Browsing by Author "Oyarzabal, Guilherme"
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- 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.
- Dos Dados à Ação: Estudos de Longo Prazo e Estratégias de Conservação para a Biodiversidade dos Artrópodes dos Açores.Oyarzabal, GuilhermeOs artrópodes (animais invertebrados como os insectos, aracnídeos e centopeias) desempenham papéis vitais em diversos ecossistemas, contribuindo para processos como a polinização, decomposição, predação e herbivoria. As características funcionais dos artrópodes fornecem uma estrutura para compreender como espécies e comunidades respondem a perturbações ambientais.
- 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.
- 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.
- 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.