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Habitat associations and diversity of rodents were studied in four vegetation types associated with a Chihuahuan Desert/desert plains grassland ecotone in southern New Mexico during spring 1993 and 1994. Vegetation types included two types of draw (i.e., wide bottomed vegetated drainage) (Rhus and grass) and two types of upland (Acacia and mesa relic) characterized by occurrence of unique shrub and/or grass species. In 14,400 trap nights 1,314 individuals of 16 species ware collected. Of these, 13 demonstrated associations with vegetation types that remained constant even as rodent populations increased 99% from 1993 to 1994. Only a population increase of 1,309% for Perognathus flavus in grass draws was sufficient to cause a vegetation type x year interaction. Diversity measurements also remained consistent among vegetation types. This suggests that within the ecotone studied, vegetation types support consistent rodent populations when compared to other nearby vegetation types. Ecotones are probably important reservoirs of biodiversity within landscapes. whereas the prevailing view of ecotones is that they comprise edges or regions of intergradation between habitats, data from this suggest that (for rodents) ecotones such as those investigated may be more appropriately understood to comprise a patchwork of adjacent discrete habitats. Under this view, habitats within ecotonas can be identified and classified on their own merit without specific reference to the biomas that border the ecotone.