Browsing by Author "Aranda, Silvia C."
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- Assessing the completeness of bryophyte inventories: an oceanic island as a case study (Terceira, Azorean archipelago)Publication . Aranda, Silvia C.; Gabriel, Rosalina; Borges, Paulo A. V.; Lobo, Jorge M.How useful, complete or unbiased are comprehensive databases in order to provide reliable estimations of diversity? Using compiled data from bryophytes in Terceira Island (Azores), we specifically aim (1) to describe the register of species over time, (2) to assess the inventory completeness, i.e., the ratio between the observed and the maximum expected species, and (3) to locate the most promising areas for further surveys. First, each new recorded species was plotted against its collecting year, using the number of database-records as a surrogate of survey effort, to get the accumulation curves. These curves were then extrapolated to obtain the theoretical number of existing species according to Clench and exponential models. Spatial and habitat characteristics of the recorded taxa were also explored. Our results show an increasing trend in the rate of recorded species (c. five species per year), as well as a maximum of around a third of the theoretically “real” number of expected species that could yet remain unknown. Nevertheless, predictions of species richness were highly variable depending on the fitting curve used. Survey effort was similar between liverworts and mosses, as were inventory completeness values, but the rate of new recorded species was higher for mosses. Although bryologists visited preferably native habitats, we show that new species citations may also be found in modified habitats (e.g., exotic forests and semi-natural grasslands). We conclude that the analysis of extensive databases is a useful tool in revealing the recording and taxonomic gaps, further showing that bryophyte inventories could still be incomplete in Terceira Island. A strategy on how to improve species’ collections in remote areas is suggested, hoping to contribute to all-inclusive biodiversity studies in the Azores and elsewhere.
- Azorean Bryophytes : a preliminary review of rarity patternsPublication . Gabriel, Rosalina; Homem, Nídia; Couto, Adalberto Borges; Aranda, Silvia C.; Borges, Paulo A. V.Os briófitos podem ser tão raros e estar tão ameaçados como os demais organismos do planeta, apesar de o seu pequeno tamanho, cores discretas e difícil identificação no campo poderem mascarar o seu verdadeiro estatuto de conservação. De facto, é reconhecido que cerca de um quarto de todos os briófitos da Europa estão efectiva ou potencialmente ameaçados. O primeiro “Livro Vermelho dos Briófitos da Europa” foi produzido em 1995, amplamente baseado em listas vermelhas nacionais e no trabalho de uma vasta equipa de briólogos que avaliaram o estatuto de conservação para as espécies Europeias. A classificação de briófitos em listas vermelhas tem contribuído para aumentar a sensibilidade dos gestores para este grupo de organismos e alguns esforços têm sido desenvolvidos na Europa, para preservar locais tendo como característica o seu interesse briológico. Consequentemente, uma lista vermelha para os briófitos dos Açores pode auxiliar os gestores regionais a identificar espécies particularmente ameaçadas, tornando-se o primeiro passo para assegurar a sua protecção. Neste artigo usamos uma adaptação dos trabalhos de Deborah Rabinowitz (1981), que criou uma tipologia para desocultar e avaliar várias formas de raridade, utilizando três variáveis: Distribuição Geográfica, Abundância e Especificidade do Habitat. Todas as 480 espécies e subespécies dos Açores foram investigadas: 215 taxa não tinham informação suficiente para ser analisados (deficientes em dados), 121 não foram consideradas raros e 144 briófitos (1 antocerota, 56 hepáticas e 87 musgos) foram considerados raros pelo menos num dos parâmetros considerados. Os benefícios e limitações desta metodologia são brevemente discutidos. São propostas algumas sugestões práticas para melhorar a estratégia de conservação dos briófitos seleccionados.
- Climate threat on the Macaronesian endemic bryophyte floraPublication . Patiño, Jairo; Mateo, Rubén G.; Zanatta, Florian; Marquet, Adrien; Aranda, Silvia C.; Borges, Paulo A. V.; Dirkse, Gerard; Gabriel, Rosalina; Gonzalez-Mancebo, Juana M.; Guisan, Antoine; Muñoz, Jesús; Sim-Sim, Manuela; Vanderpoorten, AlainOceanic islands are of fundamental importance for the conservation of biodiversity because they exhibit high endemism rates coupled with fast extinction rates. Nowhere in Europe is this pattern more conspicuous than in the Macaronesian biogeographic region. A large network of protected areas within the region has been developed, but the question of whether these areas will still be climatically suitable for the globally threatened endemic element in the coming decades remains open. Here, we make predictions on the fate of the Macaronesian endemic bryophyte flora in the context of ongoing climate change. The potential distribution of 35 Macaronesian endemic bryophyte species was assessed under present and future climate conditions using an ensemble modelling approach. Projections of the models under different climate change scenarios predicted an average decrease of suitable areas of 62–87% per species and a significant elevational increase by 2070, so that even the commonest species were predicted to fit either the Vulnerable or Endangered IUCN categories. Complete extinctions were foreseen for six of the studied Macaronesian endemic species. Given the uncertainty regarding the capacity of endemic species to track areas of suitable climate within and outside the islands, active management associated to an effective monitoring program is suggested.
- A comparison of bryophyte diversity in the Macaronesian Islands: island versus habitat approachPublication . González-Mancebo, Juana M.; Gabriel, Rosalina; Otto, Rüdiger; Sim-Sim, Manuela; Luís, Leena Margarida; Sérgio, Cecília; Garzón-Machado, Víctor; Aranda, Silvia C.; Capelo, Jorge; Vanderpoorten, AlainIn this paper, we present a comparison of richness patterns and floristic similarity for bryophytes in the five most important altitudinal habitat types in the Macaronesian islands. We evaluate the importance of different factors discussed in the literature in predicting species diversity applying the traditional island approach and within the framework of the new habitat approach, including area, isolation, climatic factors, geological age and human influence. From the analysis of patterns of bryophyte species distribution for selected habitats across islands and archipelagos, we specifically test the hypothesis that (i) floristic similarity is primarily determined by climatic factors, but not by geographical distance due to high dispersal ability in this species group and (ii) bryophyte richness is best predicted by area, but not by geological age of the habitat due to very low endemicity or speciation rate and high colonization rate.
- Designing a survey protocol to overcome the Wallacean shortfall: a working guide using bryophyte distribution data on Terceira Island (Azores)Publication . Aranda, Silvia C.; Gabriel, Rosalina; Borges, Paulo A. V.; Azevedo, Eduardo B.; Lobo, Jorge M.The increasing availability of open access data on species occurrences is leading researchers to generate more hypotheses about patterns of species distributions. However, when all of this information is mapped onto a particular geographical scale, gaps usually appear due to lack of knowledge and sampling spatial bias (the so-called Wallacean shortfall). To overcome these problems as efficiently as possible, field surveys should be designed after distinguishing well-surveyed places from those with incomplete inventories in order to carry out the extra survey effort in those areas not represented environmentally and spatially by the well-surveyed places. This procedure requires (1) gathering, cleaning and standardizing data; (2) selecting environmental variables that are important for the group considered according to field experience and the literature; and (3) making statistical decisions about the number and location of areas that should be surveyed according to the available resources. Here, we summarize most concepts and procedures devoted to the evaluation of biodiversity data, offering some general recommendations on how to use them for optimizing new survey designs. As a practical guide for potential users, we provide an example describing its application to a comprehensive database on bryophyte distribution on Terceira Island (Azores, Portugal). More than 8,000 bryophyte records were gathered, but (i) less than half of the island area has been surveyed at least once and (ii) less than 1% of these have reliable inventories (placed on the few remnants of laurel forests that have been traditionally better surveyed). Nevertheless, surveying just 15 additional localities evenly distributed across the major environmental regions and habitats on Terceira Island seems to represent the existing environmental diversity. We believe that the survey protocol presented here for bryophytes of Terceira Island could be flexibly applied to other taxa or areas.
- Geographical, temporal and environmental determinants of bryophyte species richness in the Macaronesian IslandsPublication . Aranda, Silvia C.; Gabriel, Rosalina; Borges, Paulo A. V.; Santos, Ana M. C.; Azevedo, Eduardo B.; Patiño, Jairo; Hortal, Joaquín; Lobo, Jorge M.Species richness on oceanic islands has been related to a series of ecological factors including island size and isolation (i.e. the Equilibrium Model of Island Biogeography, EMIB), habitat diversity, climate (i.e., temperature and precipitation) and more recently island ontogeny (i.e. the General Dynamic Model of oceanic island biogeography, GDM). Here we evaluate the relationship of these factors with the diversity of bryophytes in the Macaronesian region (Azores, Madeira, Canary Islands and Cape Verde). The predictive power of EMIB, habitat diversity, climate and the GDM on total bryophyte richness, as well as moss and liverwort richness (the two dominant bryophyte groups), was evaluated through ordinary least squares regressions. After choosing the best subset of variables using inference statistics, we used partial regression analyses to identify the independent and shared effects of each model. The variables included within each model were similar for mosses and liverworts, with orographic mist layer being one of the most important predictors of richness. Models combining climate with either the GDM or habitat diversity explained most of richness variation (up to 91%). There was a high portion of shared variance between all pairwise combinations of factors in mosses, while in liverworts around half of the variability in species richness was accounted for exclusively by climate. Our results suggest that the effects of climate and habitat are strong and prevalent in this region, while geographical factors have limited influence on Macaronesian bryophyte diversity. Although climate is of great importance for liverwort richness, in mosses its effect is similar to or, at least, indiscernible from the effect of habitat diversity and, strikingly, the effect of island ontogeny. These results indicate that for highly vagile taxa on oceanic islands, the dispersal process may be less important for successful colonization than the availability of suitable ecological conditions during the establishment phase.
- How do different dispersal modes shape the species-area relationship? Evidence for between-group coherence in the Macaronesian floraPublication . Aranda, Silvia C.; Gabriel, Rosalina; Borges, Paulo A. V.; Santos, Ana M. C.; Hortal, Joaquín; Baselga, Andrés; Lobo, Jorge M.AIM: We explore the island species–area relationships (ISARs) of several plant groups differing in dispersal ability. We examine whether: (i) the ISAR slope is higher for less dispersive groups (diminishing from not-wind-dispersed seed plants to wind-dispersed seed plants, pteridophytes and bryophytes); and (ii) the regional richness is higher than that predicted by the ISAR of its constituent islands for groups with lower dispersal ability. Additionally, we relate both patterns to the compositional dissimilarity (beta diversity) between islands. LOCATION: The Macaronesian archipelagos of the Azores, Madeira and Canary Islands. METHODS: ISARs were estimated using the conventional power model. Differences in slopes among taxa were analysed through ANCOVA tests. We assessed the deviation of the total richness of the Macaronesian flora from that predicted by the ISAR and calculated several measures of beta diversity (turnover, nestedness-resultant dissimilarity and nestedness). Analyses were repeated after excluding the two Canarian islands of Lanzarote and Fuerteventura, which have unique climatic and geological conditions in the region. RESULTS: All ISAR models were significant except for pteridophytes (for which it was significant when excluding Lanzarote and Fuerteventura). ISAR slopes did not differ among taxa. Regional richness followed ISAR predictions for bryophytes and pteridophytes when Lanzarote and Fuerteventura were excluded, while the total number of Macaronesian seed plants (particularly not-wind-dispersed species) always fell above the ISAR. Turnover was higher in seed plants than in bryophytes and pteridophytes, and the opposite occurred with nestedness. MAIN CONCLUSIONS: Differences in dispersal ability influence the compositional dissimilarity between these islands, but not the rate of species increase with area. This may be because ISAR slopes are mostly determined by within-island processes of species accumulation, while differences in dispersal generate different between island patterns. The lack of relationship between the ISAR slope and species replacement or nestedness prevents its use as a proxy for beta diversity.
- The iterative process of plant species inventorying for obtaining reliable biodiversity patternsPublication . Aranda, Silvia C.; Hespanhol, Helena; Homem, Nídia; Borges, Paulo A. V.; Lobo, Jorge M.; Gabriel, RosalinaWe require representative data of species occurrence to explain plant diversity patterns, but most of the available information is incomplete and biased. To improve our knowledge, we suggest that species inventorying should be an iterative process encompassing the following: (1) the detection of taxonomic and geographical gaps; (2) the planning of a survey design to reduce such gaps; and (3) the evaluation of field sampling results. Here, we focus on the latter phase for the bryophytes of Terceira Island (Azores) for which we have previously estimated < 1% of the area as well surveyed based on historical collections. To examine the performance of our stratified survey based on two factors (land use and environmental regions), we used rarefaction curves, ANOVA tests and bootstrap sampling. We recorded 40% of all the species known for the island and presented eight new citations. The species assemblages remained similar between historical and current inventories. Most localities had completeness values > 85%, but we always exceeded the optimal sampling effort. Land uses and environmental regions affected species diversity, but, unexpectedly, to a different degree. Our study illustrates the difficulties of planning field surveys to obtain reliable biodiversity patterns, even when prior information and standardized sampling protocols are explicitly considered.
- Long-term monitoring across elevational gradients (II) : vascular plants on Pico Island (Azores) transectPublication . Coelho, Márcia Catarina Mendes; Elias, Rui B.; Kluge, Jürgen; Pereira, Fernando E. A.; Henriques, Débora; Aranda, Silvia C.; Borges, Paulo A. V.; Ah-Peng, Claudine; Gabriel, RosalinaPico Island remains one of the last remnants of natural vegetation in the Azores, including the largest natural protected area; nevertheless, habitat change and the spread of exotic plants are visible, especially in those areas where human presence prevails. Currently, the lowlands are vastly occupied by pastures dominated by exotic herbs/grasses and most forests are dominated by Pittosporum undulatum. This paper aims to: i) review previous botanical studies related to elevational gradients; ii) investigate vascular plants composition and abundance in native vegetation, following an elevational transect (from 10 to 2200 m); and iii) investigate some patterns of the recorded diversity and distribution of vascular plants. Methodology follows a standardized protocol with observations in 100 m2 plots. A total of 88 species were recorded, representing 35% of the indigenous but only 5% of the exotic species previously known from Pico. The richest areas were found between 600 and 1000 m and the areas with the lowest proportion of indigenous species occurred between 1800 and 2200 m. The recorded composition and richness values of endemic and native vascular plants support the high ecological and conservation value of the studied areas and constitute a good basis for long-term monitoring projects.
- New national and regional bryophyte records, 26 : Rhynchostegiella litorea (De Not.) Limpr., 16Publication . Aranda, Silvia C.; Gabriel, Rosalina; Hedeñas, Lars