Dynamic simulation of water depletion in the root zone

The joint effect of the distribution of the soil water potential and of the root mass in the crop root zone upon the water uptake by the crop is represented by a simple equation. This expression is used to join a layered crop canopy model for finding the evapotranspiration, as controlled by stomatal action and the weather, with a hydraulic flow model for the root zone and the underlying soil. The complete model is used for the calculation of the water extraction pattern and the changes, with time, of other plant and soil processes. A simulation of a 20-day drying period is performed, using S/360 CSMP, for a constant diurnal weather pattern, and for a fully developed sorghum crop. The results show that, after a few days of essentially constant water use by the crop, a monotonic decline sets in, that is principally attributable to the decrease in transpiration. For the entire drying period a substantial amount of water - about 30% of the total used - is contributed by upward flow into the root zone from the soil below. The results demonstrate the difficulty of quantitative definition of concepts such as “field capacity”, “wilting percentage”, and “available” or “extractable” water.     

Social regulation of egg-laying by queenless honeybee workers (Apis mellifera L.)

Summary If a honeybee (Apis mellifera L.) colony loses its queen and remains queenless, a small percentage of the workers will develop into egg-layers and subsequently will produce males. The process of differentiation into laying and non-laying workers is accompanied by a great deal of aggression within the colony. In this study, I tried to establish the relationship between the potential to become egg-layers and behavioural differences at the individual level. To eight observation hives, I introduced 200 individually marked workers of similar age and observed their behavioural differentiation during a queenless period. Shortly after the first egg-laying worker appeared, the marked workers were dissected in order to determine their level of ovarian activation. The future laying-workers seemed to be slightly more involved in the rearing of new queens than other workers. As reported by other authors, aggression was mostly directed towards workers with activated ovaries. Only a very small number of aggressive workers were aggressive; on an average, slightly fewer of these marked workers had activated ovaries. Aggression resulted in physical damage in only a small number of cases. The possible disadvantage of aggression for the bees under attack is discussed, as well as the possible benefit for the aggressors. Evidence is presented that the most detrimental effect of aggression for bees under attack is the fact that they lose considerable quantities of food through trophallaxis to other workers. Workers with activated ovaries withdrew inside empty cells significantly more often than other workers, possibly to avoid attacks. Aggressive workers were (almost) never seen to receive food from the bees they attacked. It is suggested that by preventing other workers from becoming egg-layers, aggressors increase their own chances of future reproduction.     

Simple and reliable methods for the fixation,mounting and staining of small and delicate marine plankton for light microscopic identification

The fixation capacity of mixtures of acrolein, glutaraldehyde, and tannic acid, was investigated to arrive at a fixative for small and delicate marine plankton that is more universal than the current selective fixatives. A mixture containing 4% acrolein, 4% glutaraldehyde and 2% tannic acid added 1:1 to the cell suspension proved to be satisfactory. Mounting of the material in euparal before staining is recommended. Of several dyes tried, fuchsin acid proved suitable for observation of flagella and cell shapes. Delafield haematoxylin staining gave the best results for internal details. Fuchsin base staining, requiring a complex procedure, is recommended when it is necessary to search for flagellar hairs as found in Ochromonas spp. Schedules for the fixation, mounting and staining are given.     

Temporary natural resource cartels

We analyze the behavior of a nonrenewable resource cartel that anticipates being forced, at some date in the future, to break up into an oligopolistic market in which its members will then have to compete as rivals. Under reasonable assumptions about the value function of the individual firms in the oligopolistic equilibrium that follows the breakup, we show that the cartel will then produce more over the same interval of time than it would if there were no threat of dissolution, and that its rate of extraction is a decreasing function of the cartel's life; that there are circumstances under which the cartel will attach a negative marginal value to the resource stocks, in which case the rate of depletion will be increasing over time during the cartel phase; that, for a given date of dissolution, the equilibrium stocks allocated to the post-cartel phase will increase as a function of the total initial stocks, whereas those allocated to the cartel phase will increase at first, but begin decreasing beyond some level of the total initial stocks.     

Floristic composition and vegetation ecology of the Malindi bay coastal dune field, Kenya

A short outline is given of the floristic composition, structure and distribution of coastal dune vegetation found at Malindi Bay, Kenya. The area was studied by air photo interpretation and field sampling to determine the relationship of plants to aeolian features. TWINSPAN classification was used to distinguish geomorphological units on the basis of their species composition. In this paper, an inventory and first quantitative analysis of vegetation distribution is presented. We identified 174 plant species from 62 families in the sand dunes and several plant communities are distinguished based on the species content and the connection with morphological units.Papilionaceae with 18 species andPoaceae with 17 species were the most represented families. A distinct zonal distribution of the plant communities was found. The most important plant species are the pioneer vegetation consisting ofHalopyrum mucronatum, Ipomoea pescaprae andScaevola plumieri. The woody shrub species which have colonized the established primary dunes and hummock dunes areCordia somaliensis, Pluchea discoridis, Tephrosia purpurea (dunensis). Succulent herbs were identified in the dune slacks and salt marsh that are moist and damp environments.     

Distribution and conservation status of littoral vascular plant species along the European coasts

A comprehensive list of 1068 typical littoral plant species and subspecies has been composed. They are considered endemic in a wide sense and are subdivided into widespread, transregional, regional and local endemics, the latter three categories being considered as endemics s.s. For each taxon the distribution, habitat preference, endemic status and conservation status are given. The list, which is available upon request, is summarized in a number of figures and tables, from which it appears that 61% of all species are endemics s.s., that ca. 30% of all species are dune and beach species and another nearly 30% are maritime rock species. Species of wet habitats are concentrated in northern and northwestern Europe, dune species in western and southwestern Europe, western Mediterranean and Black Sea. The conservation status of most species is indicated; 37% is considered threatened. It is concluded that the Bern Convention and the European Habitat Directive offer an entirely insufficient framework for effective conservation action. It is suggested to take the present list as a starting point for a geographical/taxonomical/ecological data base of European coastal endemics.     

Ökologische, ökonomische und rechtliche umweltbewertung

This article provides information about a Series dealing with Integrated environmental assessment’ (IEA). We describe the development and the structure of a ‘Graduiertenkolleg’ (interdisciplinary course of study) which has been established in two phases at the University of Kiel from 1996–2002. The central terms ‘integration’, ‘environment’, and ‘assessment’ are discussed. Here, we take a special look at the chances and problems of interdisciplinary cooperation and communication (ecosystem research, jurisprudence, economics, social sciences) with regard to the general subject of IEA as a subject of research and schooling. Finally, we give a short review about the articles in the series.     

The effects of air pollution on work loss and morbidity

The pending revision of U.S. air standards and the analytic requirements of Executive Order 12291 will force regulators to examine closely the data showing possible human health effects from air pollution. A number of studies have investigated the relationship between air pollution and human mortality using an epidemiological approach. This study uses a data set on individuals, the Health Interview Survey, conducted by the National Center for Health Statistics, to examine the relationship between air pollution and various measures of morbidity. Regressions run with the total sample and a subsample of male nonsmokers indicate a statistically significant relationship between particulates and both work loss and restricted activity days. Further analysis considering alternative functional forms also indicates that the ambient level of particulates is still significantly related to the measure of morbidity.     

Ungulate Reintroductions: Experiences with the Takhi or Przewalski Horse (Equus ferus przewalskii) in Mongolia

Experiences with the reintroduction of the takhi, or Przewalski horse ( Equus ferus przewalskii , in Mongolia can serve as valuable lessons for reintroduction of ungulates in general. We discuss the present taxonomic, historical, and biological evidence and conclude that the takhi should be viewed as a typical steppe herbivore. Its last refuge, the Dzungarian Gobi, should therefore be seen as a marginal habitat because it consists mainly of desert and semidesert. Since 1992 two reintroduction projects have been in the acclimatization phase in Mongolia. Despite promising developments, problems with cooperation, management, habitat choice, insufficient knowledge of the ethology of the species, and current land use within the different project areas could jeopardize the successful reintroduction of takhi. We review the conditions required for a potentially successful ungulate reintroduction. The planning of a reintroduction within the framework of safeguarding an entire ecosystem with an integrated management plan appears essential. Each potential reintroduction site should be assessed thoroughly for its suitability, including size, habitat types, current land use, socioeconomics, legislation, and potential problems. Each site should be provided with one or more acclimatization facilities to harbor genetically and physically healthy, socially adapted animals in biologically sound groups. An organization structure should be established for each reintroduction site. Its objective should be to develop an effective management plan and to carefully monitor the population and its surrounding ecosystem. Special attention should be given to local socioeconomic situations, community participation, and training of staff for management, research, and ranger and warden activities.