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Background: Long-term studies are key to understand the drivers of biodiversity erosion, such as landuse change and habitat degradation, climate change, invasive species or pollution. The long-term project SLAM (Long Term Ecological Study of the Impacts of Climate Change in the natural forest of Azores) started in 2012 and focuses on arthropod monitoring, using SLAM (Sea, Land and Air Malaise) traps, aiming to understand the impact of the drivers of biodiversity erosion on Azorean native forests (Azores, Portugal). This is the fourth contribution including SLAM project data and the second focused on the spider fauna (Arachnida, Araneae) of native forests on two islands (Pico and Terceira). In this contribution, we describe data collected between 2019 and 2021 and we analyse them together with a previously published database that covered the 2012-2019 period, in order to describe changes in species abundance patterns over the last ten years. New information: We present abundance data of Azorean spider species for the 2019-2021 period in two Azorean Islands (Terceira and Pico). We also present analyses of species distribution and abundance of the whole sampling period. In the period of 2019-2021, we collected a total of 5110 spider specimens, of which 2449 (48%) were adults. Most juveniles, with the exception of some exotic Erigoninae, were also included in the data presented in this paper, since the low diversity of spiders in the Azores allows a relatively precise specieslevel identification of this life-stage. We recorded a total of 45 species, belonging to 39 genera and 16 families. The ten most abundant species were composed mostly of endemic or native non-endemic species and only two exotic species (Tenuiphantes tenuis (Blackwall, 1852) and Dysdera crocata C. L. Koch, 1838). They included 4308 individuals (84%) of all sampled specimens and were the dominant species in Azorean native forests. The family Linyphiidae was the richest and most abundant taxon, with 15 (33%) species and 2630 (51%) specimens. We report Cheiracanthium mildei L. Koch, 1864, a non-native species, from Pico Island for the first time. We found no new species records on Terceira Island. This publication contributes to increasing the baseline information for future longterm comparisons of the spiders on the studied sites and the knowledge of the arachnofauna of the native forests of Terceira and Pico, in terms of species abundance, distribution and diversity across seasons for a 10 years period. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Oceanic islands host a high proportion of the world's endemic species. Many such species are at risk of extinction owing to habitat degradation and loss, biological invasions and other threats, but little is known about the effects of climate change on island native biodiversity. The Azorean archipelago provides a unique opportunity to study species-climate-change relationships. We used ensemble forecasting to evaluate the current and future distribution of well-studied endemic and native bryophytes (19 species), endemic vascular plants (59 species) and endemic arthropods (128 species), for two of the largest Azorean Islands, Terceira and São Miguel. Using a Regional Climate Model (CIELO), and assuming the extreme scenario RCP8.5, we examined changes in the potential distributions of the species and possible loss of climate space for them. Models projected that 23 species (11 %) could lose all adequate climate on either one or both islands. Five additional species were projected to lose ≥90 % of climate space. In total, 90 % of the species were projected to lose climate space: 79 % of bryophytes, 93 % of vascular plants and 91 % of arthropods. We also found for vascular plants and arthropods a tendency for upward shift in altitude in their suitable climate space, while for bryophytes the shift was towards the coastal areas. Our results have profound implications for future conservation priorities on islands, such as for the redrawing of conservation borders of current protected areas. [ABSTRACT FROM AUTHOR]

Carine & Schaefer ( Journal of Biogeography, 2010, 37, 77-89) suggest that the lack of past climate oscillations in the Azores may have contributed to the low plant endemism in this archipelago compared to that of the Canary Islands, a pattern they term the Azorean diversity enigma. Here we challenge their hypothesis, and discuss how the particular characteristics of the Azores may have driven current diversification patterns in this archipelago. We argue that the restricted number of Azorean endemic species and their wide distribution is explicable by the geological, geographical and ecological attributes of the archipelago. That is, the Azores are too young, too small, and too environmentally homogeneous to have hosted many in situ diversification events, so they do not host as many endemic species as other Macaronesian archipelagos, such as Madeira and especially the Canary Islands. [ABSTRACT FROM AUTHOR]

The largest standardised database available to date for arthropods in native forests of the Azores archipelago was used to determine the minimum optimal set of native forest fragments needed to accomplish four different targets of species occurrence (presence-absence) and abundance (20, 50 and 80%) using different groups of arthropods and all data combined. The results showed that occurrence and 20% abundance targets gave similar optimal solutions for most of the groups considered. At least one fragment on each of the seven studied islands was required to accomplish any occurrence and abundance target. To achieve 80% of abundance for all species, all fragments were necessary and to guarantee 50% of the overall abundance of endemics, 17 out of 18 native forests were needed. A suggestion is made to apply a measure of biotic integrity related to disturbance to select, among alternative optimal solutions, the set of areas that will help to guarantee the viability of populations. Some guidelines for the selection of priority areas for conservation in the Azores are presented. [ABSTRACT FROM AUTHOR]