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- Strands of connection: unraveling livestock grazing effects on orb-weaver spidersPublication . Oyarzabal, Guilherme; Guimarães, MuriloStudies on the effects of grazing disturbances in grasslands have shown mixed results for spider diversity, mainly regarding their guilds. While ungrazing, low, and moderate grazing potentially enhance the diversity of orb-weavers in spider communities, heavy grazing seems to reduce species’ richness. On the population level though, studies of orb-weavers are scarce, and the effects of grazing in natural grasslands are unknown. In this way, we investigated the effects of different grazing levels on population persistence of orb-weaver spiders, hypothesizing that low to intermediate disturbances benefit populations. We predict that high grazing, due to the removal of vegetation structure, will negatively affect the occupancy and abundance of orb-weavers. For that, we experimentally controlled grazing pressure and obtained population occurrence and counts of two orb-weaver spider species, Argiope argentata and Alpaida quadrilorata. We found that A. argentata was negatively affected by grazing, as it relies on higher vegetation for web-building. In contrast, A. quadrilorata, which occurs in cattle-resistant rosette plants, showed no effects of grazing. Implications for insect conservation: Our study emphasizes the need for balanced grazing practices and habitat conservation to protect orb-weaver spiders and other arthropods, as well as species-specific effects for species from the same guild, underscoring their ecological significance in maintaining ecosystem stability.
- What do plants tell spiders about disturbances in grasslands?Publication . Oyarzabal, Guilherme; Guimarães, Murilo; Hebets, EileenGrazing and mowing constitute two important ways of reducing vegetation structure, which causes mechanical injuries in plants. In response to these injuries, plants emit herbivore-induced plant volatiles (HIPVs) that can act as recruitment signals for arthropod predators. Among these arthropods, spiders have been suggested to respond to HIPVs. It is unknown, however, if spiders make microhabitat choice based on the detection of those HIPVs or based solely on the availability of vegetal structure. In this study, we investigated microhabitat choice of the orb-weaver spider Argiope trifasciata (Forsskål, 1775) and its potential relationship with impacted and not impacted vegetation structure availability. Our major results corroborate other findings that microhabitat choice in orb-weaver spiders is driven not by HIPVs, but rather by vegetation structure. Habitat structure influences a variety of ecological factors such as predation risk, prey availability, and mate finding in orb-weavers. The mechanisms underlying assessment by A. trifasciata of the vegetative structure remains unknown, and future studies might investigate their capacity to perceive light and shade and/or their assessment of vertical positioning. Practically, our results can be useful in evaluating the impact of land management on spider populations and their resilience to these impacts.
- Arthropod traits as proxies for abundance trends in the Azorean IslandsPublication . Oyarzabal, Guilherme; Cardoso, Pedro; Rigal, François; Boieiro, Mário; Santos, Ana M. C.; Amorim do Rosário, Isabel; Malumbres-Olarte, Jagoba; Costa, Ricardo; Lhoumeau, Sebastian; Pozsgai, Gabor; Gabriel, Rosalina; Borges, Paulo A. V.Human activities drive ecological transformation, impacting island ecosystems from species diversity to ecological traits, mainly through habitat degradation and invasive species. Using two unique long-term datasets we aim to evaluate whether species traits (body size, trophic level, dispersal capacity and habitat occupancy) can predict temporal variations in the abundance of endemic, indigenous (endemic and native non-endemic) and exotic arthropods in the Azores Islands. We found that body size is crucial to predict arthropod abundance trends. Small-bodied herbivorous arthropods showed a decrease in abundance, while large-bodied indigenous arthropods increased in abundance, mainly in well-preserved areas. Also, large-bodied exotic arthropods increased in abundance across the entire archipelago. Moreover, endemic canopy dwellers increased in abundance, while endemic ground-dwellers decreased in abundance. Simultaneously, exotic arthropods showed the opposite result, increasing in abundance in the ground while decreasing in abundance in the canopy. Finally, habitat influenced both endemic and exotic spider abundance trends. Endemic spiders that occupy solely natural habitats experienced a decline in abundance, while exotic spiders in the same habitats increased in abundance. Our study underscores the significance of arthropod species traits in predicting abundance changes in island ecosystems over time, as well as the importance of monitoring species communities. Conservation efforts must extend beyond endangered species to protect non-threatened ones, given the increased extinction risk faced by even common species on islands. Monitoring and restoration programs are essential for preserving island ecosystems and safeguarding endemic arthropod populations.
- The BALA project: A pioneering monitoring of Azorean forest invertebrates over two decades (1999–2022)Publication . Pozsgai, Gabor; Lhoumeau, Sébastien; Rosário, Isabel Amorim Do; Boieiro, Mário; Cardoso, Pedro; Costa, Ricardo; Ferreira, Maria Teresa; Leite, Abrão; Malumbres-Olarte, Jagoba; Oyarzabal, Guilherme; Rigal, François; Ros Prieto, Alejandra; Santos, Ana M. C.; Gabriel, Rosalina; Borges, Paulo A. V.Globally, there is a concerning decline in many insect populations, and this trend likely extends to all arthropods, potentially impacting unique island biota. Native non-endemic and endemic species on islands are under threat due to habitat destruction, with the introduction of exotic, and potentially invasive, species, further contributing to this decline. While long-term studies of plants and vertebrate fauna are available, long-term arthropod datasets are limited, hindering comparisons with better-studied taxa. The Biodiversity of Arthropods of the Laurisilva of the Azores (BALA) project has allowed gathering comprehensive data since 1997 in the Azorean Islands (Portugal), using standardised sampling methods across islands. The dataset includes arthropod counts from epigean (pitfall traps) and canopy-dwelling (beating samples) communities, enriched with species information, biogeographic origins, and IUCN categories. Metadata associated with the sample protocol and events, like sample identifier, archive number, sampled tree species, and trap type are also recorded. The database is available in multiple formats, including Darwin Core, which facilitates the ecological analysis of pressing environmental concerns, such as arthropod population declines and biological invasions.
- Biodiversity insights from BioBlitz surveys on Terceira Island, AzoresPublication . Borges, Paulo; Malumbres-Olarte, Jagoba; Gabriel, Rosalina; Videira, Sandra; Rodrigues, António Félix; Lhoumeau, Sébastien Georges André; Ros Prieto, Alejandra; Melo, Cecilia; Pozsgai, Gabor; Oyarzabal da Silva, Guilherme; Parmentier, Laurine Marie; Lamelas López, Lucas; Canelas Boieiro, Mário Rui; Barcelos, Paulo; Costa, Ricardo; Coelho, Ruben; Wallon, Sophie; Gonçalves, Susana; Arroz, Ana; Amorim do Rosário, Isabel; Elias, RuiABSTRACT: This manuscript is the first scientific publication of the project “BioBlitz Azores". The project was launched in 2019 and had a second event in 2023 under the scope of the FCT-MACRISK project, surveying the historic public garden "Jardim Duque da Terceira", in the historical centre of Angra do Heroísmo, Terceira Island (Azores, Portugal). In addition to contributing directly to the knowledge of Azorean biota, BioBlitz Azores aims to engage the non-scientific community - including volunteers, amateur naturalists, students, teachers, families and other garden visitors - to foster a sense of community and raise awareness about Azorean biodiversity and its conservation.
- Beyond native habitats: Indigenous arthropods adapted to mid-elevations find refuge in exotic forestsPublication . Borges, Paulo; Lhoumeau, Sébastien Georges André; Oyarzabal da Silva, Guilherme; Borges, P.A.V.ABSTRACT: In island ecosystems, extensive land-use changes since human colonisation has transformed native habitats into agriculture and exotic forests, raising concerns about the long-term persistence of indigenous biodiversity. This study explores the distribution of relict populations of indigenous arthropod species in exotic forests on Terceira Island (Azores) and identifies the ecological and environmental drivers shaping their presence. Using standardized SLAM (Sea, Land, and Air Malaise) traps and pitfall traps data from native and exotic forest plots, we investigated the distribution and abundance of 85 indigenous arthropod species across 15 orders, of which 65 were recorded at least once in exotic forests. We modelled the effects of species traits and biogeographic variables on species abundance and presence in exotic forests. Elevation emerged as the dominant predictor in both models, with species associated with mid-elevation habitats (300 – 500 m a.s.l.) showing higher abundance and occurrence in exotic forests, while high-elevation specialists (above 500 m a.s.l.) were largely absent. Endemic species generally had lower relative abundances in exotic forests compared to native non-endemics, even when their overall elevational range was broad. These results suggest that species historically present in mid-elevation zones find refuge in exotic forests. While relict populations may offer a degree of resilience and restoration potential, their long-term persistence is uncertain, particularly under climate change scenarios that limit available habitat at higher elevations. Conservation strategies should therefore recognize the role of exotic forests as transitional refuges and prioritize their management and restoration of native forests, especially in non-protected and privately-owned landscapes.
- Species traits may predict extinction risk of Azorean endemic arthropodsPublication . Oyarzabal da Silva, Guilherme; Cardoso, Pedro; Rigal, François; Canelas Boieiro, Mário Rui; Coelho dos Santos, Ana Margarida; Amorim do Rosário, Isabel; Malumbres-Olarte, Jagoba; Costa, Ricardo; Lhoumeau, Sébastien Georges André; Pozsgai, Gabor; Gabriel, Rosalina; Borges, Paulo; Littlewood, Nick; Bahlai, ChristieABSTRACT: Oceanic islands, recognised for their isolation, high endemic species richness and unique evolutionary paths compared with their continental counterparts, are extremely susceptible to anthropogenic activities. The fragmentation of island habitats and disruption of native ecosystems has increased the risk of extinction for many endemic species, including arthropods. Extinction is not random, and some species traits may increase the probability of species entering an extinction trajectory. Studying species traits alongside International Union for Conservation of Nature (IUCN) threat levels may offer valuable insights into their vulnerability and inform targeted conservation strategies. Here, we aim to test the predictability of IUCN threat categories and conservation status based on endemic Azorean arthropods' functional traits: body size, trophic group and vertical strata occupancy. We demonstrate that species with limited vertical occupancy, particularly those restricted to ground level, are more vulnerable to extinction than those that inhabit the forest canopy. Contrary to our expectations, body size and trophic group did not appear to be direct predictors of the threat level. Overall, our findings underscore previous and ongoing effects of human activities in island ecosystems. Hence, we emphasise the need to look at species traits as predictors of future extinctions in endemic island arthropods.
- Threats and conservation status of the endemic terrestrial arthropods of the AzoresPublication . Oyarzabal da Silva, Guilherme; Pozsgai, Gabor; Tsafack, Noelline; Cardoso, Pedro; Rigal, François; Canelas Boieiro, Mário Rui; Coelho dos Santos, Ana Margarida; Amorim do Rosário, Isabel; Malumbres-Olarte, Jagoba; Costa, Ricardo; Lhoumeau, Sébastien Georges André; Gabriel, Rosalina; Borges, P.A.V.ABSTRACT: Insular ecosystems are disproportionately threatened by human activities, leading to an unprecedented decline in species diversity, particularly on remote archipelagos like the Azores. However, the impacts of humans on arthropods, which typically represent a big proportion of island biotas, remain poorly documented. We present an assessment of threats affecting different groups of species, examining the relationship between species occupancy, IUCN threat categories and trophic interactions for arthropods in the Azores (Macaronesia). We compiled data on endemic arthropods from published lists and IUCN assessments, including extinction risk, direct threats, and geographical ranges, to identify key pressures on species. Using network analyses, we examined the association between extinction risk and number of species, also estimating the IUCN Red List Index (RLI) for each island conservation status. We found that some of the Azorean endemic arthropod species have already gone extinct and more than half are classified as threatened by the IUCN Red List. Of these, predatory beetles (Coleoptera) and spiders (Araneae) have the highest numbers of threatened species, mainly due to habitat degradation, the spread of invasive plant species, and climate change. The RLI differs greatly among islands, being the lowest in Santa Maria, which concentrates a large number of critically endangered (CR) single-island endemic species, and higher in islands with larger and better-preserved native forest fragments, such as Terceira. A comprehensive approach integrating habitat protection, invasive species management and conservation measures is essential to ensure the long-term survival of Azorean arthropod endemic species in particular and island biota in general.
- A comprehensive trait dataset for Terrestrial Arthropods of the Azores: insights for conservation, island ecology and species invasionPublication . Oyarzabal da Silva, Guilherme; Rigal, François; Cardoso, Pedro; Amorim do Rosário, Isabel; Costa, Ricardo; Lhoumeau, Sébastien Georges André; Wallon, Sophie; Macías-Hernández, Nuria; Terzopoulou, Sofia; Triantis, Kostas; Borges, P.A.V.; Silva, DanielABSTRACT: Species functional traits provide critical insights into how organisms interact with and respond to their environment. Key characteristics, such as body size, dispersal ability and trophic specialisation influence species' survival, reproduction and adaptability. Island ecosystems, particularly oceanic archipelagos like the Azores, serve as ideal natural laboratories for studying these traits due to their unique biogeographic history and high endemism. Arthropods, as dominant colonisers and ecosystem engineers, exhibit rapid adaptation and trait diversification in these isolated settings. However, island arthropods face escalating threats from habitat loss, climate change and invasive species, which disrupt ecological functions and increase extinction risks. Under the scope of BALA (Biodiversity of Arthropods from the Laurisilva of Azores) project (1999-2021) and SLAM (Long Term Ecological Study of the Impacts of Climate Change in the natural forest of Azores) project (2012-2025), we obtained a comprehensive and standardised dataset of arthropods functional traits currently known to occur in the Azores Archipelago.
- The Ripple Effects of Climate Change on Tibetan Alpine ArthropodsPublication . Oyarzabal da Silva, Guilherme; Borges, P.A.V.