Impacts of alien invasive Parthenium hysterophorus on flower visitation by insects to co-flowering plants

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

Modeling Boran cattle populations under climate change and varying carrying capacity

This research article published by Elsevier, 2017Cattle populations in semiarid rangelands are currently facing severe threats due to erratic rainfall and increasing drought frequencies, leading to poor vegetation quality and a consecutive cattle population decline. However, little is known about how particular sex- and age-cohorts of cattle respond to these environmental threats and on how sales influence population trajectories. In the Borana rangelands, southern Ethiopia, much detailed information is available on the Boran cattle (Bos indicus) population demographics, a special breed, which is highly adapted to semiarid environmental conditions. We collected data on Boran cattle demographic and environmental factors such as carrying capacity, market values, and herderś management decisions. We generated stochastic models and assessed the future development of cattle population trajectories under four different drought scenarios. We analyzed changes in age- and sex-cohorts of cattle populations by introducing different drought frequencies and their effect on vital rates, carrying capacity, and sales. We calibrated the model on the basis of a 12-year data set of a neighboring Boran cattle group. In our population model, the cattle numbers significantly declined after 18 years under the higher drought frequency scenarios (scenarios 3 and 4) while numbers remained high over 100 years for the lower drought frequency scenarios 1 and 2. The sale of senescent and adult females most strongly (77%) affected population trajectories, and model outcomes were most sensitive to sale rates of senescent, adult, and juvenile females compared to vital rates and male sale rates of the population. Management should focus on lowering herd crashes through increasing sale of mature males, which increases feed availability to females during drought years in the Ethiopian Rangelands. Drought early-warning systems and market information must be strengthened so that pre-planned selling of cattle can be realized for a sustainable use of the animal resource

Diet of the Common Warthog (Phacochoerus africanus) on Former Cattle Grounds in a Tanzanian Savanna

In otherwise nutrient-poor savannas, fertile vegetation patches are particularly attractive to ungulates because of the higher-quality food they provide. We investigated forage plants and diet of the common warthog (Phacochoerus africanus) on an abandoned cattle ranch in coastal Tanzania. The forage grasses of highest nutritional quality occurred in former paddock enclosures (bomas) where cattle had been herded at night. In the dry season, grass samples from bomas contained approximately 4 times as much nitrogen and phosphorus as those of the surrounding vegetation. δ15N values of soil and plants also were highest in bomas and decreased significantly with distance, and high δ15N values in feces suggest that warthogs preferentially fed in the vicinity of the former bomas. δ13C values of warthog feces indicate that warthogs ingested on average 83% (77-98%) C4 grasses, with this proportion varying regionally but not seasonally. We conclude that, for medium-sized selective grazers such as warthogs, bomas represent attractive feeding grounds. We also hypothesize that by promoting nutrient turnover in these patchily distributed areas, grazing animals help to maintain them as sources of high-quality forag

Rainfall, fire and large-mammal-induced drivers of Vachellia drepanolobium establishment: Implications for woody plant encroachment in Maswa, Tanzania

This research article published by John Wiley & Sons, Inc., 2021Worldwide, open grass areas of savannah ecosystems are being transformed into shrubland. This woody plant encroachment is likely a result of factors such as rainfall, fire and secondary dispersal by ungulate herbivory. However, few experiments have been conducted to disentangle and quantify the role of these factors for seed germination in savannahs. We assessed in situ germination success of Vachellia drepanolobium seeds under simulated rainfall variability patterns, fire treatments and dung experiments in Maswa Game Reserve, Tanzania. Fire reduced seed germination by more than 13%, whereas germination in buffalo and elephant dung increased by 1% and 3% respectively. Additionally, intermediate simulated rainfall was more beneficial for seedling emergence success than large, infrequent simulated rainfall amounts, while shoot growth was twice as high under frequent and intermediate simulated rainfall treatments than under large infrequent simulated rainfall. Our results provide insights that bush fires, drought stress, and large rainfall events can suppress V. drepanolobium seedling emergence and growth. Hence, bush encroachment may be linked to management practices such as fire regimes and climatic conditions, i.e., frequent low rainfall conditions. Our results can help predict future patterns of encroachment under varying rainfall and fire events

Mammalian wildlife diversity in rubber and oil palm plantations.

This research article published by CABI, 2016In the face of globally diminishing natural habitats in biodiversity-rich regions, agricultural landscapes around protected areas have increasingly gained importance as extended habitat for wildlife species. Rubber (Hevea brasiliensis) and oil palm (Elais guineensis) plantations are two of the dominant land-use systems in Southeast Asia that have seen a tremendous expansion over the last decades. Despite far-reaching ecological consequences of these intensively cropped monocultures on natural ecosystems, relatively little is known about their utilization by wildlife populations. With this review we want to give an overview of mammalian diversity in rubber and oil palm plantations with reference to human-wildlife conflicts occurring as a result of overlapping resource use. We searched the literature for studies on wild mammalian diversity in rubber and oil palm plantations and found 17 publications. We considered 29 additional publications that provided information on single species in such plantations. We discuss the potential of 'wildlife-friendly' farming for mammalian assemblages in plantations and its importance in the case of rubber and oil palm production. Our review showed that most wild mammal species found in these plantations were likely to be visitors that use cultivated landscapes as fringe habitat but some adapted well to plantations and few even became resident. We conclude that although plantations in the tropics and subtropics cannot substitute for forests and the preservation of natural habitats is indispensable, the reality of ongoing forest degradation and transformation into plantations will make wildlife-friendly farming a key strategy in maintaining mammalian diversity, particularly in land-use matrices surrounding natural habitats

Quantifying nutrient re-distribution from nutrient hotspots using camera traps, indirect observation and stable isotopes in a miombo ecosystem, Tanzania

This research article published by Elsevier B.V., 2020Nutrient hotspots strongly attract mammalian herbivores in nutrient-poor habitats such as savanna systems. However, little is known about their seasonal importance for mammalian herbivore species, particularly grazers. In addition, no study has fully quantified the potential re-distribution of nutrients into the surroundings of these hotspots. We assessed nutrient hotspot (i.e., grazing lawns and termite mounds) use by herbivores in a Miombo ecosystem of the Issa valley, Tanzania, using dung counts, camera traps and stable isotope analyses over a one year period, from May 2016 to October 2017. We conducted dung counts along four transects each radiating away from ten termite mounds and six grazing lawns as well as in 16 control sites 100 m away from each nutrient hotspot. In addition, we sprayed grasses around five termite mounds with urea and traced the isotopic signature back in grazing herbivore dung. Grazer dung deposition was twice as high in hotspot areas vs control sites. A total of 32 camera stations recorded 244 wildlife encounters, with mammalian herbivores using hotspot areas four times more frequently compared to control plots. Stable isotope analyses highlighted that dung deposited by mammalian grazers around hotspots likely originated from grasses within or close to hotspot areas, indicating that grazers are responsible for maintaining nutrient stability of these hotspots. We, therefore, emphasize the importance of grazing mammal species for the long-term persistence of hotspots and, thus, their contribution to the maintenance of a heterogeneous landscape within the Miombo ecosystem

Effects of clipping and irrigation on carbon storage in grasses: implications for CO2 emission mitigation in rangelands

This research article published by Taylor & Francis Online, 2018Understanding how individual grasses respond to herbivory and rainfall has been hampered by the difficulty of quantifying above- and belowground carbon (C) storage in grasses. Particularly by restoring degraded rangelands through reseeding, their C storage potential can be greatly enhanced. The responses of reseeded grasses to the effects of herbivory and precipitation were assessed to evaluate the potential of individual grasses for C storage as a technique for climate change mitigation. Clipping experiments were conducted on mature grass tufts of two native grass species, Chloris gayana and Cenchrus ciliaris, in the semi-arid Borana rangelands, Ethiopia. Further, above- and belowground C storage of young grasses of the same species in pot and field plot trials was experimentally quantified under simulated grazing and variable rainfall. The results showed that aboveground C was significantly 4 times lower in the clipped compared to unclipped mature grasses. In contrast, 3 times higher C was found in young reseeded grasses that were clipped compared to unclipped ones. Clipping and irrigation in combination significantly influenced belowground C in young grasses, with reduced irrigation overriding clipping effects. The paper concludes that moderate grazing should be encouraged to enhance CO2 uptake, consequently contributing to climate change mitigation in rangelands

Effectiveness of Zygogramma bicolorata as a biocontrol agent against Parthenium hysterophorus in Arusha, Tanzania

This research article published by Taylor & Francis Online, 2020Parthenium hysterophorus is an invasive weed that poses significant threats to crop production, biodiversity, human and animal health. Few experiments have been carried out to test the effectiveness of biological control agents such as the beetle Zygogramma bicolorata against this invasive. We released Z. bicolorata beetles as bio-agent to control P. hysterophorus at the Tropical Pesticides Research Institute in Arusha, Tanzania, across two seasons, from February – July 2019 (wet) and August 2019 – January 2020 (dry). Feeding by Z. bicolorata reduced P. hysterophorus leaves, flowers, height as well as biomass, both in the dry and wet season. During the wet season, 100% of all P. hysterophorus leaves were eaten already 28 days after the onset of the experiment, particularly under the highest beetle population treatment (30 individuals). Parthenium hysterophorus flower numbers were greatly reduced under high beetle populations (30 individuals) compared to the control treatment (0 individuals) during both the wet and dry season. Parthenium hysterophorus height was reduced by 87% and 90% during the wet and dry season, respectively when 30 beetles were released. Similarly, biomass was reduced by 90% and 87% during the wet and dry season, respectively. Parthenium hysterophorus responses to beetle treatments did not differ significantly across seasons but the development of both the invasive and its control, Z. bicolorata, was slightly delayed in the dry season. We conclude that Z. bicolorata can be used as bio-agent to manage P. hysterophorus in Tanzania, particularly when released in large numbers

Is wild meat luxury? Quantifying wild meat demand and availability in Hue, Vietnam

This research article published by Elsevier B.V., 2016Increasing urban wild meat consumption in Vietnam poses a major threat to faunal biodiversity. However, little is known about the numbers, demand, social status, and frequency of wildlife meat consumers in Thua Thien Hue province, where wild meat consumption appears to be common. We combined the results of 329 semi-structured interviews of male Hue citizens in Thua Thien Hue province, Vietnam, with interviews in 20 restaurants to quantify the supply and demand of urban wildlife consumption. We found that 58% of respondents were current wild meat consumers. The most common species reported (in 30% of the cases) was wild pig (Sus scrofa). Our results described a typical consumer as a student or being unemployed, usually with higher education, and eating wild meat three times a year. Most (72%) wild meat consumption in Hue city took place in restaurants. Restaurant surveys showed that government staff were the most observed customers in restaurants. Farmed wild meat consumption in Hue was rarely reported (in 23% of the cases); and a typical consumer of farmed wild meat had high education levels. Missing legal mechanisms such as the inability to punish and fining the wild meat consumers was claimed to be an important reason why wild meat consumption has not yet declined. Our combination of survey methods provided different stakeholder views and highlighted the urgent need to monitor the patterns and frequency of wild meat consumption for further law amendments

Assessing the Sustainability of Different Small-Scale Livestock Production Systems in the Afar Region, Ethiopia

This research article published by MDPI, 2013Livestock production is a key income source in eastern Africa, and 80% of the total agricultural land is used for livestock herding. Hence, ecological and socio-economically sustainable rangeland management is crucial. Our study aimed at selecting operational economic, environmental and social sustainability indicators for three main pastoral (P), agro-pastoral (AP), and landless intensive (LI) small scale livestock production systems for use in sustainability assessment in Ethiopia. Quantitative and qualitative data were collected through grey literature and semi-structured interviews, assessing livestock and feed resources, production technology, land tenure, financial and gender issues. Our results suggested that feed shortages (FS) are directly related to grazing pressure (G) and inversely related to grass recovery rates (R). According to our indicators, AP was the most sustainable while P and LI were only conditionally sustainable production systems. 93% of 82 interviewees claimed that private land ownership was the best land tenure incentive for efficient rangeland management. Farmers perceived Prosopis juliflora expansion, sporadic rainfall, and disease infestation as the most significant causes for decreasing livestock productivity. Landless intensive farmers had the highest equality in income distribution (Gini Index: GI = 0.4), followed by P and AP (each with a GI = 0.5). Neither educational background nor income seemed to determine grazing species conservation efforts. We claimed that sustainability indicators are valuable tools to highlight shortcomings and strengths of the three main livestock production systems and help with future livestock management in Ethiopia. Selecting suitable indicators, however, is crucial as data requirements and availability can vary across livestock system