Photosynthesis and related physiological processes in two mangrove species,Rhizophora mucronata and Ceriops tagal,at Gazi Bay,Kenya

Measurements were carried out of the gas exchange properties (namely, photosynthesis, stomatal conductance and transpiration rates), water use efficiency and water relations of two mangrove species, Rhizophora mucronata and Ceriops tagal at Gazi Bay, Kenya. Rhizophora mucronata had significantly higher photosynthetic rates than C. tagal. Internal CO₂ concentrations were higher during the wet season than the dry season in both species. Gas exchange properties were correlated positively with photon flux density in both species. Leaf water potentials were highest during the morning and lowest at midday and were also highest in the lower canopy leaves in both species. The two mangrove species had conservative water use. Management potential for the East African mangroves based on the results of this study is suggested.     

Growth-inhibiting and larvicidal effects of Melia volkensii extracts on Aedes aegypti larvae

Extracts from dry Melia volkensii fruits contain growth-inhibiting activity against larvae of the mosquito Aedes aegypti. The active fraction may be eluted from silica gel using hexane-ethyl acetate (1:1, v:v). At a concentration of even 2 g/ml in water, this fraction prolongs larval instars. Mortality in treated larvae is high, especially during the moulting and melanisation processes. The LC₅₀ for larval mortality is 50 g/ml in 48 h. The active compound of this fraction is not identical with azadirachtin. It may be more potent as an insect growth-inhibitor and more lethal to Aedes larvae than azadirachtin.

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Zusammenfassung Samen von Melia volkensii wurden mit 80-proz. wäßrigem Methanol extrahiert und daraus das in reinem Methanol lösliche Material gewonnen. Dieses wurde dann mit Aceton erschöpfend digeriert. Der in Methanol und Aceton lösliche Anteil wurde über Kieselgel fraktioniert und mit Larven von Aedes aegypti auf wachstumshemmende bzw. toxische Wirkung getestet. Das von einem Hexan-Essig-ester (1:1, v:v)-Gemisch eluierte Material hat noch in einer Konzentration von 2 g/ml wachstumshemmende und mit einer LC₅₀ von 50 g/ml innerhalb von 48 Stunden larvicide Wirkung. Sein biologisch aktiver Bestandteil ist nicht mit einem der Azadirachtine aus Azadirachta indica identisch. Im Vergleich mit Azadirachtin ist er für die Larven von A. aegypti ein wesentlich potenterer Wachstumshemmer bei gleichfalls höherer Letalität.

     

Spatial Distributions of HIV Infection in an Endemic Area of Western Kenya: Guiding Information for Localized HIV Control and Prevention

HIV is still a major health problem in developing countries. Even though high HIV-risk-taking behaviors have been reported in African fishing villages, local distribution patterns of HIV infection in the communities surrounding these villages have not been thoroughly analyzed. The objective of this study was to investigate the geographical distribution patterns of HIV infection in communities surrounding African fishing villages. In 2011, we applied age- and sex-stratified random sampling to collect 1,957 blood samples from 42,617 individuals registered in the Health and Demographic Surveillance System in Mbita, which is located on the shore of Lake Victoria in western Kenya. We used these samples to evaluate existing antibody detection assays for several infectious diseases, including HIV antibody titers. Based on the results of the assays, we evaluated the prevalence of HIV infection according to sex, age, and altitude of participating households. We also used Kulldorff’s spatial scan statistic to test for HIV clustering in the study area. The prevalence of HIV at our study site was 25.3%. Compared with the younger age group (15–19 years), adults aged 30–34 years were 6.71 times more likely to be HIV-positive, and the estimated HIV-positive population among women was 1.43 times larger than among men. Kulldorff’s spatial scan statistic detected one marginally significant (P = 0.055) HIV-positive and one significant HIV-negative cluster (P = 0.047) in the study area. These results suggest a homogeneous HIV distribution in the communities surrounding fishing villages. In addition to individual behavior, more complex and diverse factors related to the social and cultural environment can contribute to a homogeneous distribution pattern of HIV infection outside of African fishing villages. To reduce rates of transmission in HIV-endemic areas, HIV prevention and control programs optimized for the local environment need to be developed.     

Irrigation scheme or mosquito hazard: a case study in Mwea Irrigation Scheme

A survey of the mosquito fauna in the Mwea-Tebere Irrigation Scheme in Kenya was conducted between 1984 and 1985. Two genera, Anopheles and Culex were found indoors in large numbers. The major species were Anopheles gambiae s.l., Anopheles pharoensis, and Culex quinquefasciatus, comprising 66% and 21% of the total catch, respectively. The large numbers of mosquitoes found resting indoors showed seasonal population fluctuations. The seasonal population increases observed were due to the availability of larval breeding conditions over a long period of time and to man-made environmental changes. These changes included irrigation canals and rice paddies. The irrigation canals and rice paddies were flooded from August till December, thus linking the flooding effects of the two rainy seasons. This enabled mosquitoes to breed continuously for up to 9 months per year.     

Nest survival in year‐round breeding tropical red‐capped larks Calandrella cinerea increases with higher nest abundance but decreases with higher invertebrate availability and rainfall

Nest survival is critical to breeding in birds and plays an important role in life‐history evolution and population dynamics. Studies evaluating the proximate factors involved in explaining nest survival and the resulting temporal patterns are biased in favor of temperate regions. Yet, such studies are especially pertinent to the tropics, where nest predation rates are typically high and environmental conditions often allow for year‐round breeding. To tease apart the effects of calendar month and year, population‐level breeding activity and environmental conditions, we studied nest survival over a 64‐month period in equatorial, year‐round breeding red‐capped larks Calandrella cinerea in Kenya. We show that daily nest survival rates varied with time, but not in a predictable seasonal fashion among months or consistently among years. We found negative influences of flying invertebrate biomass and rain on nest survival and higher survival of nests when nests were more abundant, which suggests that nest predation resulted from incidental predation. Although an increase in nest predation is often attributed to an increase in nest predators, we suggest that in our study, it may be caused by altered predator activity resulting from increased activity of the primary prey, invertebrates, rather than activity of the red‐capped larks. Our results emphasize the need to conduct more studies in Afro‐tropical regions because proximate mechanisms explaining nest predation can be different in the unpredictable and highly variable environments of the tropics compared with the relatively predictable seasonal changes found in temperate regions. Such studies will aid in better understanding of the environmental influences on life‐history variation and population dynamics in birds.     

An annotated checklist of mammals of Kenya

Kenya has a rich mammalian fauna. We reviewed recently published books and papers including the six volumes of Mammals of Africa to develop an up-to-date annotated checklist of all mammals recorded from Kenya. A total of 390 species have been identified in the country, including 106 species of rodents,104 species of bats, 63 species of even-toed ungulates(including whales and dolphins), 36 species of insectivores and carnivores, 19 species of primates,five species of elephant shrews, four species of hyraxes and odd-toed ungulates, three species of afrosoricids, pangolins, and hares, and one species of aardvark, elephant, sirenian and hedgehog. The number of species in this checklist is expected to increase with additional surveys and as the taxonomic status of small mammals(e.g., bats, shrews and rodents) becomes better understood.     

Positive interactions between nitrogen-fixing legumes and four different neighbouring species in a biodiversity experiment

The importance of facilitative processes due to the presence of nitrogen-fixing legumes in temperate grasslands is a contentious issue in biodiversity experiments. Despite a multitude of studies of fertilization effects of legumes on associated nonfixers in agricultural systems, we know little about the dynamics in more diverse systems. We hypothesised that the identity of target plant species (phytometers) and the diversity of neighbouring plant species would affect the magnitude of such positive species interactions. We therefore sampled aboveground tissues of phytometers planted into all plots of a grassland biodiversity–ecosystem functioning experiment and analysed their N concentrations, δ¹⁵N values and biomasses. The four phytometer species (Festuca pratensis, Plantago lanceolata, Knautia arvensis and Trifolium pratensis) each belonged to one of the four plant functional groups used in the experiment and allowed the effects of diversity on N dynamics in individual species to be assessed. We found significantly lower δ¹⁵N values and higher N concentrations and N contents (amount of N per plant) in phytometer species growing with legumes, indicating a facilitative role for legumes in these grassland ecosystems. Our data suggest that the main driving force behind these facilitative interactions in plots containing legumes was reduced competition for soil nitrate (“nitrate sparing”), with apparent N transfer playing a secondary role. Interestingly, species richness (and to a lesser extent functional group number) significantly decreased δ¹⁵N values, N concentrations and N content irrespective of any legume effect. Possible mechanisms behind this effect, such as increased N mineralisation and nitrate uptake in more diverse plots, now need further investigation. The magnitude of the positive interactions depended on the identity of the phytometer species. Evidence for increased N uptake in communities containing legumes was found in all three nonlegume phytometer species, with a subsequent strong increase in biomass in the grass F. pratensis across all diversity levels, and a lesser biomass gain in P. lanceolata and K. arvensis. In contrast, the legume phytometer species T. pratense was negatively affected when other legumes were present in their host communities across all diversity levels.     

The forgotten Grevy's zebra Equus grevyi population along the Kasigau Corridor ranches,SE Kenya: recent records and conservation issues

Since the 1970s, the globally endangered Grevy's zebra Equus grevyi has suffered a substantial reduction in range and population size. Grevy's zebra was introduced into the Tsavo ecosystem in two translocations: 22 individuals released in Tsavo East National Park in 1964 and 30 individuals released in Tsavo West National Park in 1977. This study focuses on the Tsavo East subpopulation within the Kasigau Corridor REDD+ Project Area. Data were collected from 2011 to 2014 using systematic and ad lib methods, while vegetation stratification was based on tonnes of CO₂e per hectare. Cumulatively, 785 Grevy's zebra were seen in 210 encounters. The largest single group comprised of 24 individuals; mean group size was 4 ± 3. Foals comprised 10% of all individuals seen and were recorded across most months, suggesting year‐round breeding. The range core for the Grevy's zebra in this area was estimated to be 400 km². Its density was estimated at 0.09 ± 0.038 individuals per km², translating to a population of 36 ± 15 individuals (range: 6–67) based on the estimated core range. Grasslands and sparse Acacia–Commiphora vegetation strata were used significantly more than expected. Despite constituting only about 2–3% of the global Grevy's zebra population, this subpopulation could still play a role as a – disconnected – reserve population.