A Simulation Approach to Investigating the Response of a Coypu Population to Climatic Variation1

Abstract

The main environmental constraint on the population of feral coypus (Myocastor coypus) in eastern England is cold weather. This paper describes the use of population simulations to explore the effect of various combinations of cold and mild winters. Winter severity is defined‐using an expression that accumulates weighted sequences of freezing days. Descriptions of fecundity, recruitment to the adult sector of the population and mortality were obtained from dissections of over 20,000 coypus and from records of the control trapping operation between 1970 and 1982. These data were summarized in average years containing either cold or mild winters and used as inputs to a realistically constructed model of the population. The simulations presented show the seasonal consequences of cold and mild winters, the effect of continuous sequences of each type of winter, and the effect of random sequences of cold and mild winters occurring at the relative frequency (5:6) observed in recent years. The results give a quantitative assessment of the interaction between control trapping and cold weather and its effect in limiting the population. A simulated population curve over the 12‐year study was significantly correlated with the results of a continuous retrospective census over the same period.