Riverine barriers and the geographic distribution of Amazonian species

Abstract

Rivers have been suggested to have played an important role in shaping present-day patterns of ecological and genetic variation among Amazonian species and communities. Recent molecular studies have provided mixed support for the hypothesis that large lowland Amazonian rivers have functioned as significant impediments to gene flow among populations of neotropical species. To date, no study has systematically evaluated the impact that riverine barriers might have on structuring whole Amazonian communities. Our analyses of the phylogeography of frogs and small mammals indicate that a putative riverine barrier (the Juruá River) does not relate to present-day patterns of community similarity and species richness. Rather, our results imply a significant impact of the Andean orogenic axis and associated thrust-and-fold lowland dynamics in shaping patterns of biotic diversity along the Juruá. Combined results of this and other studies significantly weaken the postulated role of rivers as major drivers of Amazonian diversification.

Figure 1

Map of the study area (Inset showing relative location within South America). The Juruá River extends from its headwaters in Peru to the Amazon River just outside of Tefé. Numbers correspond to sampling sites within four regions (headwaters, upper central, lower central, and mouth). 1, Igarapé Porongaba (8°40′S, 72°47′W); 2, opposite Igarapé Porongaba (8°40′S, 72°47′W); 3, Nova Vida (8°22′S, 72°49′W); 4, Sobral (8°22′S, 72°49′W); 5, Sacado (6°45′S, 70°51′W); 6, Seringal Condor (6°45′S, 70°51′W); 7, Penedo (6°50′S, 70°45′W); 8, Igarapé Nova Empresa (6°48′S, 70°44′W); 9, Altamira (6°35′S, 68°54′W); 10, opposite Altamira (6°35′S, 68°56′W); 11, Jainu (6°28′S, 68°46′W); 12, Barro Vermelho (6°28′S, 68°46′W); 13, Ilha Paxiuba (3°19′S, 66°00′W); 14, Colocação Vira-Volta (3°17′S, 66°14′W); 15, Lago Vai-Quem-Quer (3°19′S, 66°01′W); 16, Ilhazinha (3°17′S, 66°14′W). Terra firme sites are indicated by open circles; várzea sites are indicated by closed circles. See ref. for more details.