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Fluctuation dynamics (studied for 9–27 years) of the abundance, density, age, and spatial structure of the Dactylorhiza maculata (L.) Soó population on Lake Dolgoe of the Volga-Kama Reserve reflects the mechanisms of maintaining the population at the southern border of the range. The data were stored into the database. Abiotic and biotic factors of transitional shrub–sedge sphagnum bogs are the most suitable for the conservation of a rare species, where boreal and arctoboreal species are preserved, and favorable microsites are open and moist areas of the mire, with pH 4.1–4.5. The biodiversity of sphagnum mosses in the habitats of Dactylorhizamaculata is represented by nine species, where the carpet species is Sphagnumangustifolium, and Sphagnum divinum appears in open and wet microareas and Sphagnum centrale appears in areas overgrown with open forest. A significant relationship of the species abundance with climatic factors is revealed: a positive relationship with precipitation and a negative relationship with average temperatures of the growing season. The number of reproductive D. maculata does not depend on precipitation in moist microsites. Age stages are reliably identified using the morphometric parameters of vegetative and reproductive plants: juvenile (j), immature (im), virginal (v), young reproductive (g1), and mature reproductive (g2). The ontogenetic spectrum is 11.5: 17: 29: 42.5 (j: im: v: g), and the proportion of prereproductive individuals fluctuated between 57–66% in the period of 9–27 years of study due to a high percentage of fruit formation (up to 60%). The spatial distribution of individuals is predominantly clustered, consisting of aggregations with a radius of 0.5–1.2 m, distributed randomly. The dynamics of spatial mosaics, accompanied by the migration of seeds and individuals of D. maculata to favorable microsites, is a natural compensatory resistance mechanism that ensures the dynamic balance of the population. [ABSTRACT FROM AUTHOR]

Understanding the ecological mechanisms driving the dynamics of field rotifer populations remains a challenge in ecology. Brachionus angularis (Rotifera) is preferred in such studies because of their planktonic behavior, high fecundity, and absence of cryptic species. In this study, one-year zooplankton samples were collected twice a month from a subtropical lake and the roles of abiotic and biotic factors regulating the population dynamics of B. angularis were analyzed. The sampled B. angularis were composed of two discontinuous populations: ‘summer and autumn’ and ‘spring and winter’, segmented by high mixis rates. The ‘summer and autumn’ population had high egg ratios, but low egg volumes. Water temperature was the main factor driving temporal dynamics in density, thereby counteracting the negative effect of top-down force. Based on the synchronous dynamics of two fractions of chlorophyll-a, the densities of B. angularis, its potential competitors and predators, together with the reverse correlations between the egg ratio and population density, and Secchi-disk depth, we found that bottom-up and top-down forces were plausible factors regulating variations in population density in spring (March and April). However, the density peak of B. angularis in winter might be primarily ascribed to recruitment from the sediment. We further addressed the necessity for diverse evidence from the speciation of cryptic species, abundance, reproduction, and morphology, in understanding the population dynamics of a field rotifer population.

Understanding the ecological mechanisms driving the dynamics of field rotifer populations remains a challenge in ecology. Brachionus angularis (Rotifera) is preferred in such studies because of their planktonic behavior, high fecundity, and absence of cryptic species. In this study, one-year zooplankton samples were collected twice a month from a subtropical lake and the roles of abiotic and biotic factors regulating the population dynamics of B. angularis were analyzed. The sampled B. angularis were composed of two discontinuous populations: 'summer and autumn' and 'spring and winter', segmented by high mixis rates. The 'summer and autumn' population had high egg ratios, but low egg volumes. Water temperature was the main factor driving temporal dynamics in density, thereby counteracting the negative effect of top-down force. Based on the synchronous dynamics of two fractions of chlorophyll-a, the densities of B. angularis, its potential competitors and predators, together with the reverse correlations between the egg ratio and population density, and Secchi-disk depth, we found that bottom-up and top-down forces were plausible factors regulating variations in population density in spring (March and April). However, the density peak of B. angularis in winter might be primarily ascribed to recruitment from the sediment. We further addressed the necessity for diverse evidence from the speciation of cryptic species, abundance, reproduction, and morphology, in understanding the population dynamics of a field rotifer population. [ABSTRACT FROM AUTHOR]