[The place of ixodid ticks (Ixodidae) in forest ecosystems].

The ticks Ixodes ricinus and I. persulcatus are the dominant tick species in the forest ecosystems of the temporary zone of Eurasia. They occur within their areals in every types of forests except arid and marsh biotopes. The density of tick populations per square unit exceed many times those of dominant species of mammals and birds living in the same ecosystems. In optimal conditions the abundance of hungry larvae per 1 square km varies from hundreds of thousands to several millions, that of nymphs-from thousands to several hundreds of thousands, and that of imago counts several thousands. The number of larvae and nymphs simultaneously feeding on rodents or shrews usually not exceeds several specimens. However, in case of 50-100% infection rate of hosts and long seasonal period of parasitizing the greater part of individuals in the main host population is repeatedly attacked by ticks and therefore supports a significant number of parasites. Despite of annual fluctuations of ticks and hosts abundance the parasitic systems formed by them are characterized by high stability in time and space. The high resistance of the tick parasitic systems to the influence of unfavorable factors is caused by several independent and duplicated systems of tick's interaction with their hosts and environment. The ticks and their hosts together with agents of the tick borne encephalitis, Lime disease, babesiosis and other transmissive infections form the three component parasitic systems of higher rank. These systems are referred to as the natural foci of diseases and their geographical distribution in general lines coincide with species areals of I. ricinus and I. persulcatus.