Arachnids from Araripe Plateau , Ceará , Brazil

The Araripe Plateau is situated in the states of Ceará, Piauí and Pernambuco, northeastern Brazil, in the Caatinga biome, semiarid domain. This region of Brazil is characterized by high temperatures and low rainfall. Nevertheless, due to its high elevation and large amount of orographic rainfall, the Araripe Plateau is an exception as a seasonal semi-deciduous forest with high humidity in the semiarid domain and the Caatinga biome. Herein a species list of Araripe Plateau arachnids is presented from the compilation of data from in situ sampling from January to May 2013, from the literature, and from Brazilian arachnid collections data. A total of 68 species were recorded for the area, of which 53 were spiders, eight harvestmen and seven scorpions. The species richness recorded here is considered significant regarding the known diversity of Arachnida in the semiarid region and contributes to expanding our knowledge of the area.


INTRODUCTION
The Caatinga biome is one of the least studied Neotropical biomes (Leal et al. 2005;Santos et al. 2011), with current data suggesting that about 41% of the area has never been surveyed by scientists and 80% has been poorly sampled (Tabarelli and Vicente 2004).This situation is even worse for taxa such as invertebrates (Lewinson et al. 2005).Among arachnids, recent estimates indicate that there are no records of spiders (Carvalho et al. 2014) or scorpions (Porto et al. 2014) for about 70% of the Caatinga area.
Even considering such heterogeneous sampling, presently there are 271 spiders (Carvalho et al. 2014), 28 scorpions (Porto et al. 2014) and 28 Laniatores harvestmen (De Souza et al. 2014) species recorded for the Caatinga biome.These numbers represent about 8.5%, 21% and 5%, respectively, of the spiders, scorpions and Laniatores harvestmen species recorded in Brazil (Carvalho et al. 2014;Porto et al. 2014;De Souza et al. 2014).The potential explanations for these numbers are different for each group.Considering that the Caatinga occupies about 10% of Brazilian territory, the number of spider species might represent a clear effect of sampling deficiency, as it is lower than expected by chance (Carvalho et al. 2014).The scorpion species richness in the Caatinga is higher than expected by chance.However, considering that the world's highest scorpion species richness (4-13 sympatric species at one site) occurs in drier areas (Polis 1990), more scorpion species would be expected to be found in the Caatinga.On the other hand, for harvestmen, the low species richness in the Caatinga biome was expected, as many species are ineffective at preventing water loss (Santos 2007a), thus resulting in higher species richness in humid areas throughout Brazil, such as the Atlantic Forest (Pinto-da-Rocha et al. 2005).
In the present paper, we present a list of the spiders, scorpions and harvestmen from the Araripe Plateau, northeastern Brazil.The arachnid fauna of the area has been the focus of only a few published papers, mainly consisting of the description of fossil (i.e., Campos 1986;De Carvalho and Lourenço 2001;Selden et al. 2006) or living taxa (i.e., Bonaldo and Brescovit 1998;Corronca 1998;Rheims and Brescovit 2004;Lourenço 2010Lourenço , 2014;;Ruiz 2013;Huber et al. 2014).None of these publications directly dealt with the Araripe Plateau arachnid fauna, but focused on taxonomic issues rather than providing species lists.The present paper is the first to compile published records and new records gathered from field work into a species list for the area.(with and without UV lamps) and litter sampling (1 m 2 of litter sifted and hand sorted in each sample).All standardized samplings followed usual arachnid sampling methods, as described in Carvalho (2015).The species were identified using keys for spiders (Levi 1968(Levi , 1991(Levi , 1997(Levi , 2004;;Corronca 1998;Bonaldo 2000;Brescovit and Rheims 2000;Rheims and Brescovit 2004;Santos 2007b;Abrahim et al. 2012), scorpions (Lourenço 2002;De Souza et al 2009)  The species list herein also includes information gathered from previous publications on arachnids of the Araripe plateau: Bonaldo and Brescovit (1998), Corronca (1998), Lourenço (2010Lourenço ( , 2014)), Lourenço et al. (2013), Maury (1982), Rheims and Brescovit (2004), Ruiz (2013) and Huber et al. (2014).

MATERIALS AND METHODS Study area
The Araripe Plateau is located in northeastern Brazil, in the states of Ceará, Piauí and Pernambuco.It includes the Araripe National Forest (Floresta Nacional do Araripe, 07°20ʹ42ʺ S, 039°25ʹ6ʺ W).The region is within the Caatinga biome, a warm (mean annual temperature 26°C − 28°C; Nimer 1972) semiarid biome.Despite the dry and warm environment, the high elevation of the region (more than 500 m above sea level), contributes to the production of approximately 1,200 mm of orographic rainfall (Andrade-Lima 1982;Prado 2003;Leal et al. 2005).This allows the formation of forested enclaves on the windward slopes of hills, known as "brejo-dealtitude" (Prado 2003;Leal et al. 2005).

Data collection
Since 2010, occasional arachnid surveys have been carried out by various researchers in several localities, both inside and outside the Floresta Nacional do Araripe, such as the municipalities of Crato, Juazeiro do Norte and Barbalha, state of Ceará, (Figure 1).The sampling points map (Figure 1) was constructed using ArcGis 10.3 software (ESRI 2015).
The arachnids were sampled using three techniques: pit-fall traps for invertebrates (500 ml plastic buckets buried at ground level, with 70% ethanol as preservative, placed at least 5 m apart and kept open for at least five consecutive days), diurnal and nocturnal hand searches

RESULTS
The compiled list includes 68 arachnid species, represented by 53 spider, seven scorpions and eight harvestmen species (Table 1).Thirty-five species were identified to species level and six un described species were recognized, belonging to the genera Ortho nops Chamberlin, 1924 (Caponiidae)
Selenops maranhensis, B. rochai and R. agamemnom are widespread species (Corronca 1998;Lourenço 2002) and their absence from our sampling is attributed to sampling bias.Conversely, A. verhaaghi is rare in spider samplings, because most species of the Attacobiini (a tribe of Corinnidae) are ant-clinging spiders and are expected to live near ant nests, where spider samplings were rarely performed.The buthid scorpions R. brejo and H. araripe are both recorded from Araripe based on specimens whose precise type localities and preferable microhabitat are unknown (Lourenço 2010(Lourenço , 2014)).
The Araripe Plateau constitutes a natural forested enclave (Prado 2003;Leal et al. 2005), also known as "brejo-de-altitude" (Andrade-Lima 1982).The fauna and flora of these areas are different from the typical Caatinga environment and usually exhibit a trend toward high diversity (Werneck 2011).These warmer environmental conditions are also more suitable for a myriad of arachnid species which are absent from the arid environment surrounding the forested area, such as harvestmen (Curtis and Machado 2007), which prefer more humid environments (Santos 2007a;De Souza et al. 2014).
The harvestmen fauna of the Araripe Plateau is composed of eight species, a species richness that falls within the expected number for Brazilian open biomes (Bragagnolo and Pinto-da-Rocha 2003;Pinto-da-Rocha et al. 2005).However, the harvestmen community is composed of a mixture of taxa typical of different environments.Pseudopucrolia discrepans (Roewer, 1943) is usually found in forested enclaves in northeastern Brazil and in the Atlantic Forest in Paraíba and Parnambuco (Mendes 2011).Parapachyloides uncinatus (Soerensen, 1879) (Figure 3) is widely distributed throughout the Cerrado and Caatinga biomes (Kury et al. 2010), mostly associated with more humid areas (pers.obs.).Conversely, Stygnus polyacanthus (Mello-Leitão, 1923) is widely distributed in northeastern Brazil, often occurring in drier areas, where it can be found under termite nests or fallen trunks (Pinto-da-Rocha 1997;Pinto-da-Rocha and Carvalho 2009).
This work constitutes the first species list of arachnids for Araripe Plateau.Although the number of identified species or the total species richness is not especially high, the records herein presented are important as they fill a gap in the known geographical distribution of many arachnid species in the Caatinga biome.These records are important data for proposing and delimiting areas of endemism (see Oliveira et al. 2015), one of the most important tools for selecting priority areas for conservation.This list is also a first step for further ecological and taxonomical investigation on the arachnids of the region.The huge Wallacean shortfall related to invertebrates from the Caatinga biome prevents the proposition of such wide studies, while with plants, for example, Caatinga ecoregions were proposed more than a decade ago (Velloso et al. 2002).Thus, it is expected that with the increase in number of published papers on arthropod geographical distribution, species inventories and new records from the Caatinga, more ecological, taxonomic and biogeographic studies can be conducted.

Figure 1 .
Figure 1.Map of the sampled localities (black dots) and its location in the Araripe National Forest (in green) and the Araripe Plateau (in grey).Municipalities below the thick line are located in the State of Pernambuco, and those above are located in the State of Ceará.

Table 1 .
Spider, scorpion and harvestman species list from the Araripe Plateau, Ceará, Brazil, with the number of specimens collected and source of information gathered.