Variability in Light-Use Efficiency for Gross Primary Productivity on Great Plains Grasslands

Gross primary productivity (GPP) often is estimated at regional and global scales by multiplying the amount of photosynthetically active radiation (PAR) absorbed by the plant canopy (PARa) by light-use efficiency (ε _g ; GPP/PARa). Mass flux techniques are being used to calculate ε _g . Flux-based estimates of ε _g depend partly on how PAR absorption by plants is modeled as a function of leaf area index (LAI). We used CO₂ flux measurements from three native grasslands in the Great Plains of USA to determine how varying the value of the radiation extinction coefficient (k) that is used to calculate PARa from LAI affected variability in estimates of ε _g for each week. The slope of linear GPP–PARa regression, an index of ε _g , differed significantly among the 18 site-years of data, indicating that inter-annual differences in ε _g contributed to the overall variability in ε _g values. GPP–PARa slopes differed among years and sites regardless of whether k was assigned a fixed value or varied as an exponential function of LAI. Permitting k to change with LAI reduced overall variability in ε _g , reduced the slope of a negative linear regression between seasonal means of ε _g and potential evapotranspiration (PET), and clarified the contribution of inter-annual differences in precipitation to variation in ε _g . Our results imply that greater attention be given to defining dynamics of the k coefficient for ecosystems with low LAI and that PET and precipitation be used to constrain the ε _g values employed in light-use efficiency algorithms to calculate GPP for Great Plains grasslands.     

Circadian Typology: A Comprehensive Review

The interest in the systematic study of the circadian typology (CT) is relatively recent and has developed rapidly in the two last decades. All the existing data suggest that this individual difference affects our biological and psychological functioning, not only in health, but also in disease. In the present study, we review the current literature concerning the psychometric properties and validity of CT measures as well as individual, environmental and genetic factors that influence the CT. We present a brief overview of the biological markers that are used to define differences between CT groups (sleep–wake cycle, body temperature, cortisol and melatonin), and we assess the implications for CT and adjustment to shiftwork and jet lag. We also review the differences between CT in terms of cognitive abilities, personality traits and the incidence of psychiatric disorders. When necessary, we have emphasized the methodological limitations that exist today and suggested some future avenues of work in order to overcome these. This is a new field of interest to professionals in many different areas (research, labor, academic and clinical), and this review provides a state of the art discussion to allow professionals to integrate chronobiological aspects of human behavior into their daily practice.     

The Central Plains Tradition Revisited

Abstract

Recent interpretations of the Central Plains Tradition are critically evaluated. In the process special attention is given to:( 1) alternative interpretations of the extant data base, (2) the cogency of taxonomic proposals, and (3) the construal of radiocarbon determinations. Blakeslee’s ”trade network thesis” is examined and an origin in the exigencies of population growth and spread is suggested.     

Plains Apache Archaeology: A Review

Abstract

A review of the literature on the Dismal River Aspect in the light of recent additional work at Plains Apache sites has led to more specific suggestions as to probable sources of various Dismal River traits. Most of the traits that appear to have been borrowed from sedentary neighbors seem to have an eastern Plains origin. Many trade items from the Southwest may have been secured from or through the Jicarilla Apaches. Frequency of some triJ, its at Dismal River sites form a gradient from north to south. Many problems remain unsolved.     

A Mathematical Theory of Horse Adoption on The North American Plains

Abstract

The horse complex and its subsequent influence on Plains culture is a major topic of Plains anthropology. Treatment of the topic has involved three trains of thoughts: 1) the process (form and rate) of horse adoption, 2) the spatial diffusion of the horse northward, and 3) the influence of the horse on Plains culture. This paper contributes to the study of the horse complex by focusing primarily on the adoption aspect of the problem and, secondarily, on the social implications for the plains area of the temporal regularity evident. The paper outlines a new theoretical explanation of the actual process of horse adoption-an S-curve hypothesis suggesting that adoption initially accelerated rapidly and then declined more slowly as all Plains tribes ultimately adopted the horse. We verify this hypothesis with documented empirical evidence on the adoption process derived from Ewers (1955). The empirical evidence and S-curve interpretation suggest: 1) two distinct groups of Plains tribes existed on the Plains, a southern and northern, separated by two webs of communication, 2) that this communication was frequent, and 3) that the two systems were well developed before the arrival of the horse.     

The Abundance of Protein in Amazonia: A Reply to Gross

A critical examination of Gross's hypothesis that aboriginal Amazonian populations were limited to low levels by lack of adequate protein resources concludes that (1) evidence either for or against the hypothesis is still in short supply; (2) the role of vegetable protein in aboriginal diets needs much more attention and may ultimately overthrow the protein-limitation hypothesis; (3) the abundance of animal protein in the tropical forest has likely also been underestimated; (4) the abundance of people in precontact Amazonia may well have been underestimated as well. [Amazonia, protein, cultural ecology, limiting factors, population].     

Human Skeletal Populations Of The Northwestern Plains: A Preliminary Analysis

Abstract

Preliminary analysis has been completed on samples of American Indian skeletons from three museums in Wyoming, and special collections from Montana, Wyoming, northern Colorado and western Nebraska. All 84 specimens come from burial sites within the Northwestern Plains geographical region, and cover a temporal span of approximately 5,000 years. Fifty-four cranial and postcranial measurements, and 47 morphological observations were recorded for each complete specimen; and means and indices were compared among the various regional and temporal samples. Important temporal changes and a few regional differences are suggested by the preliminary results.