Competing Traps

Abstract

Traps are defined as competing when the presence of one or more traps reduces the catch in a given trap below what would have been registered if the additional trap or traps were not present. Two traps compete completely when the catch is halved. Traps compete less severely when their plumes do not overlap. Plotting competing trap density on the x-axis vs. 1/catch on the y-axis can test whether the trap competition was complete or incomplete. The value of the x-intercept will be negative 1 for complete competition and progressively more negative as the strength of the competition subsides. The radius for detectable trap competition was shown to be less than half of the measured trapping radius because competition for a particular mover cannot occur unless that mover would have reached both traps. Equations relating catch in a focal trap to: T _fer , competing trap density, and mover density were developed for both complete and incomplete competition by the traps. Physical screening of movers incoming to a focal trap was shown to be the mechanistic explanation for competition. Arranging traps in a 3 × 3 square grid creates conditions where the intensity of competition is modulated by the amount of screening a trap experiences. Depending upon the duration of the trapping interval, catch increased markedly in the corner traps relative to the central trap. Thus, progressively higher catch in corner relative to interior traps can serve as a clock for trapping interval. This chapter demonstrates how the pattern in catch across a competing grid of traps can be analyzed to simultaneously quantify T _fer and trapping area along with the number of random walkers in it, thereby sidestepping the problem of relying on historically established measures of T _fer and trapping area under shifting environmental conditions.