Biology ETDs

Publication Date

1-5-1965

Abstract

Grasslands of the San Juan-Chaco Drainage are separated from grasslands of other New Mexican drainages by plant associations characteristic of higher altitudes. Connection with other grasslands in the Colorado Drainage is restricted to a narrow corridor in the northwest.

Grassland habitat of the present type was absent from the basin during the last major Pleistocene pluvial as were those amphibians, reptiles, and mammals closely associated with this habitat. An effort has been made to determine which of these vertebrates invaded the area from the northwest in post-pluvial time and which have entered the basin via relatively low-lying areas along the Continental Divine to the southweast. Taxonomic, ecologic, and distributional data have been utilized.

Scaphiopus bombifrons, Scaphiopus hammondi hammondi, Cnemidophorus inornatus, Airzona elegans, and Dipodomys spectabilis reach their northwesterly limits in the San Juan-Chaco Drainage; all appear to be post-pluvial invaders from the southeast.

Uta stansburiana, Cnemidophorus tigris, Citellus spilosoma, and Dipodomys ordi are of different subspecies than populations in the Rio Grande Drainage to the southeast and have their closest relationships to the west and northwest. There taxa are believed to have invaded the study area from the northwest.

Holbrookia maculate seemingly occurred in both the Colorado and Rio Grande drainages during the last pluvial, but inadequacy of data prevents knowledge of the immediate origin of the study area population.

Populations of Perognathus apache apache and Citellus leucurus in both the San Juan-Chaco Drainage and Rio Grande Drainage are believed to be post-pluvial invaders from further northwest.

Pipistrellus Hesperus and Myotis californicus populations were isolated in both the Rio Grande and Colorado River drainages during the last pluvial. Populations from both basins moved into the study area post-pluvially, resulting in intergradation in the San Juan-Chaco Drainage. The northwestern population has had more effect in determining the make-up of the study area population than has that of the Rio Grande Drainage.

Populations of Myotis yumanensis were separated during the last pluvial by the highlands between the Colorado and Rio Grande drainages. The few data available suggest members of both populations have invaded the area post-pluvially with little or no interbreeding.

Perognathus apache relictus probably was in the Rio Grande Drainage during the last pluvial interval and has since invaded the higher portions of the San Juan-Chaco Drainage, likely with occasional interbreeding with P. a. apache.

Study area populations of Bufo punctatus, Perognathus flavus, and Onychomys leucogaster do not reveal their post-pluvial origin.

Data suggesting a warm, dry Altithermal interval are few. There is some inconclusive evidence for a warm, relatively wet period following the last pluvial. Most data suggest the Continental Divide area to have been as great a barrier to xerophilic animals during the entire post-pluvial time as at present.

Language

English

Document Type

Dissertation

Degree Name

Biology

Level of Degree

Doctoral

Department Name

UNM Biology Department

First Committee Member (Chair)

James Smith Findley

Second Committee Member

William Jacob Koster

Third Committee Member

William Clarence Martin

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