Browsing by Author "Ojija, Fredrick"

Now showing 1 - 4 of 4

The distribution, control techniques and impact of Parthenium hysterophorus on flower visitors and soil chemical properties in Meru district, Tanzania
(2020-08) Ojija, Fredrick
In Tanzania, the invasive plant Parthenium hysterophorus threatens natural and semi–natural environments. Little is known about how this species affects plant–pollinator interactions and soil–chemical properties. Roadside survey was conducted to assess P. hysterophorus invasion status within and outside Arusha National Park (ANP), Tanzania. Soil samples were also collected in invaded and uninvaded plots to investigate the impact of P. hysterophorus on soil–chemical properties. To test alternative natural–based management strategies, the study examined the bio–herbicide potential of Desmodium uncinatum leaf (DuL) crude extract and the competitive ability of fodder legume plant species (Lablab purpureus, Desmodium intortum and Medicago sativa) to suppress P. hysterophorus in pot and plot experiments. Results showed that ANP is currently uninvaded with P. hysterophorus, but some adjacent villages i.e. King’ori, Maleu, Napoco, Ngongongare, Ngurdoto, Oligilai and Sakila have already invaded by this invasive. Parthenium hysterophorus invaded site was more acidic with lower electrical conductivity, less calcium and phosphorus, and high cation exchange capacity. The DuL extract suppressed P. hysterophorus growth vigour, particularly at higher concentrations (>70%). At these concentrations, the invasive seedling stem height was >30% shorter, and seed germination was inhibited by >55% compared to seedlings sprayed with lower concentrations. When P. hysterophorus was grown in combination with all three test plants, its seedling stem heights and total fresh biomass were reduced by >60% and >59% in pots, and >40% and >45% in field plots respectively, compared to when grown alone or in mixture with just D. intortum or M. sativa. Moreover, surveys conducted on invaded and uninvaded sites to investigate the impact of P. hysterophorus on plant–pollinator interactions when two common target plants (Ocimum gratissimum and Ageratum conyzoides) were present showed that flower visitation rate to target plants was significantly lower in invaded plots than in uninvaded plots. This implies that P. hysterophorus may be disrupting pollen flow. The study recommends that the use of bio–herbicide and suppressive plant species to control the invasive should be promoted. However, it emphasizes the use of native suppressive plant species because non–natives may turn into invasives in the future.
Effect of artisanal fishing and water pollution on the stock of Bagrid catfish (Bagrus meridionalis) in the northern part of Lake Nyasa/Niassa/Malawi in Tanzania: An insight from Nyasa district
(Elsevier, 2026-01) Mayowela, Farida; Ojija, Fredrick; Kavishe, Regan; Mataba, Gordian
The critically endangered Bagrus meridionalis is one of the large fish species endemic to Lake Nyasa/Niassa/Malawi. Its population from the southern part of the lake, in Malawi and Mozambique, has declined by over 90 % within 10 years from 2006 to 2016 due to over- harvesting. Despite that less is known from the northern part of the lake in Tanzania where studies on B. meridionalis population dynamics and trends are conspicuously missing. This is affecting effective monitoring and sustainable management of the species in this part of the lake. The lake is also under the influence of unsustainable agricultural practices in the lake basin which are thought to pollute the lake. However, it is also not known how this has affected the growth and survival of the fish in the lake. We, therefore, investigated the effect of artisanal fishing and anthropogenic pollution on the status of the stock of B. meridionalis in the northern part of Lake Nyasa/Niassa/Malawi in Tanzania using the catch per unit effort technique, length-frequency distribution, and relative condition factor. We sampled water and fish, and measured fish stan- dard lengths, weights, and levels of water physical-chemical variables. We found that the stock B. meridionalis population in the northern part of Lake Nyasa/Niassa/Malawi is very low and is experiencing recruitment overfishing with most of the fish being caught while immature. Despite this, the caught fishes had good body condition indicating that they are surviving in a favorable ecological environment. Urgent mitigation measures are therefore required to halt overfishing to safeguard community livelihood and the endangered B. meridionalis
Impacts of alien invasive Parthenium hysterophorus on flower visitation by insects to co-flowering plants
(Springer Nature, 2019-05-11) Ojija, Fredrick; Arnold, Sarah; Treydte, Anna
The exotic invasive plant Parthenium hysterophorus is invading many tropical habitats. While much work has been done on its interactions with other native plants, little is known about its interaction with insect floral visitors and how it impacts pre-existing pollination networks when it invades a site. We carried out surveys on sites with and without P. hysterophorus (invaded and uninvaded, respectively) to investigate its impact on plant–pollinator interactions with two common indicator or target plants (Ocimum gratissimum and Ageratum conyzoides) in Tanzania. During multiple 15 min observation periods in quadrats, the number of arriving flower visitors, duration of visits and visitation rate were measured and compared between sites. Visitation networks of flower visitors were developed by observing flower visitor taxonomic groups and plants visited across both invasion categories. Parthenium hysterophorus was heavily visited by a diversity of flies as taxonomic groups. Indicator plants received fewer flower visitors overall in the invaded site, implying P. hysterophorus may be disrupting pollen flow. Foraging behaviour and flower visitation by Apis mellifera and flies on target plants were particularly negatively affected in the invaded quadrats. Flower visitation rate to target plants was significantly lower in invaded quadrats than in uninvaded quadrats. This study supports work in other parts of the world demonstrating that invasive species can strongly disrupt pollination networks. By attracting flower visitors that could otherwise serve as pollinators of native plant species, P. hysterophorus which is rapidly spreading in eastern African ecosystems could have complex deleterious effects on the wider ecosystem.
Suppressive abilities of legume fodder plants against the invasive weed Parthenium hysterophorus (Asteraceae)
(Elsevier Inc, 2021-03-13) Ojija, Fredrick; Ngimba, Christopher
The alien invasive plant Parthenium hysterophorus (Asteraceae) has been reported to impend smallholder farmers’ livelihood, and biodiversity conservation in sub-Saharan Africa. While earlier studies reported that the invasion may be supressed if plant density in invaded habitats is sufficiently maintained, only a few quantitative experiments on competition between legume (Fabaceae) fodder plants and invasive plant species have been conducted. We determined whether three selected test legume fodder species, Desmodium intortum (greenleaf desmodium), Lablab purpureus (hyacinth bean) and Medicago sativa (lucerne), can suppress P. hysterophorus growth. These legumes were selected because they have been used to suppress various weeds in sub-Saharan Africa owing to their rapid growth, strong root systems, bigger leaf canopy, high biomass production and capacity to form many branches. Also, they are used by livestock as forage when other fodders are dry and become limited. The legume fodder plant species and P. hysterophorus were grown as mono- and mixed cultures in pot experiments. Fifty-dayold P. hysterophorus seedlings were harvested to determine any suppressive abilities of the legume species against the invasive. We found that the growth of P. hysterophorus was negatively impacted when grown with two or three test legume species compared with monoculture. Respectively, stem height, total fresh biomass and leaf chlorophyll content of P. hysterophorus seedling were reduced by >60%, >59%, and >70% when grown in combination with all three legume fodder species compared with sole cropping or in mixture with just D. intortum or M. sativa. The results suggest that the selected legume fodder plants have the ability to suppress growth of P. hysterophorus. Further, this study demonstrates the potential importance of using legume fodder plant species in the management of alien invasive plants.