Influence of agricultural land transformation and pest management practices on the arthropod diversity of a biodiversity hotspot, the Cape Floristic Region, South Africa

The Cape Floristic Region (South Africa), is a global biodiversity hotspot that has undergone considerable landscape change in recent years. The impact of habitat transformation on arthropod taxa and the effect of pesticides on non-target arthropods in this area were studied. Arthropod diversity in a remnant patch of natural vegetation (fynbos) was compared with that in two apple orchards, one under intensive chemical pest management (sprayed), and the other under fungicide treatments only (unsprayed). Pitfall traps and vacuum sampling collected 221, 152 and 106 insect species in the fynbos, unsprayed and sprayed orchards, respectively. Far more species of Hemiptera, Hymenoptera, and Orthoptera were found in fynbos than in either orchard. Cydnids, rove and ground beetle families were as species rich in the sprayed as in the unsprayed orchards whereas Diplopoda and Isopoda were more abundant in the unsprayed than the sprayed orchard. The introduced Argentine ant, Linepithema humile (Mayr), was the most abundant species in both orchards. The study clearly indicated that habitat transformation and the use of pesticides had a negative impact on arthropod diversity in the Cape Floristic Region.Articl

The impact of an invasive ant, Linepithema humile (Mayr), on the dispersal of Phylica pubescens Aiton seeds in South Africa

Myrmecochory, or seed dispersal by ants, is a mutualistic plant-ant interaction common to the fire-prone shrublands of the southwestern Cape, South Africa. Elaiosome-bearing seeds are located rapidly by ants and transported to nests where they are protected from granivorous rodents, desiccation and fire. This interaction is threatened by the invasive Argentine ant, Linepithema humile, which has displaced important myrmecochorous ant species in previously undisturbed areas. The impact of this infestation was assessed. Linepithema humile, which was active mainly at night, dispersed few seeds and removed most of the elaiosomes in situ. The majority of seeds were dispersed from invaded areas during the day by two indigenous species of ants, Tetramorium quadrispinosum and Ocymyrmex cilliei. Dispersal in uninvaded areas occurred mainly between 19:00 and 21:00 but was generally spread overa 24-hour period, indicating the participation of a complex of ant species. Significantly more seeds were dispersed in uninvaded areas than in areas invaded by L. humile. In invaded areas, there were no significant differences in the numbers of seeds dispersed by ants and the numbers eaten by rodents. In contrast, significantly more seeds were dispersed by ants than were eaten by rodents in uninvaded areas.Articl

Prospects for the biological control of the weedy sporobolus grasses in Australia.

Bill Palmer and colleagues recently published their paper 'Prospects for the biological control of the weedy sporobolus grasses in Australia' in Proceedings of the 16th Australian Weeds Conference. The paper gives a summary of a recent project to find a biological control for the weedy sporobolus grasses, which include giant rat's tail grass. Southern Africa was surveyed for potential agents and two, a leaf smut and a stem wasp, were selected for follow up studies. Unfortunately, they could not rear the stem wasp in the laboratory and the leaf smut infected four of the Australian native Sporobolus spp. and was therefore rejected. This project was one of the first attempts at biological control of a grass

The impact of an invasive ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae), on the dispersal of the elaiosome-bearing seeds of six plant species

Linepithema humile has invaded pristine areas in the Western Cape Province, South Africa, displacing important myrmecochorous ant species. The impact of this invasion on the dispersal of six species of elaiosome-bearing seeds varying in size, shape and mass was investigated. Linepithema humile failed to disperse heavy elaiosome-bearing seeds, although it readily removed lighter seeds like those of Polygala myrtifolia. This suggests that areas dominated by small ant species like L. humile would be characterized by low dispersal rates for heavy seeds. Indigenous ants in areas uninvaded and invaded by L. humile did not respond equally well to six elaiosome-bearing seeds. More of the heavier Leucospermum cordifolium than the lighter Pudalyria calyptrata and Paranomus reflexus seeds were removed by ants in uninvaded areas. In invaded areas the heavier P. myrtifolia seeds were dispersed more readily than the lighter Agathosma ovata seeds. There was no indication of any specificity in the seed-ant interaction because the introduced ant, L. humile, dispersed smaller seeds. In addition, R calyptrata, which occurs naturally in the study area, was not taken preferentially to other species of seed by myrmecochorous ants.Articl

Chromolaena odorata (Siam Weed) in eastern Africa: distribution and socio-ecological impacts

Invasive alien plant species such as Chromolaena odorata have negative impacts on biodiversity, ecosystem services and human well-being. Ecological impacts of this shrub are relatively well understood, but its impacts on local livelihoods and perceptions are poorly documented. We mapped C. odorata distribution in eastern Africa (Ethiopia, Kenya, Rwanda, Tanzania and Uganda) and compared perceptions and quantified the impacts of this species across Tanzanian villages with varying degrees of invasion density. Data were collected through 240 household questionnaires. Results indicate that C. odorata is a relatively new invader that already has severe negative impacts and is threatening livelihoods and the environment. Impacts include reductions in native biodiversity and the amount of available forage for livestock, reduced crop and water yields, and impaired mobility. Continued spread will cause additional negative impacts on poor rural communities. Implementation of a biological control programme targeting C. odorata is needed as a cost effective management approach along with other control and restoration measures

Distribution and socio-ecological impacts of the invasive alien cactus Opuntia stricta in eastern Africa

Many cactus species have been introduced around the world and have subsequently become major invaders, inducing social and ecological costs. We recorded the distribution of Opuntia stricta in eastern Africa, and conducted 200 household interviews using semi-structured questionnaires to assess local perceptions of O. stricta in Laikipia County, Kenya. Opuntia stricta was widespread and abundant in parts of Kenya, Tanzania and Ethiopia and present at low densities in Uganda. In Laikipia County, pastoralists identified that O. stricta had been present for more than 10 years, and were of the opinion that it was still spreading and increasing in density. Two-thirds of respondents estimated that 50–75% of valuable grazing land had been invaded, and all felt that it contributed to the ill-health and death of livestock. Other negative impacts included reductions in native plant populations, rangeland condition, human health, and mobility of humans and animals. These negative impacts resulted in economic losses of US$ 500–1000 per household per year for 48% of households. Only 20% of respondents reported actively managing O. stricta, yet all respondents believed a reduction in the abundance of this weed would improve well-being. Management interventions are needed to reduce negative impacts

Distribution of the invasive alien weed, Lantana camara, and its ecological and livelihood impacts in eastern Africa

Lantana camara (lantana) is a major invasive shrub globally, impacting upon biodiversity, economies, ecosystem services, and driving socio-ecological change. The aim of this study was to determine the current and potential distribution of lantana in eastern Africa and its livelihood impacts in one region in Uganda. Data were collected by means of roadside surveys, and then compared with potential distributions based on ecoclimatic models. Household interviews were conducted to understand the impacts of lantana on local livelihoods. Lantana is currently widespread in eastern Africa, and has the potential to spread, especially in Tanzania. According to 40% of respondents, lantana reduced the amount of forage available to livestock by more than 50%, while one-third of those interviewed reported a 26–50% reduction in crop yields. Lantana invasions also cost individual households substantial amounts of money (US$400–500 per annum). Furthermore, lantana reduced the availability of natural resources, such as native medicinal plants, and hindered the movement of people and livestock. Based on the potential distribution of lantana, and its current impacts, we suggest that an integrated management strategy be developed and implemented, including the introduction of additional biological control agents to reduce the negative effects of lantana on local livelihoods

A premilinary assessment of the extent and potential impacts of alien plant invasions in the Serengeti-Mara ecosystem, East Africa

This article provides a preliminary list of alien plant species in the Serengeti-Mara ecosystem in East Africa. The list is based on broad-scale roadside surveys in the area and is supplemented by more detailed surveys of tourist facilities in the Masai-Mara National Reserve and adjoining conservancies. We encountered 245 alien plant species; significantly more than previous studies, of which 62 (25%) were considered to have established self-perpetuating populations in areas away from human habitation. These included species which had either been intentionally or accidentally introduced. Of the 245 alien plants, 212 (including four species considered to be native to the region) were intentionally introduced into gardens in the National Reserve and 51 (24%) had established naturalised populations within the boundaries of these tourism facilities. Of the 51 naturalised species, 23 (11% of the 212 alien species) were recorded as being invasive within the ecosystem, outside of lodges and away from other human habitation. Currently, the Serengeti-Mara ecosystem is relatively free of widespread and abundant invasive alien plants, with a few exceptions, but there are extensive populations outside of the ecosystem, particularly to the west, from where they could spread. We address the potential impacts of six species that we consider to pose the highest risks (Parthenium hysterophorus, Opuntia stricta, Tithonia diversifolia, Lantana camara, Chromolaena odorata and Prosopis juliflora). Although invasive alien plants pose substantial threats to the integrity of the ecosystem, this has not yet been widely recognised. We predict that in the absence of efforts to contain, or reverse the spread of invasive alien plants, the condition of rangelands will deteriorate, with severe negative impacts on migrating large mammals, especially wildebeest, zebra and gazelles. This will, in turn, have a substantial negative impact on tourism, which is a major economic activity in the area. Conservation implications: Invasive alien plants pose significant threats to the integrity of the Serengeti-Mara ecosystem and steps will need to be taken to prevent these impacts. The most important of these would be the removal of alien species from tourist facilities, especially those which are known to be naturalised or invasive, the introduction of control programmes aimed at eliminating outlier invasive plant populations to slow down the spread, and the widespread use of biological control wherever possible