Population structure of coypus (Myocastor coypus) in their region of origin and comparison with introduced populations

The first population recapture study of indigenous coypus Myocastor coypus is reported in protected areas of Argentine pampas within a region where the species is hunted for food and fur. Quarterly live trapping at two sites captured a high proportion of all coypus present (96% of juveniles; 85% of adults, independently of season, site and sex). Survival (from mortality or emigration) was constant across sites and seasons, and higher for juvenile males than females (88% and 71%, respectively) and lower for adult males than females (45% and 81%). Most turn-over in numbers was replaced by births, and immigrating males tended to be the largest individuals present. Sex ratios were male-biased amongst juveniles and female-biased amongst adults. Taken together, these results are consistent with local resource competition in habitat rendered low in quality by crowding inside the locally protected areas. The indigenous coypu population matured more slowly, and to a smaller maximum body size, than coypus studied in introduced populations in North America and particularly in northern Europe. Cold European winters may have contributed to the evolution of precocious sexual maturity and larger body sizes in European compared with indigenous populations.