35 research outputs found
Local and regional factors influencing dung beetle assemblage structure across an environmental gradient in Botswana
The taxonomic composition, structure, and diversity of current local species assemblages results from an interacting complex of historical, regional ecological and local ecological factors. Structural differences between such current species assemblages are primarily determined by changing ecological conditions across spatial gradients. These conditions may change abruptly or they may represent a gradual divergence. Across the Botswana Kalahari basin there is a gradual northeast-southwest aridity and dung type gradient, which was demonstrated to strongly influence dung beetle assemblage structure at six study sites from Chobe National Park to the Central Kalahari Reserve to the Kgalagadi Transfrontier Park using carrion and four dung types as bait (pig, elephant, cattle, sheep). Regional patterns were primarily influenced by climate (rainfall) while dung type mainly showed a local influence on patterns of variation. Four distinct biogeographical groups were defined for the study region comprising widespread, northeast/widespread, northeast, and arid southwest Kalahari-centred species. Biogeographical diversity was higher in the more mesic NE than the arid SW but varied somewhat between bait types. In the SW, Kalahari endemics dominated all bait types. In general, abundance and species richness declined along the aridity gradient although the pattern was uneven due to low numbers in the north of the Central Kalahari Game Reserve. Species showed high turnover (beta – diversity), particularly between the moister NE and the Kalahari/Savanna ecotone. Hierarchical Analysis of Oblique Factors showed statistically distinct separation between assemblage structure at the six study sites and that the proportion of mesic NE shared influence on assemblage composition declined towards the SW where there was an increase in Kalahari endemics. Similarly the proportion of arid SW shared influence declined towards the NE. Plotting these results onto a map showed that the point of intersection between shared NE or SW influence lay very close to the ecotone between SW (Kalahari Xeric Savanna) and NE-centred ecoregions (Acacia-Baikiaea Savanna) defined for the area by Olson et al. (2001). In terms of dung type diversity, increasing aridity across the Kalahari represents a gradient of diminishing resources with the loss of large dung types to the SW and increasing dominance of dung pellets. Several different patterns of response were shown using different methods. Four principal patterns of bait type association were indicated by one method. Another method showed that, rather than diminishing numbers of competing species leading to widening niche widths to the SW, niche widths were narrowest at the Kalahari / mesic Savanna ecotone. Using several other multivariate techniques, three different patterns of dung type resource partitioning were demonstrated that paralleled the aridity gradient, one common to the NE and two to the SW. The historical, regional and local ecological factors influencing these patterns of dung beetle assemblage structure are discussed as well as implications and recommendations for conservation.Thesis (PhD)--University of Pretoria, 2011.Zoology and Entomologyunrestricte
Dung beetle assemblage structure across the aridity and trophic resource gradient of the Botswana Kalahari : patterns and drivers at regional and local scales
Understanding pattern and process at both regional and local scales is important for conservation planning although such knowledge of insects is frequently lacking. To assess patterns along a regional gradient of increasing aridity and diminishing food resources in the Botswana Kalahari, Scarabaeine dung beetles were sampled quantitatively using four dung types at three local sites in six regional areas. At regional scale, factor analysis of species abundance extracted a maximum of six factors, each dominated by a single area. Therefore, the statistical significance of regional spatial variation far outweighed that of dung type association. At local scale, six factor analyses of species abundance extracted from four to six factors. The importance of local dung type associations was relatively high but diminished with increasing local spatial heterogeneity. At regional scale, hierarchical analysis of oblique factors divided assemblages into unique local and shared regional components. Primary extended factors accounted for 40–50 % of unique local faunal composition in five out of six areas. Two secondary extended factors showed either high shared proportional contribution to regional assemblage structure in the northeast with a steep decline to the southwest, or an opposite trend. Their point of intersection was consistent with a boundary zone between mesic northeast and arid southwest faunal components in the central Kalahari. Despite some inconsistencies in rank position between regression methods, rainfall, temperature, and mammal density/diversity were the strongest influences on regional patterns defined by secondary factors. Patterns are discussed according to conservation and changes in land usage around reserves.The GEF-Small Grant Programme and the University of Pretoriahttp://www.springerlink.com/content/100177/hb2013ab201
Does an aridity and trophic resource gradient drive patterns of dung beetle food selection across the Botswana Kalahari?
1. Aridity gradients are paralleled by both reductions in resources and decreased species richness of animals. Across the aridity gradient of the Botswana Kalahari, a reduction in mammal species richness leads to reduced density and diversity of dung types, accompanied by reduced dung beetle species richness. We investigated whether this gradient also drives changes in dung beetle food type association and specialisation owing to a loss of some dung types to the arid southwest.
2. Dung beetles were sampled from three study sites in each of the six study areas using 2 × 10 grids of pitfall traps baited with dung (pig, elephant, cattle, and sheep) or carrion (chicken livers).
3. Canonical correspondence analysis (CCA) showed that distributions of dung beetle species between bait types deviated significantly from random associations.
4. Central Kalahari assemblages were more specialist than those at the mesic and arid extremes of the gradient.
5. Patterns of selection and specialisation to bait types differed between mesic northeast and arid southwest study areas. There were specialist faunas on carrion and more generalist faunas on ruminant herbivore dung (cattle and sheep) in each region. However, specialist species associated with elephant dung in the northeast were replaced by a more generalist fauna in the southwest with an opposite trend on pig dung.
6. Reduced species richness and high species turnover from the mesic northeast to the arid southwest is paralleled by a shift in patterns of food association that may reflect changes in the diversity of food types, particularly the absence of elephant dung from the southwest.The GEF-Small Grant Programme and the University of Pretoriahttp://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2311hb2013ab201
Species richness - energy relationships and dung beetle diversity across an aridity and trophic resource gradient
Understanding factors that drive species richness and turnover across ecological gradients is important
for insect conservation planning. To this end, we studied species richness e energy relationships and
regional versus local factors that influence dung beetle diversity in game reserves along an aridity and
trophic resource gradient in the Botswana Kalahari. Dung beetle species richness, alpha diversity, and
abundance declined with increasing aridity from northeast to southwest and differed significantly between
dung types (pig, elephant, cattle, sheep) and carrion (chicken livers). Patterns of between-study
area species richness on ruminant dung (cattle, sheep) differed to other bait types. Patterns of species
richness between bait types in two southwest study areas differed from those in four areas to the
northeast. Regional species turnover between study areas was higher than local turnover between bait
types. Patterns of southwest to northeast species loss showed greater consistency than northeast to
southwest losses from larger assemblages. Towards the southwest, similarity to northeast assemblages
declined steeply as beta diversity increased. High beta diversity and low similarity at gradsect extremes
resulted from two groups of species assemblages showing either northeast or southwest biogeographical
centres. The findings are consistent with the energy hypothesis that indicates insect species richness in
lower latitudes is indirectly limited by declining water variables, which drive reduced food resources
(lower energy availability) represented, here, by restriction of large mammals dropping large dung types
to the northeast and dominance of pellet dropping mammals in the arid southwest Kalahari. The influence
of theoretical causal mechanisms is discussed.The GEF-Small Grant Programme and the University of Pretoriahttp:// www.elsevier.com/locate/actoechb2013ab201
Local and regional ecological morphology of dung beetle assemblages across four biogeographic regions
Aim Niche partitioning within species assemblages is thought to influence species packing and/or total niche space occupied. The evolution of dung beetles (Scarabaeinae) is likely to have been strongly influenced by inter-specific competition, leading to niche partitioning. We consider whether local-scale processes leave a signature in regional patterns of functional diversity in dung beetle assemblages, and investigate the correlation between total exploited ecomorphological space and density of species packing with increased species richness. We test whether ecomorphological space occupied by local assemblages reflects that of their regional species pool, and the extent to which ecomorphological space is convergent or divergent within functional groups across regional pools. Location Neotropics, Africa, Australia and Madagascar. Methods Dung beetle assemblages were collected in a standardized manner from four biogeographic regions. Ecomorphological similarity among the assemblages was assessed by multivariate analysis of 19 linear measurements for 300 species and three functional nesting types (roller, tunneller or dweller), firstly on a local level within the Neotropics and Afrotropics, and then between the regional species pools. Results Key body measurements, in particular the hind tibia, separated rollers and tunnellers into largely non-overlapping entities along the first three axes of the shape analysis. Three Neotropical assemblages, which vary widely in species numbers, each harboured a similar amount of morphometric variation, resulting in increasingly dense species packing with greater species richness. Similar findings were obtained in two South African assemblages. Assemblages in the four biogeographic regions showed largely similar distributions of ecomorphological variation, including the separation of rollers and tunnellers, despite their distant phylogenetic relationships. Ecomorphological similarity among regions was particularly high in tunnellers, whilst the rollers exhibited greater regional differentiation. Main conclusions Local assemblages evidently represent the full diversity of functional groups available in the regional pool, even in species-poor assemblages. There is a strong trend towards convergence in morphology separating tunnellers and rollers in phylogenetically independent lineages. The ecomorphological similarity of regional assemblages suggests that morphological convergence is the result of common selective forces active within the assemblages themselves. This lends support to the widely hypothesized effect of inter-specific interactions and niche partitioning in determining assemblage composition and lineage evolution in the Scarabaeinae. © 2011 Blackwell Publishing Ltd
Roles of environmental variables and land usage as drivers of dung beetle assemblage structure in mopane woodland
Colophospermum mopane woodland covers large areas of dry lowland savanna in southeastern Africa.
Dominant land usage is conservation (45%) with the remainder mostly modified by farming. Dung beetle
responses to environment (dung type, habitat, weather) and land usage (conservation, farming, mining) were
examined at Phalaborwa (23.9431°S 31.1411°E) in the Phalaborwa-Timbavati Mopaneveld, South Africa. Partitioning
of gamma species richness and diversity showed lower alpha values in mine areas than in farm and
conserved areas. However, between-land usage differences in species richness, alpha diversity, abundance and
biomass, showed lower significance than those between dung type and different weather. At two sampling scales,
three multivariate techniques variously separated assemblages according to land usage, dung type and weather.
Analysis of 21 mean samples separated clusters according to dung type (Canonical Correspondence Analysis,
CCA) or mine assemblages, conserved plus farm assemblages on pig plus elephant, or cattle dung (NMDS, Factor
Analysis) with shared variance of >80% and unique variance of 16–18% per cluster. In analysis of 188 samples
(CCA), each overlapping dung type cluster was offset in ordinal space with congruent patterns of separation
according to land usage and weather (drier days distant from moister days; conserved plus farm areas distant from
early succession mine areas, which were distant from disturbed and later succession mine areas). Mining, dung
types, and moist conditions were the strongest contributors to between-assemblage differences. Compared with
conserved areas, dung beetle diversity is appreciably altered by mining but only slightly altered by intensive game
farming or livestock ranching with subsistence agriculture.SAEON and the Palaborwa Mining Companyhttp://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1442-9993hb201
Spatial and temporal variations of aridity shape dung beetle assemblages towards the Sahara desert
Assemblage responses to environmental gradients are key to
understand the general principles behind the assembly and functioning of
communities. The spatially and temporally uneven distribution of water availability
in drylands creates strong aridity gradients. While the effects of spatial variations
of aridity are relatively well known, the influence of the highly-unpredictable seasonal
and inter-annual precipitations on dryland communities has been seldom addressed.
Aims: Here, we study the seasonal and inter-annual responses of dung beetle. Dung beetle abundance and species richness showed large seasonal
variations, but remained relatively similar between years. Indeed, aridity and its
interaction with season and year were the strongest correlates of variations in species
richness and composition. Increasing aridity resulted in decreasing species
richness and an ordered replacement of species, namely the substitution of the
Mediterranean fauna by desert assemblages dominated by saprophagous and
generalist species both in space towards the Sahara and in the dry season.Indradatta deCastro-Arrazola was funded by an FPI grant from the Spanish Ministry of
Science and Innovation (BES-2012-054353). This work was supported by the Spanish
Ministry of Science and Innovation project SCARPO (grant CGL2011-29317)
Rift Valley fever vector diversity and impact of meteorological and environmental factors on Culex pipiens dynamics in the Okavango Delta, Botswana
BACKGROUND : In Northern Botswana, rural communities, livestock, wildlife and large numbers of mosquitoes
cohabitate around permanent waters of the Okavango Delta. As in other regions of sub-Saharan Africa, Rift Valley
Fever (RVF) virus is known to circulate in that area among wild and domestic animals. However, the diversity and
composition of potential RVF mosquito vectors in that area are unknown as well as the climatic and ecological
drivers susceptible to affect their population dynamics.
METHODS : Using net traps baited with carbon dioxide, monthly mosquito catches were implemented over four sites
surrounding cattle corrals at the northwestern border of the Okavango Delta between 2011 and 2012. The
collected mosquito species were identified and analysed for the presence of RVF virus by molecular methods. In
addition, a mechanistic model was developed to assess the qualitative influence of meteorological and
environmental factors such as temperature, rainfall and flooding levels, on the population dynamics of the most
abundant species detected (Culex pipiens).
RESULTS : More than 25,000 mosquitoes from 32 different species were captured with an overabundance of Cx.
pipiens (69,39 %), followed by Mansonia uniformis (20,67 %) and a very low detection of Aedes spp. (0.51 %). No RVF
virus was detected in our mosquito pooled samples. The model fitted well the Cx. pipiens catching results (ρ = 0.94,
P = 0.017). The spatial distribution of its abundance was well represented when using local rainfall and flooding
measures (ρ = 1, P = 0.083). The global population dynamics were mainly influenced by temperature, but both
rainfall and flooding presented a significant influence. The best and worst suitable periods for mosquito abundance
were around March to May and June to October, respectively.
CONCLUSIONS : Our study provides the first available data on the presence of potential RVF vectors that could
contribute to the maintenance and dissemination of RVF virus in the Okavango Delta. Our model allowed us to
understand the dynamics of Cx. pipiens, the most abundant vector identified in this area. Potential predictions of
peaks in abundance of this vector could allow the identification of the most suitable periods for disease occurrence
and provide recommendations for vectorial and disease surveillance and control strategies.Additional file 1: Serological analysis (Sampling strategy, laboratory
analysis and results).Additional file 2: Mapping flooding extent method. Figure in Additional
file 2. Maps of Modified Normalized Difference Water Index (MNDWI)
derived from MODIS imagery at different dates corresponding to the
study period.Additional file 3 Detail of the ordinary differential equation system.Funding was provided by FAO. Award Number: LoA OSRO/INT/602/USA/B1.http://www.parasitesandvectors.comam2016Zoology and Entomolog