BackgroundThe tropical Andes and Amazon are among the richest regions of endemism for mammals, and each has given rise to extensive in situ radiations. Various animal lineages have radiated ex situ after colonizing one of these regions from the other: Amazonian clades of dendrobatid frogs and passerine birds may have Andean ancestry, and transitions from the Amazon to Andes may be even more common. To examine biogeographic transitions between these regions, we investigated the evolutionary history of three clades of rodents in the family Echimyidae: bamboo rats (Dactylomys-Olallamys-Kannabateomys), spiny tree-rats (Mesomys-Lonchothrix), and brush-tailed rats (Isothrix). Each clade is distributed in both the Andes and Amazonia, and is more diverse in the lowlands. We used two mitochondrial (cyt-b and 12S) and three nuclear (GHR, vWF, and RAG1) markers to reconstruct their phylogenetic relationships. Tree topologies and ancestral geographic ranges were then used to determine whether Andean forms were basal to or derived from lowland radiations.ResultsFour biogeographic transitions are identified among the generic radiations. The bamboo rat clade unambiguously originated in the Amazon ca. 9 Ma, followed by either one early transition to the Andes (Olallamys) and a later move to the Amazon (Dactylomys), or two later shifts to the Andes (one in each genus). The Andean species of both Dactylomys and Isothrix are sister to their lowland species, raising the possibility that highland forms colonized the Amazon Basin. However, uncertainty in their reconstructed ancestral ranges obscures the origin of these transitions. The lone Andean species of Mesomys is confidently nested within the lowland radiation, thereby indicating an Amazon-to-Andes transition ca. 2 Ma.ConclusionsDifferences in the timing of these biogeographic transitions do not appear to explain the different polarities of these trees. Instead, even within the radiation of a single family, both Andean and Amazonian centers of endemism appear enriched by lineages that originated in the other region. Our survey of other South American lineages suggests a pattern of reciprocal exchange between these regions—among mammals, birds, amphibians, and insects we found no fewer than 87 transitions between the Andes and Amazon from Miocene-Pleistocene. Because no clear trend emerges between the timing and polarity of transitions, or in their relative frequency, we suggest that reciprocal exchange between tropical highland and lowland faunas in South America has been a continual process since ca. 12 Ma.

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In this study we present the results of inventory efforts of non-volant mammals in Sangay National Park (SNP), one of the least studied regions of Ecuador. We conducted inventories at 9 locations between December 2010 and June 2015 along a gradient of elevations between 1.300 and 3.650 m. To document the presence of non-volant mammals we used capture techniques (Sherman, Tomahawk, and pitfall traps) and direct and indirect detection techniques (track and sign surveys, interviews). The trap effort consisted of 5.730 trap/nights. We detected 86 species in the study area of which rodents were the most diverse group with 36 species (41.8%). The small mammals Chilomys instans, Neusticomys vossi, Ichthyomys cf. stolzmanni, Thomasomys fumeus, Dactilomys dactylinus and Echimys saturnus, the marsupial Marmosa rubra were detected in the SNP for the first time. The shrew-opossum Caenolestes sangay, shrew Cryptotis montivaga and rodents Phyllotis haggardi, Thomasomys fumeus, T. hutsoni, T. cf silvestris, Rhipidomys sp. nov., y Cavia patzelti are endemic species that speak to the biogeographic importance of SNP. Our results with additions from other published studies indicate the presence of 103 species of non-volant mammal, positioning it as the most diverse natural area in the Andes of Ecuador, and as the second most diverse of the tropical Andes.

Nests are described for Thomasomys aureus and T. paramorum in a high Andean forest in northern Ecuador. Nests of T. aureus were found in the tree canopy to 6 and 7 m in height andthose for T. paramorum were located under the roots from 15 cm to 1.5 m above the surface.

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