Steppe Populations Research Articles

Stable isotope analyses of mammal skeletal remains of Holocene age from European Russia: A way to trace dietary and environmental changes

Fifty-five samples of human and animal fossil skeletal remains (sheep, cattle, horse and deer) collected at six different sites in European Russia were measured for the oxygen isotopic composition of bone phosphate (δ 18Op) and for the carbon (δ 13C) and nitrogen (δ 15N) isotopic composition of bone collagen. The age of these samples ranges from 10 500 to 200 BP covering a time period of about 10 000 years. The samples come from the steppe area of southern European Russia, from the northern Black Sea coast and from an area near Moscow. From the results obtained it can be suggested that the steppe tribes were nomads, at least after 4000 BP, and that they probably moved from east to west and vice-versa (i.e. from the Volga area to the Black Sea coast). C 4 plants were present in the steppe area since 5000 BP. On the contrary, in the area near Moscow and on the Black Sea coast no C 4 species are documented at least until 5000 and 6000 BP respectively. Arid environmental conditions dominate the steppe area even though the N isotope values suggest a climatic improvement-taking place from 5000 BP towards present in terms of more humid conditions. As regards diet, it seems that the subsistence of the steppe populations was based mainly on terrestrial food and in particular on sheep with a minor contribution of fish. The populations from the Moscow area probably had a permanent economy mainly based on fishing.

Seed aging, delayed germination and reduced competitive ability in Bromus tectorum

In annual plants, increased competitive advantage has often been attributed to rapid germination and early establishment. In contrast, many annual species exhibit some degree of delayed germination (i.e., seed dormancy) that results in the formation of age structure within the seed population. Delayed germination can be an effective bet-hedging strategy in variable or unpredictable environments as a seed bank can buffer against years with reproductive failures and reduce the probability of local extinction. However, there has been little consideration of the direct effects of aging within the seed pool although the potential demographic costs of such a strategy (e.g., mortality in the seed bank or delayed reproduction) are well known. We used aged (4 year-old) and freshly produced seed from meadow steppe and sagebrush steppe populations of an annual grass (Bromus tectorum)to investigate the importance of seed age on seedling vigor and competitive ability. Aged seed from the meadow steppe population exhibited delays in germination that reduced plant growth and final biomass when the plants were grown with competition. Aged seed from the sagebrush steppe population did not exhibit delays in germination. By including a treatment that experimentally delayed the germination of freshly produced meadow steppe seed, we also examined the effects of delayed germination alone. A comparison of results from this delay treatment with those from the aged seed treatment suggested that the reduced competitive ability of meadow steppe plants produced from aged seed, although largely a result of the temporal delay in germination, was partly due to reduced seed vigor. Together these results indicate that physiological costs associated with seed age may affect aboveground competitive interactions and, in turn, the relative fitness of older cohorts in the soil seed bank.

Photosynthesis, Growth, and Biomass Allocation in Habitat Ecotypes of Cheatgrass (Bromus tectorum)

Bromus tectorum (cheatgrass), an alien annual grass, has become naturalized in a variety of habitats ranging from arid steppe to mesic forest communities within the intermountain region of western North America. To examine the contribution of genetic differentiation to the success of cheatgrass, we measured photosynthesis, growth, phenology and biomass allocation in populations collected as seed from contrasting habitats and grown in a glasshouse. In addition, we examined the effects of drought and population seed source on characteristics of photosynthesis and growth. In general, leaf-level photosynthetic response to variation in light, temperature and soil moisture did not vary significantly among the different habitat populations. Water-use efficiencies were not detectably different among populations. Growth, phenology and biomass allocation were also relatively insensitive to variation in soil moisture induced by the watering treatments. In contrast, phenology and biomass allocation exhibited marked variation among populations. Populations from arid steppe sites flowered earlier, set seed earlier and allocated less biomass to root growth than did populations from mesic steppe or forest habitats. Higher biomass allocation to shoot growth in arid steppe populations allows a plant to reach reproductive size more rapidly and set seed before moisture becomes limiting in late spring. These results suggest that mechanisms of adaptation such as drought avoidance may be better understood by focusing on whole-plant phenology and allocation patterns rather than on the physiology of a particular organ.

The effect of shading on photosynthesis, growth, and regrowth following defoliation for Bromus tectorum

The effect of full sunlight, 60%, or 90% attenuated light on photosynthetic rate, growth, leaf morphology, dry weight allocation patterns, phenology, and tolerance to clipping was examined in the glasshouse for steppe populations of the introduced grass, Bromus tectorum. The net photosynthetic response to light for plants grown in shade was comparable to responses for plants grown in full sunlight. Plants grown in full sunlight produced more biomass, tillers and leaves, and allocated a larger proportion of their total production to roots than plants grown in shade. The accumulation of root and shoot biomass over the first two months of seedling growth was primarily responsible for the larger size at harvest of plants grown in full sunlight. Plants grown under 60% and 90% shade flowered an average of 2 and 6 weeks later, respectively, than plants grown in full sunlight. Regrowth after clipping was greater for plants grown in full sunlight compared to those grown in shade. Even a one-time clipping delayed flowering and seed maturation; the older the individual when leaf area was removed, the greater the delay in its phenology. Repeated removal of leaf area was more frequently fatal for plants in shade than in full sunlight. For plants originally grown in full sunlight, regrowth in the dark was greater than for shaded plants and was more closely correlated to non-flowering tiller number than to plant size. This correlation suggests that etiolated regrowth is more likely regulated by the number of functional meristems than by differences in the size of carbohydrate pools. Thus, shading reduces the rate of growth, number of tillers, and ability to replace leaf area lost to herbivory for B. tectorum. These responses, in turn, intensify the effect of competition and defoliation for this grass in forests. B. tectorum is largely restricted to forest gaps at least in part because of its inability to acclimate photosynthetically, the influence of shade on resource allocation, and the role of herbivory in exacerbating these effects.

The Sayano-Altaic centre of early medieval cultures

South Siberia – bordered by Lake Baikal, the Irtysh river, the west Siberian forest-steppe zone, and the basin of the Great Lakes of Mongolia – is broadly coextensive with the foothills of the Sayan and Altai ranges. It occupies a special place in the early medieval history of the Eurasian steppe populations. The ethno-cultural processes which operated here over thousands of years have a significance which goes far beyond South Siberia.

Human chromosomal polymorphism. I. Chromosomal Q polymorphism in Mongoloid populations of Central Asia.

A comparative study of frequencies and types of Q-polymorphic variants in seven autosome pairs (3, 4, 13-15, 21, and 22) was performed in three steppe Mongoloid populations of Central Asia (Kazakhs, Dunghans, Mongolians) and three highland Kirghiz populations of Pamir and Tien-Shan. The three steppe Mongoloid populations showed statistically significant homogeneity both in the frequency of Q-polymorphic variants and the distribution of homo- and heteromorphs, with complete agreement of observed frequencies with those theoretically predicted by the law of Hardy-Weinberg. Similar homogeneity was revealed in the three highland Kirghiz populations of Pamir and Tien-Shan. However, comparative analysis of highland and steppe Mongoloids revealed significant differences in the following variables: (1) mean number of Q variants per individual, 2.50 and 3.49 in the highland and steppe populations, respectively; (2) frequency of Q variants in 7 of the 12 autosomes studied; and (3) distribution of homo- and heteromorphs in four autosomal pairs (13-15, 21), with a preponderance of individuals with increased hemomorph (-/-) frequency in highlanders. The following questions are discussed: (1) the possible selective value of chromosomal Q-heterochromatin material in the adaptation of human populations to extreme environmental factors, in particular to the high-altitude environment of Pamir and Tien-Shan; (2) the existence of intraracial heterogeneity in Mongoloids living in different ecological zones; and (3) the possible taxonomic value of Q-variant inversion in chromosome 3.

Human chromosomal polymorphism. II. Chromsomal C polymorphism in Mongoloid populations of Central Asia.

C polymorphism of chromosomes 1, 9 and 16 was studied in 447 Mongoloids of Central Asia living under different ecological conditions; two highland (Kirghiz) and three steppe (Kazakh, Mongolian, and Dungan) populations. C band sizes were estimated according to the semiquantitative 5-level method of Patil and Lubs (1977). All the ethnic groups studied showed statistically significant homogeneity in the frequency of C variants. It is suggested that chromosomal C-heterochromatin material has no selective value in the process of human adaptation to extreme high-altitude factors.

The genetic structure of some steppe populations of the snailCepaea vindobonensis (Pf.)

The snailCepaea vindobonensis, which is polymorphic for the number of bands on the shell and for intensity of band pigmentation, was studied in an area of steppe in Eastern Romania. There are marked geographical variations in phenotype frequency which, unlike the similar variation found in populations from mountainous areas, show no detectable associations with any easily identifiable component of the environment. These patterns of variation may be due to selection by cryptic ecological factors or to a balance between climatic selection and selection by the “genetic environment” of the population.