Population pressure,labor availability,and agricultural disintensification: The decline of farming on Rusinga Island,Kenya

Despite a steady increase in population since the 1930s, farmers on Rusinga Island in Kenya have abandoned many traditional intensive agricultural practices, including the construction of hillside terraces. At the same time, low crop yields have led to a chronic shortage of food on the island. This paper, based on an analysis of archival materials and a detailed agronomic study of the farming system, analyzes the causes of this process of disintensification. Labor scarcity resulting from migrant wage employment and the growing importance of the fishing industry has been a major factor in the decline of agriculture on the island. The loss of soil conservation practices and serious weed infestations have contributed to the collapse of farm productivity. This study highlights the importance of understanding not only the local ecology but also the broader political and economic environment in order to explain farmers' decisions and the process of agricultural change.     

Population and agricultural intensity in the humid tropics

A review of models of agricultural intensification and their application to the agricultural systems of the humid tropics is presented. Taken into account are the distributions of these systems at various population densities, available data on labor efficiencies, the costs of establishing continuous cropping, and data regarding soils under cultivation and various types of fallow. The findings that fallows much longer than 10 or 15 years serve no known agronomic function, that given preindustrial technology, grass fallows are disadvantageous, even environmentally destructive, and that continuous cropping usually entails a considerable amount of environmental modification support the interpretations that agricultural intensification in the humid tropics is best understood in terms of ecologically optimal strategies at different population densities. Points needing further investigation are highlighted: the reasons for very long fallows, and the comparative labor efficiencies of fallow and continuous cropping systems where crops and environments are similar.     

Population status and feeding habits of the translocated sub-population of Hunter's antelope or hirola (Beatragus hunteri,Sclater, 1889) in Tsavo East National Park,Kenya

The population status and feeding habits of Hunter's antelope or hirola (Beatragus hunteri) in Tsavo East National Park were determined in this study in 1995. This is the first study that has ever been undertaken on the hirola population of about 20 animals that were translocated to Tsavo East National Park from South Garissa District in 1963. Relevant data and information were collected using different ecological research techniques. A total of eight nursery herds (5–11 individuals per herd) comprising 60 individuals, five lone bulls and 11 lone sub-adults was observed. This gave a total population estimate of 76 animals in the entire study area. Adult animals dominated the population (60.53%), indicating a population skew towards adults. The adult sex ratio was biased towards females (43.42%). Hirola were observed to feed mainly on short, green grasses. The dominant feed species were Panicum infestum, Digitaria rivae, Latipes senegalensis and Cenchrus ciliaris. Occasionally, hirola was observed to feed on forbs (e.g. Portulaca oleraceae, Tephrosia subtriglora and Commelina erecta). Results of this study show that the population growth of the hirola sub-population in the Park has been low (1.8 individuals per year). Factors thought to contribute to this low growth include predation and low genetic variability.     

Descent Group Composition and Population Pressure in a Fringe Enga Clan, Papua New Guinea

Genealogical data, land clearance patterns, and garden inheritance histories from a patrilineal clan in the Highlands of Papua New Guinea are used to reconstruct population size and agrarian resources for the descent group over a period of 170 years. The resulting analysis reveals a strong relationship between fluctuations in population pressure on agrarian resources and changes in the composition of social groups that in turn accelerates change, then regulates it. Two quantitative relationships show that numbers of outsiders incorporated into the group and their kinship distance both covary closely with pressure on land as measured by an occupational density index.     

Drought and recovery: Livestock dynamics among the Ngisonyoka Turkana of Kenya

From 1980–1985, the Turkana District of Kenya experienced both drought and above average rainfall. The effects of a 2-year drought on the livestock population of the nomadic pastoral Ngisonyoka are discussed. Detailed data on mortality rates and offtake are presented for the animals of four herd owners, and the recovery process is followed for the 5-year period for one herd owner. It is concluded that during the drought, 63% of the cattle, 45% of the camels, and 55% of the small stock left the sample herds. The livestock population of one herd had recovered to pre-drought levels 3 years after the drought.     

Seaweeds of potential economic importance in Kenya: field survey and future prospects

Kenya is a net importer of agar and alginate based on recent government statistics, although it may have the potential to be self-sufficient or even an exporter of these phycocolloids. There is little information on carrageenan importation into Kenya since government statistics incorporate it as agar. Seaweeds are relatively unimportant in the Kenyan diet since they are consumed rarely by coastal people. A survey of 15 sites along of the Kenyan coast evaluated the potential for harvesting seaweeds and for establishing seaweed farms. Gracilaria appears to comprise the bulk of the low grade agar import, even though local species of this genus are widely distributed along the Kenyan coast. Major populations of Gelidium may be a potential source of high quality bacteriological grade agar. Eucheuma may be farmed locally to support the increasing local and regional demands for carrageenan. Recommendations for a national program of management and production for Kenya will be discussed.     

Consumption of Domestic Cat in Madagascar: Frequency,Purpose, and Health Implications

ABSTRACT

The domestic cat Felis catus has a long history of interaction with humans, and is found throughout the world as a household pet and a feral animal. Despite people's often sentimental association with cats, cat meat is sometimes consumed by them; this practice can have important implications for public health. In Madagascar, a least developed country that has experienced recent political instability, cat consumption is known to occur, but remains poorly understood. To improve our understanding of cat consumption practices in Madagascar we interviewed 512 respondents in five towns. We used semi-structured interviews to: 1) clarify the preference for, and prevalence, correlates, and timing of, cat consumption; 2) describe methods used to procure cats for consumption; 3) identify motives for consuming cat meat; and, 4) evaluate to what extent patterns of cat-meat consumption are influenced by taboos. We found that, although cat was not a preferred source of meat, many (34%) Malagasy respondents had consumed cat meat before, with most (54%) of these indicating such consumption occurred in the last decade. We did not detect a link between consumption of cat meat and recent access to meat (a proxy for food security). Cat meat was almost never purchased, but rather was obtained when the owners consumed their own pet cat, as a gift, or by hunting feral cats. Cat meat was usually consumed in smaller towns following cat–human conflict such as attacks on chickens, but in the large capital city, cat meat was procured primarily from road-killed individuals. These results suggest cat-meat consumption is typically an opportunistic means to obtain inexpensive meat, rather than principally serving as a response to economic hardship. These results further suggest cat handling and consumption may present a potential pathway for transmission of several diseases, including toxoplasmosis, that may warrant heightened public health efforts.     

Food security: contributions from science to a new and greener revolution

There is an intrinsic link between the challenge we face to ensure food security through the twenty-first century and other global issues, most notably climate change, population growth and the need to sustainably manage the world''s rapidly growing demand for energy and water. Our progress in reducing global poverty and achieving the Millennium Development Goals will be determined to a great extent by how coherently these long-term challenges are tackled. A key question is whether we can feed a future nine billion people equitably, healthily and sustainably.Science and technology can make a major contribution, by providing practical solutions. Securing this contribution requires that high priority be attached both to research and to facilitating the real world deployment of existing and emergent technologies. Put simply, we need a new, ‘greener revolution’. Important areas for focus include: crop improvement; smarter use of water and fertilizers; new pesticides and their effective management to avoid resistance problems; introduction of novel non-chemical approaches to crop protection; reduction of post-harvest losses; and more sustainable livestock and marine production. Techniques and technologies from many disciplines, ranging from biotechnology and engineering to newer fields such as nanotechnology, will be needed.     

Significance of Population Size on the Fixation of Nonsynonymous Mutations in Genes Under Varying Levels of Selection Pressure

Previous studies observed a higher ratio of divergences at nonsynonymous and synonymous sites (ω = d_N/d_S) in species with a small population size compared to that estimated for those with a large population size. Here we examined the theoretical relationship between ω, effective population size (N_e), and selection coefficient (s). Our analysis revealed that when purifying selection is high, ω of species with small N_e is much higher than that of species with large N_e. However the difference between the two ω reduces with the decline in selection pressure (s → 0). We examined this relationship using primate and rodent genes and found that the ω estimated for highly constrained genes of primates was up to 2.9 times higher than that obtained for their orthologous rodent genes. Conversely, for genes under weak purifying selection the ω of primates was only 17% higher than that of rodents. When tissue specificity was used as a proxy for selection pressure we found that the ω of broadly expressed genes of primates was up to 2.1-fold higher than that of their rodent counterparts and this difference was only 27% for tissue specific genes. Since most of the nonsynonymous mutations in constrained or broadly expressed genes are deleterious, fixation of these mutations is influenced by N_e. This results in a higher ω of these genes in primates compared to those from rodents. Conversely, the majority of nonsynonymous mutations in less-constrained or tissue-specific genes are neutral or nearly neutral and therefore fixation of them is largely independent of N_e, which leads to the similarity of ω in primates and rodents.     

Occurrence of Bondar's Nesting Whitefly,Paraleyrodes bondari (Hemiptera: Aleyrodidae), on cassava in Uganda

Cassava is a valued calorific source to millions of Africans who eat it daily and a vital staple for their food security. One of the key constraints to this crop is whiteflies which are both a vector of viral diseases and a direct pest. Although the African cassava whitefly is known to cause physical damage on cassava with considerable tuberous yield loss, a recent whitefly outbreak caused unusually severe damage, which prompted the current reported investigation. Molecular identification of whitefly adults sampled from the affected cassava field revealed the presence of a new whitefly species, Paraleyrodes bondari. This communication is the first report of the occurrence of P. bondari on cassava in Uganda.     

Habitat associations and breeding success of yellowhammers on lowland farmland

1.  Yellowhammers began to decline on British lowland farmland in the late 1980s and losses are presently 10% per year. This study examined variation in the habitat selection and breeding success of yellowhammers, allowing an evaluation of whether Britain's yellowhammer decline might have been caused by recent changes in agriculture.
2.  Yellowhammer territories were associated with hedgerows, vegetated ditches and wide uncultivated grassy margins around fields. Pasture and silage leys were avoided. Nests were built among herbaceous vegetation in ditches or in the shrubby vegetation of hedgerows.
3.  Breeding started slightly earlier on organic farms than on intensively managed farms, but no measure of breeding success differed between farm types. Predation was the cause of most (64%) nest failures. A maximum of three breeding attempts (two successful) was observed per pair, with a mean clutch size of 3·3, a Mayfield nest success rate of 0·46, and 2·6 nestlings fledged per successful brood. These data, together with published estimates of adult yellowhammer survival and of post-fledging survival among other passerines, suggest that breeding productivity is too low to maintain a stable population.
4.  The removal of hedgerows or abandonment of hedge management, filling or clearing of ditches, intensification of grassland management and cropping or grazing right up to the field edge, are all likely to have adversely affected yellowhammers on lowland farmland in southern England. Policy reforms that redirect subsidy support to environmentally beneficial management of field margin habitats and retention of winter-feeding sites such as stubbles should assist in restoring populations of breeding yellowhammers on lowland farmland.
5.  Our data expand further the array of farmland bird species for which interactions between agricultural change and population change are increasingly understood.     

Paleogeographic variations of pedogenic carbonate delta13C values from Koobi Fora, Kenya: implications for floral compositions of Plio-Pleistocene hominin environments

Plio-Pleistocene East African grassland expansion and faunal macroevolution, including that of our own lineage, are attributed to global climate change. To further understand environmental factors of early hominin evolution, we reconstruct the paleogeographic distribution of vegetation (C(3)-C(4) pathways) by stable carbon isotope (delta(13)C) analysis of pedogenic carbonates from the Plio-Pleistocene Koobi Fora region, northeast Lake Turkana Basin, Kenya. We analyzed 202 nodules (530 measurements) from ten paleontological/archaeological collecting areas spanning environments over a 50-km(2) area. We compared results across subregions in evolving fluviolacustrine depositional environments in the Koobi Fora Formation from 2.0-1.5 Ma, a stratigraphic interval that temporally brackets grassland ascendancy in East Africa. Significant differences in delta(13)C values between subregions are explained by paleogeographic controls on floral composition and distribution. Our results indicate grassland expansion between 2.0 and 1.75 Ma, coincident with major shifts in basin-wide sedimentation and hydrology. Hypotheses may be correct in linking Plio-Pleistocene hominin evolution to environmental changes from global climate; however, based on our results, we interpret complexity from proximate forces that mitigated basin evolution. An approximately 2.5 Ma tectonic event in southern Ethiopia and northern Kenya exerted strong effects on paleography in the Turkana Basin from 2.0-1.5 Ma, contributing to the shift from a closed, lacustrine basin to one dominated by open, fluvial conditions. We propose basin transformation decreased residence time for Omo River water and expanded subaerial floodplain landscapes, ultimately leading to reduced proportions of wooded floras and the establishment of habitats suitable for grassland communities.     

Food Preference of Perch (Perca fluviatilis) Stocked in a Previously Fishless,Acid Bog Lake and Development of the Fish Population in Absence of Piscivory

The almost fishless, acid Lake Fuchskuhle was physically partitioned into 4 sections and stocked with young, 10‐ to 13‐cm perch. Their body growth was normal only up to age 4 years. Although the perch spawned successfully, reproduction was negligible because only few offspring survived the first year of life. Food for young perch was plentiful, benthic invertebrates composing the main source. Because the population included only 2 to 3 year classes, the perch could not shift from benthic feeding to piscivory as they grew. As a result, growth rate decreased in older fishes (over 4–5 years old). The benthic food supply alone could not satisfy the energy requirements of the older perch.