale led by UAlberta researchers examines impact of livestock grazing worldwide.

Andrew Lyle - 20 August 2020

A worldwide synthesis of the effects of livestock grazing led by University of Alberta researchers is examining its impact on animal abundance and biodiversity on a larger scale than ever before—and finding that it reduces the biodiversity of herbivores and pollinators.

“We looked at the effects of livestock grazing on every continent except Antarctica and what it means for biodiversity,” said Alessandro Filazzola, lead author on the paper and a Killlam and NSERC postdoctoral fellow under the supervision of Professors Jens Roland and JC Cahill in the Department of Biological Sciences

“Livestock grazers consume the plants where they are found, which could have effects that trickle up the food web, such as reducing food resources for herbivores”.

The researchers compiled thousands of papers and more than 100 datasets comparing livestock grazing to areas without livestock. The results point to detritivores, or decomposers, as benefiting but many other animal groups as negatively affected.

The researchers explain that livestock could have replacement effects—filling the role of natural herbivores—which can reduce vertebrate abundance or invertebrate diversity. The decline of these herbivores can negatively affect predatory animals, which were also lower in abundance on grazed sites. However, that was not all the researchers found.

“Our finding that the diversity of pollinators decreased under grazing was quite striking, illustrating that some species can be particularly vulnerable,” said Alessandro Filazzola. “Taken all together, our findings highlight that groups most closely linked with plants are the ones most affected by grazing.”

Research in this field has typically been restricted to a single trophic level—such as predators, herbivores, or omnivores—due to the complexity of examining how grazing impacts many layers of the food web. By drawing on results from more than 100 studies, the team was able to construct a more complete picture of the impact on biodiversity.

“This research opens a window into understanding the multi-faceted nature of grazing effects on the environment,” said Jessica Grenke, co-author and PhD student under the supervision of Professor JC Cahill in the Department of Biological Sciences. “Our results highlight the importance of considering complex ecosystem responses to grazing within a management context. The global scope and huge scale of our work also allow us to generalize the effects of the presence of grazing in a way that simply hasn't been possible before.”

The study, “The effects of livestock grazing on biodiversity are multi‐trophic: a meta‐analysis,” was published in Ecology Letters (doi: 10.1111/ele.13527).