Revista Chilena de Historia Natural 84 (3): 365-377, 2011
RESEARCH ARTICLE
Geographic patterns of richness distribution of rodents species from the Oryzomyini
tribe (Rodentia: Sigmodontinae) in South America: Evaluating the importance of colonization and extinction
processes
The Oryzomyini rodent tribe is the most diverse taxon within the
Sigmodontinae subfamily. This tribe includes 120 species and 31 genera, of which 83 are endemic to the South American
continent. This tribe presents a wide distribution, covering the entire Neotropical biogeographic province, and is
characterized by the presence of greater richness in the Amazonian area, with a monotonic decrease towards the south and
north of South America. This pattern is well known in many taxa, for which various causal mechanisms have been
proposed. However, the mechanisms that explain this pattern of species richness along the latitudinal gradient in the
Oryzomyini tribe are unknown. Given that these species are native to Amazonia, and that throughout their history they
colonized new and more variable environments (towards the south and north), we evaluated the source-sink hypothesis,
mediated by processes of colonization and extinction, as a potential explanation for the observed pattern of richness. To
test this hypothesis we built a database of species’ distribution and richness every one degree of latitude for the entire
South American continent. Subsequently we assessed the degree of nestedness using the T (temperature), BR (discrepancy)
and NODF indices. Our results show a significant degree of nesting in the Oryzomyini distribution, and a significant degree
of nesting of the rows and columns of the data matrix, separately. Therefore, we conclude that source-sink dynamics affect
the pattern of richness distribution of Oryzomine rodents, through a process of colonization during its expansion in South
America, which was conditioned by the range of tolerance of the species. This resulted in the extinction of the less tolerant
species, which finally resulted in a lower number of species towards the south and north of Amazonia.
Key words:
biodiversity,
latitudinal gradient, macroecology, nesting, source-sink hypothes
