Solving the pitfalls of pitfall trapping: a two-circle method for density estimation of ground-dwelling arthropods
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1. Pitfall traps are widely used for investigating ground -dwelling arthropods, but have been heavily criticized due to their species-, habitat- and attractant-specific trap ping radius which produces unr eliable estimation of spe- cies diversity and density. 2. We developed a two-circle method (TCM ) for simultaneously estimating de nsities of ground-dwelling arthro- pods and the effective trapping radius. Multiple pairs of tr aps are located different distances apart, and the inter- section of trapping areas can be calculated using the inverse trigonometric function. The density and effective trapping radius can be estimated from a nonlinear regression of the change in the total number of individuals caught with the distance betwe en the paired pitfall traps. 3. We compared the performance of TCM with the estimato r based on the nested-cross array (NCA) for arrang- ing pitfall traps, by comparing predicted densities fro m these two methods with the real density obtained from the suction sampling method (SSM). 4. Simulations with known arthropod densities and effe ctive trapping radius suggested that TCM produced accurate density estimation, while NCA significantly u nderestimated the known density. Pitfall trapping of ground-dwelling arthropods o n two habitats (crop field and desert step pe) confirmed this conclusion when com- paring estimation from TCM and NCA with densities obtained from the SSM. 5. TCM is a promising technique for the density estimation of ground-dwelling arthrop ods, especially for traps with liquid attractant and areas with relatively ho mogenous habitat and away from habitat edges.
- RESEARCH: Hui C