Epiphytic and epipelic diatoms were collected from six sites in the Njoro River, Kenya, during the dry season between January and March 1997. Diatom assemblage descriptors, such as composition, distribution, species diversity as well as diatom habitat preferences and growth-form guilds were considered. Human activities in the Njoro River watershed included small-scale livestock keeping, subsistence farming, horticultural farming, and canning activities; all these activities have polluted the river. The diatom assemblages found in the Njoro River resembled those of polluted European rivers. The diatom assemblages in the Njoro River comprised eight families and 60 species. Epiphytic diatoms were obtained from the fronds of Cladophora (Cladophoraceae) and the assemblages were richer in species than the epipelic assemblages. Nitzschia amphibia Grun. and Gomphonema parvulum (Ku¨tz.) Grun. were found, either epiphytically and/or epipelically, in all the six sites. Percent similarity index showed that Ng'iria and Beeston sites, and Magadi and Turkana sites, were site pairs that were more similar in diatom composition. Habitat preferences were consistently demonstrated by the diatoms, distributing themselves into epipelic, epiphytic, and/or a combination of these two. The dominant diatom growth-form guild in the Njoro River was the biraphid guild, with the adnate guild being dominant in Mary Joy site, which was frequently disturbed by domestic animals and riparian human communities for water and laundry. This work fills a significant gap in that there is virtually no available data on diatoms in Kenyan streams for comparison. It further emphasizes the importance of macroflora in diversifying habitats of organisms and also in enhancing diversity in streams. Further research on diatom composition, distribution and growth-form guilds in relation to low and high hydrologic regimes is needed to address the role of environmental variability on diatom ecology.
Miombo woodlands cover extensive areas in southern and southeastern Africa, but are under high anthropogenic pressure. A conspicuous feature of this ecosystem is the presence of high termitaria (>2 m high) built by fungus‐growing termites (Macrotermitinae).
Despite the fundamental role of termites in African ecosystems, miombo termite communities remain poorly known. We suspected high termitaria to play a structuring role for the whole termite assemblage of miombo woodlands in southern Burundi. In a formerly cleared area, in regeneration since 2009, we expected the termite assemblage to be highly impoverished. The newly growing termitaria of fungus growers might provide suitable bases for recolonisation by soil‐feeding species.
We recorded 25 species from more than 1000 termite samples. Fungus growers were abundant everywhere. In preserved miombo, high termitaria were home to secondary soil‐feeding termite species, seldom encountered in the matrix between mounds. Bushes growing on termitaria also sustained wood‐feeding species. The most remarkable feature of the assemblage was the high frequency and diversity of soil‐feeding soldierless Apicotermitinae, especially in the matrix. Besides scarce Coptotermes wood feeders, Macrotermitinae were the sole inhabitants of the regenerating area.
Our results emphasize the importance of high termitaria for particular soil‐feeding species and wood feeders associated with the vegetation growing on termitaria. They raise the question of the ecological factors allowing the coexistence of a rich assemblage of soldierless Apicotermitinae species in the nutrient‐poor matrix between mounds. The observations from regenerating miombo confirm the vulnerability of soil‐feeding termites to habitat degradation and provide baseline data for future studies of ecosystem restoration.
Drought is a natural phenomenon experienced by many intermittent and also seasonal lotic systems. It has diverse effects on the structure and distribution of biological communities through habitat transition from wetted to terrestrial conditions. The Njoro River, a tropical stream, was drought-stressed between late 1999 and mid 2000, providing an opportunity to sample and describe the distributional patterns of diatoms and Limnodrilus oligochaetes in the vertical sediment profile. The dispersion of Limnodrilus oligochaetes with sediment depth profile varied from quasi-random (i.e. exponent k of the negative binomial distribution >2.0 or <0) at the surface to strong aggregation (0 < k < 1.0) in the deeper sediments. Diatoms were heterogenous, with most species contributing less than 1% of all the diatoms collected from the riverbed. Contagious dispersion was a common feature among the diatom species. The distribution of Fragilaria ulna was largely quasi-random in all sites, with Nitzschia amphibia and Cocconeis placentula demonstrating quasi-random distribution in the Kerma vertical sediment profile. Escape from stranding to deeper sediment strata as the drought progressed was not a universal response among the diatom species. Our results showed that drought-stress altered the structure of biological assemblages and also emphasized the need for the management of tropical lotic systems and their catchments for flow permanence.
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