Latitudinal gradient of nestedness and its potential drivers in stream detritivores

Understanding what mechanisms shape the diversity and composition of biological assemblages across broad-scale gradients is central to ecology. Litter-consuming detritivorous invertebrates in streams show an unusual diversity gradient, with α-diversity increasing towards high latitudes but no trend in γ -diversity. We hypothesized this pattern to be related to shifts in nestedness and several ecological processes shaping their assemblages (dispersal, environmental filtering and competition). We tested this hypothesis, using a global dataset, by examining latitudinal trends in nestedness and several indicators of the above processes along the latitudinal gradient. Our results suggest that strong environmental filtering and low dispersal in the tropics lead to often species-poor local detritivore assemblages, nested in richer regional assemblages. At higher latitudes, dispersal becomes stronger, disrupting the nested assemblage structure and resulting in local assemblages that are generally more species-rich and non-nested subsets of the regional species pools. Our results provide evidence that mechanisms underlying assemblage composition and diversity of stream litter-consuming detritivores shift across latitudes, and provide an explanation for their unusual pattern of increasing α-diversity with latitude. When we repeated these analyses for whole invertebrate assemblages of leaf litter and for abundant taxa showing reverse or no diversity gradients we found no latitudinal patterns, suggesting that function-based rather than taxon-based analyses of assemblages may help elucidate the mechanisms behind diversity gradients

A multivariate analysis of water quality in lake Naivasha, Kenya

Water quality information in aquatic ecosystems is crucial in setting up guidelines for resource management. This study explores the water quality status and pollution sources in Lake Naivasha, Kenya. Analysis of water quality parameters at seven sampling sites was carried out from water samples collected weekly from January to June and biweekly from July to November in 2011. Principal component analysis (PCA) and cluster analysis (CA) were used to analyse the dataset. Principal component analysis showed that four principal components (PCA-1 to PCA-4) explained 94.2% of the water quality variability. PCA-1 and PCA-2 bi-plot suggested that turbidity in the lake correlated directly to nutrients and iron with close association with the sampling site close to the mouth of Malewa River. Three distinct clusters were discerned from the CA analysis: Crescent Lake, a more or less isolated crater lake, the northern region of the lake, and the main lake. The pollution threat in Lake Naivasha includes agricultural and domestic sources. This study provides a valuable dataset on the current water quality status of Lake Naivasha, which is useful for formulating effective management strategies to safeguard ecosystem services and secure the livelihoods of the riparian communities around Lake Naivasha, Keny

Land use and land cover changes on a tropical lake basin : the socioeconomic drivers and cascading impacts on hydrology and ecological system : powerpoint

Lake Naivasha experiences frequent lake level fluctuations despite being on the decline in the last three decades. The main possible cause has been postulated to be increased abstraction around the lake. However, land use land cover changes (LULC) in the basin may be impacting on the level fluctuations and decline. The LULC interfere with runoff, evapotranspiration, and infiltration conditions of a catchment. The frequent lake levels fluctuations resulting from LULC impact significantly on riparian vegetation productivity and species composition. In addition, it has impact on the aquatic ecosystem water quality especially in terms of turbidity. Lake Naivasha basin has experienced significant LULC transformations predominantly caused by socio-economic drivers. Implications of past, present and future patterns of socio-economic drivers of LULC is vital to the understanding of social, ecological and limnological functioning of the basin. These factors are proposed to impact on the entire hydrological regime of the lake. In this study we present first results of the Earth Observation Integrated Assessment (EOIA) project for the governance of Lake Naivasha basin using Interdisciplinary approach that applies GIS and RS towards the understanding of the dynamics of Lake Naivasha ecosystem