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Se presenta una revisión de las 27 especies de Macrodactylus que habitan en los Estados Unidos y México, que incluye la descripción de seis especies nuevas: M. batesi n. sp. de la región de Cuautia, Jalisco; M. manantlecus n.sp. de la sierra de Manantlán, Jalisco; M. montanas n.sp. colectado en la reserva Huitepec, San Cristóbal de las Casas, Chiapas; M. pokornyanus n.sp. procedente de la región de Atlacomulco, estado de México; M. surianas n.sp. de la sierra de Atoyac, Guerrero; y M. carrilloi n.sp. de las montañas de Chiapas y Guatemala. Macrodactylus championi Bates se registra por primera ocasión para México. Se propone clasificarlas en cuatro grupos de especies denominados: Grupo I, "lineatus") Grupo II, "dimidiatus") Grupo III "virens"y Grupo IV "subspinosus". Se actualizan los datos sobre los huéspedes vegetales de casi todas las especies, y se incluyen claves para la identificación de todos los taxa indicados, con ilustraciones de las estructuras empleadas en la taxonomía del grupo, y comentarios sobre sus patrones de distribución en la Zona de Transición Mexicana.

Taxonomic distinctness combines species richness and phylogenetic diversity to detect changes in taxonomic structure. Most studies have reported on changes due to marine impacts, with little emphasis on habitat influences or freshwater systems. The composition and organizational structure of aquatic Coleoptera assemblages are susceptible to local influence, yet their colonization capacities suggest greater assemblage similarity over larger spatial scales. Surveys were conducted in two contrasting local streams (approximately 20 km apart), one intermittent with multiple stair-step cascades and intervening pools during the rainy season (and only pools during the dry season), and the other perennial with low gradient, in Hidalgo, Mexico. Published information from these initial surveys and their associated collections of adults were examined and the data converted to monthly presence/ absence data for analysis using taxonomic distinctness. Despite reported physicochemical differences between the streams, only the average monthly proportion of swimmer species was significantly higher in the intermittent stream where elmids and psephenids were largely missing due to the general absence of protective substrate and the presence of pools; higher taxonomic structure was not affected. Well-developed colonization capabilities and a widely distributed species pool likely reduced detectable differences between the stream assemblages. Although the average monthly value of Sorenson's Similarity Index for aquatic Coleoptera between both streams was low, differentiation was not achieved using taxonomic distinctness and presence/absence data.

The selection of the most appropriate model is essential to predict the potential species richness of a site or landscape. Species accumulation curves have been used as a basic tool for comparing richness when different sampling protocols have been applied. Among the parameters generated by these models the slope has been cited as an indicator of completeness without regard to a defined cut-off value. In this work, we fit 12 field data sets of aquatic Coleoptera (Hidalgo) and Odonata larvae (Michoacán) to 2 asymptotic models (Clench and Linear Dependence) in order to calculate the slopes at the maximum effort and relate them with efficiency. Then, the theoretical effort needed to achieve the 95% of the lists was calculated for each data set in order to get the theoretical slopes. The average slope value found was 0.01 with a variance of <0.001, so we propose this value as indicative of a list reaching 95% of completeness for data obtained from similar sampling protocols. Additionally, we propose the use of number of rare species as an additional criterion to evaluate the inventories completeness. The effect of different sampling intensity on fitted models and estimation of parameters and the importance of a cut-off slope value in asymptotic models as a criterion to evaluate completeness of biological inventories are discussed.

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