Historical connection routes between Amazonia and Atlantic Forest used by mammals
8 April 2021 | Duration of reading: 6 min
By Arielli Fabrício Machado
The Amazonian and the Atlantic forests are the largest tropical rainforests in South America and are among the most diverse in the world. Tropical forests have occupied the continent for at least 65 million years, having its origin recently related to the meteor fall that extinguished the dinosaurs (see here). Since then, these forests have undergone several changes over time, such as expansions and retractions related to geological and climatic changes. Currently they are separated by a wide area of dry environments (called the dry diagonal). However, there is a mosaic of forests within the dry diagonal considered as a historic bridge between these biomes. Evidence based on fossils, paleoclimates and genetics suggests that they have been connected in the past by at least three routes: 1) the Northeast route, 2) the Central route and 3) the Southwest route.
This topic was previously addressed here on the Conexões Amazônicas blog by showing a review of the data available for mammal species with the potential to assess these connections (read more here). It would be ironic if, on the Conexões Amazônicas blog, we didn't talk about the historical connections of this vast and ancient forest. Other types of Amazonian routes have also been discussed here on the blog, such as the routes of indigenous dispersion revealed through genetic studiesread more here) and also through the integration of genetics, geography and linguistics (read more here); or even on how connections between Amazonia and the Andes can be revealed through ice core samples (read more here). Today we are going to talk about the study of these historical connection routes between Amazonia and the Atlantic Forest proposed for animal species, showing how we tested these routes using data from the known distribution of multiple mammal species.
On the left, connection routes between forests in Amazonia (AM) and the Atlantic Forest (AF): 1) the Northeast route, 2) the Central route and 3) the Southwest route. The size of the arrows represents the frequency of use of these routes by animal species suggested in the literature. Modified from Machado et al. 2021. On the right, humid tropical forest in South America in the National Park of the Amazon, in the state of Pará (Photo by Thomas L. P. Couvreur published in Couvreur et al., 2011).
We conducted a study to evaluate the possible connection routes used by populations of different species of mammals that inhabit Amazonian and Atlantic forests. We used data on the geographic distribution of forest mammal species that occur in both the Amazonian and the Atlantic forests extracted from IUCN. IUCN provides a database with maps of the known distribution of various species from around the world for conservation purposes. Additionally, we delimit the areas of connections suggested in the literature using a map of ecoregions (see map), also considering fossil, paleoclimatic and genetic evidence for these connections. These areas delimited for each connection route between the Amazon and the Atlantic Forest (Northeast route, Central route and Southwest route) were superimposed on the geographic distribution maps of the species, identifying the occurrence of these species in each of these routes.
We found 127 species of different groups of mammals with the potential to investigate these connections, from marsupials, rodents, anteaters, armadillos, sloths and tapirs to felines, canids, tayras, ferrets, coatis, monkeys and bats, among others. Comparing the distributions of these species along each of the three connection routes, differently from what was previously proposed, we found that most of these species are distributed along the Northeast route. The Southwest route would have been the least frequent of the routes.
Tropical rainforests in South America highlighting the Amazonia (AM) and the Atlantic Forest (AF) in green and their connection routes: 1) the Northeast route, 2) the Central route and 3) the Southwest route. The size of the arrows represents the frequency of occurrence of mammal species from the forests of the Amazon and the Atlantic Forest for each connection route found in the study carried out by researchers at UFRGS (read more here).
Considering species that occur in more than one of the routes simultaneously, most species occur along all routes. The second largest number corresponds to the Northeast route together with the Central route. The minority of species occur simultaneously in the areas of the Central route and the Southwest route. Once again these results are different from what was expected according to the literature.
With these results, it was possible to identify the different patterns of geographic distribution of these species and the connection areas in the geographic space. For example, these data not only provide an indication that the Northeast route has been used most frequently by populations of the same species of mammals, including possible access through habitats of the coast of Northeast Brazil, but also highlights that it can have been used more often than previously imagined.
Spatial patterns of the geographic distribution of mammal species with the potential to investigate connections between Amazonian and Atlantic forests revealed in this study (leia mais neste link. A) Species that occur in the areas of the three connection routes (Northeast, Central and Southwest); B) Species that occur on the Northeast route; C) Species that occur on the Central route; D) on the Southwest route; E) both in the areas of the Northeast and Central routes; F) Central and Southwest; G) Northeast and Southwest and H) species with very disjunct distribution, impossible to identify possible routes. Warm colors represent values of high overlap of the geographic occurrence of species and cold colors represent values of low occurrence.
Through this study, we also released a list of this compilation of potential mammal species to investigate these connections and the amount of genetic data available for these species in an important genetic database (read more here). Previous studies, including data compilations, have looked at a limited number of mammal species (see a literature review in Ledo & Colli 2017). We were able to include 127 species of mammals that currently occur in Amazonia and the Atlantic Forest to add information about the historical connections between these forests. Our results highlight the need for studies that look at genetic relationships within multiple species, since such studies may shed light on the complexity of the evolution and existence of connections between Amazonian and the Atlantic forests over time.
Science is done collaboratively
This research was part of Arielli F. Machado 's PhD Thesis in Ecology at UFRGS. The work was completed under the guidance of Professor Leandro Duarte, and was done in collaboration with Dr. Maria João R. Pereira at the Lab of Systematic Evolution and Ecology of Birds and Mammals (BiMa-Lab) from the Graduate Program (PPG) in Animal Biology at UFRGS, Dr. Cleuton L. Miranda from the PPG in Zoology at Museu Paraense Emílio Goeldi at Universidade Federal do Pará (UFPA), Dr Camila D. Ritter at the University of Duisburg-Essen in Germany and PhD candidate Yennie K. Bredin at the Norwegian University of Life Sciences in Norway. This research had the financial support of the Brazilian government through CNPq.
Want to know more? Access the links below!
Arielli Fabrício Machado. Potential mammals to investigate historical connections between Amazonian and Atlantic forests. Blog Conexões Amazônicas, January 28th 2021Link)
Batalha-Filho, H., Fjeldså, J., Fabre, P. H., Miyaki, C. Y. (2013). Connections between the Atlantic and the Amazonian forest avifaunas represent distinct historical events. Journal of Ornithology, 154(1): 41-50. (Link)
Costa, L. P. (2003). The historical bridge between the Amazonia and the Atlantic Forest of Brazil: a study of molecular phylogeography with small mammals. Journal of Biogeography, 30: 71-86. (Link)
Dinerstein, E., Olson, D., Joshi, A., Vynne, C., Burgess N. D., Wikramanayake, E., et al. (2017). An ecoregion-based approach to protecting half the terrestrial realm. BioScience, 67(6): 534-545. (Link)
Wing, S. L., Herrera, F., Jaramillo, C. A., Gómez-Navarro, C., Wilf, P., Labandeira, C. C. (2009). Late Paleocene fossils from the Cerrejón Formation, Colombia, are the earliest record of Neotropical rainforest. Proceedings of the National Academy of Sciences, 106(44): 18627-18632. (Link)
Ledo, R. M. D., Colli, G. R. (2017). The historical connections between the Amazonia and the Atlantic Forest revisited. Journal of Biogeography, 44(11): 2551-2563. (Link)
Machado, A. F., Ritter, C. D., Miranda, C. L., Pereira, M. R., Duarte, L. (2021). Potential mammalian species for investigating the past connections between Amazonia and the Atlantic Forest. PLoS ONE 16(4): e0250016. (Link)
Sobral-Souza, T., Lima-Ribeiro, M. S. (2017). De volta ao passado: revisitando a história biogeográfica das florestas neotropicais úmidas. Oecologia Australis, 21(2), 93-107. (Link)
Arielli Fabrício Machado is a biologist from the Federal University of Santa Maria (UFSM) and holds a master's degree in Ecology from the National Institute for Research in the Amazon (INPA) and a PhD in Ecology from the Federal University of Rio Grande do Sul (UFRGS). Currently she is Scientific Technical Support by CNPq at the Federal University of Amazonas (UFAM).