Browsing by Author "Gaspar, Clara"
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- Abundance, spatial variance and occupancy: arthropod species distribution in the AzoresPublication . Gaston, Kevin J.; Borges, Paulo A. V.; He, FangLiang; Gaspar, Clara1. The positive abundance-occupancy and abundance-variance relationships are two of the most widely documented patterns in population and community ecology. 2. Recently, a general model has been proposed linking the mean abundance, the spatial variance in abundance, and the occupancy of species. A striking feature of this model is that it consists explicitly of the three variables abundance, variance and occupancy, and no extra parameters are involved. However, little is known about how well the model performs. 3. Here, we show that the abundance-variance-occupancy model fits extremely well to data on the abundance, variance and occupancy of a large number of arthropod species in natural forest patches in the Azores, at three spatial extents, and distinguishing between species of different colonization status. Indeed, virtually all variation about the bivariate abundance-occupancy and abundance-variance relationships is effectively explained by the third missing variable (variance in abundance in the case of the abundance-occupancy relationship, and occupancy in the case of the abundance-variance relationship). 4. Introduced species tend to exhibit lower densities, less spatial variance in these densities, and occupy fewer sites than native and endemic species. None the less, they all lie on the same bivariate abundance-occupancy and abundance-variance, and trivariate abundance-variance-occupancy, relationships. 5. Density, spatial variance in density, and occupancy appear to be all the things one needs to know to describe much of the spatial distribution of species.
- Áreas UrbanasPublication . Maduro-Dias, Francisco; Borges, Paulo A. V.; Gaspar, Clara; Silva, Luís"[…]. A ocupação deu-se pela costa e implicou a largada de animais domésticos para desbravar o sub-bosque da densa vegetação que caracterizava a cobertura vegetal dos Açores. No entanto, muitos dos povoados iniciais dos Açores são mais interiores que costeiros ou, pelo menos, colocam-se no cimo de rochas, junto ao mar mas sobranceiras e difíceis de atingir. Nesta situação estão ainda hoje Vila do Porto em Santa Maria, o Topo em São Jorge, o vale dos Flamengos no Faial, São Sebastião, herdeira de Santana de Porta Alegre, na Terceira, as Lajes nas Flores. A segurança de terra e o receio do mar levavam a isso, mas a necessidade de um porto para comunicar obrigava à proximidade do oceano. Esse esforço de aproveitar as capacidades produtivas do território e garantir, ao mesmo tempo, as comunicações, tem um bom exemplo, ainda hoje disponível, no modo como Santa Cruz das Flores completa, junto à água, os pequenos povoados altaneiros, situados nas montanhas em redor. Visite-se ainda, como outro exemplo disso, o magnífico diálogo entre a Povoação, na ilha de São Miguel, bem próxima do mar e encaixada na foz de uma ribeira caudalosa, e as suas sete Lombas, terra adentro, onde, já longe do perigo e sobre melhores espaços de cultivo, asseres humanos se instalaram, vigiando. Assim, entre o mar, por um lado, e as cordilheiras e planaltos centrais selvagens no sentido que mantinham uma densa floresta subtropical (designada por Laurissilva), por outro, os primeiros Açorianos estabeleceram-se, procurando sempre cotas abaixo dos 400 metros de altitude, onde começam os nevoeiros e mares de nuvens mais frequentes. Aliás, os registos históricos mais antigos apontam para que apenas abaixo da cota dos 350 metros estivessem instaladas as terras de cultivo e habitações. São locais preferencialmente voltados a Sul e a Nascente para aproveitar o calor do Sol, evitar os vendavais mais frequentes, acautelar distâncias entre pontos necessários, garantir, em suma, o melhor conforto possível. […]".
- Arthropods as surrogates of diversity at different spatial scalesPublication . Gaspar, Clara; Gaston, Kevin J.; Borges, Paulo A. V.This study evaluates the effectiveness of taxonomic, colonization and trophic groups of arthropods from native forests of the Azores archipelago as surrogates of the diversity of other arthropod groups and of the remaining arthropods. Consistency in the performance of surrogates was tested across three spatial scales and using two measures of diversity. Pitfall and beating samples from 109 transects, 18 forest fragments and seven islands were analysed. The results showed that Araneae, Hemiptera and small orders taxonomic groups; native, endemic and introduced colonization groups; and the herbivores trophic group were consistent surrogates of the remaining diversity across the three spatial scales analysed, for both alpha and dissimilarity diversities. However, none of the subsets considered was significantly related with all of the other subsets at any of the three spatial scales. The effectiveness of surrogacy was dependent on the spatial level considered, and groups behaved inconsistently depending on the measure of diversity used. The value of a group as a diversity surrogate should be evaluated for a study area for a given spatial scale and diversity measure, in accordance with the scale and measure that will be used for biodiversity assessments and monitoring programs in that area.
- Biotic integrity of the arthropod communities in the natural forests of AzoresPublication . Cardoso, Pedro; Borges, Paulo A. V.; Gaspar, ClaraThe loss of biotic integrity in ecosystems due to human pressure has been receiving much attention from the scientific community. The primary aim of this study is to understand how the increasing human pressure on natural forests in the Azorean archipelago (North Atlantic) is affecting their epigean arthropod communities and which biological parameters it affects most. An expert team did fieldwork covering most of the natural forests (mainly inside nature reserves) of the archipelago using standardized pitfall trapping. To build a multimetric index we tested a number of taxonomic and ecological parameters that can potentially be influenced by disturbance. Sixteen of these were found to be significantly influenced by disturbance in forests. We retained seven metrics due to both, desirable scalability properties and relatively low correlation between them. These included the percentages of endemic and predator species richness and also predator abundance, which are inversely related to disturbance; and the percentages of native and saprophagous species richness and introduced and herbivore abundance, which are positively related to disturbance. All seven metrics were combined in an Index of Biotic Integrity (IBI) value. We then proceeded to understand which potential disturbance factors are influencing the biotic integrity of communities and how such influence is felt. Five disturbance factors were found to influence the IBI, although in different ways: the size and fragmentation of reserves, the distance of sites to the reserve borders, the invasion by alien plants and the density of human paths at the sites. Given that only percentages of taxonomical or ecological characteristics were chosen as metrics, we tested and found the scalability of the IBI to be possible, allowing the comparison of sites with different collecting effort or even the comparison of reserves with different areas and numbers of collecting sites in each. Finally, we propose a novel graphical representation for multimetric indices like the IBI, one which allows retaining much of the information that is usually lost in multimetric indices.
- Canopy insect herbivores in the Azorean Laurisilva forests: key host plant species in a highly generalist insect communityPublication . Ribeiro, Sérvio P.; Borges, Paulo A. V.; Gaspar, Clara; Melo, Catarina; Serrano, Artur R. M.; Amaral, João; Aguiar, Carlos; André, Genage; Quartau, José A.This article explores patterns of insect herbivore distribution in the canopy of the Laurisilva forests on seven islands in the Azores archipelago. To our knowledge, this is one of the first extensive studied of this type in tree or shrub canopies of oceanic island ecosystems. One of the most frequently debated characteristics of such ecosystems is the likely prevalence of vague, ill-defined niches due to taxonomic disharmony, which may have implications for insect-plant interactions. For instance, an increase in ecological opportunities for generalist species is expected due to the lack of predator groups and reduced selection for chemical defence in host plants. The following two questions were addressed: 1) Are specialists rare species, and insect herbivore species randomly distributed among host plant species in the Azores? 2) Are the variances in insect herbivore species composition, frequency and richness explained by host plants or by regional island effects? We expect a proportional distribution of herbivore species between host plants, influenced by host frequency and distinct island effects; otherwise, deviation from expectation might suggest habitat preference for specific host tree crowns. Canopy beating tray samples were performed on seven islands, comprising 50 transects with 1 to 3 plant species each (10 replicates per species), giving 1320 samples from ten host species trees or shrubs in total. From a total of 129 insect herbivore species, a greater number of herbivore species was found on Juniperus brevifolia (s=65) and Erica azorica (s=53). However, the number of herbivore species per individual tree crown was higher for E. azorica than for any other host, on all islands, despite the fact that it was only the fourth more abundant plant. In addition, higher insect species richness and greater insect abundance were found on the trees of Santa Maria Island, the oldest in the archipelago. Insect species composition was strongly influenced by the presence of E. azorica, which was the only host plant with a characteristic fauna across the archipelago, whereas the fauna of other plant crowns was grouped by islands. The great insect occurrence on E. azorica reflects strong habitat fidelity, but only four species were clearly specialists. Our findings indicate a broadly generalist fauna. The simplicity of Azorean Laurisilva contributed to the understanding of insect-plant mechanisms in canopy forest habitats.
- De marginal a bem patrimonial: processos de divulgação científica na exposição "Tesouros de seis patas"Publication . Arroz, Ana Margarida Moura; Amorim, Isabel R.; Gabriel, Rosalina; São Marcos, Rita; Gaspar, Clara; Borges, Paulo A. V.
- Diversity and distribution of arthropods in native forests of the Azores archipelagoPublication . Gaspar, Clara; Borges, Paulo A. V.; Gaston, Kevin J.Since 1999, our knowledge of arthropods in native forests of the Azores has improved greatly. Under the BALA project (Biodiversity of Arthropods of Laurisilva of the Azores), an extensive standardised sampling protocol was employed in most of the native forest cover of the Archipelago. Additionally, in 2003 and 2004, more intensive sampling was carried out in several fragments, resulting in nearly a doubling of the number of samples collected. A total of 6,770 samples from 100 sites distributed amongst 18 fragments of seven islands have been collected, resulting in almost 140,000 specimens having been caught. Overall, 452 arthropod species belonging to Araneae, Opilionida, Pseudoscorpionida, Myriapoda and Insecta (excluding Diptera and Hymenoptera) were recorded. Altogether, Coleoptera, Hemiptera, Araneae and Lepidoptera comprised the major proportion of the total diversity (84%) and total abundance (78%) found. Endemic species comprised almost half of the individuals sampled. Most of the taxonomic, colonization, and trophic groups analysed showed a significantly left unimodal distribution of species occurrences, with almost all islands, fragments or sites having exclusive species. Araneae was the only group to show a strong bimodal distribution. Only a third of the species was common to both the canopy and soil, the remaining being equally exclusive to each stratum. Canopy and soil strata showed a strongly distinct species composition, the composition being more similar within the same stratum regardless of the location, than within samples from both strata at the same location. Possible reasons for these findings are explored. The procedures applied in the sampling protocol are also discussed.
- Ecology and evolution of the arborescent Erica azorica Hochst (Ericaceae)Publication . Ribeiro, Sérvio P.; Borges, Paulo A. V.; Gaspar, ClaraO objectivo do presente estudo consistiu em avaliar o impacto da herbivoria por insectos na arquitectura da urze Erica azorica Hochst, planta endémica da Laurisilva dos Açores. Erica azorica é uma planta com porte arbustivo e pioneira que consegue persistir nas florestas maduras de Laurisilva, onde pode atingir porte arbóreo tornando-se emergente no copado. Testa-se a hipótese de que a arquitectura da planta pode ser modificada através do dano provocado por insectos dando-se esta alteração através do decréscimo do número de ramificações no botão terminal, alteração do comprimento dos ramos terminais de um módulo, e consequentemente alteração da estrutura do módulo. Fez-se uma amostragem em 1999 (Agosto - Setembro) e 2000 (Julho) de três populações distintas na ilha do Pico: "Manhenha", população pioneira; ''Caiado'', população em pastagem abandonada nas margens da Lagoa do Caiado; e "Mistério da Prainha - Chão Verde", uma população emergente, com árvores de 8 a 11 metros de altura numa floresta madura localizada numa corrente de lava recente. Foram amostradas ao acaso um total de 10 plantas por população, tendo-se colhido 10 módulos de ramos a diferentes alturas e posições dentro de cada planta. Em cada módulo contou-se o número de ramificações, número de ramificações danificadas, ramificações dos botões terminais e crescimento dos ramos. O dano provocado pelos insectos foi identificado facilmente pois este provoca o reaparecimento de 3 a 4 novos ramos com origem no mesmo ponto meristemático. Deste modo, o dano provocado pelos insectos foi quantificado através da contagem do número de botões destruídos e de botões não danificados por módulo. Quantificou-se igualmente o número de larvas de insectos por módulo. Dependendo dos objectivos, a análise estatística dos dados fez-se utilizando ANOVA Hierárquica, "Repeated Measures ANOVA", testes-t emparelhados e regressão múltipla. Observou-se que a herbivoria provocada pelas larvas de insectos afectou negativamente o número de ramificações e o comprimento dos ramos, sendo em termos absolutos menos afectada a população costeira da "Manhenha" e mais afectada a população do "Caiado". Não se notou uma relação entre a herbivoria e número de ramificações num módulo de ramos o que pode estar relacionado com o facto de um módulo de ramos saudável se desenvolver mais rápido do que um módulo danificado, num novo módulo por expansão. Encontrou-se ainda uma cena variabilidade dentro de cada população e alguma evidência de tolerância da planta à herbivoria pelos insectos. Discute-se as implicações dos resultados em termos da resposta da planta à herbivoria em cenário de competição e impacto das forças da seleção natural. Finalmente discute-se as consequências dos resultados em termos de conservação e gestão dos habitats.
- Efficiency of sampling methods and effort to assess arthropod diversity in Azorean native forestsPublication . Gaspar, Clara; Cardoso, Pedro; Borges, Paulo A. V.; Gaston, Kevin J.The BALA project (Biodiversity of Arthropods of Laurisilva of the Azores) is a research initiative to quantify the spatial distribution of arthropod biodiversity in native forests of the Azores archipelago. Arthropods were collected using a combination of two techniques, targeting epigean (ground dwelling) and canopy (arboreal) arthropods: pitfall traps (with Turquin and Ethylene solutions) and beating samples (using the three most dominant plant species). A total of 109 transects distributed amongst 18 forest fragments in seven of the nine Azorean islands were used in this study. The performance of alternative sampling methods and effort were tested. No significant differences were found in the accumulated number of species captured whether an alternative method was used or whether another transect with similar effort was established in another location within the same fragment. A combination of Ethylene and Turquin traps captured more species per individual, Turquin and beating captured more species per sample, and Turquin captured more species per unit time. An optimization exercise was performed and we found that the protocol applied during recent years is very close to optimal, allowing its future replication with confidence. The minimum combinations of sampling effort and methods, in order to monitor or to inventory diversity, taking into account different proportions of sample completeness are discussed.
- Evaluating the performance of species richness estimators: sensitivity to sample grain sizePublication . Hortal, Joaquín; Borges, Paulo A. V.; Gaspar, Clara1. Fifteen species richness estimators (three asymptotic based on species accumulation curves, 11 nonparametric, and one based in the species-area relationship) were compared by examining their performance in estimating the total species richness of epigean arthropods in the Azorean Laurisilva forests. Data obtained with standardized sampling of 78 transects in natural forest remnants of five islands were aggregated in seven different grains (i.e. ways of defining a single sample): islands, natural areas, transects, pairs of traps, traps, database records and individuals to assess the effect of using different sampling units on species richness estimations. 2. Estimated species richness scores depended both on the estimator considered and on the grain size used to aggregate data. However, several estimators (ACE, Chao1, Jackknife1 and 2 and Bootstrap) were precise in spite of grain variations. Weibull and several recent estimators [proposed by Rosenzweig et al. (Conservation Biology, 2003, 17, 864-874), and Ugland et al. (Journal of Animal Ecology, 2003, 72, 888-897)] performed poorly. 3. Estimations developed using the smaller grain sizes (pair of traps, traps, records and individuals) presented similar scores in a number of estimators (the above-mentioned plus ICE, Chao2, Michaelis-Menten, Negative Exponential and Clench). The estimations from those four sample sizes were also highly correlated. 4. Contrary to other studies, we conclude that most species richness estimators may be useful in biodiversity studies. Owing to their inherent formulas, several nonparametric and asymptotic estimators present insensitivity to differences in the way the samples are aggregated. Thus, they could be used to compare species richness scores obtained from different sampling strategies. Our results also point out that species richness estimations coming from small grain sizes can be directly compared and other estimators could give more precise results in those cases. We propose a decision framework based on our results and on the literature to assess which estimator should be used to compare species richness scores of different sites, depending on the grain size of the original data, and of the kind of data available (species occurrence or abundance data).
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