Standardised arthropod (Arthropoda) inventory across natural and anthropogenic impacted habitats in the Azores archipelago

Abstract Background In this paper, we present an extensive checklist of selected arthropods and their distribution in five Islands of the Azores (Santa Maria. São Miguel, Terceira, Flores and Pico). Habitat surveys included five herbaceous and four arboreal habitat types, scaling up from native to anthropogenic managed habitats. We aimed to contribute to the ongoing effort to document the terrestrial biodiversity of the world, in particular the Portuguese archipelago of the Azores, as islands harbour a significant portion of unique terrestrial biodiversity. Selection of Arthropoda groups for the current checklist was based on their known richness and abundance (Arachnida, Collembola, Hemiptera, Neuroptera, Coleoptera, Hymenoptera), in almost all terrestrial ecosystems, as well as their importance in current Integrated Pest Management and alternative Biocontrol protocols at large (i.e. hymenopteran parasitoids and beneficial Coleoptera). In addition, we include the list of Dermaptera, Orthoptera, Psocoptera and Thysanoptera species. These assembled groups represent part of the monitoring programme EDEN Azores (2008-2014), where all Arthropod fauna, at all strata, within nine representative habitats of the abovementioned five Islands of the Azores was recorded. New information In this study, a total of 116,523 specimens, belonging to 483 species and subspecies of selected groups of arthropods, are reported by order, family and, when possible, genus and species. Hymenopteran, mostly parasitoids, accounted for the most represented taxa across all the monitoring and sampling phase of EDEN Azores (193 species and mophospecies), followed by Coleoptera (95 species); Collembola (89 species); and Araneae (72 species). A total of 37 non-native species are reported for the first time in the Azores. Coleoptera: Asaphidion flavipes (Linnaeus, 1761) (Carabidae); Tachyporus dispar (Paykull, 1789) (Staphylinidae). Hemiptera: Acrosternum heegeri Fieber, 1861 (Pentatomidae). Collembola: Entomobrya regularis Stach, 1963 (Entomobryidae); Lepidocyrtus lusitanicus piezoensis (Simón-Benito, 2007) (Entomobryidae); Jordanathrix articulata (Ellis, 1974) (Sminthuridae); Sminthurinus quadrimaculatus (Ryder, 1879) (Katiannidae); Himalanura sp. (Entomobryidae); Protophorura sp. (Onychiuridae). Hymenoptera, parasitoids: Aphidius colemani Viereck, 1912 (Braconidae); Aphidius ervi Haliday, 1834 (Braconidae); Aphidius matricariae Viereck, 1912 (Braconidae); Aphidius rhopalosiphi Stefani-Perez, 1902 (Braconidae); Aphidius rosae (Haliday, 1834) (Braconidae); Aphidius urticae Haliday, 1834 (Braconidae); Centistidea ectoedemiae Rohwer, 1914 (Braconidae); Meteorus unicolor (Wesmael, 1835) (Braconidae); Meteorus collaris (Spin.) Hal. – Ruschka, Fulmek, 1915 (Braconidae); Orthostigma cratospilum (Thomson, 1895) (Braconidae); Orthostigma latriventris Ratzeburg, 1844 (Braconidae); two other species of Orthostigma sp.; Pseudopezomachus bituberculatus (Marshall, 1905) (Braconidae); Tanycarpa punctata (van Achterberg, 1976) (Braconidae); Gonatopus clavipes (Thunberg, 1827) (Dryinidae). New genera not previously recorded for the Azores include: Pycnetron sp. (Chalcidoidea: Pteromalidae); four species of Aspilota sp. (Braconidae: Alysiinae); four species of Chorebus sp. (Braconidae: Aphidiinae: Alysiinae); Microgaster sp. (Braconidae: Microgastrinae); Homolobus sp. (Braconidae: Homolobinae); Lodbrokia sp. (Braconidae: Alysiinae). These 37 taxa were found in several Islands and five are new species for Flores Island, 10 species are new for Pico Island, 12 species are new for Terceira Island, 19 species are new for S. Miguel Island and five species are new for S. Maria Island. Additional species records for the Islands included: Flores (5 Collembola, 9 Araneae; 2 Hemiptera; 8 Coleoptera, 8 Hymenoptera), Pico (4 Collembola; 7 Araneae; 4 Hemiptera; 11 Coleoptera; 9 Hymenoptera), Terceira (4 Collembola; 1 Araneae; 3 Hymenoptera), S. Miguel (1 Araneae; 2 Coleoptera; 3 Hymenoptera), S. Maria (5 Collembola; 3 Araneae; 2 Hemiptera; 2 Hymenoptera).


Introduction
Biodiversity loss is accelerating at an unprecedented rate (Maxwell et al. 2016, Borges et al. 2019, particularly in islands (Whittaker et al. 2017). Current drivers of biodiversity loss include habitat change (i.e. habitat loss, degradation and fragmentation), invasive species, pollution and contamination and climate change (Titeux et al. 2016, Sanchez-Bayo andWyckhuys 2019). Land-use reconversion is a catalyst for major biodiversity changes in the world, namely in island ecosystems (Russell and Kueffer 2019). The inventory and monitoring of island biodiversity is critical for understanding current and future trends in biodiversity erosion (Borges et al. 2019) as remote archipelagoes enclose high endemism levels and a significant portion of terrestrial biodiversity.
In the current study, we focus in Azores Islands (Portugal) and on its arthropod diversity inventory. Arthropods are recognised as one of the most endangered taxa in the globe, vital for ecosystem stability and food security (Hochkirch 2016, Harvey et al. 2020, Raven and Wagner 2021 Islet -Flores]), these Islands, when discovered, were completely covered by dense forests (Frutuoso 1978). These forests included Erica-Morella woodlands at levelled coastal areas and Picconia-Morella forests up to 300 m a.s.l. From 300 m to 600 a.s.l., the sub montane forests dominated (the Azorean Laurel forests, predominatly Laurus azorica), which probably covered more than two thirds of the Islands (Elias et al. 2016). Above the Laurus forests, between 600 m and 1000 a.s.l., Juniperus-Ilex forests and Juniperus woodlands would have covered most of the areas (Elias et al. 2016). At higher elevations, Calluna-Juniperus scrublands may have covered mountain ridges and Calluna-Erica scrublands and Calluna scrublands would have occupied Pico Mountain, above 1200 m a.s.l., as they still do today (Elias et al. 2016).
The topography of the Azores is characterised by the presence of numerous catchments, ravines and mainly seasonal water streams. Climate and hydrography, together with remote geographic isolation (i.e. central zone of the North Atlantic) and absence of any close continental masses (the nearest landmasses are Europe > 1300 km away and North America > 3200 km away), as well as the complex marine Current System (Caldeira and Reis 2017), contribute to a temperate climate and high humidity throughout the year. These environmental conditions and a nutrient-rich volcanic soil, still support an abundant flora in spite of intense anthropogenic influence and land reconversion to agriculture and forestry activities. Mixed and pristine forests [predominantly native evergreen Laurel forests (Laurisilva), a humid broadleaf Laurus azorica (Seub.) Franco forest] covers many islands' hillsides (Cardoso et al. 2007, Hortal et al. 2006. Thirteen percent of their land surface is protected (World Heritage, Biosphere and Natura 2000 Networks).
The Azorean Islands have a long history of habitat loss and land-use changes, with only circa 5% of the native forest remaining intact ). Deforestation has occurred extensively, initially at low elevations, but subsequently extended to mid-and higher elevations due to anthropogenic intervention and timber use as an energy source. Currently, six main habitats can be found in Azores, i.e. i) the original native forests, restricted to high elevations with some small pockets at mid-elevations and disturbed mixed vegetation at low elevation; ii) exotic fast-growing tree plantations, dominated by Cryptomeria japonica; iii) exotic mixed forests, dominated by the invasive tree Pittosporum undulatum; iv) several types of grasslands, including high elevation natural grasslands, although mostly dominated by intensive pastureland at low and mid-elevations and seminatural pastures at mid-and high elevations; v) native bogs and fens at high elevations; and vi) several types of agro-ecosystems including vineyards, orchards and corn fields.
The Azorean arthropod fauna is well known and includes approximately 2332 species and subspecies, with less than 300 of these being endemic . Land-use changes had an impact on the composition of Azorean arthropod fauna, now dominated by exotic species, particularly in anthropogenic habitats (Borges et al. 2008), but also, to some extent, in native forest, such as in the case of soil arthropods, particularly Collembola (Cicconardi et al. 2017). Endemic arthropods are mostly restricted to native habitats (Borges et al. 2008, Rigal et al. 2018). However, endemic and native insect pollinators successfully adapted to new anthropogenic habitats and are providing essential ecosystem services in agro-ecosystems (Picanço et al. 2017). The impact of anthropogenic disturbance on vascular plants was also investigated in parallel with the arthropod distribution , Silva et al. 2017, observing that endemic and native plant species are not restricted only to natural habitats, but also occur in human-managed arborescent habitats. Invasive species dominate human-managed habitats, whilst also found at the edges of natural habitats.

General description
Purpose: This study intended to contribute to the current international directives concerning biodiversity, aiming to document and safeguard biological resources of the globe. Our objective was to present the most widely distributed and diverse taxa recorded during the sampling phase of the EDEN project (2008-2014) , Marcelino et al. 2020, specifically all arthropod fauna, at all strata, within eight representative habitats of five Islands of the Azores archipelago (Santa Maria, São Miguel, Terceira, Flores and Pico) (Fig. 1).
Collembola -i) the existence of a profuse diversity and abundance in a wide variety of soil systems from Islands to Continents to Antarctic habitats (Hawes et al. 2007); ii) their rapid response to changes in ecological and pedological patterns within a given ecosystem (Sousa et al. 2006).
Hymenopteran parasitoids -i) important role as regulators of host density (Henri and Van Veen 2011); ii) critical biological pest control agent, with circa $20 billion/year beneficial impact on US agriculture (Pennisi 2010).
Beneficial Coleoptera -i) the Coccinellidae groups ca. 6,000 species (Vandenberg 2002) with an ubiquitous distribution worldwide. The majority of species are predators providing relevant ecosystem and agricultural services, constituting one of the most studied groups of beneficial insects (Hodek et al. 2012, Ameixa et al. 2018 for a comprehensive revision). The rove-beetles (Staphylinidae) are one of the most diverse lineages of arthropods, inhabiting practically all terrestrial niches (Thayer 2005). They are also an ecologicallyimportant component of soil fauna, reported to be potential bioindicators of environmental quality (Pohl et al. 2007) due to their sensitivity in detecting cryptic changes in the ecological dynamics of their ecosystems (Hodkinson and Jackson 2005) In addition, we report widely-distributed species across sampling sites or new records for the Azores, in the orders Dermaptera, Heteroptera: Hemiptera, Neuroptera, Orthoptera, Psocoptera and Thysanoptera. The distribution of sampling sites across the five studied Islands (n = 80).

Study area description:
We selected the Islands, based on the relative proportion of land used in agriculture and pristine areas (based on published data by Costa et al. 2014), taking into consideration all possible combinations, i.e. São Miguel (SMG), with a high proportion of land allocated to pastureland (61%) and a low proportion of scattered native and naturalised habitats (19.1%); (ii) Terceira (TER), with high proportion of pastureland (66.9%) and a similar proportion of native and naturalised habitats as SMG, but less fragmented (21.3%); (iii) Pico (PIC), with high proportion of pastureland (50.3%) and medium/high proportion of native habitats at higher elevation (35.5%); (iv) Flores (FLO), with scarce agricultural development (17.7%) and a high proportion of native and naturalised habitats (43%); and, (v) Santa Maria (SMR), with high proportion of agricultural land (56.7%) and a low proportion of native and naturalised habitats (17.3%) ( The importance of incorporating ecological gradients, such as an anthropogenic impact gradient, in biodiversity and conservation projects, has been previously highlighted. They constitute valuable scenarios to infer possible causes for the distribution of species across the landscape (Ulrich et al. 2009). We therefore selected habitats that represented a gradient of increasing anthropogenic impact and management intensity. Nine habitat types, divided between herbaceous and arborescent habitats, were selected to represent a comprehensive range of the flora and fauna communities. We determined consistency, prevelance and fidelity of a given plant species across all habitats to define them, based on their flora. We used a metric called IndVal and developed another called SiteVal which can now be used to assign a location to a given habitat (and anthropogenic level of influence) (see more details in , Marcelino et al. 2014, Silva et al. 2017). The herbaceous habitat gradient (Table 2) ranged from natural meadows (MED) to corn fields (COR). The arborescent habitat gradient (Table 2) ranged from natural pristine forests of Laurus azorica (NAT) to orchards of Citrus sp. (ORC). Pristine meadows were not present on Santa Maria and Terceira and semi-natural pastures at low altitude (SNPL) were used as a surrogate for MED on these Islands.

Design description:
In order to obtain the maximum information on arthropod biodiversity, all strata present at a given habitat type were sampled, i.e. micro-epigean fauna (Berlese-Tullgren trapping), soil fauna (Pitfall trapping), aerial vagility fauna (Suction with an aspirator) and canopy fauna (sweeping nets).
One Island per week was sampled during the summer 2009 (July-August  Increasing gradients of anthropogenic influence in herbaceous communities (1-5) and arborescent communities (1-4). Description and characteristic plant species communities. Note: * -Semi-natural pastures, at low altitude (SNPL), replaced Meadow habitats (MED) in Santa Maria and Terceira Islands due to the lack of sampling sites of the latter community type in these Islands. The samples were subsequently processed in laboratory facilities and assigned to morphospecies groups, progressing to higher taxonomic degrees of identifications. Species richness and abundance were recorded. Species accumulation curves were performed for inventory completeness using EstimateS (using the ratio of observed to the estimated species richness with the non-parametric estimator Jackknife) (Colwell 2013). Inventory completeness was 70-75% for Staphylinidae and Collembola (Marcelino et al. 2011, Marcelino et al. 2016, reaching 80% for Araneae and Hymenoptera parasitoids (data not published).

Sampling methods
Study extent: Five Islands of the Azores: Santa Maria, São Miguel, Terceira, Pico and Flores.
Sampling description: Suction (SU), sweeping (SW) and soil (BT) sampling were obtained in parallel with the pitfall traps (PF) in the sites previously listed (Table 1), in equal numbers of samples and distance.
SU and SW were done to record species at strata other than the epigeic stratum. SU was made with a hand-held aspirator (Stihl BG55), collecting the arthropods in shrubs, when available. SU was made individually for ca. 8 seconds, at each of four exposures (i.e. N, S, W, E) of the shrub or agro-culture plant. The specimens from all four cardinal exposures were transferred to a single cup for each SU and SW sampling spot, respectively. SW was made by gently sweeping with a 64 cm diameter sweeping net.
Berlese-Tullgreen sampling (BT) was made by collecting ca. 100 grams of soil litter per sampling unit (15 samples for each transect established at PF sampling spots). Samples were immediately stored in a cooler to avoid proliferation of saprophytic fungi and sent by air transportation to the Department of Biology, University of the Azores, Ponta Delgada where they were placed in a cooling chamber at 4°C for subsequent processing in BT traps. BT trap units consisted of two plastic darkened containers, assembled together to provide an upper vented area (14 cm diameter x 11.5 cm high) with 4 openings (1 cm diameter covered with a 0.3 x 0.3 mm diameter mesh) and coupled with a 15 W lamp on top. The lower collecting area (13 cm diameter x 10 cm high) was partially filled with ca. 80 ml of the same mixture used in PF. Litter samples were placed on a 1.8 x 1.8 mm mesh, attached to a plastic funnel positioned in the assembling zone between the two halves of the device. In order to avoid heat and dryness, Collembola and other micro-arthropods crawled downwards to the littler sample and dropped through the funnel into the collecting mixture. Litter samples remained for 72 h in BT before specimen sorting at laboratory facilities.
Two parallel transects with fifteen pitfall traps (PF) were placed in 150 x 150 m georeferenced plots. PF consisted of plastic cylinder cups 78 mm deep and 42 mm diameter filled with ca. 80 ml of a mixture of 96% Ethanol and 0.05% liquid detergent. PFs were buried in the soil so that the lid was flush with the surface and covered with a plastic plate at ca. 3 cm height, to avoid desiccation, flooding or insectivore predation. Traps remained in the soil for 7 days prior to collection. For each habitat type and Island, two replicate sites were monitored (with a minimum distance of 5 km apart), for a total of 80 sampling sites (i.e. 5 Islands x 8 habitat types per Island x 2 sites for each habitat type).
All specimens where stored in 96% EtOH in order to maintain viability for future genetic and/or taxonomic work, as well as voucher exchanges with other institutions.
Quality control: Identifications were conducted in a progressive higher degree of taxonomy resolution, i.e. 1) morphospecies were generated and, concomitantly, an ongoing web-based image gallery stock was created (at www.eden-azores.webs.com). This secured consistency in assigning specimens to morpho-species without duplications; 2) voucher specimens of all morphospecies were taxonomically assigned to a genus and, if possible, to species level; 3) species of Collembola and Staphylinidae were genetically profiled to match genetic and morphological IDs; 4) All voucher specimens where sent to taxonomist referees in the respective Order, family, genus or group (taxonomists listed in the Personnel section of this report), which corroborated identifications from steps 1, 2 and 3. Description: The following data table includes all the records for which a taxonomic identification of the species was possible. The dataset submitted to GBIF is structured as a sample event dataset, with two tables: event (as core) and occurrences. The data in this sampling event resource have been published as a Darwin Core Archive (DwCA), which is a standardised format for sharing biodiversity data as a set of one or more data tables. The core data file contains 3214 records (eventID) and the occurrences file 19555 records (occurrenceID). This IPT archives the data and thus serves as the data repository. The data and resource metadata are available for download from Marcelino et al. (2020).

Additional information
We collected a total of 116,523 specimens belonging to 483 species and subspecies of selected groups of arthropods. Due to the unavailability of taxonomic expertise, these represent a sub-set of the Arthropoda recorded during the monitoring programme EDEN (2008-2014) carried out in the Azores archipelago. Hymenoptera, mostly parasitoids (193 species and mophospecies), Coleoptera (95 species); Collembola (89 species); and Araneae (72 species) are the most represented taxa (Table 3). A total of 28 species are endemic to the Azores archipelago (2511 specimens), 59 are native non-endemic (26,139 specimens) and 161 are introduced (54,601 specimens). For 238 taxa identified as morphospecies (mostly Collembola and Hymenoptera), the colonisation status is unknown (33,272 specimens) (see Table 3).  Table 3.
List of species and morphospecies with information on the colonisation status (CS) and abundance (n). The taxa are listed following the alphabetical sequence of classes, orders within classes, families within orders and finally species within families. When a species is a new record for a given Island, we add that information (codes for Islands as follows: FLO -Flores; PIC -Pico; TER -Terceira; SMG -S. Miguel; SMR -S. Maria). The top ten most abundant species are marked with an *. insufficient to discriminate phenotypic identical species. This was the case for Collembola (Marcelino et al. 2011) and Staphylinidae (Marcelino et al. 2016), in which, after matching morphological identifications with genetic profiles, undetected cryptic species complexes were found.
Our results indicate that increasing anthropogenic impact is a major driver for species diversity in habitats ranging from pristine to highly human-influenced habitats. Our results support the mission statement of  that there is the urgent need to inventory and monitor island biodiversiy.