Colonisation of new areas by stoats: time to establishment and requirements for detection

A simple deterministic accounting model was used to predict the rate at which a colonising stoat (Mustela erminea L.) population would reach specified sizes. The model was used to explore how the size and composition of the founder population, and the survival schedule to which it was exposed, influenced this rate. A function used in disease surveillance was modified to predict the number of tracking tunnels necessary to detect the presence of the colonising Population with a specified degree of confidence. This function was used to assess how the detection characteristics of tracking tunnels (the probability that a stoat will enter a tracking tunnel), and the degree of certainty associated with detection, might influence the number of tracking tunnels required. Founder populations consisting of females and males established more quickly than those consisting of one or two pregnant females in the absence of males. Over and above the effects of founder population size and composition, survival schedules had little influence on the time establishing populations took to attain moderate sizes (<50 individuals). The number of tracking tunnels necessary to detect the presence of a newly establishing stoat population increased exponentially below a population size of about five. Both the detection characteristics of tracking tunnels and the degree of certainty associated with detection influenced the number of tracking tunnels necessary to detect stoats at low abundance.