The Rio Nazas as a Factor in Mammalian Distribution in Durango, Mexico
1976; Southwestern Association of Naturalists; Volume: 20; Issue: 4 Linguagem: Inglês
10.2307/3669866
ISSN1943-6262
Autores Tópico(s)Bat Biology and Ecology Studies
ResumoThe effect of the Rio Nazas on mammalian distribution is discussed. This river acts as a filter barrier and as a pathway for dispersal for some mammals. Its greatest influence is at the species level, particularly in rodents, where several species are separated into different subspecies on each side of the river. This paper discusses the effect of the Rio Nazas upon mammalian distribution. The river arises in north-central Durango, M4xico, on the eastern slopes of the Sierra Madre Occidental, at an elevation of ap- proximately 2,400 m. The river is approximately 322 km long and drains about 46,000 km2 of the Mexican plateau, ending its generally eatward flow east of Torreon in the now-dry Laguna Mayrin at an elevation of about 1,130 m. Three principal tributaries are the Rio del Oro, the Rio de Ramas and the Rio San Juan. This river has cut a deep, prominent canyon midway across the state. For the initial two-thirds of its length, it flows through mesquite- grassland habitat, ending in a more desert-like situation for the re- mainder of the distance (see Baker and Greer 1962 for a description of the habitats). The canyon formed by the Rio Nazas is about 506 m deep and 33 km wide for the first two-thirds of its course, then it be- comes 145 km wide and more shallow for the remainder of its length. Desert habitat extends westward for a considerable distance within the lower elevations of the canyon, and provides a possible pathway for dispersal and occupation by some desert-dwelling mammals not other- wise found in the surrounding grassland areas. From mid-June through September (the rainy season) the river is generally at a higher level than for the remainder of the year. Cohn (1965) indicates that the semi-arid environment of Durango first appeared in the Oligocene. Prior to that time, the area was pri- marily humid tropical forest. During the Miocene uplift, the humid forests retreated in a southeasterly direction. The uplifting of the Sierra Madre Occidental resulted in a rain shadow on its east side, which accentuated the aridity. Thorn scrub vegetation was followed by true
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