Cricket (Ensifera, Grylloidea) are not commonly used as ecological indicators in contrary to other Orthoptera (e.g. grasshoppers and katydids). However, they are sensitive to environmental changes and abundant in tropical regions. To evaluate if crickets are relevant bioindicators of tropical ecosystems, we investigated cricket assemblages along a tropical ecological gradient. We collected crickets during both day and night in southern New Caledonia for three stages of an ecological succession: open shrubland, preforest and forest. Simultaneously, we measured several environmental variables, such as temperature and relative humidity, at each sampling site. Cricket species assemblages showed a clear response to ecological succession. The highest and lowest species richness and abundances of individuals were respectively found in forest and shrubland, with species specialized in each ecological stage revealing the conservation value of each of these stages. Similar results were found when considering only the part of cricket communities with ability to acoustically communicate. This work is part of a larger research program about Neocaledonian crickets and contributes to support the use of acoustic approaches to monitor tropical environments. In conclusion, these findings highlight the potential value of crickets as an environmental indicator in tropical ecosystems. The results also contribute to the discussion of the intrinsic conservational value of shrublands in New Caledonia and similar ecotypes.

Cricket communities were studied in the southern region of Grande Terre, the main island of New Caledonia, an archipelago located in the Southwest Pacific Ocean. Sites were selected along the same geological ultramafic substrate at low altitude (231 ± 66 m). To study ecological succession on cricket fauna, three vegetation stages—forest, preforest and shrubland—were considered. Four sites were chosen within each stage for a total of twelve sites.

Crickets were collected between November 2013 and April 2014. In each of the twelve sites selected, two squared parcels with 10 m sides were delimited. Sampling was performed under clear sky meteorological conditions from hours 0900 to 1700 by day, and 1900 to 0000 by night. On each parcel, crickets were collected using a same collection method of ten 30 minute sessions, with five total collections by day and five by night. Crickets were located using both sight and song cues in the field only based on human perceptions, which is the most appropriate sampling method for crickets.

For each individual, activity (e.g. singing, eating, mating, resting) and microhabitat (e.g. trunk, leaf litter, vegetation, rocks, height from ground) were noted before the capture.

Specimens are deposited in the Museum national d’Histoire naturelle de Paris with a reference collection in the Nouméa IRD center in New Caledonia. Species identifications were performed in lab by comparison to the specimens in the deposited collections and using the classification derived from the extensive molecular phylogeny of crickets (Chintauan-Marquier et al., 2016). Based on previous taxonomic description including acoustic production (i.e. Desutter-Grandcolas et al. 2016 and Anso et al. 2016b), we were able to attribute to each species a presence or absence of singing abilities.

Of the 1,030 individuals collected, 54 were discarded. These specimens were not identifiable to the species level because of their destruction due to unfavorable conservation conditions (56%) or from the absence of morphological information for crickets in the juvenile development stage (44%).

During cricket sampling, environmental attributes were measured in each parcel, including: the percentage of bare ground, the percentage of three vegetation layers (herbaceous, shrub and tree), the number and diameter (dbh) of stems, the vegetation height, and the plant species richness. Canopy openness was extracted from photos taken with a 180° hemispherical (fisheye) lens in each parcel corner and in its center. From the photos, canopy openness was then calculated using the Gap Light Analyzer software (version 2.0, Simon Fraser University, Cary Institute of Ecosystem Studies) by estimating the percentage of light in the forest overstorey (Frazer et al., 1999). Daily temperature (°C) and relative humidity (%) were recorded every 30 minutes during 15 days at a 50 cm height above the ground using waterproof thermo-hygrometer sensors (HOBO U23 Pro v2; HOBOware software).

Table S1: Crickets inventory. Details of species identification, time, date and location of collected specimens as well as their position in the vegetation at the moment of their collection. “NA” indicates an unknown information associated to the sex or the stage of development of the specimen.

Table S2: Environmental data with the following abbreviations: HER for Herbaceous layer, SHR for shrub layer, TRE for tree layer, BAR for bare ground, VH for vegetation height, DN for number of stems, DBH for number and diameter of stems, CO for canopy openness, RI for vegetation richness, MT for mean temperature, HT for maximum temperature, LT for minimum temperature, DT for daily temperature variation, MH for mean humidity, LH for minimum humidity, and DH for daily humidity variation.

Table S3: List of complete name species of crickets identified during the taxonomic inventory.

The tables 1 and 2 are in csv and can be open with several software including Libre office or Excel.

Tha table 3 is a docx and can be open by Word or Libre office Writter.