Just a few decades ago, the mammal wildlife of the cerrado and the caatinga were usually described as being an impoverished version of the animals that inhabited the two major Brazilian forests, the Amazon Rainforest in the North and the Atlantic Rainforest, along the country’s coastal region. This definition was supported by the observation that many of the species found in the two neighboring biomes were also shared with the dense, adjacent forests. Even the cerrado’s and the caatinga’s so-called endemic species, those which were only found in these areas of predominantly open vegetation, and nowhere else, were descended from ancestral lines that were linked to the forests.
A recent study by three biologists questions this view and argues exactly the opposite: roughly 80% of the known endemic species of mammals of Brazil’s Central and semi-arid Northeastern regions have their origins in the South American continent’s regions of open vegetation, a type of savanna, with few trees and more grasses, such as the cerrado itself and the neighboring chaco region, a flat, relatively dry area that stretches across parts of Paraguay, Bolivia and Argentina, in addition to a small section in Brazil’s midwestern region.
This idea is advocated by Ana Paula Carmignotto, from the Federal University of São Carlos (UFSCar), Mario de Vivo, curator of the mammals section at the University of São Paulo’s (USP’s) Zoology Museum, and Alfredo Langguth, from the Federal University of Paraíba (UFPB), in an article that will be one of the chapters of Bones, clones, and biomes – The history and geography of recent neotropical mammals, to be launched in the middle of this year by the publishing house of the University of Chicago, in the United States. “We were able to show that many of the species that are endemic to the cerrado’s and the caatinga’s open areas did not originate, as people used to think, from related species in the neighboring forests,” states Vivo, whose studies were basically financed by theme project within the scope of FAPESP’s Biota Program. “Actually, they belong to open formation lineages, with branches in other biomes of this type that can be found in South America.”
This assumption seems most plausible for the typical mammal wildlife of the cerrado, where, as in the neighboring chaco region, the vast open areas were even more pronounced about 10 thousand years ago than today. According to the researchers, the long-term existence of this enormous savanna in the heart of South America functioned as the birthplace for a large portion of the species that are the most typical of the cerrado.
In the case of the caatinga, the role of the open areas as the origin of individual species of mammals is apparently less tangible, but cannot be totally overlooked. Where there is now Brazil’s semi-arid northeastern region, there was a tropical forest a few thousand years ago. This explains why the forests of the past, as well as those of today, would indeed appear to have been more important for the development of the few species of mammals that are unique to the caatinga, a biome where this group of animals is less diversified than in the cerrado. Even so, the article’s three authors say that it is an exaggeration to believe that the forests were responsible for all the species that are endemic to the caatinga.
To arrive at these conclusions, the trio of researchers undertook a major review of the scientific literature about this issue and also went out into the field to study a few specific animals of the cerrado and the caatinga along with their geographical distribution . The result of all this work was an up-to-date list not only of the species that are only found in the two biomes in question, but of all their known mammals. The biodiversity encountered was greater than had been expected.
According to this study, the cerrado, which covers roughly 2 million square kilometers and includes the Pantanal swamplands, has 227 mammal species, 33 more than were found the last time a tally was made, in 2002. According to the new study, the caatinga, which is drier than the cerrado and covers an area less than half the size, contains 153 mammal species, 10 more than were recorded in the previous survey in 2008.
Bats and rodents are the two groups of mammals with the greatest number of known species in the two biomes. Bats accounts for more than a third of the species found in the cerrado and more than half of those encountered in the caatinga. Meanwhile, rodents account for another third of the species recorded in the cerrado and a quarter of those observed in the caatinga. The next ones in line, though with a much lower number of species, are the carnivores and the marsupials.
It is worth bearing in mind that 120 mammal species can be found in both the caatinga and the cerrado. “The majority of the mammals in these two biomes are shared between them, or with the Amazon Rainforest, the Atlantic Rainforest, or the chaco,” stated Ana Paula Carmignotto. “This point has always been highlighted in other studies and not much was said about the endemic species.” According to Vivo, many studies gave the impression that South America’s open areas had not produced anything original in terms of new types of mammal. Almost everything was regarded as an offshoot of lineages that evolved in the dense forests.
This impression, which according to the trio of authors is also false, may be due to the observation that the universe of mammals that are exclusive to Brazil’s Central Region is indeed small and concentrated. The researchers counted 25 such species in the cerrado (consisting of 21 rodent, 2 marsupial, 1 primate and 1 bat species) and another 8 in the caatinga (5 rodent, 1 primate, 1 marsupial and 1 bat species). Therefore, when one talks about mammals that are endemic to the cerrado and the caatinga, what one is really discussing is rodents. The geographical distribution of the species found in the two biomes and the phylogenetic studies, which outline their possible kinship and evolutionary relationship with animals from other regions, led biologists to argue in favor of two patterns of endemism.
The first includes species of mammals that are typical of the cerrado or the caatinga nowadays and that derived from genera that originated in the Amazon or Atlantic rainforests. Classic examples are found, particularly in the order of primates. Callithrix penicillata, popularly known as the Black-Tufted Marmoset, is an animal that only lives in the cerrado, more precisely in the tree-covered parts of this ecosystem. It is the only one out of more than 20 species of the genus Callithrix that lives in a savanna zone, outside the equatorial or coastal forests. The same thing is true of the Callicebus barbarabrownae, more popularly known as the blond titi monkey or the northern Bahian titi monkey, a species that is now threatened with extinction and that was believed to have originated in the neighboring Atlantic Rainforest. A number of rodents, marsupials and bats (such as the Lonchophylla dekeyseri) of the cerrado and the caatinga are in the same situation.
The second pattern of endemism is that of lineages of animals that for a long time have been associated with predominantly open vegetation biomes, such as the cerrado and the caatinga in the distant past and the chaco. “Most of the mammals that are endemic to the cerrado and the caatinga fall into this category,” declares Vivo. The cerrado’s three species of rodents from the genus Juscelinomys are in this situation. This is also the case of the two species of rodent of the genus Thalpomys, plus the two of the genus Wiedomys, as well as one of the genus Kunsia, among others.
The evolutionary history of the small marsupials of the genus Thylamys is even more surprising. There are nine species of this genus in South America, five of which are found in areas of open vegetation of the Andes region. The two species that are endemic to Brazil – Thylamys karimii, popularly known as Karimi’s Fat-tailed Mouse Opossum and found in the cerrado and the caatinga, and Thylamys velutinus, the Dwarf Fat-tailed Mouse Opossum, only found in the cerrado – exhibit the oldest traits (basal characteristics) of the genus and would not have any sort of kinship with marsupials that were originally from the forest areas. “This is a rare case,” comments Ana Paula. “Most of the time, the diversification of the groups of mammals associated with South America’s open areas took place in the Andes with the lineages spreading out afterwards and acquiring different traits here.”
The biologist Cleber Alho, a retired professor from the University of Brasília (UnB) and now a member of the postgraduate faculty at Anhanguera-Uniderp University, in the State of Mato Grosso do Sul State, disagrees with the idea that most of the species that are endemic to the cerrado and the caatinga are derived from lineages of animals that originated in open areas. “I don’t know how anyone could argue that the species that are endemic (to these two biomes) may have possibly originated in open areas,” says Alho. He cites examples of the cerrado’s primates, rodents and bats, whose lineages come from forested areas.
For the most part, the species mentioned by Alho are the same ones that Ana Paula, Vivo and Langguth admit originated in the forests, although they argue that these cases are the exception, rather the rule, of the evolutionary history of the mammal endemic wildlife of Brazil’s central region. There is a clear disagreement about the origins of an extinct species of rodent, Juscelinomys candango, the Candango Mouse, which was only found during the construction of Brasília in 1960 and which has never been seen since. “It also depended on the forest habitat,” states Alho. Vivo and her colleagues think differently.
Other researchers are of the opinion that the ideas presented in the book about the endemic mammals of Brazil’s central region should not be discarded without further in-depth studies. “It’s a very interesting paper and I think that they may well be right,” declared the biologist Rui Cerqueira, from the Federal University of Rio de Janeiro (UFRJ). “Their hypothesis is a very reasonable one.” According to the researcher, who was born in the State of Rio de Janeiro, the notion that the mammal wildlife of the cerrado and the caatinga is an impoverished version of that found in the forests is really an idea that is out of date and further studies on this subject, particularly in the country’s semi-arid northeastern region, where studies of animals are few and far between, should be carried out.
Systematics evolution and conservation of eastern Brazilian Mammals (n° 1998/05075-7); Modality Thematic Project; Coordinator Mario de Vivo – USP; Investment R$ 529.250,05 (FAPESP)
CARMIGNOTTO, A. P. et al. Mammals of the Cerrado and Caatinga – Distribution Patterns of the Tropical Open Biomes of Central South America. Chapter in the book Bones, clones, and biomes – The history and geography of recent neotropical mammals, which is about to be published.