Postradiation disorders of peripheral nerve regeneration and role of free-radical oxidation products in their origin

Long-term keeping of guinea pigs on antioxidant-free diet was shown to increase the rate of free-radical oxidation processes after local exposure to 20 Gy gamma-radiation. Alimentary antioxidant deficiency enhanced new formation and growth of young axons, inhibited myelinization both in the exposed and contralateral nonirradiated nerves being regenerated after ligating thereof.     

On the problem of ecological groups formation in European perch Perca fluviatilis populations

Simulation model of the intraseasonal growth dynamics of young-of-the-year European perch Perca fluviatilis has been developed and studied. The model has been constructed based on the principles of bioenergetics and covers all the main physiological utilization processes of energy that come with food, including somatic growth, expenses on metabolism, and partial loss of energy with egestion and excretion. It is assumed that there are two space-separated biotopes called “inshore” and “pelagial” with different feeding conditions. Fish move from inshore to pelagial as the amount of food in the inshore biotope gets lower, provided that the actual ration is reduced down to the predetermined threshold level. It is demonstrated that the combined distribution of fish specimens belonging to one generation according to weight by the end of their growth period mainly depends on the intensity of exchange process between the biotopes. The ratio between the abundance values of young fish localized in different biotopes is determined by the threshold ration level, which motivates fish to move, as well as the duration of spawning, and, accordingly, length of hatching period.     

A conceptual model of the dynamics of the Syamozero Lake community

We present a conceptual mathematical model of the dynamics of a spatially heterogeneous population system whose prototype is the fish community of Lake Syamozero. Analysis of the solutions of this model is used to demonstrate that interactions between the predator and prey populations in two neighboring biotopes (the pelagic and coastal zones) may result in either undamped oscillations or steady states of the population sizes. The model population densities are of the same order of magnitude as the values obtained in long-term observations of the Syamozero biota. It is also demonstrated that the transition to steady states may be accompanied by long-term (dozens or hundreds of years) damped oscillations of the prey and predator population densities. Under natural conditions, long transitional periods may prevent fish communities from reaching stationary modes.     

Resource availability and its role in development of invasion processes

The state of biotic communities inhabiting different water bodies is analyzed aiming to determination of conditions facilitating development of biological invasions. Mass-balance and dynamic models are used to reveal the factors ensuring the invasion of zebra mussel, Dreissena polymorpha, in Naroch Lakes (Byelorussia), and smelt, Osmerus eperlanus, in Lake Syamozero (Karelia). The results obtained indicate that for invasions leading to trophic chain lengthening, the main factor of successful invasion is the availability of resources that are not utilized by aboriginal species. Highest chances for successful invasion belong to invading species feeding on those trophic groups which contribute to the most extent to forming of 'excess' (i.e., available for the invader) production. It is shown that establishment of an alien species in a native community appears to be possible only when total amount of such 'excess' production is higher then some threshold value. Under conditions of spatio-temporal environmental heterogeneity, the timing factor, which determines the exact moment of an alien species intrusion, becomes important as well.     

Effect of antioxidants on the indices of free-radical lipid oxidation in the testes of rats of different ages and on the reproductive capacity in chronic multiple antioxidant deficiency

The free-radical oxidation level of lipids in the rat's testicles of different age under the conditions of chronic and multiple antioxidant insufficiency has been studied, as well as the reproductive ability of male rats, kept at the nonantioxidant ration. The increase of free radical oxidation lipids in the testicles of animals with chronic multiple antioxidant insufficiency and the decrease of their reproductive ability has been observed. The antioxidant complex in such conditions had a defensive effect. The obtained results serve as the basis of the antioxidant use as the means of normalising the reproductive functions in males during period of low receipt and high expense of alimentary oxidants.     

Stock status and current tendencies in the population dynamics of commercial fishes of Pskov-Chudskoe water body

Dynamics of eight commercial populations of fish from Pskov-Chudskoe Lake forming the main bulk (up to 80%) of annual catch was analyzed using an ADAPT-VPA model making it possible to reconstruct the dynamics of the total stock biomass and fishing mortality. The populations of five species (European smelt Coregonus albula, whitefish C. lavaretus maraenoides, perch Perca fluviatilis, roach Rutilus rutilus, ruffe Gymnocephalus cernuus) in the present period demonstrate a tendency for a decrease in biomass while the stocks of two species (bream Abramis brama and zander Sander lucioperca) beginning from the 1980s considerably increased. A particularly drastic (multifold) increase in biomass is recorded in zander population. The causes of the observed population changes are related mainly to ecosystemic transformations taking place in the water body; only with respect to two species-perch and roach-can one state that the decrease in stocks is determined in part by the fishery impact. The increase in zander population is, in all probability, the result of the combined effects of eutrophication forming favorable conditions for the feeding and survival of its juveniles and fishery that led to the decrease in the biomass of one of its main food competitors-perch. The drastic increase in zander numbers in turn promoted the decrease in the biomass of species being objects of its feeding.     

Invasion of an intermediate predator: Fish population dynamics in a mathematical model of a trophic chain (As applied to Syamozero lake)

A mathematical model is presented for the dynamics of a spatially heterogeneous predator-prey population system; a prototype is the Syamozero lake fish community. We show that the invasion of an intermediate predator can evoke chaotic oscillations in the population densities. We also show that different dynamic regimes (stationary, nonchaotic oscillatory, and chaotic) can coexist. The “choice” of a particular regime depends on the initial invader density. Analysis of the model solutions shows that invasion of an alien species is successful only in the absence of competition between the juvenile invaders and the native species.     

A conceptual mathematical model of the aquatic communities of lakes Naroch and Myastro (Belarus)

A conceptual mathematical model of the dynamics of fish and zooplankton (rotifer) populations of connected lakes Naroch and Myastro (Belarus) is built and examined with parameters based on field data. It is shown that community coupling and trophic interactions give rise to both regular and irregular oscillations in population numbers.     

Some regularities of population structure and dynamics variability in bream <Emphasis Type="Italic">Abramis brama</Emphasis> in water bodies of Eastern Europe

Structure and dynamics of populations of bream Abramis brama inhabiting water bodies of Eastern Europe of different types are investigated. With the consideration of the original and published data, the following issues are analyzed in populations from the southern part of the area (water bodies of Moldova) and from the central and northwestern areas of the European part of Russia: age composition, sex ratio, males and females growth in size and weight, and age of maturation. Over the area, all transitions from short-cycle populations to average-cycle and long-cycle populations are observed. The maximum longevity of their specimens attains 9, 15, and 26 years, respectively. The growth rate of bream is controlled by a combination of average temperature, duration of vegetation season, size of water body, number of trophic niches for various size-weight groups, multiple change of the kind of feeding in ontogenesis, and general availability of food for adults. From the north to the south the variation of maturation age and of the rate of size and weight growth increase.     

Population Dynamics of the Bream Abramis brama in Lake Peipus

Journal of Ichthyology - Population dynamics of the bream Abramis brama in lakes Peipsi and Pihkva for the period from 1980 to 2009 has been studied by means of cohort models. Bream stock increased...