Effect of river size on Amazonian primate community structure: a biogeographic analysis using updated taxonomic assessments

The mechanisms that underlie the diversification of Neotropical primates remain contested. One mechanism that has found support is the riverine barrier hypothesis (RBH), which postulates that large rivers impede gene flow between populations on opposite riverbanks and promote allopatric speciation. Ayres and Clutton‐Brock (1992) demonstrated that larger Amazonian rivers acted as barriers, delineating the distribution limits of primate species. However, profound changes in taxonomy and species concepts have led to the proliferation of Neotropical primate taxa, which may have reduced support for their results. Using the most recent taxonomic assessments and distribution maps, we tested the effect of increasing river size on the similarity of opposite riverbank primate communities in the Amazon. First, we conducted a literature review of primate taxonomy and developed a comprehensive spatial database, then applied geographical information system to query mapped primate ranges against the riverine geography of the Amazon watershed to produce a similarity index for opposite riverbank communities. Finally, we ran models to test how measures of river size predicted levels of similarity. We found that, almost without exception, similarity scores were lower than scores from Ayres and Clutton‐Brock (1992) for the same rivers. Our model showed a significant negative relationship between streamflow and similarity in all tests, and found river width significant for the segmented Amazon, but not for multiple Amazon watershed rivers. Our results support the RBH insofar as they provide evidence for the prediction that rivers with higher streamflow act as more substantial barriers to dispersal, and accordingly exhibit greater variation in community composition between riverbank

@erasmus.it

@erasmus.it è un manuale di lingua italiana per studenti universitari di livello principiante, che propone situazioni di vita universitaria. L'approccio scelto, centrato sullo studente, intende favorire lo sciluppo delle abilità comunicative

Catalysis by palladium salts

A study has been made of the reductive carbonylation of 2,4-dinitrotoluene (2,4-DNT) to 2,4-diisocyanotoluene (2,4-TDI) with catalysis either by [Pd(isoquinoline)2], in the presence of Fe2O3 and MoO3 or of Fe2(MoO4)3 as cocatalysts, or by Pdo complexes without cocatalysts. In the case of catalytic systems based upon [Pd(isoquinoline)2Cl2] the reaction can be carried out at about 200\ub0C and under 200 atm of CO to produce 2,4-TDI with high conversions and acceptable selectivities. Pd0 complexes as catalysts good conversions can be achieved at much lower temperatures (100-120\ub0 C) but with a low selectivity when a higher pressure of CO is used (300 atm or more). An investigation of the reductive carbonylation of nitrobenzene to phenylisocyanate as a model system, together with a study of the thermal stability of [Pd(isoquinoline)2Cl2] in the presence of CO, has provided evidence that the actual active catalyst could be a reduced (probably zerovalent) form of palladium stabilised by the nitroaromatic substrate or by some of the products formed from it as ligands