Megafauna fossils help explain the loss of mammalian diversity in the Pampa
Cattle introduced into Brazil's least-preserved biome do not replace the ecological functions of any of the species that became extinct approximately 12,000 years ago
Megafauna refers to the large prehistoric animals that inhabited the Earth until the end of the last Ice Age, approximately 11,000 years ago – Illustration: Julio Lacerda
In practice, the authors found that cattle do not functionally replace any of the extinct mammal species. In fact, most introduced species perform similar and redundant roles, although they do perform some of the ecological functions that have been lost. Thayara Carrasco, the paper’s first author and a postdoctoral researcher at the USP Institute of Biosciences (IB), explained that this scenario results in a fauna impoverished not only in terms of taxonomic diversity—that is, the number of species—but also in terms of functional diversity, namely the roles animals perform within the ecosystem.
Together with colleagues from the IB and Swansea University, in the United Kingdom, the researcher quantified and compared the functional diversity of three periods: the Pleistocene (before the megafauna extinction), the Holocene (the current geological epoch, after the extinction), and the recent period, which also includes species introduced by humans. The key element of the investigation, however, was the fossil record, which helped reveal the ecological functions of the species from each period based on information such as body size, diet, and occupied habitat.
The data indicate that the Pleistocene–Holocene extinction reduced terrestrial mammal diversity by 30%, while functional diversity declined by 40% in the Brazilian Pampa. On the other hand, some introduced species may be performing ecological functions once carried out by extinct deer (A. ensenadensis) and horses (Equus neogeus).
Species contributing to this increase include the chital (Axis axis), an invasive alien species that has been expanding in Brazil, and the domestic horse (Equus ferus). Their introduction into the biome resulted in a 12% increase in functional richness.
Even so, livestock farming may play an important role in maintaining grassland ecosystems. As Pedro Godoy, professor in the Department of Zoology at the IB and one of the paper’s authors, explained, it is important to take into account the social and economic importance of cattle and other domesticated livestock within the context of the Pampa. “Although cattle may represent a new impact on this environment, one that did not exist during the Pleistocene, it is still less harmful than monoculture”, he noted, referring to areas that have been converted to soybean cultivation in the region.
Historically, the Pampa is Brazil’s least-preserved and least-protected biome. Data from the National Institute for Space Research (Inpe) show that only 47.3% of its native vegetation remains preserved, and only 3% is protected as conservation areas. “We hope this article will lead to public policies for the conservation of both the species and the biome”, the professor added.
Megafauna in the Pampa
A native of Rio Grande do Sul, Thayara Carrasco grew up surrounded by the Pampa — which, in Brazil, is found only in her home state, as well as in Argentina and Uruguay. This close connection was one of the factors that led her to investigate the role of cattle in the environment. Another was the extensive fossil record available in the biome. The abundant literature enabled the researchers to infer which species lived during the Pleistocene and to characterize their ecological roles.
“From fossils, we can get an idea of what an animal ate, the substrate it occupied, whether it was terrestrial or dug burrows, as some giant ground sloths did”, explained the researcher. Characteristics such as body size, for example, indicate the extent of an animal’s environmental impact: a rat would have a smaller impact on the ecosystem’s ecological function than a mastodon (a distant relative of modern elephants). Diet and feeding habits (whether carnivorous or herbivorous) also provide insight into interactions among these species, such as predation and competition.
During the Pleistocene, between approximately 2.6 million and 11,700 years ago, South America was home to a wide variety of megafaunal species, with body masses ranging from around 10 kilograms to several tons. However, all mammals weighing more than 500 kilograms became extinct. The prevailing hypothesis is that the end of the Ice Age, combined with subsequent human hunting, contributed to the disappearance of the megafauna. At that time, giant ground sloths, glyptodonts—distant relatives of armadillos that weighed several tons—and mastodons were part of the landscape.
Because the available information is limited, the Pampa fossil record became a central element in making the research possible. “I don’t know whether, for example, I could carry out this type of analysis for the Atlantic Forest. I would have to take into account both the availability of fossils and how representative those fossils are”, she added.
Animals such as giant ground sloths, glyptodonts—distant relatives of armadillos that weighed several tons—and mastodons were part of the landscape – Photo: Julio Lacerda
Functional Diversity vs. Taxonomic Diversity
The loss of functional diversity and the loss of taxonomic diversity are not directly related concepts. Although, in this case, both stem from the extinction of the megafauna, a decline in functional diversity is not necessarily linked to a reduction in the number of species, and vice versa. According to Pedro Godoy, functional diversity considers “the number of species that have unique functional traits that no other living species, whether introduced or domesticated, possesses”. Taxonomic diversity, on the other hand, measures the number of taxa—in this case, existing species.
The professor emphasized that this distinction is important because it makes it possible to measure the imbalance in biodiversity and ecological roles. It is also in this context that, according to Thayara Carrasco, introduced species may benefit the ecosystem. “We usually see introduced species as villains. But, in this case, it [A. axis] may simply be occupying ecological niches that were vacant and not necessarily pose a threat to native species.”
She cautioned, however, that further field studies are needed to determine whether introduced species actually compete with native species.
Today, large mammal species are found primarily on the African continent, including elephants, giraffes, hippopotamuses, and rhinoceroses. Researchers, however, warn of the increasing threat of extinction facing larger-bodied species, a trend that has been observed since the beginning of the current geological epoch, the Holocene.
The article Long-term changes in functional diversity and its implications for mammalian conservation and ecological restoration in a grassland ecosystem is available online.
Further information: email: thayaracarrasco@usp.br, with Thayara Carrasco, and pedro-godoy@usp.br, with Pedro Godoy.
*Intern under the supervision of Fabiana Mariz
English version: Nexus Traduções, edited by Denis Pacheco
A reprodução de matérias e fotografias é livre mediante a citação do Jornal da USP e do autor. No caso dos arquivos de áudio, deverão constar dos créditos a Rádio USP e, em sendo explicitados, os autores. Para uso de arquivos de vídeo, esses créditos deverão mencionar a TV USP e, caso estejam explicitados, os autores. Fotos devem ser creditadas como USP Imagens e o nome do fotógrafo.