Population structure of muskrat (Ondatra zibethicus) in Lithuania

Abstract

The muskrat (Ondatra zibethicus) is a semi-aquatic rodent and it is listed as the most successfully acclimatized alien species in Europe with a wide distribution, fast increase of abundance, short colonisation time, massive spread into various ecosystems and significant ecological impact. Lithuania is no exception; after introducing, the muskrat rapidly inhabited a wide spectrum of waters throughout the whole country. The analysis of the variation in body dimensions and other characteristics of muskrats is important for assessing the effect of environmental factors on muskrat populations. The aim of this reasearch was to examine invasive species muskrat population demographic status, sex structure and ratio, weight and to count the embryons and placental scars. Population structure of muskrat were studied using muskrat population (n꞊129) hunted during 2001 – 2012 throughout Lithuania. Males predominant over females in catch numbers – 67% of all hunted males and 33 % of all hunted females. Male dominance in numbers has been attributed either to different mortality of the sexes or the differences in activity resulting in a greater proportion of males being hunted (Pankakoski, 1983). The biggest differences of caught muskrat in different years were in 2006 and 2007 (65% males and 35% females, 77% and 23%, respectively). The male and female ratio of the muskrat population was 2:1 and effective population size (Ne) 113 and it is being less than an absolute population size (N) 129. The literature on the sex ratios in muskrat populations is extensive and usually there is a clear prepoderance of males in spring (Pankakoski, 1983). Mean weight of muskrat was 936 g. Males showed slighlty higher weight in comparison to females (980 g and 900g, respectively) because of intraspecific competition. There was significant difference between weight of females and males (t = 1.682, p = 0.031). [...]