Body size, and interactions between European and American mink (Mustela lutreola and M-vison) in Eastern Europe

Body sizes of European mink (Mustela lutreola L.), polecat (M. putorius L.) and American mink (M. vison Schreber) were studied over a 10-year period i n an area of north-eastern Belarus, before and after the invasion by Americ an mink, and data are presented on interspecific interactions. On arrival i n the study area American mink males were larger than males of European min k and polecat, and American mink females were larger than females of the ot her species. After arrival of the American mink its mean body size decrease d, whilst the resident male and female European mink and female polecat inc reased as measured in absolute mass, length and relative mass. The observat ions suggest a strong character convergence most plausibly explained as a r esponse to the invading exotic by the residents as well as in the invading species itself, whilst a divergence had been expected. There was no evidenc e to show whether these differences were genetically based. The body size d ata are consistent with the hypothesis that European mink, and to a lesser extent polecat, are responding to direct aggression from American mink (rat her than merely competing for resources), with the smaller individual Europ ean mink being more likely to disappear first. We provide direct evidence f or the aggressive nature of inter-specific relations from observations usin g radio-tracking: all observed inter-specific interactions were aggressive, significantly more so than intraspecific encounters, causing the European mink to flee, and several left the study area altogether. Implications for niche theory and for conservation management are discussed.