Standardised inventories of spiders (Arachnida, Araneae) of Macaronesia I: The native forests of the Azores (Pico and Terceira islands)

Abstract Background The data presented here come from samples collected as part of two recent research projects (NETBIOME - ISLANDBIODIV and FCT - MACDIV) which aimed at understanding the drivers of community assembly in Macaronesian islands. We applied the sampling protocol COBRA (Conservation Oriented Biodiversity Rapid Assessment, Cardoso 2009) in sixteen 50 m x 50 m native forest plots in the Azorean Islands of Pico (6 plots) and Terceira (10 plots) to assess spider diversity. Through this publication, we contribute to the knowledge of the arachnofauna of the Azores and, more specifically, to that of the islands of Pico and Terceira. New information The collected samples yielded 8,789 specimens, of which 45% were adults (3,970) belonging to 13 families, 36 species and three morphospecies that have yet to be described. Species of the family Linyphiidae dominated the samples, with 17 species and two morphospecies that have yet to be described (48% of the taxa). Out of the identified (morpho)species, 16 were introduced, 13 Azorean endemic (three of which were undescribed) and seven native (five of them Macaronesian endemics). We report the first record of the introduced species Haplodrassus signifer and Agyneta decora in Pico Island.


Introduction
Despite six centuries of disturbance and land use changes, the Azorean islands still contain areas covered by unique native forest (Triantis et al. 2010). This forest accounts for about 5% of the total area of the archipelago and is mainly present on the islands of Flores, Pico and Terceira . From a conservation perspective, the importance of these forests resides in their being home to numerous endemic arthropod species, many of which have been given different status of conservation concern following the IUCN Red List criteria (see for the insects , Borges et al. 2018a). Furthermore, many species -mainly arthropods -await discovery and taxonomic description, despite the high rate of taxonomic descriptions in the last decades (Lobo and Borges 2010). For instance, 24 out of the known 26 endemic spiders have been described since 1989 (Borges and Wunderlich 2008, Crespo et al. 2013, Crespo et al. 2014).
Indeed, the effective, appropriate and efficient conservation of ecologically valuable areas requires knowing the identity and colonisation status of species (i.e. endemic, native nonendemic or introduced), often provided by large-scale projects such as the EU NETBIOME funded ISLANDBIODIV (Understanding biodiversity dynamics in tropical and subtropical islands in an aid to science based conservation action) and the Portuguese FCT funded MACDIV (Macaronesian Islands as a testing ground to assess biodiversity drivers at multiple scales). Both ISLANDBIODIV and MACDIV aim to unveil the diversity patterns in vascular plants, springtails, beetles and spiders at local and regional scales in Macaronesian islands (see Emerson et al. 2016, Cicconardi et al. 2017, Borges et al. 2018b). Here we present the information on the species collected in the Azorean forest plots that are part of the ISLANDBIODIV and MACDIV projects.

Sampling methods
Study extent: On each of the Azorean islands of Pico and Terceira, we established six and ten 50 m x 50 m plots along a longitudinal distance of 20 km and 13 km, respectively. In Pico, each plot is located at increasing distances from a first, reference plot (Table 1): 0.1, 1, 5, 10 and 20 km (Fig. 1), covering the three existing forest fragments in order to test distance decay patterns on beta diversity in a log scale within project MACDIV. In Terceira, the 10 plots were randomly distributed in the four main fragments of native forest also to test patterns of alpha and beta diversity (see Cicconardi et al. 2017, Borges et al. 2018b). All plots were located in mid to high elevation native forest dominated by Juniperus brevifolia, Laurus azorica and Ilex perado subsp. azorica trees (see Borges et al. 2018b for more details on the surveyed habitats) (Fig. 2).

Plot Longitude Latitude
Pico Sampling description: We sampled all plots using the optimised and standardised COBRA (Conservation Oriented Biodiversity Rapid Assessment) protocol for temperate forests (Cardoso 2009). Different variants of the COBRA protocol for spiders and beetles have   already been applied in oceanic islands (Emerson et al. 2016) and for spiders on tropical forests (Malumbres-Olarte et al. 2016, Malumbres-Olarte et al. 2018. Although originally developed and optimised for mainland temperate and Mediterranean habitats, COBRA protocols have been recently proposed as the standard protocols for inventorying and monitoring spiders and beetles in island forest ecosystems (Borges et al. 2018c). The COBRA protocol, when applied to temperate forests, consists of: four night aerial samples (1 hour / sample), two day sweeping samples and two night sweeping samples (1 hour / sample), two day beating samples and two night beating samples (1 hour / sample) and 12 pitfall samples (4 traps / sample). Specifically for islands, we added two sampling methodologies to also cover beetle diversity (Borges et al. 2018c 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 table contains 423 records (eventID). One extension data table also exists. An extension record supplies extra information about a core record. The number of records in each extension data table is illustrated in the IPT link. This IPT archives the data and thus serves as the data repository. The data and resource metadata are available for downloading in the downloads section. The versions table lists other versions of the resource that have been made publicly available and allows tracking changes made to the resource over time.
In Suppl. material 1, we provide a file with two tables, one with the samping event data and the other with the species abundance data.    Table 3.

Column label Column description
Abundance, biogeographic category and previous records of (morpho)species in each of the plots on Terceira island.   Four species accounted for 54% of all specimens: Rugathodes acoreensis (753 specimens) (Fig. 3), Sancus acoreensis (506) (Fig. 4), Tenuiphantes miguelensis (479) (Fig. 5) and Gibbaranea occidentalis (392) (Fig. 6). These species occur in different forest micro-habitats: the orb-weaver, G. occidentalis, occurs in both canopy and intermediate understorey; the theridiid, R. acoreensis, is mostly a canopy species; the tetragnathid, S. acoreensis, is usually associated with shrubs; and T. miguelensis is a forest ground linyphiid, building its sheet-webs between small holes in the ground or small crevices in volcanic rocks.    Of the 39 collected species, 34 have been recorded previously in both Pico and Terceira islands . In total, we recorded 13 endemic species, 16 introduced, five Macaronesian, two native and three of unknown biogeographic category but possibly also endemic (which will be subject to a molecular and morphological integrative taxonomic description). Two of the 16 introduced species (Haplodrassus signifer and Agyneta decora) were recorded in Pico for the first time (cf. ).