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.     

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.     

The biological features of the Kildin cod,Gadus morhua kildinensis Derjugin, 1920 (Gadidae)

The morphological and biological characteristics of the unique isolated population of the Kildin cod that inhabit the relic Lake Mogilnoye (Kildin Island, Barents Sea) were studied using a complex of methods. This subpolar meromictic marine lake was formed more than 1000 years ago by a filtering pebble–stone bar that separated the lagoon from the Kildin Strait. The current status of the lake has been assessed. An analysis of the properties of the Lake Mogilnoye ecosystem, including assessment of this body of water and the role and features of various groups of organisms, has been performed for the first time by using a balance model of the ECOPATH type.     

A mathematical model of the invasion of mysid (Mysidacea) into Narochan Lakes

We present a mathematical model of the invasion of mysid into the Narochan Lakes system. The model is parameterized with the use of field observation data. We show that the mysid invasion can lead to an increase in the time-averaged fish population size, and to a decrease in the time-averaged rotifer population size.     

Long-period endogenous oscillations in fish population size: Mathematical modeling

We present a mathematical model of an aquatic community, where the size-and-age structure of hydrobiont populations is taken into account and the corresponding trophic interactions between zooplankton, peaceful fish, and predatory fish are described. We show that interactions between separate components of the aquatic community can give rise to long-period oscillations in fish population size. The period of these oscillations is on the order of decades. With this model we also show that an increase in the zooplankton growth rate may entail a sequence of bifurcations in the fish population dynamics: steady states → regular oscillations → quasicycles → dynamic chaos.     

Mechanisms of the adaptation of the Kildin cod <Emphasis Type="Italic">Gadus morhua kildinensis</Emphasis> Derjugin, 1920 (Pisces: Gadidae) to the specific conditions of Lake Mogilnoye

The mechanisms of the adaptation of the Kildin cod to the conditions of a meromictic lake were analyzed based on the study of morphological, biological, and genetic characteristics. Significant differences between the Kildin cod and Atlantic cod have been found in their morphological and genetic characteristics. The results of an X-ray microanalysis of otoliths, which were conducted for the first time, confirm that the distribution range of the Kildin cod in Lake Mogilnoye also extends to brackish waters. It has been shown that the formation of the reproductively isolated lacustrine population of Kildin cod is accompanied by specialization in a number of characteristics (body color, feeding strategy, behavior, etc.) and by a decrease in genetic diversity.     

Analysis of commercial fish population size oscillations in Lake Peipus

With the use of recurrence plots, we show that the irregular oscillations in time, which commercial fish populations in Lake Peipus undergo, are deterministic.