Area of study: The Azores

The remote Azores archipelago extends for 615 km in the North Atlantic Ocean (37-40 °N, 25-31 °W), 1584 km to the east (southern Europe) and 2150 km to the west (northern America) of the nearest mainland. It comprises nine main islands and some small islets, all of volcanic origin, and is located at the triple junction of the Eurasian, African and American tectonic plates. The nine islands are divided into three groups: the western group (Corvo and Flores isls.), the central group (Faial, Pico, Graciosa, São Jorge and Terceira isls.), and the eastern group (São Miguel and Santa Maria isls) (Fig. 1). The climate is temperate and oceanic, strongly influenced by the ocean and island topography, which together produce high relative atmospheric humidity, above 95% on average on native forests.

Figure 1.  

Location of the Azores and of native forest fragments in the archipelago. Codes for forest fragments as in Table 1.

Sampling protocol

Eighteen native forest fragments distributed across seven of the nine islands were sampled (Table 1; see also Gaspar et al. 2008). Graciosa and Corvo islands were excluded as they no longer present native forest. Human settlement in the Azores lead to considerable native forest destruction which has left the entire archipelago with little over 2% of the original forest cover. During the summer (June to September) 150 m long and 5 m wide transects were set up in 100 sites from 1999 to 2004 (BALA I: 18 native forest fragments) and some were sampled twice in that period totalling 123 samples; about 29 of those sites were resampled from 2010 to 2011 using the same protocol (BALA II project; 15 native forest fragments). Along each transect, arthropods from the soil (mainly epigean) and herbaceous vegetation were surveyed with pitfall traps, while arthropods from woody plants were sampled using a beating tray. Pitfall traps consisted of plastic cups with 4.2 cm diameter and 7.8 cm height. Thirty pitfall traps were set up per transect. Half of the traps were filled with a non-attractive ethylene glycol preservative solution (antifreeze solution), and the remaining with a general attractive solution, a modified version of Turquin (Turquin 1973) prepared mainly with dark beer and preservative agents. A few drops of dishwashing liquid were added to both solutions to reduce surface tension. Traps were sunk in the soil (cup rim at surface level) every 5 m along the transects, those filled with Turquin alternating with traps containing antifreeze solution. Traps were protected from rain using a plastic plate, placed about 5 cm above surface level and fixed to the ground by two pieces of wire. Accidental collection of small vertebrates and damage by rodents was prevented using a piece of plastic mesh placed on top of the trap and fixed to the ground by pieces of wire. The traps remained active in the field for two weeks.

Canopy sampling was conducted during the trapping period, when the vegetation was dry. A 5 m wide square was established every 15 m (total of 10 squares per transect). Two woody plant specimens of the most abundant species (up to three species when available) were sampled in each square. For each selected plant, a branch was chosen at random and a beating tray placed beneath. The tray consisted of a 1 m wide and 60 cm deep cloth inverted pyramid, with a plastic bag at the vertex. Five beatings were made using a stick for each plant individual sampled.

The arthropod taxa considered in this study were selected based on the availability of expert taxonomists and ability to readily separate them by morphological criteria. All Araneae, Opiliones, Pseudoscorpionida, Diplopoda, Chilopoda and Insecta (excluding Collembola, Diptera and Hymenoptera) were assigned to morphospecies through comparison with a reference collection. Various taxonomists (PAVB, ARMS, LC, PC, HE, FI, VM, MTP, JR, AB, ABS, RzS, VV, JW, JAQ, and see also Acknowledgments) checked the assignment to morphospecies, performed species identifications and supplied additional ecological information. The taxonomic nomenclature follows the most recent list of Azorean arthropods (Borges et al. 2010).

All specimens are deposited in the Entomological Collection Dalberto Teixeira Pombo at the University of the Azores (Portugal), under the curation of Paulo A. V. Borges (pborges@uac.pt).

In this contribution we list the 286 species for which we obtained an identification. The new records for each island are marked with *. For this list two families of Coleoptera were not considered since they will be presented elsewhere, Staphylinidae (Borges et al. in prep.) and Zopheridae (Borges et al. 2016). For detailed maps on the distribution of these species in Azores consult the Azores Bioportal.

All specimens were assigned a SITE CODE composed of several letters and numbers that read as follows (see Suppl. material 1 for complete data). Detailed metadata is given in Suppl. material 2):

i) the first three letters refer to island name (FLO – Flores; FAI – Faial; PIC – Pico; SJG – São Jorge; GRA – Graciosa; TER – Terceira; SMG – São Miguel; SMR – Santa Maria);

ii) the following two letters refer to fragment name (Flores: FR - Caldeiras Funda e Rasa, MA - Morro Alto e Pico da Sé; Faial: CF – Caldeira do Faial, CG – Cabeço do Fogo; Pico: CA – Caveiro, LC – Lagoa do Caiado, MP – Mistério da Prainha; São Jorge: PP – Pico Pinheiro, TO – Topo; Terceira: BF – Biscoito da Ferraria, GM – Caldeira do Guilherme Moniz, PG – Pico do Galhardo, SB –Serra de Santa Bárbara, TB – Terra Brava; São Miguel: AT – Atalhada, GR – Graminhais, PV – Pico da Vara; Santa Maria: PA – Pico Alto);

iii) the following three characters refer to the sampling transect; and

iv) the next letter refers to the sampling technique: P - pitfall, B - canopy beating; for pitfall samples (P) TU – Turquin and ET – ethylene glycol; for canopy samples (B) the next two letters refer to the plant sampled: CA = Calluna vulgaris, CL = Clethra arborea, ER = Erica azorica, FR = Frangula azorica, IL = Ilex perado azorica, JU = Juniperus brevifolia, LA = Laurus azorica, MC = Morella faya, MS = Myrsine africana, PI = Picconia azorica, PT = Pittosporum undulatum, VA = Vaccinium cylindraceum.

For the geographical location of transects within reserves (UTM coordinates) see Suppl. material 3.

Accumulation curves were obtained using the software “Species Diversity and Richness” V.4.

Azorean Arthropod biodiversity - towards a more complete knowledge

The ultimate goal of biodiversity assessments is documenting all species inhabiting a region. However, this has often proven impossible to achieve given the unfeasibility of collecting every single species that exists in a study area. This study focuses on the terrestrial arthropod diversity of the Azores and encompasses most orders of the phylum Arthropoda. A pool of a total of 1215 species and subspecies was surveyed, representing 53% of the whole arthropod fauna known from the Azores (Borges et al. 2010). By deliberately not surveying Crustacea, Acari, Collembola, Diptera and Hymenoptera, we excluded 47% of the archipelago's species pool. Yet, this study added 10 endemic and at least 16 other species, mostly exotics, to the known Azorean arthropod fauna. More will be added soon after the on-going revision of Staphylinidae (in prep.) and Zopheridae (Borges et al. 2016, in press). Overall, at least 26 species that occur in native forests were added to the Azorean arthropod fauna list. The new 346 taxonomic records provided by this study (see Suppl. material 4 for the complete list of new records per island) represent on average an increase in species number of about 10% for each studied island (Table 2). However, the increment for São Jorge island was about 22%, while for São Miguel this represented only 3% (Table 2). 164 species were found in new islands, with an average of two islands per species. For 82 of those species only one new island was added to their known distribution contrasting with 27 species for which four or more islands were added (Fig. 2). Notably, nine out of the 27 species with more than three island added to their previous distribution belong to Arachnida. In fact, arachnids but also millipedes and centipedes experienced a large proportion of new records (more than 30%) (see Table 3).