Wendengoudi Guenda

Using macroinvertebrates for ecosystem health assessment in semi-arid streams of Burkina Faso

Efficient monitoring tools for the assessment of stream ecosystem response to urbanization and agricultural land use are urgently needed but still lacking in West Africa. This study investigated taxonomic and functional composition of macroinvertebrate communities at 29 sites, each exhibiting one of four disturbance levels [‘protected’ (P), ‘extensive agriculture’, ‘intensive agriculture’ (IA) and ‘urban’ (U)] in Burkina Faso and explored their potential for bioassessment. We recorded a total of 100 taxa belonging to 58 families, with the highest richness (16.9 taxa per site) observed in the sites with IA and lowest (3.4 taxa) in U sites. We found a gradual decrease of sensitive Ephemeroptera, Plecoptera and Trichoptera taxa and of collector-filterers feeding guild between P, agricultural and U sites accompanied by an increase in the relative abundance of tolerant dipteran taxa. Measures of overall taxonomic richness and diversity were mostly efficient in detecting the high impoverishment of the U sites, while FFG ratios did not deliver consistent results. Finally, all four land use types were successfully distinguished by identifying indicator taxa through hierarchical clustering and indicator value index. This work produced an unprecedented faunal inventory of Burkina Faso streams and laid the basis for the development of urgently needed stream assessment tools.

Developing reference criteria for the ecological status of West African rivers

Awareness of sustainable management of water and its biological resources is rising in West Africa, but application of effective tools for biomonitoring and detecting habitats at risk in aquatic ecosystems is limited. In this study, we provide key environmental descriptors to characterize reference sites by applying the following “a priori criteria” (physical and chemical, hydro-morphological, and land use parameters) by exploring their potential to determine suitable reference sites. Using data collected from 44 sites, we identified 37 criteria that reliably identify reference conditions in semi-arid rivers by reflecting the impacts of multiple pressures ranging from low to very high intensity of human uses and impairments. We integrated all these impacts in an overall pressures index, which showed that protected areas can reasonably be considered as credible reference sites as far as they show low overall impact levels from cumulative pressures. We recommend that development of bio-indicator standards should be based on the collection and integration of all the available information, especially quantitative, spatially-explicit data, from benthic macroinvertebrates and fish. Rigorous standardization of bio-indicator protocols will make them more easily applicable for management and conservation of aquatic ecosystem resources in semi-arid zones of Africa.

Bushmeat consumption in the West African Sahel of Burkina Faso, and the decline of some consumed species

To explore the patterns of bushmeat trade in the Sahel we carried out a multidisciplinary study, focusing on Burkina Faso. We conducted baseline interview surveys to examine the variation in peoples perceptions of bushmeat in relation to their place of residence (urban vs rural), sex and age. We also analysed the long-term (1985–2010) population dynamics of two ungulate species, the oribi Ourebia ourebi and the common duiker Sylvicapra grimmia, known to be among the main targets of the bushmeat trade locally. For the antelopes we chose as our study area a protected area (Nazinga Game Ranch) where poaching activities occur and are likely to represent a threat to the local wildlife. The results of the interviews underlined significant differences in bushmeat consumption between rural and urban areas. In particular, the probability of finding people who did not consume bushmeat increased in the urban area, where bushmeat is less available than in the rural areas. Sex and age did not have any effect on peoples perceptions of bushmeat. In Burkina Faso bushmeat is still widely consumed, and this could be because the bushmeat trade is poorly controlled, with a lack of enforcement of the legislation. Long-term field surveys revealed that the oribi and the common duiker have declined significantly in Nazinga Game Ranch, suggesting that the bushmeat trade in Burkina Faso may have negative consequences in terms of the conservation outlook for these species.

First assessment of age and sex structures of elephants by using dung size analysis in a West African savannah

Abstract 1. An age and sex structure study of the West African savannah elephant (Loxodonta africana africana) population of the Nazinga Game ranch (Burkina Faso) was carried out using direct sightings of individuals near water points, where they group during hot periods of the day, and droppings circumference measurements of dung pile along line transects, during the dry seasons of 2007 and 2008. The age structure, from direct observation data, was estimated by classifying the individuals into 9 age-class-categories based on body size and eruption (length) of tusks. 2. The frequency distribution of number of individuals into the age-class-categories showed high similarity with the distribution of circumference measurements of dung-piles that the individuals were seen depositing. Fifty dung-piles measured soon after they were deposited (Class A) and after they dried (to class C) showed a significant difference between the circumference measurements in relation to the time elapsed between the measurements. 3. The frequency distribution of dung circumference classes of the observed elephants was similar to that of the dung-piles measured along the transects in 2008. Therefore, dung-piles measurements were used to estimate the Nazinga Game Ranch savanna elephant population’s age and sex structures at the end of dry seasons of 2007 and 2008. We advocated that the Nazinga elephant population consisted mainly of sub-adults. 4. The sex ratio was estimated to be in favour of females (1/2). The age-class-specific sex ratio was uneven for calves and young individuals, while being in favour of females with adults. Individuals of less than 1 year represented 6% of the population during the study period.

Selective disturbance by elephants (Loxodonta africana) on eight tree species in a West African savannah

African elephants (Loxodonta africana) are ecosystem engineers in African savannahs, but their role in the modifications of the populations of trees by means of their browsing activities has been poorly studied so far in West Africa. We studied the disturbance of elephants to eight selected species of trees in the Nazinga Game Ranch (Burkina Faso), in 54 transects at the end of dry season 2008. We fitted simple models describing the number of dead individuals for each tree species in relation to their initial population density, and in relation to dung-pile density, in the assumption that there should be a positive relationship between elephant density and dung-pile density. Generalized Linear Model analyses and regression analyses showed that the more dense the woodland cover, the least the percentage of damaged plants by elephants. For each plant species, the initial density and density of elephant dung-piles explained a high proportion of the variance in the density of dead individuals. Stochastic models, generated by a purposely created simple computer program written in GW-BASIC programming language, predicted changes in tree and shrub abundance under different assumptions about elephant numbers. The models suggested that elephant browsing may cause considerable change in the selected plant populations, especially with regard to such species as Acacia gourmaensis, Vitellaria paradoxa and Maytenus senegalensis. These changes may possibly increase the meat harvest from controlled hunting activities, thus improving the income for surrounding communities.

Assessment of benthic molluscs diversity and distribution in urban reservoirs (Ouagadougou, Burkina Faso)

The urban reservoirs n° 2 and n°3 of Ouagadougou, located in the middle of the city are subject to multiple anthropogenic pressures which threaten the diversity of benthic macroinvertebrates community group like molluscs. This study was initiated to assess the diversity and distribution of benthic molluscs in these reservoirs. Molluscs samples were collected monthly using an Eckman grab (12 x 20 cm 2 ) between September 2011 and February 2012 in 24 sampling points defined on each reservoir. In parallel, physicochemical variables and water colon depth were measured. After sampling, molluscs were transported to the laboratory for identification. A total of 328 specimens were collected of which 5 species were identified: three species of Gastropods ( Bellamya unicolor , Cleopatra bulimoides , Lanistes ovum ) and two species of Bivalves ( Coelatura aegyptiaca , Mutela rostrata ). B. unicolor was the most abundant species with 71% of the collected molluscs and preferentially occupied the edges of the reservoir. It was followed by C. aegyptiaca (27%) which was abundant in the central axis of the reservoir. Physicochemical variables influence the distribution of species. For all measured physicochemical factors, B. unicolor was more tolerant than C. aegyptiaca on the occupation of available habitat.