Epilogue — Demography and anthropology

As a conclusion, this paper reviews briefly the content of the volume. The wealth of demographic data has not been adequately exploited in anthropology; this is why this publication is valuable in showing attempts to apply demographic data in a variety of anthropological problems. This symposium has explored many interesting points which we recall here. Yet it has also opened up a whole range of further questions on the material presented as well as in this broad field. Several directions of research could be developed, for instance, testing among human populations, over long periods, the ecological thoughts of ecosystems evolving as a cascade of instabilities, rather than a succession of equilibrium states. Let us also recall the pervasive nature of demographic facts in topics such as the energy cycle or the genetic structure and evolution of human populations.     

Competitive and facilitative relationships among three shrub species,and the role of browsing intensity and rooting depth in the Succulent Karoo,South Africa

Abstract. The nearest‐neighbour technique is used to infer competition and facilitation between the three most abundant species in a semi‐arid region of western South Africa. Relationships among the shrubs Leipoldtia schultzei and Ruschia robusta, which are leaf‐succulent members of the Mesembryanthemaceae (‘mesembs’) and Hirpicium alienatum a non‐succulent Asteraceae, were compared on two adjacent sites with different histories of browsing intensity. Competition was more prevalent and more important than facilitation. The only evidence for facilitation was found at the heavily‐browsed site where the palatable Hirpicium was larger under the unpalatable Leipoldtia. Generally the prevalence and importance of competition was reduced at the heavily‐browsed site. Strong evidence was obtained for intraspecific competition in each of the three species; also, competition was evident between the two mesembs, where Leipoldtia was competitively dominant over Ruschia, although neither species inhibited Hirpicium. Minimal competition between the mesembs and the asteraceous shrub was interpreted in terms of differentiation in rooting depth, and competition within the mesembs, in terms of overlap in rooting depth. The mesembs had the bulk of their roots in the top 5 cm of soil, while the asteraceous shrub had the bulk of its roots, and all its fine roots, at greater depths. The shallow‐rooted morphology of the mesembs is well adapted to utilize small rainfall events, which occur frequently in the Succulent Karoo, and do not penetrate the soil deeply. Modifications of existing methods are applied for analysing nearest‐neighbour interactions.     

Microhabitat nest‐site selection by ducks in the boreal forest

The boreal forest is one of the North America’s most important breeding areas for ducks, but information about the nesting ecology of ducks in the region is limited. We collected microhabitat data related to vegetation structure and composition at 157 duck nests and paired random locations in Alberta’s boreal forest region from 2016 to 2018. We identified fine‐scale vegetation features selected by ducks for all nests, between nesting guilds, and among five species using conditional logistic regression. Ducks in the boreal forest selected nest sites with greater overhead and graminoid cover, but less forb cover than random sites. Characteristics of the nest sites of upland‐ and overwater‐nesting guilds differed, with species nesting in upland habitat selecting nests that provided greater shrub cover and less lateral concealment and species nesting over water selecting nests with less shrub cover. We examined the characteristics of nest sites of American Wigeon (Mareca americana), Blue‐winged Teal (Spatula discors), Green‐winged Teal (Anas crecca), Mallards (Anas platyrhynchos), and Ring‐necked Ducks (Aythya collaris), and found differences among species that may facilitate species coexistence at a regional scale. Our results suggest that females of species nesting in upland habitat selected nest sites that optimized concealment from aerial predators while also allowing detection of and escape from terrestrial predators. Consequently, alteration in the composition and heterogeneity of vegetation and predator communities caused by climate change and industrial development in the boreal forest of Canada may affect the nest‐site selection strategies of boreal ducks.     

The oxo/peroxo debate: a nonheme iron perspective

The oxygen activation mechanisms proposed for nonheme iron systems generally follow the heme paradigm in invoking the involvement of iron-peroxo and iron-oxo species in their catalytic cycles. However, the nonheme ligand environments allow for end-on and side-on dioxygen coordination and impart greater flexibility in the modes of dioxygen activation. The currently available evidence for nonheme iron-peroxo and iron-oxo intermediates is summarized and discussed in light of the ongoing discussion on the nature of the oxidant(s) in heme enzymes.     

A bacterial clone carrying sequences coding for elongation factor EF-1 alpha from Artemia

A bacterial cDNA clone was identified carrying one third of the nucleotides coding for elongation factor EF-1 alpha from the brine shrimp Artemia. The sequence of codons corresponds with the known sequence of amino acids of EF-1 alpha in the region involved.     

Cell Cycle activation and ouabain-sensitive ion movements of 3T3 and C3H-10T½ fibroblasts

The introduction of either PGF_2α (10^?7 M) or TPA (10^?7 M) stimulated, ouabain-sensitive ⁸⁶Rb⁺ influx at 30 min in postconfluent 3T3-4 mouse fibroblast cultures by 117% and 124%, respectively. Both TPA and PGF_2α at these concentrations stimulated the incorporation of ³H-TdR into DNA. TPA had the greatest stimulatory effect, which was similar to that obtained with 10% fetal calf serum. In accord with the idea that modulation of membrane processes such as Na⁺/K⁺ pump activity in fibroblasts may reflect important events related to the initiation of DNA synthesis, it was observed that in both 3T3-4 and C3H-1 0T½ cells there were parallel increases in ³H-TdR incorporation and ouabain-sensitive ⁸⁶Rb⁺ influxes with 10^?7 M TPA, whereas PGF_2α stimulated a significant increase in ³H-TdR incorporation in 3T3-4 but not C3H-10T½ cells and only marginal increases in ouabain-sensitive ⁸⁶Rb⁺ influx in both. Therefore, although there appears to be a close correlation between Na⁺/K⁺ pump activation and subsequent S-phase entry following TPA stimulation, a similar correlation for PGF_2α cannot be confirmed.