Multiple effects of capybaras on vegetation suggest impending impacts of jaguar reintroduction

Prepared by Ana Belen Avila, María Jose Corriale, Debora Di Francescantonio, Pablo I. Picca, Emiliano Donadio, Mario S. Di Bitetti, Agustín Paviolo, and Carlos De Angelo

The Capybara is a large and abundant grazing rodent of about 50 kg that could greatly impact vegetation. In our study, we explored how grazing by capybaras shaped grassland communities in the Iberá Wetland, in northeastern Argentina. Using a controlled experiment, we compared areas where capybaras were allowed to graze to areas where grazing was excluded revealing that capybara grazing significantly influences vegetation.

Where capybaras were excluded, vegetation grew taller and plant biomass (weight) accumulated, reducing plant diversity as taller plants dominated the areas, overshadowing and excluding shorter species. As a result, fewer types of plants could thrive, and the overall structure of the vegetation changed. This highlights how important capybaras are for maintaining plant diversity and the structure of wet grassland communities.

Capybaras are the park’s most abundant large herbivore and an important prey species of jaguars. If jaguars reduce the number of capybaras or influence their behavior, grazing pressure could decrease, leading to changes in the plant communities. This process is known as a trophic cascade, the indirect effect of predators on a lower trophic level (plants) they do not consume.

Knowing the effect of large herbivores on vegetation is crucial for ecosystems undergoing ecological restoration through trophic rewilding, where top predators are reintroduced to restore a critical ecological function: top-down regulation of large herbivore populations through predation. In Iberá, jaguars are being reintroduced after their extirpation 70 years ago to restore their ecological role. Our findings suggest that jaguars could indirectly influence plant communities by modifying capybara grazing pressure and patterns enhancing landscape heterogeneity and favoring biodiversity. These changes could create new habitats for other species, such as endangered grassland birds, and could also affect important ecosystem processes, like nutrient cycling and carbon storage. The changes in grazing patterns might also influence wildfires, which are common in the Iberá Wetlands and have important ecological effects.

In summary, our study shows that capybaras, the main grazer in the Iberá Wetlands, shape vegetation structure and composition, which is required for trophic cascades to occur. Thus, the reintroduction of jaguars could lead to important changes in plant communities, with potential benefits for biodiversity and ecosystem processes. Understanding these interactions is crucial for conservation efforts and helps us appreciate how herbivores and predators work together to shape ecosystems.

This is a plain language summary of the paper of Avila et al. published in Applied Vegetation Science (https://doi.org/10.1111/avsc.70017)