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This paper revisits various hypotheses about oligarchic patterns in Amazonian tree communities put forward by Pitman et al. (2001). Together, these hypotheses predict that most lowland sites in the Amazon are located within large patches of relatively homogeneous edaphic and other environmental conditions, where an oligarchy of common, frequent tree species accounts for a majority of trees. To assess the degree to which these hypotheses have been corroborated or refuted over the last ten years, we reviewed > 200 studies published since 2001. We found overwhelming support for the hypo thesis that large-scale oligarchies of common and frequent species are a common feature of Amazonian tree communities. At least 22 studies have documented oligarchies in Amazonian woody plant communities to date, and no studies have looked for oligarchies as defined by Pitman et al. (2001) and failed to find them. We argue that six publications that offer critiques of the oligarchy hypothesis do not constitute valid tests. The other hypotheses in Pitman et al. (2001)- one regarding the specific oligarchic taxa that dominate forests near the eastern base of the Andes and one that attempts to explain why oligarchic species exist - are less well supported by the literature, in large part because they have not been subjected to many tests. We discuss links between these hypotheses and other well-known patterns and hypotheses in ecology (the abundance-occupancy relationship, the Janzen-Connell hypothesis, the niche-environment hypothesis, and the niche breadth hypothesis), and provide additional detail to facilitate rigorous tests in the future. The paper concludes by presenting remote sensing evidence that large patches of relatively homogeneous environmental conditions account for most of the upland forest landscape across Amazonian Peru. [ABSTRACT FROM AUTHOR]

The Bemisia tabaci complex in Ecuador was studied with respect to phylogenetic relationships and eco-geographical distribution. Whitefly samples were collected from natural and agricultural environments in nine provinces of Ecuador (latitude, 2°N–5°S; longitude, 78°–81°W). Mitotypes were identified based on phylogenetic analysis of the 30-mtCOI-tRNAleuregion (832 bp) and corrected pairwise distance analysis. The distribution of mitotypes was modeled using MaxEnt, and their predicted niches were characterized according to environmental gradients. Four B. tabacimitotypes were identified, of which three are endemic, herein ECU1–3, and the other is the introduced B mitotype. Mitotypes ECU1 (44%), ECU2 (0.74%), and ECU3 (1.47%) grouped in the American Tropics (AMTROP) species and diverged by as much as 10%, which was higher than previous estimates for the AMTROP clade of 7–8.6%. Although haplotypes of ECU1 and ECU2 are known from the American Tropics, this is the first report of the ECU3 mitotype, which may possibly be restricted to southern Ecuador. The distribution of the three ECU-endemic mitotypes spanned the high-altitude niches of the western slope of the Andes, rich in microclimates with variable temperature and humidity conditions. The non-endemic B mitotype (47%) occurred only in the irrigated cropping systems located in hot and/or dry-tropical ecological niches. Of the endemic mitotypes, ECU1 occupied the most ecological niches. Among variables contributing to ECU1 and B mitotype niche range assignments, the most significant to influence ecological range was rainfall. The B. tabaciendemic to Ecuador were more diverse with respect to mtCOI-tRNAleu sequence than previously known, and occupied distinct microclimate niches suggestive of ecological resilience. [ABSTRACT FROM AUTHOR]

• In alpine habitats, positive interactions among plants tend to increase with elevation as a result of altitudinal increase in environmental harshness. However, in mountains located in arid zones, lower elevations are also stressful because of scarce availability of water, suggesting that positive interactions may not necessarily increase with elevation. • Here we analysed the spatial association of plant species with the nurse cushion plant Laretia acaulis at two contrasting elevations, and monitored the survival of seedlings of two species experimentally planted within and outside cushions in the semiarid Andes of central Chile. • Positive spatial associations with cushions were more frequent at lower elevations. Species growing at the two elevations changed the nature of their association with cushions from neutral or negative at higher elevations to positive at lower elevations. Survival of seedlings was higher within cushions, particularly at lower elevations. • The increased facilitation by cushions at lower elevations seems to be related to provision of moisture. This result suggests that cushion plants play a critical role in structuring alpine plant communities at lower elevations, and that climatic changes in rainfall could be very relevant for persistence of plant communities. [ABSTRACT FROM AUTHOR]