Laboratory of Mathematical Ecology
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THE STRUCTURE AND DYNAMICS OF A WOODREED Calamagrostis canescens POPULATION: A MODELLING APPROACH
Ulanova, N.G., Demidova, A.N., Klochkova, I.N.
and D.O. Logofet
Summary A scale of ontogenetic states has been developed for woodreed Calamagrostis canescens, a perennial species dominating the grass layer of felled forest areas. The population structure is considered as a set of age-stage groups of individuals differing both in the ontogenetic stage and the chronological age measured in years. To describe the dynamics through years, a special kind of matrix formalism has been proposed which is reducible neither to the classic Leslie matrix for an age-structured population, nor to the well-known Lefkovitch matrix for a stage-structured one, and which does not suffer from excessiveness of the "two-dimensional" representation for the structure implying the projection matrix of a block pattern. It has been shown however that the projection matrix, matching the C. canescens life-cycle graph, embodies the canonical features of a matrix formalism for structured population dynamics, such as the exponential population growth or decline, the convergence to a stable equilibrium structure, the existence of a calculable indicator of growth/decline/equilibrium (i.e., a measure of the population reproductive potential), the possibility to determine the relative reproductive value of each group in the population structure. On the other hand, "left-sidedness of the age spectrum", a property that is often observed in real populations and is inherent in Leslie models of growing populations, may fail in the age-stage-structured model. Also, aggregation of the age-stage groups into the age classes is only possible under special strict relationships among the age-stage-specific vital rates of the population. The both circumstances serve a methodical indication that an additional dimension, such as the stages, for example, ought to be introduced into the age structure of the model population. |