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Aim Our aim is to test if long-term patterns in α alpha and β beta diversity along an elevational transect on two aspects of a mountain are consistent through time using spiders as model organisms, quantify the role of elevation and time (seasonal and inter-annual) in explaining these patterns and partition the relative contribution of nestedness, species turnover and species loss in explaining these diversity patterns. Location The transect is across the Cederberg mountains in the Cape Floristic Kingdom, Western Cape, South Africa and is constituted by 17 sites with an elevational range of 1900 m on two aspects of the mountain (east and west). Methods Spider assemblages were sampled biannually (wet and dry seasons) over 6 years. Four replicates per site, each consisting of a 5 × 2 pitfall grid, were sampled for 5 days sessions. Generalized linear mixed models with Poisson error structure for species richness (alpha diversity), binomial error structure for beta diversity (Jaccard dissimilarity βcc and its partitioned components, β-3 and βrich), and Gaussian error structure for beta diversity values standardized by a null model ( SES) were used to model the effects of elevation and season on these two indices respectively. Results Although varying considerably between years, spider alpha diversity had a hump-shaped pattern on the western aspect and U-shaped on the eastern aspect. However, season interacted with elevation to produce more complex patterns during the dry season. There was no significant nestedness except for two instances on the western aspect. Replacement accounted for 60-70% of beta diversity between sites, and elevational distance decay in beta diversity was the result of increased turnover on the western aspect and increased species loss on the eastern aspect. Standardized patterns suggest that there are no effects of season on beta diversity except for a decreased distance decay during the dry season on the western aspect. Main conclusions Large-scale predictors of spider alpha diversity explained small amounts variation in spider diversity, pointing to the importance of local and stochastic processes. Regional turnover of spider diversity is mainly the result of niche processes, suggesting localized adaptation of taxa, further supported by the lack of nestedness in assemblages. [ABSTRACT FROM AUTHOR]

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1. Invasions by alien plants into unspoiled ecosystems are a cause for concern because the pristine systems are important stores of biodiversity. Indeed, the introduction of non-indigenous species into protected areas is a direct threat to conservation. Consequently, it is fundamental to document the impact that alien invasive plants have on native communities and to determine if, and at what rate, native communities re-establish following the removal of invasives. 2. Chromolaena odorata is one of the most important invader species in the savanna biome in South Africa. It reduces vegetation heterogeneity in grasslands, savannas and forests. 3. Spiders, as ecological indicators for change, were used to investigate the impact of (i) C. odorata invasions, (ii) C. odorata invasion durations, and (iii) the impact of clearing C. odorata on abundance, assemblage patterns, diversity and estimated species richness of spiders. 4. The progressive invasion of C. odorata with increasing invasion duration brings with it changes in native spider abundance, assemblage patterns, diversity and estimated species richness. Native spider assemblages do re-establish after clearing C. odorata without further management intervention. Small lingering differences are observed between the native and the cleared sites, suggesting that other features of the habitat may have been affected by the invasion and clearing. 5. Synthesis and applications. Alien clearance is an essential and invaluable management tool. There are a substantial number of programmes that aim to control alien invasive plants but very little is known about the way in which biodiversity recovers after alien plant removal. Our data show that the removal of alien invasive plants benefits biodiversity with immediate effects, highlighting that management should be carried out to control this invasive, even if the area has been invaded for a long period of time. These data are important for policy-forming and informing policy-makers that alien invasion and removal are critical for biodiversity conservation management. [ABSTRACT FROM AUTHOR]

Studies were conducted to assess the numerical response of ground-dwelling arthropods to a habitat management system (‘push–pull’) developed to control maize stemborers using spiders (Araneae) as an indicator group. In this cropping system, maize is intercropped with a stemborer moth-repellent (push) plant while an attractant trap crop (pull) is planted around this intercrop. Two study sites in western Kenya and one site at the Grain Crops Institute of the Agricultural Research Council in Potchefstroom, South Africa, were sampled. Treatments comprised a maize monocrop and an intercrop of maize and desmodium, Desmodium uncinatum Jacq., with Napier grass, Pennisetum purpureum (Schumach), as a trap crop around the field (‘push–pull’) in each site. Experiments were laid out in a completely randomized design with four replications at each site. Ground-dwelling spiders were sampled using a combination of pitfall traps and soil samples. A total of 2175 spiders, 78 species in 18 families, were recovered in Kenya and 284 spiders, 34 species in nine families, were recovered in South Africa. Lycosidae was the most abundant family, accounting for >50% of all individual spiders and 27.6% by species richness. Spiders were significantly more abundant at the Kenyan sites than in South Africa while species diversity was significantly higher in South Africa than at the Kenyan sites. At all sites, spider abundance was significantly higher in the ‘push–pull’ than in the maize monocrop plots. However, the overall spider diversity was only significantly higher in the ‘push–pull’ than in the maize monocrop plots in South Africa. Moreover, species dominance did not differ between the two cropping systems at all sites. The results showed that the ‘push–pull’ system evidently enhances overall abundance of spiders, illustrating its potential in further pest control in the maize agroecosystems where spiders may often be one of the most important predatory groups. [ABSTRACT FROM AUTHOR]

Copyright of Biotropica is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)