A CASE STUDY OF SINGULAR SPECTRUM ANALYSIS APPLICATION IN PARASITOLOGY: DYNAMICS OF PREVALENCE OF CRYPTOCOTYLE CONCAVUM AND BUNOCOTYLE PROGENETICA TREMATODE PARTHENITAE IN HYDROBIA VENTROSA SNAILS AT THE WHITE SEA
In this study parasitological data were analyzed by different methods of revealing the structure of time series, namely. auto-correlation analysis (ACA), Fourier spectrum analysis (SA) and singular spectrum analysis (SSA), and the results of these analysis were compared (SSA makes it possible to present non-stationary time series as a sum of independent components and to determine the contribution of each component into the dispersion of the initial series — Golyandina et al., 2001). This case study was based on the result of 10-year-long monitoring of changes in the prevalence of Cryptocotyle concavum and Bunocotyle progenetica trematode parthenitae in intertidal snails Hydrobia ventrosa at the White Sea (in total, 45 observations). ACA did not reveal any statistically significant oscillations in the analyzed series. The application of SSA and SA allowed us to reveal at least two quasi-periodical components. In addition, SSA made it possible to reveal a significant dome-shaped trend in the prevalence of B. progenetica parthenitae, which were described by SA as an oscillation with a period equal to the duration of the study, as well as to give proof that there was no trend in the changes of C. concavum parthenitae prevalence. The components (modes) extracted by the SSA described the changes in the prevalence better that the harmonics extracted by the SA. In particular, SSA modes (contrary to SA harmonics) reflected that the amplitude of oscillations of the B. progenetica prevalence increased as the prevalence grew. The sums of SSA modes correlated more with initial prevalence series that the sums of SA harmonics. A possible interpretation of the trends and modes extracted by the SSA in the light of the transmission features of the investigated trematode species in the study area was proposed.