Economic and demographic trends of municipalities in South Africa: An application of Zipf’s rule

There are vast differences among South African local municipalities, with a limited number of large municipalities (both in terms of population size and economic activity) and a seemingly disproportionate number of intermediate-sized and small municipalities. No clear systematic national approach has yet been adopted to assess the distribution of core variables at municipal level in South Africa. Zipf’s rule, which postulates a consistent regularity in the size and rank of cities, is applied to disaggregate the performance of South African local municipalities in terms of three variables (population, Gross Value Added and municipal income) within the overall national settlement pattern. The results indicate that the Zipf rank size rule distribution is applicable to municipal level population data in South Africa, but less so for Gross Value Added and municipal income. The position and relative changes of municipalities along the Zipf curve between 2001 and 2011 also provide plausible indications of potential future trajectories of the three variables classified according to the dominant settlement typology within each municipality. The results also emphasise the significant conceptual limitations when using only legally defined administrative municipal boundaries for analysis purposes without also considering economically functional boundaries.&nbsp

Bancos de semillas en dos estadios sucesionales de bosque andino en el noreste de Colombia

"Background: Soil seed banks play an important role in post-disturbance regeneration and succession of species from different successional stages. Questions: 1) What is the most effective method for determining the composition and structure of the soil seed bank of Andean forests? 2) What is the composition and structure of soil seed banks in old-growth forest and shrubland sites in the Andean montane tropical forest of the North Santander region of Colombia? Study site: Andean forest, Pamplona, Colombia Methods: We surveyed the soil seed bank in two successional stages of Andean forest and examined its structure using two sampling methods: direct separation and germination. Results: Soil seed bank density was higher (18-fold in old-growth forest and 666-fold in shrubland) with the direct separation method than with germination; however, under the germination method, we found four species that we did not detect through the direct separation method. Soil seed banks from shrublands were mainly dominated by species from disturbed areas (91 %), while those from the old-growth forest presented early, intermediate and late species; e.g., Miconia summa, Myrsine dependens and Solanum sp., respectively. In the old-growth forest (especially for late species), density increased with depth. This pattern was not observed in shrubland. Seeds obtained by using the direct separation method presented low (< 7 %) viability. Conclusion: We consider the two methods to be complementary and recommend the use of both for a thorough characterization of soil seed banks from Andean forests. At different successional stages in the Colombian Andean forest, the soil seed bank may contain early, intermediate and late species, and it therefore plays an important role in the regeneration of this threatened ecosystem.""Antecedentes: Los bancos de semillas del suelo juegan un papel importante en la regeneración de especies de diferentes etapas de sucesión. Preguntas: 1) ¿Cuál es el método más eficaz para la descripción de la composición y la estructura del banco de semillas del suelo de los bosques andinos? y 2) ¿Cómo es la composición y estructura de los bancos de semillas del suelo en un bosque primario y un matorral en el bosque andino en Colombia? Sitio de estudio: Bosque andino en Pamplona, Norte de Santander, Colombia Métodos: Se estudiaron el banco de semillas del suelo en dos etapas de sucesión de bosque andino y se examinó la estructura mediante dos métodos de muestreo: separación directa y la germinación. Resultados: La densidad del banco de semillas en el suelo fue mayor (18 veces en bosques primarios y 666 veces en matorral) con el método de separación directa que con el método de germinación; Sin embargo, bajo el método de germinación, se encontraron cuatro especies que no detectamos a través del método de separación directa. Los bancos de semillas de matorrales fueron dominados principalmente por especies de las áreas perturbadas (91 %), mientras que en el bosque primario se encontraron especies de estados sucesionales tempranos, intermedios y tardíos, por ejemplo, Miconia summa, Myrsine dependens y Solanum sp., respectivamente. En el bosque maduro (especialmente para las especies de estapas sucesionales tardías), la densidad aumenta con la profundidad. Este patrón no se observó en el matorral. Aunado a esto, las semillas obtenidas mediante el método de separación directa presentaron baja (7 % <) viabilidad. Conclusión: Consideramos que los dos métodos son complementarios y recomendamos el uso de las dos metodologías para una adecuada caracterización de los bancos de semillas del suelo de los bosques andinos. El banco de semillas del suelo puede contener especies de diferentes estadios sucesionales, por lo que tiene un papel importante en la regeneración del bosque andino de Colombia.

The commonness of rarity: Global and future distribution of rarity across land plants

A key feature of life’s diversity is that some species are common but many more are rare. Nonetheless, at global scales, we do not know what fraction of biodiversity consists of rare species. Here, we present the largest compilation of global plant diversity to quantify the fraction of Earth’s plant biodiversity that are rare. A large fraction, ~36.5% of Earth’s ~435,000 plant species, are exceedingly rare. Sampling biases and prominent models, such as neutral theory and the k-niche model, cannot account for the observed prevalence of rarity. Our results indicate that (i) climatically more stable regions have harbored rare species and hence a large fraction of Earth’s plant species via reduced extinction risk but that (ii) climate change and human land use are now disproportionately impacting rare species. Estimates of global species abundance distributions have important implications for risk assessments and conservation planning in this era of rapid global change

Microbial Community Dynamics and Assembly: Drinking Water Treatment and Distribution

The supply of safe drinking water is a necessity for our societies. The microbiological quality of drinking water is the most important measure of water quality directly related to public health risks from waterborne diseases. Despite the long history of water research, the processes controlling microbiological quality of drinking water remain elusive to both researchers and practitioners in the field of drinking water treatment and management, representing a critical but long standing knowledge gap. The microbial communities in drinking water systems may be influenced by multiple processes including the source water, treatment barriers, persistence to disinfection, as well as biofilm development and detachment throughout the distribution system. Previous efforts, however, are mostly limited to only one of these processes, leading to inconsistent results and incomplete understanding as expected. Taking advantages of high-throughput metagenomics tools, this research for the first time applied a systematic approach linking all relevant processes to the microbiological quality of drinking water. It is revealed that the core populations of the sampled drinking water microbial communities are dominated by Alphaproteobacteria and Betaproteobacteria affiliated to the families of Methylobacteriaceae, Sphingomonadaceae, Comamonadaceae, and Oxalobacteraceae. The characteristics of the source water and the disinfection step in the drinking water treatment process train are found to be the most important factors controlling the bacterial community structure in drinking water. Despite its potential in enhancing the removal of microbial contaminants, membrane filtration as an increasingly popular treatment alternative to rapid sand filtration is not shown to have impact differing from that of conventional rapid sand filtration on drinking water microbial communities. The compositions of drinking water microbial communities examined in this study were dominated by a few very abundant species followed by a long tail of rare species, which is well represented by the Zipf-Mandelbrot model, accounting for 90% of the total variances and revealing low niche diversity in drinking water and distribution systems. Findings from this research provide much needed insight into the processes shaping the microbial communities in drinking water and the knowledge base for the development of effective strategies for the control of microbial contaminants in drinking water