Consistent Effects of Biodiversity on Ecosystem Functioning Under Varying Density and Evenness

Biodiversity experiments typically vary only species richness and composition, yet the generality of their results relies on consistent effects of these factors even under varying starting conditions of density and evenness. We tested this assumption in a factorial species richness x density x evenness experiment using a pool of 60 common grassland species divided into four functional groups (grasses, legumes, tall herbs and short herbs). Richness varied from 1, 2, 4, 8 to 16 species, total planting density was 1,000 or 2,000 seeds/m², and species were sown in even or uneven proportions, where one functional group was made dominant. Aboveground plant biomass increased linearly with the logarithm of species richness in all density and evenness treatments during all three years of the experiment. This was due to a convergence of realized density and evenness within species richness levels, although functional groups which were initially made dominant retained their dominance. Between species richness levels, realized density increased, and realized evenness decreased with species richness. Thus, more individuals could coexist if they belonged to different species. Within species richness levels, higher biomass values were correlated with lower density, suggesting an underlying thinning process. However, communities with low realized evenness also had low biomass values; thus high biomass did not result from species dominance. So-called complementarity and selection effects were similar across density and evenness treatments, indicating that the mechanisms underpinning the biodiversity effects were not altered. Species richness was the dominant driver of aboveground biomass, irrespective of variations in total densities and species abundance distributions at the start of the experiment; rejecting the hypothesis that initial differences in species abundance distributions might lead to different “stable states” in community structure or biomass. Thus, results from previous biodiversity experiments that only manipulated species richness and composition should be quite robust and broadly generalizable.     

Elevated oxidase and esterase levels associated with permethrin tolerance in Anopheles gambiae from Kenyan villages using permethrin-impregnated nets

The permethrin tolerance (PT) of a population of the mosquito Anopheles gambiae (Diptera: Culicidae) increased following the introduction of permethrin-impregnated nets for malaria control in certain villages near Kisumu, western Kenya. Using a biochemical test that indirectly measures oxidases associated with permethrin resistance, we found that this population had higher oxidase levels than a comparison population from villages without impregnated nets. Mosquitoes from a colony of An. gambiae selected for PT, the RSP (reduced susceptibility to permethrin) strain, were exposed to permethrin with or without the oxidase inhibitor piperonyl butoxide (PB). Significantly higher mortality rates occurred when permethrin was synergized by PB, presumably by suppression of oxidases responsible for PT. An unselected (UNS) colony of An. gambiae that was more susceptible than RSP in a permethrin-susceptibility bioassay (i.e. LT50 22 min for UNS, vs. 42min for RSP) was compared with the RSP colony for levels of oxidases and esterases. The levels of both enzymes were very significantly higher in the RSP strain (P<0.0001). We speculate that use of impregnated nets selected for higher oxidase and esterase levels in An. gambiae to metabolize permethrin acquired from the nets. Both oxidase and esterase mechanisms could confer cross-resistance to other pyrethroids.     

The Effects of a Tsetse DNA Virus Infection on the Functions of the Male Accessory Reproductive Gland in the Host Fly Glossina morsitans centralis (Diptera; Glossinidae)

Freshly deposited third instar Glossina morsitans centralis larvae were infected with the tsetse DNA virus by microinjection, and at emergence adult males were separated from the females and fed on rabbit blood every second day for 8 days. A control group treated with sterile saline were handled similarly. They were dissected, and comparative observations made on the appearance and size of the accessory reproductive glands (ARG) in infected and control males. Regularly fed 8-day-old males from infected and control groups were mated to 2-day-old normal females obtained from the insectay. After separation from copula, the females were dissected and the uteri examined for the presence and quality of the spermatophore. The spermathecae were also examined for insemination. ARG tissues from the control and virus infected regularly fed 8-day-old male flies were fixed and processed for electron microscopic studies. The ARGs from control flies were found to be milky in appearance, whereas those from virus-infected flies were transparent in most parts. The ARGs from virus-infected males were significantly smaller in diameters (F = 42.26, p < 0.0001) and shorter (F = 200.4, p < 0.0001) than those of the controls. Most of the virus-infected males failed to form a complete spermatophore, whereas almost all the controls formed complete spermatophore as observed in the uteri of the female mates (Χ² = 111.661, p < 0.0001). The infected males that formed partial spermatophores and those that did not form any at all failed to inseminate their female mates. Histological studies of the ARGs revealed some lesions in the epithelial cells characterized by degeneration of cytoplasmic organelles and detachment of the muscle layer from the basal plasma membrane. However, no virus particles were observed in the affected cells. Received: 18 November 1998 / Accepted: 10 December 1998     

The effects of allatectomy and ovariectomy on haemolymph proteins and lipid mobilization in Locusta

After ovariectomy the concentrations of diacylglycerol and protein in the haemolymph increase markedly. The increased diacylglycerol is associated with increased quantities of the ‘heparin-precipitable’ protein (lipoprotein A) that carries diacylglycerol in the blood of normal resting locusts. After the injection of adipokinetic hormone (AKH), the blood of ovariectomized locusts contains only slight quantities of the ‘heparin-soluble’ lipoprotein A⁺ whereas this forms in large amounts in the blood of sham-operated locusts after AKH injection. After allatectomy, the increase in the adipokinetic response is slower and the full level of responsiveness observed in sham-operated locusts is never attained. Nevertheless, allatectomized locusts develop a marked adipokinetic response which tends to stabilize as they age; it does not deteriorate as it does in aged sham-operated locusts.The effects of ovariectomy on blood metabolites can be prevented completely by allatectomy, but only partially by cautery of the cerebral neurosecretory cells. Treatment with a juvenile hormone analogue (JHA R-20458) counteracts the effects of allatectomy in ovariectomized locusts.     

Predators,parasitoids and pathogens of ticks: A review

Research conducted on natural enemies of ticks, namely predators, parasitoids and pathogens, is reviewed. Predators include ants, birds, rodents, lizards, shrews, spiders and domestic chickens. All the known parasitoids are hymenopteran wasps belonging to the genera Ixodiphagus and Hunterellus. The work so far done on bacteria, fungi, viruses and rickettsiae which are pathogenic to ticks is reviewed, both with regard to experimental infections and natural infections. The possibilities of using natural enemies as biological control agents of ticks are discussed.     

Diglyceride-transporting lipoproteins inLocusta

Summary The majority of haemolymph proteins obtained from resting mature locusts are soluble in 50% saturated (NH₄)₂SO₄ solution. Chromatographically, these proteins may be resolved on Sepharose 6B into three partially included fractions. The leading high molecular weight fraction, A, is predominant and all the diglyceride in resting blood is associated with it. An additional higher molecular weight fraction, A⁺, is present in the haemolymph of locusts injected with extracts of the glandular lobes of the corpora cardiaca (elevated blood), and this fraction carries all the increased diglyceride. Fraction A⁺ is better resolved on Ultrogel ACA 22. A useful rapid technique for studying the formation of A⁺ lipoprotein during lipid mobilization has been developed by the use of lipoproteinpolyanion-metal ion complex formation. A⁺ is soluble after heparin treatment whereas the yellow leading edge of fraction A precipitates. Concomitant with the appearance of A⁺ there is a marked depletion of a lower molecular weight non lipid-carrying protein fraction, C. The ability to form fraction A⁺ after injections of glandular lobe extract cannot be demonstrated in fledglings (immature locusts within 2 or 3 days after the imaginal moult) where fraction C is virtually absent. It is suggested that during lipid mobilization, some lipoprotein from fraction A combines with protein from fraction C to form A⁺. A direct effect of adipokinetic hormone on the process of A⁺ formation cannot be excluded.     

Monitoring Important Bird Areas in Africa: Towards a Sustainable and Scaleable System

The need for effective global monitoring of biodiversity is clearer than ever, but our measurements remain patchy and inadequate. In the biodiversity-rich tropics, a central problem is the sustainability of monitoring schemes. Locally-based, participatory approaches show promise in overcoming this problem, but may not contribute effectively to monitoring at larger scales. BirdLife International’s framework for monitoring Important Bird Areas (IBAs) in Africa is designed to be simple, robust and locally-grounded, but to produce scaleable results that can be compiled into national or regional indices. Focusing on key sites for bird conservation, identified according to standard criteria, the framework institutionalises monitoring in site management authorities and Site Support Groups (community-based organisations of local people working for conservation and sustainable development). A small, central monitoring unit co-ordinates the programme nationally, compiles, analyses and manages data, and provides feedback. ‘Basic’ monitoring (taking place at all sites) involves scoring of state, pressure and response trends using site information submitted on simple forms. ‘Detailed’ monitoring (taking place at a selected sub-set of sites) involves more intensive measurement of particular variables that relate to site management targets. IBA monitoring is now underway in at least 10 African countries, with implementation of the framework most advanced (thanks to a pilot project) in Kenya. The 2004 IBA monitoring report for Kenya provides extensive information on individual IBAs, plus indices for national trends in state, pressure and response, based on data from 49 out of 60 sites. The experience in Kenya shows that institutionalisation is vital, but takes considerable time and effort; that adequate co-ordination (including timely feedback) is key; and that participatory monitoring has many valuable benefits beyond the data collected. Further work is being undertaken to refine the process, improve its scientific underpinning, and strengthen the feedback loop from data and analysis to action on the ground.     

The impact of Ixodiphagus hookeri, a tick parasitoid, on Ambl yomma variegatum (Acari: Ixodidae) in a field trial in Kenya

In an experiment to investigate the effect of the tick parasitoid, Ixodiphagus hookeri, on tick numbers on cattle, 150 000 parasitoids were released over a period of 1 year in a field where ten cattle infested with multiple tick species were kept. Amblyomma variegatum was reduced from 44 to two ticks per animal while Rhipicephalus appendiculatus increased over the time of parasitoid release. During the time of release 51% of the nymphs of A. variegatum collected from the animals were parasitized. The recovery of the parasitoids after the releases were stopped was only 9%. The total numbers of A. variegatum remained low up to 1 year after the parasitoid release was stopped. This study gives an insight into how I. hookeri could be used strategically for the management of A. variegatum on small-scale farms.     

Environmental factors affecting the distribution of African elephants in the Kasigau wildlife corridor,SE Kenya

The African elephant, Loxodonta africana, is under threat from habitat loss, poaching and human–elephant conflict. To mitigate for impact of habitat loss and reduce conflict, connectivity between elephant habitats can be improved through the protection of corridor areas. This study looks at elephant distribution and movement patterns within the Kasigau Wildlife Corridor (KWC) within the Tsavo Conservation Area in South‐east Kenya. Elephant presence data were obtained from observations by rangers during routine patrols across KWC, and were analysed in MaxEnt. The environmental factors predicting elephant distribution and density were tested, as well as the relationship between elephant maximum entropy and the presence and abundance of other wildlife. Seasonal variations in temperature and precipitation, plus presence of waterholes were found to play significant roles in elephant distribution across KWC. Higher elephant densities were not found to correlate with lower densities of other wildlife species; indeed, during the dry seasons, elephant presence was associated with greater wild herbivore densities. Besides illustrating the importance of the KWC for elephant conservation in the Tsavo ecosystem, both as a key corridor and habitat, this study also hopes to highlight the untapped utility of routine ranger patrol data, and encourage the use of such presence‐only data for deducing important knowledge for conservation of biodiversity.