Nesta contribuição pretendemos avaliar a aplicação dos modelos RESTAN, "Relação entre o número de Espécies e o número de Táxones de Alto Nível", à fauna de artrópodes de vários habitats das ilhas dos Açores. Utilizámos várias bases de dados recentemente obtidas baseadas em amostragens estandardizadas de artrópodes epígeos do solo em florestas de áreas protegidas, artrópodes fitófagos e predadores de pastagens semeadas e semi-naturais e artrópodes da copa da árvore endémica Juniperus brevifolia. Os modelos RESTAN são aplicados não só usando dados puramente taxonómicos, mas igualmente agrupando os taxa em termos de estratégias ecológicas (e.g. herbívoros, predadores) e de colonização das ilhas (e.g. endémicos). Deste modo pensamos poder avaliar a aplicabilidade destes modelos em estudos de estrutura de comunidades e de conservação. Para os Açores, a aplicação dos modelos RESTAN constitui uma forma muito prática e eficaz de obter estimativas de diversidade. De facto, em todas as matrizes de dados analisadas a riqueza de espécies pode ser estimada eficazmente usando apenas a riqueza em géneros, sendo a relação linear. Ao nível da família, os modelos estimadores possuem um menor poder explicativo e são melhor explicados por uma função exponencial. O escalonamento de Reservas Florestais Naturais dos Açores em termos de biodiversidade de artrópodes endémicos pode ser efectuado usando informação taxonómica ao nível do género. A aplicação de métodos de estimativa rápida de biodiversidade fica assim facilitada, podendo usar-se parataxonomistas bem treinados para o processo de triagem do grande número de amostras geralmente necessárias em estudos ecológicos. Discute-se igualmente a aplicabilidade dos modelos RESTAN a dados de diversidade alfa, beta e gama.ABSTRACT: In this contribution we examine the predictive power of numbers of higher taxa (orders, families and genera) as surrogates of species richness ("RESTAN" models – models based on linear relationship between species and higher taxa numbers) for the Azorean arthropod fauna. Recently, two large entomological and ecological studies were performed in the Azores, using standardized sampling protocols to estimate the diversity of arthropods in grassland and native forests. We use datasets available from those studies to address a few technical questions: A. what is the impact of using several measures of diversity (alpha, gamma and beta species diversity; Shannon-Wiener index of diversity; Evenness) based on numbers of families and genera for canopy arthropods? For instance, could be predicted that values of beta-diversity decrease with the use of higher-taxa estimates. All the measures of diversity could be used, being the genera the best predictor; B. how well behave the RESTAN models for functional groups of species like grass-feeding and web-building spiders in grasslands? The predictive power of higher-taxa is low using web-building spiders, due to few families being envolved and some genera having many species locally represented; C. assuming at least one sample with no species then there will be also no highertaxa in that sample. Consequently, the curve of the relationship between highertaxa richness and species richness should be anchored to the origin (y= bx). What is the predictive value of this model in comparison with the linear (y =a + bx), log-log (log y = a + b log x) and exponential (y = A • e b x) models? The best fit was obtained with the linear model for the genus-species relationship, but the variables are not normally distributed and the log-log model should be preferable. For the family-species relationship the exponential model is the best. The linear model anchored to the origin (y =bx) has some statistical pitfalls and was of less predictive value; D. in conservation studies what is the predictive value of higher-taxa in ranking protected areas? We found that the numbers of arthropod genera could successfully rank the Natural Forest Reserves as well as numbers of species (using endemic species dataset). We found that in the Azores the predictions of species richness using higher-taxa are quite reasonable, mainly because of low levels of diversity. Therefore, costeffective studies could use only genera, since the species richness of arthropods could be predicted reasonably closely from their genus-level richness. Family and order-level data were less informative for all datasets. We suggest that in the Azores as a consequence of the low levels of species diversification with a great proportion of monospecific genera, the use of parataxonomists trained in genus-level identification could be appropriate for sorting large numbers of ecological samples
