Standardised inventories of spiders (Arachnida, Araneae) of Macaronesia II: The native forests and dry habitats of Madeira archipelago (Madeira and Porto Santo islands)

Abstract Background Here we present the data obtained from the samples collected as part of a large research project (MACDIV) which aims at understanding the drivers of spider (Araneae) community assembly in Macaronesian islands. To obtain the data, we applied the sampling protocol COBRA (Conservation Oriented Biodiversity Rapid Assessment), in twelve 50 m x 50 m native forest plots and five dry habitat plots on the island of Madeiraand in 5 dry habitat plots on the island of Porto Santo. Through this publication, we contribute to the knowledge of the arachnofauna of the Madeiran archipelago. New information From the samples that we collected, we obtained a total of 14,902 specimens, of which 49% were adults (7,263). We identified these specimens to 87 species and 18 morphospecies (undescribed), belonging to 26 families. Species of the family Linyphiidae dominated the samples, with 24 (morpho)species. Out of the 105 recorded (morpho)species, 34 were endemic, 26 native non-endemic, 22 introduced and 23 species of unknown origin. We report seven new records of possibly recently introduced species in the Madeiran archipelago. We also present 21 new records for Madeira island and 32 for Porto Santo (33 for the whole archipelago).


Introduction
The north Atlantic archipelago of Madeira is composed of the volcanic islands of Madeira, Porto Santo and the Desertas, as well several islets. At approximately 700 km from the African coast and at more than 400 km from the Canary Islands, it is the second most isolated Macaronesian archipelago, after the Azores. This intermediate distance, combined with an geological age of 5-27 My, has allowed frequent colonisation rates and enough diversification time to generate diverse species communities (Fernández-Palacios 2010, Fernández-Palacios et al. 2011. Since its settlement in the XV Century by the Portuguese, the archipelago has gone through a profound environmental transformation. Nevertheless, the main island of the archipelago, i.e. Madeira, still preserves a considerable area of unique native laurel forest (laurisilva), covering 20% of the island (Boieiro et al. 2015).
The laurisilva is indeed a unique and iconic ecosystem, that is often seen as representative of the Macaronesian archipelagos as a whole and contains a great deal of endemic species (Boieiro et al. 2010, Boieiro et al. 2013. However, the archipelago is also the home of more open habitats, such as scrublands and thermophilous grasslands, present in drier conditions than those where laurisilva is found. Although these often overlooked dry habitats may not be as species-rich as forests, they do contribute to the endemic fauna of the archipelago, which represent 20% of all the species . Moreover, Madeiran dry habitats may also contain a substantial number of unknown species that have eluded recent taxonomic, conservation and faunistic research, including IUCN Red List assessments (Martín et al. 2008, Martín et al. 2010, as well as unrecorded exotic species ).
The need for an update in many taxa is exemplified by spiders. Although, according to the last available checklist , the spider fauna of Madeira archipelago is composed of 183 species (including 58 endemic species), new taxa have been discovered since then (e.g. Crespo et al. 2009, Crespo et al. 2014).
This publication is the second of a series on Macaronesian spider fauna (see Malumbres-Olarte et al. 2019) and provides habitat, biogeographic and colonisation information on the species collected in 12 native forest plots and 10 native dry habitat plots on the islands of Madeira and Porto Santo through the project MACDIV.

Sampling methods
Study extent: We established twenty-two 50 m × 50 m plots, grouped according to habitat and between-plot distances. Twelve plots were located in areas covered with laurisilva and grouped in two sets of six. Within each set, plots were placed at increasing distances from a first, reference plot (Table 1): 0.1, 1, 5, 10 and 20 km (Fig. 1). The remaining 10 plots were located in areas of open dry habitat, five on Madeira island and five on Porto Santo, also at increasing distances from a reference plot (0.1, 1, 5 and 10 km). This design allowed for testing of distance decay patterns on beta diversity on a log scale. We set up the forest plots in well-preserved native forest areas, where native tree species, such as Clethra arborea, Laurus novocanariensis, Ocotea foetens and Persea indica, were dominant (Neves et al. 1996, Menezes et al. 2005 (Fig. 2). We set the dry plots in grasslands at low-altitude, where the vegetation cover was dominated by herbaceous species and several shrubs, like Echium spp, Euphorbia piscatoria and Globularia salicina (Medeiros et al. 2010) (Fig. 3 Sampling description: We applied two versions of the optimised and standardised COBRA protocol (Conservation Oriented Biodiversity Rapid Assessment) (Cardoso 2009): the protocol for temperate forests (which we applied in forest plots) and the protocol for open habitats (applied to dry habitat plots). The COBRA protocols have been proposed as part of standard inventorying and monitoring programmes on island and continental ecosystems and have already been used for a number of studies on spiders and beetles (Cardoso 2009    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 562 records (eventID). One extension data table also exists with 3281 occurrences. 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.

Results
We collected a total of 14,902 specimens -of which 49% were adults (7,263) -belonging to 105 (morpho) species and 26 families (Tables 2, 3 Table 3. Abundance, biogeographic category and previous records of (morpho)species in five of the forest plots and two of the dry habitat plots on Madeira island. Abbreviations: Madeira forest plot (MF), Madeira dry plot (MD).  Table 4.
Abundance of (morpho)species in three of the plots on Madeira island and in the plots on Porto Santo island. Abbreviations: Madeira dry plot (MD), Porto Santo plot (PS).

Taxonomic and biogeographic classification
In this section, we point out, explain and discuss the identification of some of the species and morphospecies found -the ones for which information is limited and ordered as in Tables 2, 3 and 4 -and their classification as endemic, native non-endemic, introduced and unknown.

Synaphris saphrynis
This species is known from Spain and Selvagens Islands. It is also present on Bugio island (Desertas), as one of the authors (L. Crespo) identified a specimen collected by M. Boieiro et al. in 2011/12 (unpublished record). The limited number of available records does not allow us to infer its total distribution with certainty.

Haplodrassus omissus
Although Haplodrassus omissus had not been recorded previously in Madeira, it does not come as a surprise to be present there, given its known distribution across the Mediterranean basin and the Canary Islands.

Haplodrassus sp. 164
This morphospecies is present in Porto Santo and, possibly, in other locations of the Madeira archipelago. Haplodrassus MS 164 belongs to the dalmatensis group.
Haplodrassus sp. 158 The morphospecies Haplodrassus MS158 belongs to a different group from that of Haplodrassus MS164, as its genitalia is more similar to species such as H. deserticola, which is present in the Canary Islands or H. minor, which has been recorded from Europe to Turkey, according to the World Spider Catalogue. It is possible that more species of this group are present in the Madeira archipelago.

Macarophaeus cultior
Macarophaeus cultior may be a single-island endemic from Madeira. Although the World Spider Catalog and the Banco de Datos de Biodiversidad de Canarias (based on Oromí et al. (2002)) shows records from the Canary Islands (Oromí et al. (2002), according to Wunderlich (Wunderlich 2011), there are no new records or mentions of M. cultior in this archipelago.

Zelotes aeneus
We classified this species as introduced, because of its distribution throughout Europe up to Azerbaijan.

Agyneta canariensis
We have considered this species as native non-endemic, because it is present in the Canary Islands, Selvagens and Madeira.
Canariellanum sp. 21 We considered this species as a new endemic species of a genus so far restricted to the Canary Islands.
Given the morphological mismatch of this morphospecies with other described species from the region, we have considered it as endemic to the island of Madeira.

Tenuiphantes sp. 259
This morphospecies is probably a new Tenuiphantes from the archipelago of Madeira and we, therefore, considered it endemic.

Tenuiphantes tenebricoloides
This species has been found and cited several times from the forests of Madeira island. There is a citation from the Canary Islands by Denis (Denis 1941) that was based on a single female specimen that has not been revised since then. Furthermore, the species has not been cited again from the Canary Islands and, according to J. Wunderlich -who described a very similar species, T. canariensis, from the Canary Islands -Denis probably misidentified the species, given the resemblance in the female epigyne between T. tenebricoloides and T. canariensis, Therefore, we considered T. tenebricoloides as a Madeiran endemic (Wunderlich 1987). Future molecular phylogenetic work might resolve the relationship between these two species.
Mesiotelus cf. grancanariensis The species Mesiotelus grancanariensis has been cited from the south west coast of Portugal and across the entire archipelago of Madeira -in treeless dry habitats and along the central mountain chain of Madeira. Hence the classification of this species as a native species.

Oonops cf. pulcher
Although it is possible that this species is an undescribed cryptic species native to Madeira, based on morphological characters, it is very likely to be Oonops pulcher and, therefore, introduced.
Orchestina sp. 160 We classified this morphospecies as archipelago-endemic, based on previous findings by L. Crespo in areas with dry habitats of Porto Santo and Desertas.
Oxyopes sp. 80 Since this morphospecies has not been described or cited before, it is very likely endemic to the Madeiran archipelago.

Philodromus sp. 266
This morphospecies has not been described or cited before, hence our classification as endemic.
Lasaeola sp. 268 Based on the morphological features of this morphospecies, we considered it as a new species and, therefore, an archipelago endemic.

Rhomphaea nasica
Rhomphaea nasica is known to be present in Africa and on the remote island of St.
Helena. Specimens of this species have also been identified in modified habitats such as the Funchal Botanical Garden (Madeira Island). Therefore, we considered this species as introduced.

Theridion hannoniae
This species has a Mediterranean distribution and, in the Madeiran archipelago, it is usually found in dry, relatively disturbed areas. We classified this species as of unknown biogeographic category, given the impossibility of knowing whether it arrived at the Madeiran archipelago naturally or with human intervention.
Theridion sp. 89 This morphospecies is most likely a new species, so we considered it to be single-island endemic, probably from laurel forest.

Misumena cf. nigromaculata
Here we considered this morphospecies to be a new endemic species given the little information on Misumena nigromaculata, whose female has been described only once and whose male is unknown.

Xysticus nubilus
Xysticus nubilus has a Mediterranean distribution and is usually found in dry habitats in the Madeiran archipelago. Therefore, as with Theridion hannoniae, we classified it as of unknown biogeographic category in Madeira.

Hyptiotes flavidus
Although the distribution of this species is largely Mediterranean, given that it is usually found in laurel forests, we classified it as native to Madeira.