Browsing by Author "Kasigwa, Peter F."

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Dispersion Factors in the Arboreal Snail Sitala Jenynsi (Gastropoda: Ariophantidae)
    (Taylor and Francis, 1999) Kasigwa, Peter F.
    Sitala jenynsi snails from the University and Wazo populations of Dar es Salaam, Tanzania, were released on grass, and on forest terrain, in both regions during the dry (February, March) and the rainy seasons (April). Snail dispersion was assessed as weekly quadratic means and as the overall Diffusion Coefficient 0.423 nr/week. The coefficient was enhanced by grassy habitats, continuous vegetation cover, absence of edible plants and rainy weather; conversely, dispersion was retarded by shrubs, vegetation discontinuities, presence of edible plants and dry weather. There were differences in the rate of dispersion between populations, snails from the University Campus being faster. In each release a broadly unidirectional dispersion was recorded. The populations in question, seasons and the direction of origin of the snails seemed immaterial to directionality of dispersion, The dispersion rates of Sitala jenynsi exceeded those of the helicids Cepaea nemoralis and Theba pisana and of the partulid Pariula taeniata. While observed dispersion rates of S jenynsi may warrant the mixing of individuals in a population, they seem insufficient to facilitate appreciable migration of snails between neighboring populations.
  • Thumbnail Image
    Item
    Ecology and Conservation of the Land-Snails of the Eastern Arc Mountains
    (1998) Tattersfield, Peter; Seddon, Mary B.; Meena, C.; Kayumbo, N.; Kasigwa, Peter F.
    The history of the study of the terrestrial molluscs of the Eastern Arc Mountains is summarised and a checklist of species known from each range is presented. Current knowledge of the fauna is patchy but each of the ranges contains endemic species and collectively they support a major proportion of the Tanzanian land-snail fauna. Recent research in the East and West Usambara, Uluguru and Nguru Mountains has revealed high levels of mollusc diversity in Bomole and Monga Forests (East Usambara Mountains) and in the limestone forest at Kimboza (Uluguru Mountains); these forests support the richest faunas reported so far from East Africa. In contrast, diversity and abundance is low in the forests of the Nguru Mountains. A similarity analysis is used to identify several clusters of sites that are related to geographical position and altitude. The significance of these findings for the conservation of East African land snails is discussed.
  • Thumbnail Image
    Item
    High Diversity and Regional Endemism in Land-Snails of Eastern Tanzania
    (Springer Link, 1997) Emberton, Kenneth C.; Pearce, Timothy A.; Kasigwa, Peter F.; Tattersfield, Peter; Habibu, Zambia
    In February/March 1995 we collected land snails (including slugs) at 12 stations in eastern Tanzania. A total of 571 person-hours yielded 9174 snails assigned to 159 morpho-species. The richest two sites each (<4ha of uniform forest) had 50 species (Amboni Cave) and 48 species (near Amani, Usambaras), nearly as great as the most species-rich sites known in the world; sieving of litter and soil would probably yield more species. In lowland (coastal) forests, both diversity and endemism seemed to decrease from north to south. Most snail species were found within only one of four coastal or one montane geographic regions, indicating substantial regional endemism. Only one species (Achatina fulica) appeared in all five regions, and 84% of all other species were found in only one (61%) or two regions (23%). The predatory streptaxids comprised about half the species and a third of the individuals at the Usambara site, an extremely high ratio of carnivores. Small snails (< 5mm greatest adult shell dimension) – many of which are probably undescribed species – comprise a substantial proportion of Tanzanian molluscan diversity; more surveys are needed, especially because of human pressures on the few forest patches remaining.
  • Thumbnail Image
    Item
    Quantification of Shell Banding Polymorphism in the East African Tree Snail Sitala Jenynsi (Pulmonata: Ariophantidae)
    (Taylor and Francis, 2007) Kasigwa, Peter F.; Allen, John A.
    In eastern Africa, populations of the tree snail Sitala jenynsi are monomorphic, dimorphic or trimorphic for the width of the upper brown band on their shells.We measured the variation in the width of this band in several populations and analysed it using two mutually verifiable methods: arithmetical probability paper and regressions of log-transformed shell metrics. The demarcations of the three morphs in areas of spatial overlap between the band-width states have been defined. We recognized existence of type I narrow-banding which associates monomorphism, and type II narrow-banding, medium banding and wide-banding forms which associate polymorphism. We have also quantified the variation in three other characters, two of which are also polymorphic: a lower pigmented band and an upper unpigmented ‘ghost band’. The evolutionary implications of the findings are discussed. Continued use of varietal names to describe the banding polymorphism of S. jenynsi is recommended, in preference to the multidimensional colour pattern notation commonly applied to gastropods.
  • Thumbnail Image
    Item
    Snail Arboreality: The Microdistribution of Sitala Jenynsi (Gastropoda: Ariophantidae)
    (Taylor and Francis, 1999) Kasigwa, Peter F.
    The habitats and patterns of vertical migration of the shell banding morphs of the snail Sitala jenynsi (Pfeiffer) were studied in Dar es Salaam and Wazo regions of central coastal Tanzania Both dimorphic and trimorphic populations were arboreal throughout the year. The snails occurred randomly within mid-heights 180 to 360 cm. without apparent morph differences in micro-distribution. The pattern of circadial vertical distribution consisted of upward migrations during mornings and downward shifts during late evenings. These oscillations regressed negatively on relative humidity (RH), a unit advance in RH representing an eight-fold descent of snails on daytime height. Variations in RH accounted for much of the total variance in the mean vertical distance. During high RH, however, temperature and mating behaviour probably exerted major influences on snail micro-distribution. The effects of arboreality on snail survival and initiation of differentiating subpopulations are proposed