Alexandra Narvaez’s research while affiliated with Federal University of Viçosa and other places

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.

Diversity, permanence, and activity of terrestrial arthropods were investigated in four areas of different land use in the lowlands of the Pacific coast of Colombia with the aim to identify potential predator species for the palm root borer, Sagalassa valida. Ten pitfall traps were established along a 100 m transect in four areas: a secondary forest, a 20 year.-old peach palm plantation, and two hybrid oil palm plantations of three and seven years of age, respectively. Twenty-two collections were made covering a whole year. All ants were identified to species or morphospecies level, the other arthropods to order or where possible to family level. In total, 50,603 arthropods were captured, the most abundant were ants (37.0 %), followed by Collembola (35.4 %), Acari (10.6 %), Coleoptera (7.0 %) and Diptera, Hemiptera and Araneae in almost equal numbers (around 2.5 %). Orthoptera (92 % Gryllidae) were present in all collections, always at low numbers. The highest number of ants were recorded in the oil palm transects; Diptera, Hemiptera and Orthoptera were more numerous in the secondary forest, Acari, Araneae and Collembola in the palm transects. Ectatomma ruidum was by far the dominant ant species (84.9 % of all specimens) and absent from only 20 of the 880 captures. The second most frequent ant genus were army ants with two species, Labidus praedator and L. coecus. Rainfall, even area-wide flooding, and temperature did not explain variability in captures of any taxonomic group satisfactorily. We conclude that E. ruidum might be the predator to provide control of the root borer and recommend further studies on its efficiency.