Response to drought among farmers and herders in southern Kajiado District,Kenya

From 1972 to 1976 rainfall in Kajiado District of Kenya was below normal. The capacity of the farming and herding systems to cope with the consequent reduction in production is discussed within a context of changing land-use patterns and altered resource availability. It is concluded that land-use planning to allocate the available land and water resources and to promote off-farm employment is required to reduce the vulnerability of the population to future drought conditions.     

Decreasing functional responses as a result of adaptive consumer behavior

Summary Several different mechanisms that may produce decreasing functional responses are investigated using models that assume that an optimally foraging consumer is exploiting one or two resources. Decreasing functional responses are associated with situations in which there are costs to resource consumption. If the process of resource acquisition has costs, decreasing functional responses may occur when there is a single homogeneous resource. If the cost is solely a function of the amount of resource ingested, decreasing functional responses on a single resource do not occur. Both types of cost can produce decreasing functional responses when there are two resource types and a trade-off relationship between consumption of one and consumption of the other. Decreasing functional responses seem to be most likely to occur on a food that yields high benefits and costs per unit of foraging time or effort when there is an alternative resource which yields low benefits and costs. Given this type of foraging choice, the functional response is most likely to decrease when the benefits of ingestion increase at a decreasing rate, and the costs of ingestion increase at an increasing rate with amount ingested. An important and unique consequence of decreasing functional responses is the possibility of population cycles in differential equation models of consumer-resource systems with non-reproducing resources; this is illustrated with a simple comsumer-resource model.     

Biotyping of pathogenic fungi by the killer system and with monoclonal antibodies

Biotyping of pathogenic yeasts and hyphomycetes based on their suceptibility to selected killer yeasts and their reactivity with monoclonal antibodies are described. Both methods were used to differentiate fungi isolated from patients providing valuable epidemiological information on mycotic infections. The functional biotyping obtained with the two systems and the conventional auxenographic biocoding approaches commercially available for opportunistic yeasts are comparatively evaluated. The potential for biotyping of industrial fungal isolates is also discussed.     

On the classification of regular systems of inbreeding

Regular systems of inbreeding are defined as those with discrete, nonoverlapping generations and with the same number of individuals and mating pattern in every generation. Given the number of individuals in a generation, there are many possible regular mating systems. A notion of when two such mating systems are equivalent is introduced, and several necessary conditions are given for such an equivalence. The use of these conditions is illustrated for N = 2, 3, 4 and 5 individuals, and a complete enumeration has been found for these cases: the numbers of inequivalent mating systems are 1, 5, 57 and 858, respectively. The maximal eigenvalue of the matrix q that specifies the recursion relations satisfied by the probabilities of identity have also been found for these cases. For N = 3 and 4 (and 2 trivially), circular mating gives the slowest rate of approach to genetic uniformity of those systems that do evolve to uniformity, but for N = 5 there are two other mating systems that have a slower rate of convergence, and for N = 6 partial results show that there are many such examples.Deceased     

The abundance of the blue shark,Prionace glauca,in the western English Channel

Synopsis Since 1952, a sport fishery for the blue shark,Prionace glauca, has existed off the south coast of Cornwall in England. Annual catches from this fishery have ranged from < 200 to>6000 sharks. The fishery was based on a previously unexploited stock in the 1950s. The abundance of the species in the English Channel declined in the early 1960s and again in the mid-1970s. The declining abundance was investigated in relation to sea surface temperature (SST), prey abundance, and fishing pressure. Short-term fluctuations in SST were found to be responsible for changes in the distribution of the population, but not for changes in abundance. The abundance of prey species in the Channel was observed to be inversely related to the abundance of blue sharks. The reduced abundance of blue sharks lowered the level of effective predation on the prey populations, allowing their abundance to increase. It was concluded that the nature of the fishing practice off the Cornish coast was responsible for a significant part of the decrease in shark abundance. By killing large numbers of sub-adult females, the reproductive capacity of the population was lowered. Continued fishing pressure prevented the population from recovering; and as of 1987, the abundance of the species in the Channel is still declining. Various conservation measures have been proposed.     

Non-resource based territoriality in males of the butterflyXamia xami (Lepidoptera: Lycaenidae)

In the Pedregal de San Angel reserve, in Mexico City, males of the butterfly Xamia xamiperch in and defend areas with well-defined topographic limits. These areas lack concentrations of receptive females and of larvae and adult resources. One individual defends the same territory an average of 5 h/day, up to a maximum of 23 days. The same areas are used as territories by different males during the year. These areas share some characteristic features which are described. Evidence is presented in support of the hypothesis that the territories function as mating stations. A possible scenario for the evolution of this territorial mating system is advanced.     

Breeding Systems in American and Asian Trillium Species by Means of Chromosome Analyses

Abstract Species of Trillium have a disjunct distribution occurring in both North America and eastern Asia. In North America all 36 species are diploid. The 11 species of eastern Asia, however, include only a single diploid with all the other species being polyploids. Why do different patterns of speciation develop in North America and in eastern Asia? The breeding systems of populations in the North American T. erectum, T. grandiflorum and T. ovatum , and in Asian T. kamtschaticum were investigated by estimating the inbreeding coefficient from cold-induced banding patterns which reveal homozygotes and heterozygotes. From the analyses of the inbreeding coefficients, T. erectum, T. grandiflorum and the Pacific coastal species, T. ovatum are predominantly inbreeding species. T. ovatum populations from the Rocky Mountain region are outbreeders. However the Japanese species, T. kamtschaticum has a mixture of outbreeding and inbreeding among populations. The development of polyploid systems in Asia is possibly the result of the diversity of the breeding systems among the populations. The shift from outbreeding to inbreeding appears to be an important key step in the occurrence of poliploids by hybridization between the different species.     

Phytosociology and ecology of old hay meadows in Hordaland,western Norway in relation to management

Well-drained mown hay meadows in Hordaland, western Norway, were investigated. The hay meadows are either managed in a traditional or in a semi-traditional way. Traditional management in the area involves little or no use of manure or fertilizer, mowing once or twice a year with a first cut later than June 23, clearing in spring and intensive grazing for short periods in spring and autumn. Semi-traditional management involves use of small to medium quantities of commercial fertilizer, often in addition to manure. Grazing may be irregular, light or lacking.Eight units of hay meadow vegetation are described, all assigned to the class Molinio-Arrhenatheretea, order Arrhenatheretalia; four units to the Atlantic alliance Cardaminion pratensis, association Cardamino pratensis-Conopodietum majoris (with three subassociations); one unit to the alliance Arrhenatherion elatioris, three units are provisionally grouped as Galium uliginosum-Knautia arvensis meadows.Continuous management of these meadows has resulted in characteristic species compositions, which vary along a west-east climatic gradient, and are related to the amount of commercial fertilizer used and the natural mineral-content of the soil.These hay meadows seem to be best maintained by continuing the traditional management regime. Grazing in spring and in autumn reduces fast growing dominants and creates openings for new seedlings of annuals and biennials. A late first cut allows for ripening of the seeds and creates openings for light for the species of the lower field layer. A list of species characteristic of traditionally managed permanent hay meadows is presented, and possible effects of present changes in management on the species composition of the meadows are discussed.The amount of organic matter in the topsoil is small in most stands. The pH values are between 4.0 and 5.6. The highest values were recorded in soil where little or no commercial fertilizer is used, and where the subsoil is naturally rich in minerals. A tendency to Mg impoverishment in the best fertilized stands is demonstrated. Species-rich stands on Ca-rich soils are poor in P.The expected changes in vegetation, future use, and conservation of permanent hay meadows in Hordaland are discussed.     

Effect of Zeitgeber Intensity Reduction on a Simulated Dual-Oscillator Human Circadian System: Classical and Dynamic Analysis

The two-oscillator model of human circadian rhythmicity was analyzed when a zeitgeber relative intensity of 1, 0.5, or 0.1 was introduced into the equations. Fourier analysis was compared with dynamic analysis such as attractor reconstruction or Liapunov exponent calculation. After a 50 or 90% reduction in zeitgeber intensity, the dynamics of the system became equivalent and differed significantly from those of a system with maximal zeitgeber intensity. When 10% aleatory noise was added to the data, the analysis was still applicable, and the results obtained were essentially the same as in the absence of noise. Dynamic analysis could thus provide a distinct classification for periodic data, based on the type of analysis.     

The regulatory status of the fixL- and fixJ-like genes in Bradyrhizobium japonicum may be different from that in Rhizobium meliloti

Summary The cloning, sequencing and mutational analysis of the Bradyrhizobium japonicum symbiotic nitrogen fixation genes fixL and fixJ are reported here. The two genes were adjacent and probably formed an operon, fixLJ. The predicted FixL and FixJ proteins, members of the two-component sensor/regulator family, were homologous over almost their entire lengths to the corresponding Rhizobium meliloti proteins (approx. 50% identity). Downstream of the B. japonicum fixJ gene was found an open reading frame with 138 codons (ORF138) whose product shared 36% homology with the N-terminal part of FixJ. Deletion and insertion mutations within fixL and fixJ led to a loss of approximately 90% wildtype symbiotic nitrogen fixation (Fix) activity, whereas an ORF138 mutant was Fix⁺. In fixL, fixJ and ORF138 mutant backgrounds, the aerobic expression of the fixR-nifA operon was not affected. NifA itself did not regulate the expression of the fixJ gene. Thus, the B. japonicum FixL and FixJ proteins were neither involved in the regulation of aerobic nifA gene expression nor in the anaerobic NifA-dependent autoregulation of the fixRnifA operon; rather they appeared to control symbiotically important genes other than those whose expression was dependent on the NifA protein. The fixL and fixJ mutant strains were unable to grow anaerobically with nitrate as the terminal electron acceptor. Therefore, some of the FixJ-dependent genes in B. japonicum may be concerned with anaerobic respiration.