The ecological significance of terrestrial ecotone and its biological quality on the population dynamics of soil oribatid mite communities was studied. Three distinctive zones namely orange orchard, date palm orchard and a transition zone in between at Kafr El-Zayat city in the Nile delta were sampled all over the four seasons of the year. Abundance, species diversity, Evenness, dominance index, species richness, stability, coefficient of variations and similarity were determined. The results showed that the oribatid mites were found to be spatially distributed into three ecological ranges, a wide range which included six species, a moderate which included twelve species and a narrow which included ten species. Seasonal distribution of oribatid mites showed that their abundance was significantly correlated with the site quality. The least seasonal fluctuation intensity of oribatid abundance was recorded in ecotone site. In the view of the present results, it seems that the ecotone between the two biotopes; orange orchard and date palm orchard represents a favourable site for oribated mites by contributing in the progress in their soil activities such as high species richness and more even distribution of the dominant species, in addition to supporting a successful life for the rare species as well as providing a seasonal alteration among different species. These, in turn, result in a high biological quality of the ecotone. In addition, the oribatid mites can be considered as a bio-indicator for the habitat quality of such biotopes.
Key words: Oribatid mites, seasonal distribution, terrestrial ecotone, orange orchard, date palm orchard.
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