Experimental Design

A balanced nested sampling design was applied from a broader to narrower spatial scale: seven islands; within each island, two native forest fragments; within each fragment, several transects; and within each transect, five blocks of samples. In other words, 7 islands × 2 fragments × n transects × 5 blocks.

Along each transect, arthropods from the soil (mainly epigean) and herbaceous vegetation were surveyed with a set of pitfall traps, while arthropods from woody plant species were sampled using a beating tray.

Pitfall traps consisted of plastic cups with 4.2 cm diameter and 7.8 cm deep. Thirty pitfall traps were used per transect. Half of the traps were filled with a non-attractive solution (ethylene glycol antifreeze solution), and the remaining with a general attractive solution (Turquin), prepared mainly with dark beer and some preservatives (for further details see Turquin 1973 and Borges 1992). A few drops of liquid detergent were added to both solutions to reduce surface tension. The traps were sunk in the soil (with the rim at the surface level) every 5 m, starting with a Turquin trap and alternating with the ethylene traps. They were protected from rain using a plastic plate, about 5 cm above surface level and fixed to the ground by two pieces of wire. The traps remained in the field for two weeks.

Canopy sampling was conducted during the period that pitfall traps remained in the field, when the vegetation was dry. A square 5 m wide was established every 15 m (10 squares in total per transect). In each square, a replicate of the three most abundant woody plant species was sampled. In most of the study sites, three species clearly dominated over the remaining plants and the choice was evident. However, in some transects, less than three were present and only those were considered. For each selected plant, a branch was chosen at random and a beating tray placed beneath. Five beatings were made using a stick. The tray consisted of a cloth inverted pyramid 1 m wide and 60 cm deep (adapted from Basset1999), with a plastic bag at the end.