Aim This paper has two objectives. First, we examine how a variety of biotic, abiotic and anthropogenic factors influence the endemic and introduced arthropod richness on an oceanic island. Second, we look at the relationship between the endemic and introduced arthropod richness, to ask whether areas with high levels of endemic species richness deter invasions.Location The work was carried out on a young volcanic island, Terceira, in the Azores.Methods We used standard techniques to collect data on arthropod species richness. Environmental data were obtained from the CIELO climatic model and using GIS. The explanatory value of environmental variables on a small-scale gradient of endemic and exotic arthropod species richness was examined with generalized linear models (GLMs). In addition, the impact of both endemic and exotic species richness in the communities was assessed by entering them after the environmental variable(s) to see if they contributed significantly to the final model (the hierarchical method).Results Abiotic (climatic and geomorphological) variables gave a better explanation of the variation in endemic species richness, whereas anthropogenic variables explained most of the variation in introduced species richness. Furthermore, after accounting for all environmental variables, part of the unexplained variance in the endemic species richness is explained by the introduced species richness and vice-versa. That is, areas with high levels of endemic species richness had many introduced species. There is evidence of a somewhat inverse spatial distribution between a group of oceanic-type, forestdwelling, endemic, relict arthropods and a group of more generalist endemic arthropods that are able to survive in disturbed marginal sites particularly rich in non-indigenous species.Main conclusions Richness of endemic species is mainly driven by abiotic factors such as a climatic axis (oceanic-type localities with lower temperatures and summer precipitations) and a binary variable CALD (location of sites in caldeiras or ravines), whereas richness of introduced species depends on disturbance related factors. However, after factoring out these major influences, there is a correlation between endemic and introduced richness, suggesting thatindependent of the environmental and geographical factors that affect the distribution of endemic or introduced species -the richest endemic assemblages are more prone to invasion, due probably to a facilitation process. Inconclusive evidence suggests that non-indigenous species are limited to those sites under anthropogenic influence located mainly near forest edges, but the rate of expansion of those species to high-altitude, core pristine sites has still to be tested.

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The objective of this study is to investigate whether presence/absence models can be used as surrogates of arthropod abundance, and eventually under which circumstances such surrogacy is guaranteed. Presence/absence data for 48 arthropod species from Terceira Island were modelled using artificial neural networks. Probabilities of occurrence were correlated with abundance data from a standardized arthropod survey programme. Although a tendency was found for vagile species to show relationships, only nine species showed significant positive correlations between probability of presence and abundance. Five of these were exotic spider species with high abundances and wide distributions in several human-modified habitats. The patchy distribution of pristine habitats, the capacity to reach them and the probable low dependence on limiting resources, other than food, enhance the relationship. A lack of significant correlations for the majority of the species may be due to historical events, inappropriate scale, demographic controls of density, or the incapacity of presence/absence models to account for environmental suitability. The difficulty to identify a priori the species for which the relationship will hold advises against the use of species distribution models as surrogates of arthropod abundance.

Aims Human landscape disturbance can drive the degradation of natural environments, thereby contributing to indigenous (endemic and native nonendemic) species extinctions, facilitating the establishment of exotic species and ultimately resulting in more similar species compositions over time and space. We assessed whether similarities in epigean arthropod assemblages differ between indigenous and exotic species in an oceanic archipelago, and we also examined whether such assemblage similarities depend on the most dominant species, the island, the type of habitat, the degree of landscape disturbance or local environmental variables.Location Four oceanic islands in the Azores archipelago, Portugal.Methods We examined the degree of assemblage similarity and the effect of environmental variables and spatial disturbance to explain the epigean arthropod distributions for indigenous and exotic species.Results Exotic species increased overall assemblage similarity. Distinct arthropod assemblages occurred on the different islands and in the different habitats. Assemblage differences between the habitats depended on the island. This pattern was largely explained by the abundance patterns of the most abundant indigenous and exotic species (ten indigenous and ten exotic species accounted for 75% of total individuals). In comparison with the high explanatory capacity of the habitats and islands per se, local environmental variables and disturbance hardly explained the assemblage composition in both groups of species.Main conclusions We demonstrate that exotic species promote assemblage homogenization on these oceanic islands, and that such process is contingent and independent between islands and habitats. General habitat characteristics seemed to be the main driver of assemblage structure, independently of the different climatic conditions or disturbance levels.

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With their extensive coverage, marine low clouds greatly impact global climate. Presently, marine low clouds are poorly represented in global climate models, and the response of marine low clouds to changes in atmospheric greenhouse gases and aerosols remains the major source of uncertainty in climate simulations. The Eastern North Atlantic (ENA) is a region of persistent but diverse subtropical marine boundary layer clouds, whose albedo and precipitation are highly susceptible to perturbations in aerosol properties. In addition, the ENA is periodically impacted by continental aerosols, making it an excellent location to study the cloud condensation nuclei (CCN) budget in a remote marine region periodically perturbed by anthropogenic emissions, and to investigate the impacts of long-range transport of aerosols on remote marine clouds. The Aerosol and Cloud Experiments in Eastern North Atlantic (ACE-ENA) campaign was motivated by the need of comprehensive in-situ measurements for improving the understanding of marine boundary layer CCN budget, cloud and drizzle microphysics, and the impact of aerosol on marine low cloud and precipitation. The airborne deployments took place from June 21 to July 20, 2017 and January 15 to February 18, 2018 in the Azores. The flights were designed to maximize the synergy between in-situ airborne measurements and ongoing long-term observations at a ground site. Here we present measurements, observation strategy, meteorological conditions during the campaign, and preliminary findings. Finally, we discuss future analyses and modeling studies that improve the understanding and representation of marine boundary layer aerosols, clouds, precipitation, and the interactions among them.

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