engleski

Spatial patterns and species associations of earthworms in relation to habitat microtopography

Earthworms show clumped, patchy distribution. This horizontal distribution is mainly a response to a spatial heterogeneity primarily determined with physico-chemical parameters of soil and food availability on various scales. In a given plot, the earthwormdensity depends on a group of different factors and which factor is the most limiting varies between ecosystems and earthworm species. The aim of this study was to characterize the spatial variability of earthworm communities and earthworm species co-occurrence in grassland habitat in two consecutive seasons in relation to the habitat microtopography. Sampling was carried out in mid-April and early July. On each site a plot 33.5x33.5m was selected, on each plot 49 sampling points were placed in a regular grid (7x7) with 5m inter-sample distance. To obtain high resolution microtopographic profile, elevation on each site was measured with the optical leveling instrument on multiple points. To test the spatial distribution of a single species a Morisita index of intraspecificaggregation (Id)was calculated, spatial autocorrelation was tested with Geary's C and Moran's I index and semivariograms were calculated for each species, season and location. The results of this research show a patchy distribution of majority of adult individuals, and almost all juveniles. The Morosita index values from the literature are mostly higher, i.e.indicate a stronger aggregation from the values obtained within this research. In this research the range of semivariograms for all species and lifestages was 8.67 m. For adult earthworms a range was somewhat smaller (8.37m), while for juveniles it was larger (9.2m). Kriged sampling areas show that earthworm populations are not static and that both position and coverage within the sampling location is variable. Additionally, observed and expected frequencies of co-occurrence between pairs of species were calculated.

earthworm species associations ; microtopography ; co-occurrence ; geostatistical analysis

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