An Attempt to Determine the Absolute Number of Rats on a Given Area

Abstract

ONE of the most interesting problems for the ecologist is the estimation of the density of a particular animal species and in an attempt to determine this a system of trapping is among the devices most commonly employed. The reaction between a number of traps and a population of animals is essentially a special case of the predator-prey relationship; and perhaps it would not be too much to say that the experimental study of this trap-animal reaction is fundamental to the development of quantitative ecology in the field. The proper procedure would be to formulate a theory of trapping in the simplest terms possible and then to experiment with a given number of animals under known conditions. On the comparison of the results with the equations deduced from theory would depend whether the hypothesis be accepted or recast. The observations discussed in this paper were made in order to see whether any consistent results could be obtained by means of a standardized trapping method: they are not experiments in the sense we have outlined since the number of animals at risk was unknown. But, although a number of details will be noticed in which, from this point of view, an improvement or economy of design might have been achieved, the design as a whole fulfilled certain essential conditions of such an experiment. It is interesting to observe that the arithmetical analysis of this data has not revealed any result which