Monitoring large herbivore diversity at different scales: comparing direct and indirect methods

Monitoring of large herbivores is central to research and management activities in many protected areas. Monitoring programs were originally developed to estimate (trends in) population sizes of individual species. However, emphasis is shifting increasingly towards conservation of diversity and communities instead of individual species, as a growing literature shows the importance of herbivore diversity for ecosystem functioning. We argue that the design of monitoring programs has not yet been adapted well to this new conservation paradigm. Using large herbivore census data from Hluhluwe-iMfolozi Park, South Africa, we studied how monitoring methodology (observational counts vs. dung counts) and spatial scale interact in influencing estimates of large herbivore species richness and diversity. Dung counts resulted in higher herbivore species richness and diversity estimates than direct observational counts, especially at finer monitoring resolutions (grid cells smaller than 25 km²). At monitoring resolutions coarser than 25 km² both methods gave comparable diversity estimates. The methods also yielded different spatial diversity estimates, especially at finer resolutions. Grid cells with high diversity according to the dung count data did not necessarily have high diversity according to the observational counts, as shown by low correlation of grid cell values of both methods. We discuss these results in the light of estimates of the sampling effort of each method and, hence, suggest new monitoring designs that are more suitable for tracking temporal and spatial trends in large herbivore diversity and community composition.     

How reliable are dung counts for estimating elephant numbers?

Dung counts are the most commonly used techniques for estimating elephant numbers in forests, yet there is considerable scepticism concerning their accuracy. Published accounts of dung counts show that they give estimates similar to those from other methods for vertebrates ranging in size from lizards to elephants. For ungulates, macropods and elephants there are strong correlations between estimates from dung counts and other methods. Thus, dung counts are as accurate or inaccurate as other methods for estimating vertebrate numbers, including elephants. Dung counts for elephants give estimates that are as precise as, and sometimes more precise than, those from aerial surveys of elephants. This is because the variance in dung density is usually low and results in a lower than expected variance for the final elephant estimate when combined with the variances of defecation and decay rates. Dung counts may be more appropriate than aerial surveys for monitoring small or declining elephant populations.     

“Ordinary biodiversity” in western Burkina Faso (West Africa): what vegetation do the state forests conserve?

The role of state forests in the conservation of the savannah environment of western Burkina Faso (West Africa) was assessed by considering the customary and fundamental biological components of plant diversity. The focus is on the “ordinary biodiversity” which constitutes the current environment of human populations and which generates their resources. Overall floristic composition, α, β, γ diversities and species accumulation curves of landscape units were compared inside and outside protected areas. Common species were identified according to their frequencies in landscape units and their local abundance. The occurrences of functional (life form, dispersion, etc.) and human-valued (current uses, potential threats, etc.) traits were compared. Current land uses outside protected areas have an unequal effect on the various components of plant diversity. Species richnesses and specific structures were all the more altered for woody species as agricultural pressure is high; conversely, they were maintained for herbaceous communities for which the proportion of wide-ranging species increased. The preservation of useful plant species on cultivated lands was obvious for woody species with edible fruits but less tangible for timber and service wood. It was deficient for species that furnish other non-wood products (e.g. leaves used as food or fodder), the conservation of which may be jeopardized where anthropic pressure is high. Given current land uses and dynamics, maintaining conservation areas in land use planning is crucial in order to preserve ordinary biodiversity. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The decline of raptors in West Africa: long-term assessment and the role of protected areas

Comparative large‐scale roadside counts (8353 km), through Burkina Faso, Mali and Niger, conducted in 1969–73, were repeated 30–35 years later with the same observer and methodology and at the same season. The transect was divided into three geographical zones and between protected and unprotected areas. All diurnal raptors were recorded (22 801 individuals), as well as large game birds. Large vultures suffered a dramatic decline (98%) outside protected areas. The Hooded Vulture Necrosyrtes monachus population also collapsed in some regions, but survived in central Burkina Faso. Conversely, their abundance index did not decrease significantly in national parks. Four eagle species decreased by 86–93% and seven were not even recorded in the later study outside protected areas; by contrast, in national parks, only three species had declined marginally. Smaller Accipitridae (kites, goshawks, buzzards) also exhibited significant declines outside but not within national parks where woodland species reached their highest densities. The Common Kestrel Falco tinnunculus, mostly European migrants, declined sharply everywhere. African falcons decreased only outside protected areas. Among Palearctic migrants, Montagu's Circus pygargus and Pallid Harriers C. macrourus decreased significantly, Short‐toed Eagle Circaetus gallicus less markedly, and Marsh Harrier Circus aeruginosus and Booted Eagle Hieraaetus pennatus not at all. Similar trends had previously been documented in Cameroon. They are associated with human population growth and development, global habitat degradation and ecosystem impoverishment (woodcutting, agricultural intensification, overgrazing, desertification). Heavy use of pesticides, control of locust outbreaks and overhunting have suppressed major food sources. Vultures may suffer from a shortage of carcasses, poisoning for predator control or persecution for trade of meat and body parts. Protected areas play a prominent role in the maintenance of vulture and eagle populations, even though they currently cover less than 2% of the Sudan zone and are virtually absent in the Sahel.     

The problem of precision and trend detection posed by small elephant populations in West Africa

The precision of elephant estimates from aerial sample surveys and dung counts is inversely proportional to abundance. West African elephant populations are already small, and the power of a monitoring programme to detect changes in abundance diminishes as the population shrinks in size. Thus it will be difficult to evaluate the effects on elephant numbers of new management policies in West Africa. The same will be true of monitoring schemes for antelope and primate populations that are hunted for bushmeat. Elephant estimates from dung counts are more precise than those from aerial sample surveys, and changes in elephant numbers are more likely to be detected in the subregion by dung counts than by aerial sample surveys.     

Estimating abundance for a savanna elephant population using mark–resight methods: a case study for the Tembe Elephant Park, South Africa

Elephants living in dense woodlands are difficult to count. Many elephant populations in Africa occur in such conditions. Estimates of these populations based on total counts, aerial counts and dung counts often lack information on precision and accuracy. We use standard mark–recapture field methods to obtain estimates of population size with associated confidence limits. We apply this approach to a closed elephant population in the Tembe Elephant Park (300 km²), South Africa. A registration count completed in 4 months gives a known population size. We evaluate mark–recapture models against the known population size. Individual identification profiles obtained for elephants during the registration count and mark–recapture events indicate that at least 167 elephants live in the park. We consider this value as an estimate of the minimum number alive. We include 189 sightings of bulls and 37 sightings of breeding herds in the mark–recapture modelling. Of the models we test (Petersen, Schnabel, Schumacher, Jolly–Seber, Bowden's, Poisson and negative binomial), Bowden's gives an estimate closest to the registration count. Assumptions of the model are not violated. For all models except one (negative binomial), our estimates improve with increased sampling intensity. Confidence intervals do not improve with increased effort except for the Schnabel model. Mark–recapture methods should be considered as reliable estimators of population size for elephants occurring in dense woodlands and forests when other methods cannot be relied on.     

Phylogeography of Mus (Nannomys) minutoides (Rodentia,Muridae) in West Central African savannahs: singular vicariance in neighbouring populations

We studied the phylogeography of the strict savannah pygmy mice Mus (Nannomys) minutoides in West Central Africa. A total of 846 base pairs of the cytochrome b sequence were obtained for 66 individuals collected in Gabon, Cameroon, Republic of Congo and Central African Republic. These sequences were compared to those of M. minutoides from other African countries and to eight other species of the genus Mus. We performed maximum likelihood, Bayesian and nested clade analyses, as well as neutrality tests and time estimates. We show that M. minutoides is a well‐differentiated monophyletic species that separated from other pygmy mice 1.17 Myr ago. A distinct West Central African M. minutoides clade diverged early from the other African populations of the species, with a more recent common ancestor dating 0.14 Myr. West Central African populations are globally homogeneous, despite the present fragmentation of savannahs by the rain forest. However, our analyses show an unexpected vicariance between geographically close savannahs, embedded in the rain forest in Central Gabon. One of these populations is genetically more similar to very distant peripheral populations than to three closely neighbouring populations situated on both sides of the Ogooué River. A non‐river geographical barrier probably persisted in this area, durably isolating these local populations. This hypothesis about the history of the savannah landscape should be testable through the biogeographical analysis of other strict savannah small mammal species.     

Trapping tsetse flies on water

Riverine tsetse flies such as Glossina palpalis gambiensis and G. tachinoides are the vectors of human and animal trypanosomoses in West Africa. Despite intimate links between tsetse and water, to our knowledge there has never been any attempt to design trapping devices that would catch tsetse on water. In mangrove (Guinea) one challenging issue is the tide, because height above the ground for a trap is a key factor affecting tsetse catches. The trap was mounted on the remains of an old wooden dugout, and attached with rope to nearby branches, thereby allowing it to rise and fall with the tide. Catches showed a very high density of 93.9 flies/"water-trap"/day, which was significantly higher (p < 0.05) than all the catches from other habitats where the classical trap had been used. In savannah, on the Comoe river of South Burkina Faso, the biconical trap was mounted on a small wooden raft anchored to a stone, and catches were compared with the classical biconical trap put on the shores. G. p. gambiensis and G. tachinoides densities were not significantly different from those from the classical biconical one. The adaptations described here have allowed to efficiently catch tsetse on the water, which to our knowledge is reported here for the first time. This represents a great progress and opens new opportunities to undertake studies on the vectors of trypanosomoses in mangrove areas of Guinea, which are currently the areas showing the highest prevalences of sleeping sickness in West Africa. It also has huge potential for tsetse control using insecticide impregnated traps in savannah areas where traps become less efficient in rainy season. The Guinean National control programme has already expressed its willingness to use such modified traps in its control campaigns in Guinea, as has the national PATTEC programme in Burkina Faso during rainy season.     

Using sample aerial surveys to estimate the abundance of the endangered Grevy’s zebra in northern Kenya

The effective management of endangered mammals requires reliable estimates of population size. This is challenging for species such as Grevy’s zebra (Equus grevyi) that are distributed over large areas at low densities. Less than 2500 Grevy’s zebra remain in the wild, scattered across 85,000 km² of savannah in northern Kenya and Ethiopia. An efficient, accurate and repeatable survey method is required to guide conservation planning for the species. Currently, total aerial counts are used to census endangered species within Kenya, but are costly in terms of resources. In this study, we evaluated the suitability of sample survey methods for Grevy’s zebra. We estimated population size using sample aerial counts for a known population of Grevy’s zebra in Lewa Wildlife Conservancy (LWC), providing the opportunity to test the accuracy of sample methods, while comparing resource costs with total count methods. We sampled one‐third of LWC using parallel 500‐ m strip transects at 1500‐ m intervals. The population estimate was comparable to the known population size and was less than half as expensive as the equivalent total count survey. Our results suggest sample aerial surveys provide an accurate and cost‐effective means of monitoring Grevy’s zebra and other endangered species in open habitats.     

The relationships between the burden of adult parasites, host age and the microfilarial density in human onchocerciasis

We investigate the relationship between the microfilarial density in the skin and the burden of adult female Onchocerca volvulus by analysing pre-control nodulectomy data which allow for a direct approach, independent of exposure. The data of 169 patients in Burkina Faso and 182 patients in Liberia represent savannah and forest onchocerciasis in West Africa, respectively. Whereas in Burkina Faso, a saturating relationship between microfilarial density and worm burden suggests the operation of density-dependent processes within human hosts, the Liberian data show a linear relationship implying no density dependence. The differences may derive from differences between both parasite strains, i.e. the savannah or the forest strain of O. volvulus. Consistently for both parasite strains and independent of the worm burden, the microfilarial density increases with host age emphasising the concept of the acquisition of immunological tolerance. In male hosts in Liberia, the microfilarial density increases stronger with the worm burden than in female hosts, whereas such sex-specific differences cannot be found in Burkina Faso. In the methodological part of this investigation, we suggest the beta-distribution to be most appropriate for describing variability in microfilarial densities and we present an approach to consider the uncertainty in the adult parasite burden which cannot be determined precisely in helminth infections. Implications of density dependence are discussed with respect to immunological processes in the human host and with respect to the success of control programs. The relationships described show that regulatory processes between the parasite and the human host are multi-dimensional, operating within a high degree of biological variability.     

Zoogeography of a South African Province: A framework for management

State‐level conservation in South Africa is structured around distinct political entities (i.e. municipalities). This is problematic because an ecological approach that considers species distribution is required to delineate meaningful management units. To do so, vegetation types can be used as management units—however, it is uncertain whether vertebrate communities are associated with vegetation types as defined by the national vegetation map. Here, we investigate mammal diversity patterns within and among biomes (savannah and grassland) and bioregions and test whether different mammal communities were associated with different vegetation types. We used an extensive database of species occurrences in the North West Province. We found that species richness was higher in the savannah than grassland biome. Beta diversity was higher within the savannah than grassland biome, due to greater environmental heterogeneity, though one grassland bioregion was similar to the savannah bioregions. Mammal communities were significantly different among bioregions, but not biomes, suggesting mammal communities are congruent with vegetation type at finer scales (i.e. bioregional), but not at coarser scales (biomes). It thus makes sense to use a bioregional framework to design mammal management strategies. The invasion of grasslands by savannah species should be monitored, specifically given the predicted changes in climate.     

The second record of Diaphanosoma senegal Gauthier, 1951 (Crustacea : Daphniiformes : Sididae) in Africa,with a redescription of the species and ecological and distributional setes

The rare Diaphanosoma senegal has been found for the second time in Africa, in a water body North of Uagadugu (Burkina Faso). The species is here redescribed, with attention to individual and age variation. It combines primitive and evolutionarily advanced structural features, and inhabits temporary and intensely fluctuating water bodies of the equatorial and tropical zones. According to available data, its range is confined to West Africa and India.     

Age determination of the West African buffalo Syncerus caffer brachyceros and the constancy of tooth wear

Maxillae of 34 West African buffalo Syncerus caffer brachyceros were collected from three sites in Burkina Faso, West Africa, and age determined from tooth appearance and the enamel height of M1 according to the criteria of Grimsdell (1973) for Ugandan buffalo Syncerus caffer caffer. Good agreement between the two methods was found. Ground and decalcified sections were prepared from M1 and the interradicular cementum lines counted. Although this gave inconsistent results in terms of assumed age compared with the other two methods, it is concluded that agreement was sufficiently close to suggest that the rate of attrition with age was similar in both populations.     

Monitoring populations of Western Sandpipers and Pacific Dunlins during northward migration on the Fraser River Delta,British Columbia, 1991–2013

The Fraser River Delta in British Columbia, Canada, is a globally significant stopover site for shorebirds, but the population status and trends of many species that use the site remain uncertain. We describe an ongoing program to monitor population trends of the two most abundant species, Western Sandpipers (Calidris mauri) and Dunlins (Calidris alpina), during northward migration. Counts of these species were conducted at a mudflat where large flocks assembled at mid‐tide from 15 April to 15 May, 1991–2013, and we estimated species‐specific counts as the product of daily total flock counts and species proportions obtained during supplementary sampling. The median peak count of both species combined was 177,000 birds, and occurred between 24 April and 3 May. Ratios (proportions) of the two species followed a predictable pattern during the migration period, with a low proportion of Western Sandpipers (3%–20%) in flocks before 20 April, followed by a rapid increase to 80%–100% between 25 April and 10 May and a variable decrease to 30%–80% by 15 May. Mean counts of Western Sandpipers showed no significant trend over the study period. Mean counts of Dunlins showed a non‐linear trend, decreasing until 2001 and then increasing to 2013. Bias and random error in field counts were quantified by comparing field counts to counts made from photographs taken during surveys, and analysis revealed that field counts had a downward, but predictable, bias, accounting for >90% of birds present, with a stochastic error rate of 28.0%. Uncertainty in total population estimates was high after accounting for the effect of length of stay and sampling error. Population estimates suggested that 600,000 Western Sandpipers and 200,000 Dunlins typically passed through the site during northward migration. Our estimates indicate the usefulness of daily counts at major stopover sites during northward migration as an effective tool for monitoring shorebird populations, and underscore the need for conserving such sites.     

Assessing introgression of Sahelian zebu genes into native Bos taurus breeds in Burkina Faso

A total of 350 samples were analyzed to estimate zebu gene proportions into two different taurine cattle breeds of Burkina Faso (Lobi and N’Dama) using 38 microsatellites and various statistical methodologies. West African and East African zebu samples were sequentially used as reference parental populations. Furthermore, N’Dama cattle from Congo, the composite South African Bonsmara cattle breed and a pool of European cattle were used successively as second parental populations. Independently of the methodology applied: (a) the use of West African zebu samples gave higher admixture coefficients than the East African zebu; (b) the higher zebu proportions were estimated when the European cattle was used as parental population 2; and (c) the use of the N’Dama population from Congo as parental population 2 gave the more consistent zebu proportion estimates for both the Lobi and the N’Dama breeds. In any case, the zebu admixture proportions estimated were not negligible and were always higher in the N’Dama cattle than in the Lobi cattle of Burkina Faso. This suggested that the introgression of Sahelian zebu genes into the taurine cattle of Southern West Africa can follow a complex pattern that can depend on local agro-ecological features. The current research pointed out that the estimation of admixture coefficients is highly dependent on both the assumptions underlying the methodologies applied and the selection of parental populations. Our analyses suggest that either too high or nil genetic identity between the parental and the expectedly derived populations must be avoided.     

Variation and geographical distribution of ploidy levels inPennisetum sectionBrevivalvula (Poaceae) in Burkina Faso,Benin and southern Niger

Pennisetum sect.Brevivalvula is a species complex characterized by polyploidy and apomixis. Ploidy level was assessed by DAPI-flow cytometry for 304 plants of the section, originating from Burkina Faso, Benin and southern Niger. The results were confirmed for 54 plants based on chromosome counts. The samples show four euploidy levels (with x = 9) distributed among five species:P. hordeoides (2n = 36, 54),P. pedicellatum (2n = 36, 45, 54),P. polystachion (2n = 18, 36, 45, 54),P. setosum (2n = 54), andP. subangustum (2n = 18, 36, 54). The geographical distribution of these ploidy levels seems related to major vegetation zones present in Africa. Diploid populations ofP. polystachion andP. subangustum were found in the Banfora area, in Burkina Faso.     

Herbarium collections and field data-based plant diversity maps for Burkina Faso

A map of plant species diversity in Burkina Faso is presented based on field observations and specimen data from the Ouagadougou University Herbarium (OUA) and the Herbarium Senckenbergianum (FR). A map of collecting intensity and field observations illustrates centres of botanical research activities in Burkina Faso. To overcome problems associated with biased sampling intensity, distributions of species have been modelled and extrapolated to maps of vascular plant diversity, life forms and diversity of four selected families (Poaceae, Cyperaceae, Dioscoreaceae and Rubiaceae). The area of most intensive collection and observation is around Gorom‐Gorom and Fada N’Gourma. Modelled diversity generally increases towards the south, as does the proportion of phanerophytes, lianas and hemicryptophytes, while the opposite trend is observed for therophytes. Poaceae diversity is highly correlated with total vascular plant diversity, making the family especially suitable as an indicator for overall plant diversity. Cyperaceae are rather evenly distributed throughout the country, Dioscoreaceae are restricted to the Sudanian Zone. Rubiaceae have their highest diversities in the very south. Our approach can be transferred to areas with a similar database, certainly to other areas within West Africa. Future research should focus on distribution data for rare species, enabling our approach to evaluate the West African system of protected areas.     

The worst drought in 50 years in a South African savannah: Limited impact on vegetation

South Africa experienced a severe multiyear drought from 2014 to 2016. Here, we explore the response of a South African savannah ecosystem to this drought focusing on tree and grass dynamics. We used open long‐term monitoring plots established in 2000 and distributed across broad rainfall gradients in the Hluhluwe‐iMfolozi Park in KwaZulu‐Natal. Analysis showed negligible tree mortality due to drought in 2016 (0.03%) and 2017 (0.49%). However, there was an apparent increase in the tree population especially among the small size classes (0.1–0.3 m) in 2016 and 2017 relative to the predrought 2012 census. Drought effects may be confounded with changes in browser populations. The impala population declined in a mesic savannah (Hluhluwe), as measured with dung counts; however, this decline started before the drought. Impala decline in a semi‐arid savannah (iMfolozi) was more coincident with drought. Grass biomass and cover decreased in 2016 compared to predrought 2012 but showed rapid recovery once rains began. In iMfolozi grass species, composition improved from a grazing perspective as a result of the recovery of the decreaser species, an increase in palatable species and a marked decline of unpalatable species. The minor changes in woody plants and grasses from before the drought until rain resumed and the rapid recovery of grasses suggest that this South African savannah ecosystem was resilient to severe drought.     

Comparison of point counts and territory mapping for detecting effects of forest management on songbirds

Point counts are commonly used to assess changes in bird abundance, including analytical approaches such as distance sampling that estimate density. Point‐count methods have come under increasing scrutiny because effects of detection probability and field error are difficult to quantify. For seven forest songbirds, we compared fixed‐radii counts (50 m and 100 m) and density estimates obtained from distance sampling to known numbers of birds determined by territory mapping. We applied point‐count analytic approaches to a typical forest management question and compared results to those obtained by territory mapping. We used a before–after control impact (BACI) analysis with a data set collected across seven study areas in the central Appalachians from 2006 to 2010. Using a 50‐m fixed radius, variance in error was at least 1.5 times that of the other methods, whereas a 100‐m fixed radius underestimated actual density by >3 territories per 10 ha for the most abundant species. Distance sampling improved accuracy and precision compared to fixed‐radius counts, although estimates were affected by birds counted outside 10‐ha units. In the BACI analysis, territory mapping detected an overall treatment effect for five of the seven species, and effects were generally consistent each year. In contrast, all point‐count methods failed to detect two treatment effects due to variance and error in annual estimates. Overall, our results highlight the need for adequate sample sizes to reduce variance, and skilled observers to reduce the level of error in point‐count data. Ultimately, the advantages and disadvantages of different survey methods should be considered in the context of overall study design and objectives, allowing for trade‐offs among effort, accuracy, and power to detect treatment effects.