Positions of ten study areas in the Kalahari. Inside the stippled area is the "sandveld" of the Kalahari as delineated by Leistner (1967).

In western North America, deserts form a continuous and enclosed series, uninterrupted by major physical barriers, over a latitudinal range of 1500 km, from southern Idaho and Oregon through Sonora and Baja California (Mexico). Three distinct regions are generally recognized within this region: a northern Great Basin Desert, a southern Sonoran Desert, and an intermediate area in southern California and southern Nevada known as the Mojave Desert. The Great Basin desert is structurally simple, with predominantly a single perennial plant life form (low "microphyllous semi-shrubs" including Atriplex confertifolia and Artemesia tridentata). Vertical heterogeneity is minimal. Because these small shrubs in northern deserts are usually very densely packed and uniformly spaced, horizontal spatial heterogeneity is also low.

The Great Basin Desert is a very repetitive and rather monotonous landscape. In contrast, the Sonoran is an arboreal desert with several species of trees and, in addition to small semi-shrubs such as Atriplex, many large woody shrubs (the most conspicuous of which is creosote bush, Larrea divaricata). As a result, the vertical component of spatial heterogeneity is considerably greater than it is in the Great Basin Desert. The Mojave Desert is also dominated by Larrea, but is virtually treeless, except for a few Yucca brevifolia "trees." The diversity of different plant life forms reaches an apex in the Sonoran Desert. The addition of perennial plant life forms in southern U.S. deserts is often accompanied by fewer plant individuals per unit area and much greater horizontal heterogeneity in their distribution in space. Rivulets and dry washes along bajadas are lined with different species of plants than intervening areas.

Saurofaunas in the flatland deserts of western North America consist of a basic "core" set of four ubiquitous species (the whiptail Aspidoscelis (formerly Cnemidophorus) tigris, the side-blotched lizard Uta stansburiana, the leopard lizard Gambelia wislizeni, and the desert horned lizard Phrynosoma platyrhinos) to which various combinations of other species are added, with the total number of species increasing from 4 or 5 in the north to 9-10 in the south (Pianka 1967). Three Great Basin areas were studied (areas G, I, and L), four sites were selected in the Mojave Desert (areas M, P, S, and V), along with a further three Sonoran sites (areas C, T, and W). Incidental observations were also made at two Sonoran desert sites in northern Mexico (areas A and B). North American fieldwork was undertaken primarily during 1962 through 1964, but a few observations were also made in Mexico during the summers of 1966 and 1969. Censuses of North American lizards collected on each of these study sites were compiled, as follows.

North American Datasets

My Ph. D. research took place in the early 1960's when data were entered on to mainframe computers using punched 80 column computer cards. I wrote my own programs to analyze these data. Information on each individual lizard was input on two 80 column fields using a continuation card, with study site, a unique specimen ID number, species identity, sex, date, time of collection, length of fat bodies, gonad condition (testis lengths for males, number of eggs and average egg diameter for females), weight, fresh field-measured snout-vent length, fresh tail length, tail condition, body temperature, ambient air temperature at chest height, where the lizard was when first sighted, where it ran to, how many times it ran, total number of prey items and total volume of prey in the stomach. Items in stomach contents were scored by number and volume using the above-mentioned 20 basic prey categories. These data files for almost 4,000 lizards were originally in simple text file format, they have been converted into files with a single line of data for each individual lizard. Most of my information on North American lizards has now been imported into mySQL tables -- I have written queries to extract various subsets of information, such as diets by species and sex, study site, and time. However, much more can still be done. For example, sex has been cross-linked accurately to separate data sets with preserved morphometrics to allow analyses of sexual dimorphisms in anatomy, thermal relations, diet and microhabitat.

Data for almost 4,000 North American lizards are summarized in seven CSV files:

• NAall.csv
• NAkey.csv
• NAanat.csv
• NAdiet.csv
• NAdietfreq.csv
• NAfemales.csv
• NAtestes.csv

Field notebooks were scanned and made into pdf files

I also made up some prey size data files for North American lizards. All snakes were collected and small mammals were trapped (these are deposited in the Burke Memorial Museum at the University of Washington in Seattle). Bird lists were also assembled (Pianka 1967).

References

• Pianka, E. R. 1966. Convexity, desert lizards, and spatial heterogeneity. Ecology 47: 1055-1059. Download pdf.

• Pianka, E.R. 1967. On lizard species diversity: North American flatland deserts. Ecology 48: 333-351. Download pdf.