Ecological similarities and differences among littoral species of Ceriodaphnia
The occurrence of six littoral species of Ceriodaphnia (C. affinis, C. laticaudata, C. megops,C. reticulata, C. rotunda and C. setosa)living at the same time and locality is described.Basic population characteristics were studied in allspecies coexisting in the field, except for C. setosa, which was too scarce. Abundances,proportions of gamogenetic individuals, mean bodylengths and clutch sizes were compared among species.Dissolved oxygen, temperature, chlorophyll-a and totalseston volume were measured and related to populationchanges. C. laticaudata and C. rotundawere closely similar to each other in many featuresand showed significant differences to other species.C. reticulata and C. megops seem to besimilar in some features, while C. affinis wasecologically different.
Comparative Life Table Demography and Population Growth of Alona rectangula and Macrothrix triserialis (Cladocera: Crustacea) in Relation to Algal (Chlorella vulgaris) Food Density
ABSTRACT We conducted survivorship and population growth studies with two littoral-benthic cladocerans, Alona rectangula and Macrothrix triserialis, littoral-benthic cladocerans, under low and high food levels (0.5×106 and 2.0×106 Chlorella vulgaris cells ml−1). The net reproductive rate ranged from 13 to 15 offspring/female in the case of A. rectangula and between 19 and 27 for M. triserialis. The generation time was also lower (10 d) for A. rectangula but higher (16–18 d) for M. triserialis. Thus, the growth rates of M. triserialis were around 0.25 d−1 while those of A. rectangula around 0.32. The rates of population increase from the population growth experiments were lower than those from the life table demography studies.
D'une application pratique des indices bio-météorologiques
Abstract The purpose of the author is to determine statistically in what part of Switzerland maize could be cultivated with certain chance of rentability. The author gives first the method he used for determining the biometeorological index of four species of maize which were selected by the Swiss agronomical research stations. He has considered two possibilities for the growing period: ( a ) raising-ripening (l'approche globale); ( b ) raising-flowering, flowering-ripening (l'approche fractionee). From the biometeorological index, he calculated retrospectively the ripening time of these four species in the years 1901–1965. Assuming a priori that maize should be harvested before October 15th at the latest, he calculated, for a number of meteorological stations, the relative number of years when such conditions were fulfilled. Dividing the country in regions of similar mesoclimates and sorting these stations per region, it is possible to average the maximum altitude where maize can ripen at least 7, 8, 9 and 10 times within 10 years. Finally, taking into account the exposure and ground slope, he draws maps of the theoretically possible extension area, which maps are more reliable and detailed than the ones derived from actual means.