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Every year exotic species are introduced into the environment worldwide; some species succeed, and others do not manage to establish themselves in the new environment. The introduction of exotic organisms affects ecological relationships, mainly by acting as potential competitors with native species. In 2004, an exotic mite from America, Raoiella indica, was detected and has consequently experienced rapid territorial expansion having a high population density. To understand the effects of the introduction of R. indica on the native mites, we selected the native mite web producing mite Oligonychus pratensis and evaluated the competition between exotic (R. indica) and native mites (O. pratensis). Four experiments were conducted to evaluate the effect of competition on oviposition rate, intrinsic growth rate, behavioural choice of colonisation site and distributional behaviour on plants. The presence of the heterospecific mites had a negative effect on both species, reducing the oviposition rate. R. indica preferred sites previously colonised by O. pratensis, but O. pratensis did not prefer sites with or without R. indica colonisation. R. indica exhibited a higher growth rate with some interactions with O. pratensis. The species altered its distribution pattern on plants when in the presence of the heterospecific mite. In our study, R. indica appeared to benefit from previous colonisation by O. pratensis, which could contribute to its territorial expansion. [ABSTRACT FROM AUTHOR]