Measuring the effect of long-term pitfall trapping on the prevalence of epigeal arthropods: A case study in the Pacific Coast of Colombia

Pitfall trapping remains one of the most frequently used methods to assess ground-active arthropods’ diversity and density. Yet, one of its main drawbacks, the possibility that repeated collecting may affect the study objects’ population, has not been formally tested. We studied the effect of a yearlong epigeal pitfall trapping exercise with 22 fortnightly capture events in four differently disturbed areas at the Colombian Pacific coast. A transect of 100 m length with ten equidistant pitfall traps was established in each area, and the traps were operated twice a month for 24 hours. Using count data regression models, we find that trapping did not affect subsequent captures when we analyzed non-ant arthropods. For ants, regression estimates indicate that each subsequent trapping in highly-disturbed environments ended, on average, reducing all ants in between -3.8 and -4.1%, and Ectatomma ruidum between -4.7 and -5.1%. We recommend bio-ecological aspects of the species under study be considered when interpreting results. This is important for future studies that rely on this method to deliver consistent estimates of population sizes or study their dynamics through time. At the same time, it is also a call for scientists to revise more carefully how species’ peculiar traits may limit the reliability of traditional methods.