Predation on Moose Calves by European Brown Bears

Abstract: In North America, brown bears (Ursus arctos) can be a significant predator on moose (Alces alces) calves. Our study in Sweden is the first in which brown bears are the only predator on moose calves. Bears and moose occurred at densities of about 30/1,000 km² and 920/1,000 km², respectively, and bears killed about 26% of the calves. Ninety-two percent of the predation took place when calves were <1 month old. Bear predation was probably additive to other natural mortality, which was about 10% in areas both with and without bears. Females that lost their calves in spring produced more calves the following year (1.54 calves/F) than females that kept their calves (1.11 calves/F), which reduced the net loss of calves due to predation to about 22%.     

Population structuring of the tsetse Glossina tachinoides resulting from landscape fragmentation in the Mouhoun River basin,Burkina Faso

The impact of landscape fragmentation resulting from human‐ and climate‐mediated factors on the structure of a population of Glossina tachinoides Westwood (Diptera: Glossinidae) in the Mouhoun River basin, Burkina Faso, was investigated. Allele frequencies at five microsatellite loci were compared in four populations. The average distance between samples was 72 km. The sampling points traversed an ecological cline in terms of rainfall and riverine forest ecotype, along a river loop that enlarged from upstream to downstream. Microsatellite DNA demonstrated no structuring among the groups studied (F_ST = 0.015, P = 0.07), which is contrary to findings pertaining to Glossina palpalis gambiensis Vanderplank in the same geographical area. The populations of G. tachinoides showed complete panmixia (F_IS = 0, P = 0.5 for the whole sample) and no genetic differentiation among populations or global positioning system trap locations. This is in line with the results of dispersal studies which indicated higher diffusion coefficients for G. tachinoides than for G. p. gambiensis. The impact of these findings is discussed within the framework of control campaigns currently promoted by the Pan African Tsetse and Trypanosomosis Eradication Campaign.     

A precise potentiometric method for determination of algal activity in an open CO2 system

Abstract. The activity of the green alga Scenedesmus obliquus was studied in simplified nutrient solutions (20 mol m₋₃ NaNO₃, 20 mol m₋₃ NH₄C1, 20 mol m₋₃ NH₄NO₃, and 20 mol m₋₃ NaCl, respectively) at 25 °C. The experiments were performed under welldefined incident photon density fluxes ranging from 10 to 200 μmol m₂ s₋₁, Light-dependent changes in pH and alkalinity (A) were followed by means of a potentiometric method using a glass electrode. In the experiments, carbon dioxide with known partial pressure was bubbled through the algal suspension, and during dark periods ul intervals of 1 h, the solution was allowed to equilibrate with the gas phase. This technique was applied to calculate equilibrium values of pH and alkalinity at regular intervals during a 12-h period. Results obtained in NaNO₃, solution show a linear increase in A with time, at each level of illumination studied. After an initial drop, A also increases in NH₄NO₃, solution in a similar way to that in NaNO₃ solution. The change in A with time was also found to increase linearly with the photon density flux studied and no saturation level could be defined. In experiments in NaCl solution, no changes in A were registered while measurements in NH₄Cl solution showed a decrease in A with time.     

Testing models of trophic dynamics: The problem of translating from model to nature

Abstract Mathematical models of interacting populations have a prominent position in population and community ecology, but are often criticized for not being testable. The authors reviewed tests of a particular model, the exploitation ecosystem hypothesis as it was formulated in Oksanen et al. (1981), in order to study problems that may be encountered when testing models. A general problem is how to determine if an experimental system should be regarded as within the model's theoretical domain or not. The theoretical domain defines the type of system the model is meant to apply to. It is noted that both liberal and strict domain definitions can be problematic. Most important is that a too liberal domain definition can result in false understanding (i.e. that it is falsely concluded that the processes included in the model are controlling the study system). Other problems encountered were more system‐specific. Equilibrium predictions were tested in experiments that were too short to reach steady state and in several studies ambiguous definitions and measurements of model variables were found such as productivity, biomass and the number trophic levels. It is concluded that a major obstacle when performing tests is the conceptual and methodological problems encountered when translating model abstractions into an empirical reality.     

Degradation of Chitotetraose to Chitobiose in the Axenic Rape Rhizosphere

In the presence of intact roots of 2-week-old axenic rape seedlings,added N, N', N', N'-tetraacetylchitotetraose was degradedto N, N'-diacetylchitobiose during 48 h of incubation. Onlyminute amounts of monomer (N-acetyglucosamine) were formed fromadded chitotetraose or chitobiose. The addition of a purifiedchitin suspension caused no measurable formation of degradationproducts. The formation of chitobiose from added chitotetraose was linear,suggesting the action of a constitutive enzyme during the incubationperiod. Key words: Brassica napus (L.) cv. Brink, rhizosphere, N, N'-diacetylchitobiose, N,N',N',N', tetraacetylchitotetraose     

ON THE GUSTATORY EFFECTS OF GYMNEMIC ACID AND MIRACULIN IN DOG, PIG AND RABBIT

The effects of gymnemic acid, 1 mg/ml, and miraculin, 1 mg/mlor in a tablet (Miralin^TM) on the taste response to sucrose,citric acid, NaCl and quinine have been studied in dog, pigand rabbit. In the dog gymnemic acid suppressed the responseto sucrose for about 5 min in two out of three animals. It alsoaffected the response to NaCl. Miraculin caused a slight short-lastingincrease in the response to acid. No effects of the taste modifierswere observed in the pig. In the rabbit gymnemic acid did notsuppress the response to sucrose while miraculin enhanced theresponse to citric acid in one out of three animals for a fewminutes.     

ON THE GUSTATORY EFFECTS OF MONELLIN AND THAUMATIN IN DOG, HAMSTER, PIG AND RABBIT

The electrical activity in the chorda tympani proper nerve ofdog, hamster, pig and rabbit was recorded during stimulationof the tongue with the sweet proteins, monellin and thaumatin,and stimuli representing the four taste qualities. It was observedthat these proteins, which to man taste extremely sweet andin the monkey elicit a significant neural response, caused,except for monellin in the dog, no significant change in theneural activity. On the basis of these results it is suggestedthat different types of ‘sweet’ receptor sites existin mammals.