Steven Declerck

Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, Gelderland, Netherlands

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Publications (74)180.14 Total impact

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    ABSTRACT: In semi-arid regions, the construction of small reservoirs is important in alleviating water shortage, although many have poor water quality with high turbidity and dense blooms of algae and cyanobacteria, and there are large differences in the ecology of such reservoirs.We took advantage of two exceptionally dry years in northern Ethiopia to study the effect of a dry period and the associated fish kills on reservoir ecology and water quality. We studied 13 reservoirs, seven of which dried up in 2009. Four of the latter dried up again in 2010. We monitored the ecology of these reservoirs from 2009 to 2011, hypothesising that the pattern of reservoir drying would explain ecological differences among them.Reservoirs that refilled after drying had a significantly lower fish biomass, lower biomass of phytoplankton (expressed as chlorophyll-a) and cyanobacteria (Microcystis), clearer water, greater macrophyte cover and lower nutrient concentrations than reservoirs that did not dry. Although the differences in water quality were most striking in the wet season after a drying event, there were persistent effects on reservoir ecology. The three categories of reservoirs we distinguished, based on their behaviour in 2009 and 2010, also showed differences in 2004, a year during which none of the reservoirs dried out. While drying evidently results in better water quality, we could not disentangle the effects of drying per se from that of reductions in fish biomass. The total combined effect was highly significant in all 3 years, whereas the separate effects of drying and loss of fish were only significant in 2004.Our results suggest that differences in water quality and ecology among reservoirs depend on their propensity to dry out. Drying might be used as a restoration measure to reduce potentially harmful cyanobacterial blooms in reservoirs.
    Freshwater Biology 02/2014; · 3.93 Impact Factor
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    Hydrobiologia 02/2014; 723(1). · 1.99 Impact Factor
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    ABSTRACT: It is well known that submerged macrophytes can suppress phytoplankton blooms in lakes and thus promote water quality and biodiversity. One of the possible mechanisms through which submerged macrophytes control phytoplankton is by producing allelochemicals that suppress phytoplankton growth rates. The in situ importance of allelopathy, however, is often questioned because it is assumed that phytoplankton communities can rapidly evolve resistance to allelochemicals.Here, we present the results of two mesocosm experiments in which we evaluated whether the submerged macrophyte Elodea nuttallii is capable of controlling phytoplankton biomass over periods of 4 to 8 weeks. Such a timescale is long relative to the generation time of phytoplankton and is therefore expected to allow the development of resistance through compositional shifts at both population and community levels.Although the mesocosms were inoculated with a diverse phytoplankton inoculum including species that had previously been exposed to Elodea, phytoplankton biomass remained consistently low during the course of the experiments in the treatments with Elodea. As zooplankton grazing and competition for nutrients and light by macrophytes were excluded in our experiments, this suggests that phytoplankton was controlled by allelopathy.Dialysis bag assays, performed at the end of each mesocosm experiment, showed that phytoplankton communities from mesocosms with Elodea were equally sensitive to exudates from Elodea than phytoplankton communities from mesocosms without Elodea.These results suggest that phytoplankton communities do not evolve resistance to allelochemicals from Elodea. This may allow Elodea to control phytoplankton in natural ecosystems over prolonged time periods through allelopathy.
    Freshwater Biology 01/2014; · 3.93 Impact Factor
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    ABSTRACT: Temperate shallow meso-to eutrophic lakes can exist in one of two alternative states with contrasting foodwebs, referred to as the clear-water and the turbid state. We describe the planktonic ciliate communities of such lakes based on a survey of 66 northwestern European lakes. Ciliates were enumerated and identified to species level according to the quantitative protargol staining technique. Ciliate biomass was on average twice as high in the turbid than in the clear-water lakes. The ciliate communities were dominated by oligotrichs and protostomatids, and no differences in functional composition or -diversity could be detected between turbid and clear-water lakes, although -diversity tended to be higher in the latter. At the species level, however, community structure strongly differed between turbid and clear-water lakes, and several indicator species could be identified for the different lake categories. Variation partitioning showed that nutrient status did not explain ciliate community structure independent of the alternative states, while lake area was identified as an additional structuring factor for the ciliate communities. These results stress the importance of the ecosystem structure in shaping ciliate communities in temperate shallow lakes and suggest that nutrient status has little direct effect on ciliate community structure in such lakes.
    10/2013;
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    ABSTRACT: Biodiversity and nature values in anthropogenic landscapes often depend on land use practices and management. Evaluations of the association between management and biodiversity remain, however, comparatively scarce, especially in aquatic systems. Furthermore, studies also tend to focus on a limited set of organism groups at the local scale, whereas a multi-group approach at the landscape scale is to be preferred. This study aims to investigate the effect of pond management on the diversity of multiple aquatic organism groups (e.g. phytoplankton, zooplankton, several groups of macro-invertebrates, submerged and emergent macrophytes) at local and regional spatial scales. For this purpose, we performed a field study of 39 shallow man-made ponds representing five different management types. Our results indicate that fish stock management and periodic pond drainage are crucial drivers of pond biodiversity. Furthermore, this study provides insight in how the management of eutrophied ponds can contribute t
    PLoS ONE 08/2013; 8:e72538. · 3.73 Impact Factor
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    ABSTRACT: Temperate shallow meso- to eutrophic lakes can exist in one of two alternative states with contrasting foodwebs, referred to as the clear-water and the turbid state. We describe the planktonic ciliate communities of such lakes based on a survey of 66 northwestern European lakes. Ciliates were enumerated and identified to species level according to the quantitative protargol staining technique. Ciliate biomass was on average twice as high in the turbid than in the clear-water lakes. The ciliate communities were dominated by oligotrichs and protostomatids, and no differences in functional composition or α-diversity could be detected between turbid and clear-water lakes, although β-diversity tended to be higher in the latter. At the species level, however, community structure strongly differed between turbid and clear-water lakes, and several indicator species could be identified for the different lake categories. Variation partitioning showed that nutrient status did not explain ciliate community structure independent of the alternative states, while lake area was identified as an additional structuring factor for the ciliate communities. These results stress the importance of the ecosystem structure in shaping ciliate communities in temperate shallow lakes and suggest that nutrient status has little direct effect on ciliate community structure in such lakes.
    European journal of protistology 07/2013; · 1.97 Impact Factor
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    ABSTRACT: Dispersal limitation is generally considered to have little influence on the spatial structure of biodiversity in microbial metacommunities. This notion derives mainly from the analysis of spatial patterns in the field, but experimental tests of dispersal limitation using natural communities are rare for prokaryotes and, to our knowledge, non-existent for viruses. We studied the effects of dispersal intensity (three levels) and patch heterogeneity (two levels) on the structure of replicate experimental metacommunities of bacteria and viruses using outdoor mesocosms with plankton communities from natural ponds and lakes. Low levels of dispersal resulted in a decrease in the compositional differences (beta diversity) among the communities of both bacteria and viruses, but we found no effects of patch heterogeneity. The reductions in beta diversity are unlikely to be a result of mass effects and only partly explained by indirect dispersal-mediated interactions with phytoplankton and zooplankton. Our results suggest that even a very limited exchange among local communities can alter the trajectory of bacterial and viral communities at small temporal and spatial scales.
    The ISME Journal 11/2012; · 8.95 Impact Factor
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    ABSTRACT: Relationships between traits of organisms and the structure of their metacommunities have so far mainly been explored with meta-analyses. We compared metacommunities of a wide variety of aquatic organism groups (12 groups, ranging from bacteria to fish) in the same set of 99 ponds to minimise biases inherent to meta-analyses. In the category of passive dispersers, large-bodied groups showed stronger spatial patterning than small-bodied groups suggesting an increasing impact of dispersal limitation with increasing body size. Metacommunities of organisms with the ability to fly (i.e. insect groups) showed a weaker imprint of dispersal limitation than passive dispersers with similar body size. In contrast, dispersal movements of vertebrate groups (fish and amphibians) seemed to be mainly confined to local connectivity patterns. Our results reveal that body size and dispersal mode are important drivers of metacommunity structure and these traits should therefore be considered when developing a predictive framework for metacommunity dynamics.
    Ecology Letters 05/2012; 15(7):740-7. · 17.95 Impact Factor
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    ABSTRACT: Dispersal is a major organising force in metacommunities, which may facilitate compositional responses of local communities to environmental change and affect ecosystem function. Organism groups differ widely in their dispersal abilities and their communities are therefore expected to have different adaptive abilities. In mesocosms, we studied the simultaneous compositional response of three plankton communities (zoo-, phyto- and bacterioplankton) to a primary productivity gradient and evaluated how this response was mediated by dispersal intensity. Dispersal enhanced responses in all three planktonic groups, which also affected ecosystem functioning. Yet, variation partitioning analyses indicated that responses in phytoplankton and bacterial communities were not only controlled by dispersal directly but also indirectly through complex trophic interactions. Our results indicate that metacommunity patterns emerging from dispersal can cascade through the food web and generate patterns of apparent dispersal limitation in organisms at other trophic levels.
    Ecology Letters 03/2012; 15(3):218-26. · 17.95 Impact Factor
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    ABSTRACT: A field survey of zooplankton communities was carried out in 32 recently established tropical semi-arid reservoirs in the highlands of Northern Ethiopia with the aim to identify to what extent environmental factors determine species composition of the cladoceran community in such isolated and young reservoirs. To address seasonal variation, the survey was carried out both at the beginning and the end of the dry season. A total of 15 species of cladocerans were identified. Daphnia was the most abundant cladoceran genus, and was present in all reservoirs. Using presence–absence data, no association between cladoceran community composition and geographic distance was found. RDA results indicate that the set of environmental variables that explained cladoceran community composition differed among seasons. Depth, altitude and fish biomass showed a significant association with cladoceran community composition during the wet season, whereas variation in cladoceran community structure was associated with phytoplankton biomass in the dry season. The relative abundance of Daphnia was much higher in the pelagic than in the littoral zone of our study systems. Two key groups of pelagic filter-feeding cladocerans, Diaphanosoma and Daphnia, showed a clear pattern, in which one or the other tended to strongly dominate the community. In addition, we observed a negative association between dominance of Daphnia in the zooplankton community and dominance of cyanobacteria in the phytoplankton community.
    Limnologica. 01/2012;
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    ABSTRACT: Summary1. In temperate regions, submerged macrophytes can hamper phytoplankton blooms. Such an effect could arise directly, for instance via allelopathy, or indirectly, via competition for nutrients or the positive interaction between submerged macrophytes and zooplankton grazing. However, there is some evidence that the positive interaction between submerged macrophytes and zooplankton grazing is less marked in warmer regions, where the interaction is less well studied, and that negative effects of higher water plants on phytoplankton biomass are weaker.2. We carried out two consecutive mesocosm experiments in Uruguay (subtropical South America) to study the effects of two common submerged macrophytes from this region (Egeria densa and Potamogeton illinoensis) on phytoplankton biomass, in the absence of zooplankton grazing. We compared phytoplankton development between different macrophyte treatments (no macrophytes, artificial macrophytes, real Egeria and real Potamogeton). We used artificial macrophytes to differentiate between physical effects (i.e. shading, sedimentation and competition with periphyton) and biological effects (i.e. nutrient competition and allelopathy).3. In Experiment 1, we found no evidence for physical effects of macrophytes on phytoplankton biomass, but both macrophyte species seemed to exert strong biological effects on phytoplankton biomass. Only Egeria affected phytoplankton community structure, particularly tempering the dominance of Scenedesmus. Nutrient addition assays revealed that only Egeria suppressed phytoplankton through nutrient competition.4. We performed a second mesocosm experiment with the same design, but applying saturating nutrient conditions as a way of excluding the effects of competition for nutrients. This experiment showed that both macrophytes were still able to suppress phytoplankton through biological mechanisms, providing evidence for allelopathic effects. Our results indicate that both common macrophytes are able to keep phytoplankton biomass low, even in the absence of zooplankton grazing.
    Freshwater Biology 05/2011; 56(9):1837 - 1849. · 3.93 Impact Factor
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    ABSTRACT: Intraspecific interactions may limit population growth of small cladoceran taxa under food-rich, hypertrophic conditions. Multiple-regression models significantly explained a large proportion of the variation in the body size adjusted fecundity and population growth rate of crustacean zooplankton taxa in a shallow, hypertrophic lake. The results of partial correlation analyses suggested exploitative competition to have only limited significance in determining the zooplankton dynamics. The analyses also revealed strong negative relationships between biomass and both body size adjusted fecundity and population growth rate within most taxa. Most of these relationships cannot be explained by food shortage or predation and suggest alternative mechanisms such as chemically mediated, intraspecific interference competition or life history shifts.
    Canadian Journal of Fisheries and Aquatic Sciences 04/2011; 60(8):919-928. · 2.32 Impact Factor
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    ABSTRACT: Metacommunity structure can be shaped by a variety of processes operating at different spatial scales. With increasing scale, the compositional variation among local communities (beta diversity) may reflect stronger environmental heterogeneity, but may also reflect reduced exchange of organisms between habitat patches. We analyzed the spatial architecture of a metacommunity of cladoceran zooplankton in temporary pools of High Andes wetlands, with the objective of explaining the spatial dependency of its structure. The spatial distribution of the pools is hierarchical and highly discontinuous: pools are clustered within small wetlands, which lay scattered over valleys that are separated from each other by mountain ridges. We studied a total of 59 pools, belonging to six different wetlands in four different valleys. We assessed pool environmental heterogeneity and sampled active communities and dormant propagule banks of cladoceran zooplankton. Environmental heterogeneity proved very high within wetlands and showed almost no increase with increasing spatial scale. Conversely, diversity partitioning analyses indicated an increase in beta diversity with spatial scale, especially among valleys. Variation partitioning on environmental data and spatial RDA models suggested environmental heterogeneity as the most important generator of beta diversity within wetlands. At the largest spatial scale, beta diversity manifested itself mainly as a differentiation of species occurrence patterns among valleys, which could not be entirely explained by environmental variables. Our study thus presents a case where environmental control seems to be the dominant metacommunity structuring process at the smallest spatial scale, whereas neutral processes and dispersal limitation are the most likely generators of beta diversity at the largest spatial scale.
    Ecography 03/2011; 34(2):296 - 305. · 5.12 Impact Factor
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    ABSTRACT: 1. In temperate regions, submerged macrophytes can hamper phytoplankton blooms. Such an effect could arise directly, for instance via allelopathy, or indirectly, via competition for nutrients or the positive interaction between submerged macrophytes and zooplankton grazing. However, there is some evidence that the positive interaction between submerged macrophytes and zooplankton grazing is less marked in warmer regions, where the interaction is less well studied, and that negative effects of higher water plants on phytoplankton biomass are weaker. 2. We carried out two consecutive mesocosm experiments in Uruguay (subtropical South America) to study the effects of two common submerged macrophytes from this region (Egeria densa and Potamogeton illinoensis) on phytoplankton biomass, in the absence of zooplankton grazing. We compared phytoplankton development between different macrophyte treatments (no macrophytes, artificial macrophytes, real Egeria and real Potamogeton). We used artificial macrophytes to differentiate between physical effects (i.e. shading, sedimentation and competition with periphyton) and biological effects (i.e. nutrient competition and allelopathy). 3. In Experiment 1, we found no evidence for physical effects of macrophytes on phytoplankton biomass, but both macrophyte species seemed to exert strong biological effects on phytoplankton biomass. Only Egeria affected phytoplankton community structure, particularly tempering the dominance of Scenedesmus. Nutrient addition assays revealed that only Egeria suppressed phytoplankton through nutrient competition. 4. We performed a second mesocosm experiment with the same design, but applying saturating nutrient conditions as a way of excluding the effects of competition for nutrients. This experiment showed that both macrophytes were still able to suppress phytoplankton through biological mechanisms, providing evidence for allelopathic effects. Our results indicate that both common macrophytes are able to keep phytoplankton biomass low, even in the absence of zooplankton grazing.
    Freshwater Biology - FRESHWATER BIOL. 01/2011;
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    ABSTRACT: The cyanobacterium Microcystis is notorious for forming extensive and potentially toxic blooms in nutrient-rich freshwater bodies worldwide. However, little is known about the factors underlying the genetic diversity and structure of natural Microcystis populations, despite the fact that this knowledge is essential to understand the build-up of blooms. Microcystis blooms are common and occur year-round in Africa, but are underinvestigated in this continent. We studied the genetic diversity and structure of Microcystis populations in 30 man-made reservoirs in Tigray (Northern Ethiopia) using Denaturing Gradient Gel Electrophoresis of the 16S–23S rDNA internal transcribed spacer (ITS) region and assessed the importance of local environmental conditions and geographic position of the reservoirs for the observed patterns. The analyses showed that both regional and local Microcystis ITS diversity in these recently constructed reservoirs was relatively low, with several dense blooms containing only a single ITS type. Especially one non-toxic ITS type dominated a considerable fraction of Microcystis blooms, but appeared restricted in its geographic distribution. The relationship between Microcystis ITS population structure and abiotic variables (water clarity, pH) and with zooplankton (Daphnia biomass) indicates a (limited) influence of environmental conditions on Microcystis population structure in the reservoirs of Tigray. Keywords Microcystis –Blooms–16S–23S rDNA ITS–Population structure–Diversity–Africa
    Aquatic Ecology 01/2011; 45(2):289-306. · 1.38 Impact Factor
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    ABSTRACT: Macrophytes and nutrient loading are two factors that can strongly determine the diversity and composition of aquatic invertebrate communities. Both factors may also interact, because macrophyte species may be differentially affected by nutrients. Macrophyte community characteristics, such as species composition, morphotype and biomass have the potential to mediate the response of invertebrate communities to nutrient loading. In 36 newly constructed experimental ponds, we orthogonally combined three macrophyte community types (Chara-, Potamogeton-and Elodea-dominated) with two levels of nutrient additions (no addition and an addition of 0.5 mg P and 3 mg N/L per week) and studied community assembly in three functional groups of invertebrates (epiphytic macroinvertebrates, littoral and pelagic crustacean zooplankton). Macrophyte biomass was negatively affected by nutrient addition. General linear models indicated negative responses of species richness in the zooplankton functional groups to nutrient addition and phytoplankton chlorophyll-a, but demonstrated no effects of macrophyte community type. Conversely, macroinvertebrate taxon richness differed among macrophyte community types but showed no response to nutrient enrichment. Macrophyte biomass correlated positively with the richness of littoral zooplankton and macroinvertebrates and was a better predictor of these diversity variables than macrophyte community type. Overall, our results indicate that lake management practices that aim at obtaining a nutrient poor and macrophyte dominated clear water state contribute also to the maintenance of aquatic invertebrate diversity.
    Basic and Applied Ecology 01/2011; 12:466-475. · 2.70 Impact Factor
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    Freshwater Reviews. 10/2010;
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    ABSTRACT: To develop strategies for the management and protection of aquatic biodiversity in water bodies at the landscape scale, there is a need for information on the spatial organization of diversity in different types of aquatic habitats. In this study, we compared the cladoceran composition and diversity between wheel tracks, pools, ponds, lakes, ditches, and streams, in 18 different areas of Flanders (Belgium). Multivariate analysis revealed significant differences in the composition of cladoceran communities among the different water body types. Average local and total diversity tended to be highest for lakes and lowest for streams. Despite the relatively high number of species supported by lakes, small water bodies seem to contribute considerably more to the total cladoceran richness of an average landscape in Flanders than lakes, because of their high abundance. With respect to biodiversity conservation at the landscape scale, our results point to the importance of maintaining a diversity of water body types of different size, permanence and flow regimes. KeywordsZooplankton-Cladoceran-Ditch-Pool-Pond-Lake-Wheel track-Stream-Species richness-Biodiversity
    09/2010: pages 19-27; · 1.99 Impact Factor
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    ABSTRACT: There is growing awareness in Europe of the importance of ponds, and increasing understanding of the contribution they make to aquatic biodiversity and catchment functions. Collectively, they support considerably more species, and specifically more scarce species, than other freshwater waterbody types. Ponds create links (or stepping stones) between existing aquatic habitats, but also provide ecosystem services such as nutrient interception, hydrological regulation, etc. In addition, ponds are powerful model systems for studies in ecology, evolutionary biology and conservation biology, and can be used as sentinel systems in the monitoring of global change. Ponds have begun to receive greater protection, particularly in the Mediterranean regions of Europe, as a result of the identification of Mediterranean temporary ponds as a priority in the EU Habitats Directive. Despite this, they remain excluded from the provisions of the Water Framework Directive, even though this is intended to ensure the good status of all waters. There is now a need to strengthen, develop and coordinate existing initiatives, and to build a common framework in order to establish a sound scientific and practical basis for pond conservation in Europe. The articles presented in this issue are intended to explore scientific problems to be solved in order to increase the understanding and the protection of ponds, to highlight those aspects of pond ecology that are relevant to freshwater science, and to bring out research areas which are likely to prove fruitful for further investigation. KeywordsBiodiversity-Conservation-Ecosystem services-European Pond Conservation Network-Small water bodies-Temporary pools-Water policy-Wetlands
    09/2010: pages 1-6; · 1.99 Impact Factor
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    ABSTRACT: The effectiveness of three commercially available direct DNA isolation kits (Mobio, Fast, Qiagen) and one published direct DNA extraction protocol (Bead) for extracting bacterial DNA from different types of activated sludge was investigated and mutually compared. The DNA quantity and purity were determined using real-time PCR targeting the bacterial 16S rDNA gene. Microbial community fingerprints were assessed by automated ribosomal intergenic spacer analysis. The resulting community profiles were analyzed with canonical correspondence analysis. Our results clearly demonstrate that direct DNA extraction methods can significantly influence the DNA quantity, purity, and observed community patterns of microbiota in activated sludge. Fast and Mobio generated high amounts of good quality DNA compared to Bead and Qiagen. Mobio also resulted in the detection of the highest number of species while Fast scored the best in discriminating between the community patterns of different activated sludge types. With respect to the characterization of community profiles, our analyses demonstrated a strong sludge type dependent variability among methods. Taking into account our results, we recommend Fast as the most suitable DNA extraction method for activated sludge samples used for bacterial community studies.
    Applied Microbiology and Biotechnology 09/2010; 88(1):299-307. · 3.69 Impact Factor

Publication Stats

983 Citations
180.14 Total Impact Points

Institutions

  • 2003–2014
    • Netherlands Institute of Ecology (NIOO-KNAW)
      Wageningen, Gelderland, Netherlands
    • University of Concepción
      Ciudad de Concepcion, Biobío, Chile
  • 2001–2014
    • KU Leuven
      • Section of Ecology, Evolution and Biodiversity Conservation
      Louvain, Flanders, Belgium
  • 1997–2013
    • Ghent University
      • Department of Biology
      Gent, VLG, Belgium
    • University of Granada
      Granata, Andalusia, Spain
  • 2005–2011
    • Leuven University College
      Louvain, Flanders, Belgium
    • University of San Simón
      Ciudad Cochabamba, Cochabamba, Bolivia
  • 2004
    • Aarhus University
      • Department of Bioscience
      Aarhus, Central Jutland, Denmark