Steven Declerck

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

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Publications (81)219.83 Total impact

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    ABSTRACT: 1. Asian topmouth gudgeon Pseudorasbora parva has been recognized as a highly invasive cyprinid fish species in Europe that may present risk to native fish communities. 2. The present study aimed to investigate whether a native piscivorous fish, pike Esox lucius, is able to reduce the establishment success and invasiveness of topmouth gudgeon in shallow ponds. A large-scale, replicated whole-pond experiment was performed in which ponds were spontaneously colonized by topmouth gudgeon and exposed to experimental native fish communities with and without pike. 3. The results of the present study provide evidence for strong negative effects of pike stocking on the abundance and biomass of topmouth gudgeon, while no effects on native fish species were found. The present study suggests that the presence of native pike can considerably enhance the biotic resistance of fish communities against invasion by topmouth gudgeon. 4. It is argued that the resistance of fish communities against invasion by exotic species may in some cases be enhanced by management strategies that reinforce the presence and abundance of pike.
    Aquatic Conservation Marine and Freshwater Ecosystems 12/2014; · 1.92 Impact Factor
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    ABSTRACT: Freshwater ponds deliver a broad range of ecosystem services (ESS). Taking into account this broad range of services to attain cost-effective ESS delivery is an important challenge facing integrated pond management. To assess the strengths and weaknesses of an ESS approach to support decisions in integrated pond management, we applied it on a small case study in Flanders, Belgium. A Bayesian belief network model was developed to assess ESS delivery under three alternative pond management scenarios: intensive fish farming (IFF), extensive fish farming (EFF) and nature conservation management (NCM). A probabilistic cost-benefit analysis was performed that includes both costs associated with pond management practices and benefits associated with ESS delivery. Whether or not a particular ESS is included in the analysis affects the identification of the most preferable management scenario by the model. Assessing the delivery of a more complete set of ecosystem services tends to shift the results away from intensive management to more biodiversity-oriented management scenarios. The proposed methodology illustrates the potential of Bayesian belief networks. BBNs facilitate knowledge integration and their modular nature encourages future model expansion to more encompassing sets of services. Yet, we also illustrate the key weaknesses of such exercises, being that the choice whether or not to include a particular ecosystem service may determine the suggested optimal management practice.
    Journal of environmental management. 07/2014; 145C:79-87.
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    ABSTRACT: Ecological Stoichiometry theory predicts that the production, elemental structure and cellular content of biomolecules should depend on the relative availability of resources and the elemental composition of their producer organism. We review the extent to which carbon- and nitrogen-rich phytoplankton toxins are regulated by nutrient limitation and cellular stoichiometry. Consistent with theory, we show that nitrogen limitation causes a reduction in the cellular quota of nitrogen-rich toxins, while phosphorus limitation causes an increase in the most nitrogen-rich paralytic shellfish poisoning toxin. In addition, we show that the cellular content of nitrogen-rich toxins increases with increasing cellular N : P ratios. Also consistent with theory, limitation by either nitrogen or phosphorus promotes the C-rich toxin cell quota or toxicity of phytoplankton cells. These observed relationships may assist in predicting and managing toxin-producing phytoplankton blooms. Such a stoichiometric regulation of toxins is likely not restricted to phytoplankton, and may well apply to carbon- and nitrogen-rich secondary metabolites produced by bacteria, fungi and plants.
    Ecology Letters 04/2014; · 17.95 Impact Factor
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    Hydrobiologia 02/2014; 723(1). · 1.99 Impact Factor
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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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    ABSTRACT: Freshwater ponds deliver a broad range of ecosystem services (ESS). Taking into account this broad range of services to attain cost-effective ESS delivery is an important challenge facing integrated pond management. To assess the strengths and weaknesses of an ESS approach to support decisions in integrated pond management, we applied it on a small case study in Flanders, Belgium. A Bayesian belief network model was developed to assess ESS delivery under three alternative pond management scenarios: intensive fish farming (IFF), extensive fish farming (EFF) and nature conservation management (NCM). A probabilistic cost-benefit analysis was performed that includes both costs associated with pond management practices and benefits associated with ESS delivery. Whether or not a particular ESS is included in the analysis affects the identification of the most preferable management scenario by the model. Assessing the delivery of a more complete set of ecosystem services tends to shift the results away from intensive management to more biodiversity-oriented management scenarios. The proposed methodology illustrates the potential of Bayesian belief networks. BBNs facilitate knowledge integration and their modular nature encourages future model expansion to more encompassing sets of services. Yet, we also illustrate the key weaknesses of such exercises, being that the choice whether or not to include a particular ecosystem service may determine the suggested optimal management practice.
    Journal of Environmental Management. 01/2014; 145:79–87.
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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. · 3.53 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: Garra species are among the most abundant fish in small rivers of northern Ethiopia. Many manmade reservoirs in the region have been colonized by Garra, which often are the only fish species present and have become very abundant. Little is known about the ecology of these reservoir populations of riverine species. In this study we investigated the distribution patterns and gut fullness of 2 dominant species, G. blanfordii and G. geba, in 3 recently created reservoirs (Gereb Awso, Tsinkanet, and Mai Gassa I) in Tigray, northern Ethiopia. Species composition differed among reservoirs. Our data on fish catch densities and the fullness of the foregut suggest that the ecology of the Garra populations in the reservoirs is likely influenced by the avoidance of predation by birds. G. blanfordii, and to a lesser extent G. geba, foraged most actively after sunset.
    Inland Waters. 04/2013; 3(3):331-340.
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    ABSTRACT: AimDendritic ecological networks (DENs), such as river systems, combine features that challenge the traditional conceptual views and empirical approaches applied to metacommunities. As a result of their dendritic branching geometry and stream flow directionality, they are strongly hierarchical and asymmetrical. We analysed the metacommunity structure of benthic diatoms in a large‐scale river system with the aim of evaluating the importance of potential causal influences. Furthermore, we hypothesized that metacommunities of diatoms that are strongly attached to their substrata show a different spatial structure than metacommunities of other, more weakly attached diatoms. LocationThe study was carried out in the Dong River, a 32,275 km2 subtropical river network located in southern China. Methods We surveyed benthic diatom communities during three seasons (dry, intermediate and wet). Using partial redundancy analysis, we partitioned community variation among environmental models and different spatial eigenfunction models to evaluate the influence of alternative dispersal pathways (overland versus water course dispersal), stream directionality, man‐made dams and diatom functional traits on diatom metacommunity structure. ResultsModels based on hydrological connections and water directionality represent spatial patterns better than overland distances, suggesting that the dynamics of benthic diatom metacommunities are mainly confined to the river network and influenced by the prevailing water flow. We found significant effects of man‐made dams on the spatial structure of important limnological variables and diatom metacommunity structure. The metacommunity of strongly attached diatoms also showed a weaker signature of flow directionality than that of other growth forms, especially in seasons with high water levels. Main conclusionsWe conclude that the consideration of among‐site connectivity, flow directionality and species traits is key to a better understanding of the spatial ecology of passively dispersing microbial organisms in river systems.
    Journal of Biogeography 01/2013; 40(12). · 4.86 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. Community concordance measures the level of association between the compositional patterns shown by two groups of organisms. If strong community concordance occurs, one group could be used as a surrogate for another in conservation planning and biodiversity monitoring. In this study, we evaluated the variability in the strength of community concordance, the likely mechanisms underlying community concordance and the degree to which one community can predict another in a set of Neotropical floodplain lakes (Upper Paraná River floodplain, Brazil).2. We used a data set including six aquatic communities: fish, macrophytes, benthic macroinvertebrates, zooplankton, phytoplankton and periphyton. We used Mantel and PROTEST approaches to evaluate the levels of community concordance in up to four sampling periods. Also, we used partial Mantel test and information about biotic interactions to investigate reasons for observed patterns of concordance. Finally, we used co‐correspondence analysis to evaluate the performance of one taxonomic group in predicting the structures of other communities.3. The levels of community concordance varied over time for almost all cross‐taxa comparisons. Concordance between phytoplankton and periphyton probably resulted from similar responses to environmental gradients, whereas other patterns of concordance were likely generated by interactions among groups. However, the levels of predictability were low, and no particular taxonomic group significantly predicted all other groups.4. The low and temporally variable levels of community concordance cast doubts on the use of surrogate groups for biodiversity management in Neotropical floodplains.
    Freshwater Biology 01/2012; 57(11). · 3.93 Impact Factor
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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

Publication Stats

1k Citations
219.83 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
  • 2008
    • Mekelle University
      • Department of Biology
      Mek’elē, Tigray Regional State, Ethiopia
  • 2005
    • University of San Simón
      Ciudad Cochabamba, Cochabamba, Bolivia
  • 2004
    • Aarhus University
      • Department of Bioscience
      Aarhus, Central Jutland, Denmark