Beta-diversity, defined as spatial replacement in species composition, is crucial to the understanding of how local communities assemble. These changes can be driven by environmental or geographic factors (such as geographic distance), or a combination of the two. Spiders have been shown to be good indicators of environmental quality. Accordingly, spiders are used in this work as model taxa to establish whether there is a decrease in community similarity that corresponds to geographic distance in the grasslands of the Campos & Malezales ecoregion (Corrientes). Furthermore, the influence of climactic factors and local vegetation heterogeneity (environmental factors) on assemblage composition was evaluated. Finally, this study evaluated whether the differential dispersal capacity of spider families is a factor that influences their community structure at a regional scale. Spiders were collected with a G-Vac from vegetation in six grassland sites in the Campos & Malezales ecoregion that were separated by a minimum of 13 km. With this data, the impact of alpha-diversity and different environmental variables on the beta-diversity of spider communities was analysed. Likewise, the importance of species replacement and nesting on beta-diversity and their contribution to the regional diversity of spider families with different dispersion capacities was evaluated. The regional and site-specific inventories obtained were complete. The similarity between spider communities declined as the geographic distance between sites increased. Environmental variables also influenced community composition; stochastic events and abiotic forces were the principal intervening factors in assembly structure. The differential dispersal capacity of spider groups also influenced community structure at a regional scale. The regional beta-diversity, as well as species replacement, was greater in high and intermediate vagility spiders; while nesting was greater in spiders with low dispersion capacity. Geographic distance, among other factors (climate, and active and passive dispersion capacity), explains assembly structure and the decrease spider community similarity between geographically distant sites. Spiders with the highest dispersal capacity showed greater species replacement. This may be due to the discontinuity (both natural and anthropic) of the grasslands in this ecoregion, which limits the dispersal capacity of these spiders, and their close dependence on microhabitats. The dispersal capacity of the least vagile spiders is limited by geographic distance and biotic factors, such as competition, which could explain the nesting observed between their communities.

This study examined arthropod community patterns over an altitudinal ecoregional zonation that extended through three ecoregions (Yungas, Monte de Sierras y Bolsones, and Puna) and two ecotones (Yungas-Monte and Prepuna) of Northwestern Argentina (altitudinal range of 2,500 m), and evaluated the abiotic and biotic factors and the geographical distance that could influence them. Pitfall trap and suction samples were taken seasonally in 15 sampling sites (1,500–4,000 m a.s.l) during one year. In addition to climatic variables, several soil and vegetation variables were measured in the field. Values obtained for species richness between ecoregions and ecotones and by sampling sites were compared statistically and by interpolation–extrapolation analysis based on individuals at the same sample coverage level. Effects of predictor variables and the similarity of arthropods were shown using non-metric multidimensional scaling, and the resulting groups were evaluated using a multi-response permutation procedure. Polynomial regression was used to evaluate the relationship between altitude with total species richness and those of hyperdiverse/abundant higher taxa and the latter taxa with each predictor variable. The species richness pattern displayed a decrease in species diversity as the elevation increased at the bottom wet part (Yungas) of our altitudinal zonation until the Monte, and a unimodal pattern of diversity in the top dry part (Monte, Puna). Each ecoregion and ecotonal zone evidenced a particular species richness and assemblage of arthropods, but the latter ones displayed a high percentage of species shared with the adjacent ecoregions. The arthropod elevational pattern and the changes of the assemblages were explained by the environmental gradient (especially the climate) in addition to a geographic gradient (the distance of decay of similarity), demonstrating that the species turnover is important to explain the beta diversity along the elevational gradient. This suggests that patterns of diversity and distribution of arthropods are regulated by the dissimilarity of ecoregional environments that establish a wide range of geographic and environmental barriers, coupled with a limitation of species dispersal. Therefore, the arthropods of higher taxa respond differently to the altitudinal ecoregional zonation.

RESUMEN Se conoce poco sobre la biología y la ecología de la especie mirmecófaga Leprolochus birabeni Mello-Leitão, 1942 (Zodariidae), el único representante de este género en la Argentina. Esta especie es típica de ambientes áridos del norte del país, y su estudio en el Chaco Seco es relevante, por ser una ecorregión altamente perturbada con uno de los pocos bosques subtropicales secos del mundo. El objetivo de este trabajo es estudiar la demografía de la especie teniendo en cuenta su variación estacional en ambientes nativos, y sí la ganadería y la agricultura, dos de las actividades antropogénicas más comunes de la ecorregión Chaco Seco en la provincia de Salta (Argentina) producen cambios en sus poblaciones. Se consideraron tres tipos de ambientes: nativo (NA); afectados por el ganado vacuno y caprino (NP); y afectados por la agricultura (NC). Este último correspondió a parches de vegetación nativa en medio de una matriz agrícola. En cada tipo de ambiente se consideraron tres sitios de muestreo donde se realizaron muestreos estacionales utilizando trampas de caída durante el otoño, invierno y primavera de 2006 y el verano de 2007. Se recolectaron 549 ejemplares de L. birabeni , siendo la mayoría juveniles con el 64,12% de la abundancia total, seguidos por machos (26,41%) y hembras (9,47%). A nivel de paisaje, la primavera presentó el mayor número de individuos, llegando al 44,99% de la abundancia total; mientras que el otoño mostró el porcentaje más bajo (7,83%). El incremento de los juveniles durante el invierno podría indicar una adaptación de los estadios de desarrollo a las condiciones ambientales. El mismo patrón se observó en ambientes NA y NC, pero no en los NP. Estos últimos mostraron una disminución en la abundancia de adultos a lo largo del año; mientras que las poblaciones NC mostraron un incremento en la abundancia de los machos durante la primavera, con una fuerte reducción de las hembras y los juveniles durante todo el año. La abundancia de L. birabeni en ambientes NA fue mayor (41,06% de la abundancia total), siendo los valores mínimos registrados en NC (24,67%). Las dos actividades antropogénicas más comunes que afectan al Chaco Seco de la provincia de Salta modifican tanto los cambios estacionales como la representación de las diferentes etapas de desarrollo y sexos de las poblaciones nativas de L. birabeni , siendo la modificación de los ambientes nativos por la agricultura, el factor más perjudicial.

Argentine tardigrades are relatively unknown and, in many cases, unstudied; in the province of Salta in northwestern Argentina the lone record of tardigrade dates to the 1980s. Here, we evaluate and compare tardigrade diversity in natural habitats (N), urban environments (U) and rural communities (R) of Yungas. This work seeks to verify the existence of a reduction in tardigrade diversity outside their native habitats and if there is a biotic homogenization in the urban communities. Tardigrade community assemblages were compared between habitats using non-metric multidimensional scaling and a multi-response permutation procedure. Beta diversity was analysed in its component parts, species turnover and nesting, using a modified Raup-Crick test. Gamma diversity was divided into alpha and several beta levels. In total, 2080 eutardigrade and heterotardigrade specimens were registered and showed differences in tardigrade assemblages between habitats; the most diverse habitat was R. The beta diversity partition showed a nesting pattern in the U communities, highlighting faunal homogenization, while species turnover was key in the R and N communities. There was species loss from N to U communities, most markedly between R and U; various forces (both stochastic and deterministic) influence the structure of these communities.

Abstract:We report new records of pholcid species for northern Argentina.

Summary Approximately 80% of neotropical forests are subject to unsustainable economic practices, such as logging. Spiders are a megadiverse taxonomic group with a particularly great diversity in forest ecosystems and could help indicate the sustainability of logging operations. At six sites at 400–700 m altitude in the piedmont forest of north-western Argentina, spiders collected using pitfall traps and forest structure and spider assemblage structure variables were quantified in order to examine the association between them and to identify indicator spider families. Logging changes forest structure and seems to generate an unsuitable habitat for spiders associated with mature forests. The family taxonomic level is a good surrogate for spider morphospecies. The Mysmenidae, Nemesiidae, Theridiidae, Pholcidae, Hahniidae and Tetragnathidae families were associated with upper canopy cover of 20% or more and with more than two dead fallen trees per 0.1 ha and >15 live trees per 0.1 ha, found in unlogged forests. Bearing in mind that the piedmont forest of north-western Argentina is being logged in the absence of sustainability criteria, we suggest including spiders in monitoring schemes to complement the information obtained from more readily used groups, such as charismatic vertebrates.

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