Search publications of the members of the Royal Belgian institute of natural Sciences
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Hydrological regime and salinity alter the bioavailability of Cu and Zn in wetlands
- In the context of the European Water Framework Directive, controlled flooding of lowlands is considered as a potential water management strategy to minimise the risk of flooding of inhabited areas. However, due to historical pollution and overbank sedimentation, metal levels are elevated in most wetlands, which can cause adverse effects on the ecosystem's dynamics. Additionally, salinity affects the bioavailability of metals present or imported into these systems. The effect of different flooding regimes and salinity exposure scenarios (fresh- and brackish water conditions) on Cu and Zn accumulation in the oligochaete Tubifex tubifex (Muller, 1774) was examined. Metal mobility was closely linked to redox potential, which is directly related to the prevalent hydrological regime. Flooded, and thus more reduced, conditions minimized the availability of metals, while oxidation of the substrates during a drier period was associated with a rapid increase of metal availability and accumulation in the oligochaetes. (C) 2009 Elsevier Ltd. All rights reserved.
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Ideal Free distribution of fixed dispersal phenotypes in a wing dimorphic beetle in heterogeneous landscapes
- According to the ideal free distribution (IFD) theory, individuals that are able to perceive the quality of different patches in a landscape and disperse freely are expected to redistribute themselves proportionally to the carrying capacities of heterogeneous patches. Here, we argue that when dispersal is unconditional and genetically fixed, a coalition of sedentary and dispersing phenotypes can attain an IFD under spatio-temporally uncorrelated variation in fitness. This not only leads to a stable polymorphism of both dispersal phenotypes, but also implies that the number of dispersing individuals should on average be equal among patches and determined by the carrying capacity of the smallest local populations in the landscape. Differences in carrying capacity among patches are thus only reflected by changes in the number of sedentary individuals. Individual-based simulations show that this mechanism can be generalized over a wide range of spatio-temporal conditions and dispersal strategies. Moreover, these expectations are in strong agreement with empirical data on the density of both dispersal phenotypes of the wing dimorphic ground beetle Pterostichus vernalis within and among ten different landscapes. Hence, for the first time, these results demonstrate that this mechanism serves as a plausible alternative to the competition-colonization model to explain the spatial distribution of fixed dispersal phenotypes in heterogeneous landscapes. Understanding of the frequency distributions of individuals expressing discrete dispersal morphs moreover improves our predictive and management capabilities for a broad range of species, for which we currently typically rely on using mean dispersal rates.
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Indicators for biodiversity in agricultural landscapes: a pan-European study
- 1. In many European agricultural landscapes, species richness is declining considerably. Studies performed at a very large spatial scale are helpful in understanding the reasons for this decline and as a basis for guiding policy. In a unique, large-scale study of 25 agricultural landscapes in seven European countries, we investigated relationships between species richness in several taxa, and the links between biodiversity and landscape structure and management. 2. We estimated the total species richness of vascular plants, birds and five arthropod groups in each 16-km(2) landscape, and recorded various measures of both landscape structure and intensity of agricultural land use. We studied correlations between taxonomic groups and the effects of landscape and land-use parameters on the number of species in different taxonomic groups. Our statistical approach also accounted for regional variation in species richness unrelated to landscape or land-use factors. 3. The results reveal strong geographical trends in species richness in all taxonomic groups. No single species group emerged as a good predictor of all other species groups. Species richness of all groups increased with the area of semi-natural habitats in the landscape. Species richness of birds and vascular plants was negatively associated with fertilizer use. 4. Synthesis and applications. We conclude that indicator taxa are unlikely to provide an effective means of predicting biodiversity at a large spatial scale, especially where there is large biogeographical variation in species richness. However, a small list of landscape and land-use parameters can be used in agricultural landscapes to infer large-scale patterns of species richness. Our results suggest that to halt the loss of biodiversity in these landscapes, it is important to preserve and, if possible, increase the area of semi-natural habitat.
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Influence of flooding, salinity and inundation time on the bioavailability of metals in wetlands
- Controlled flooding of lowlands is considered as a potential water management strategy to minimize the risk of flooding of inhabited areas during high water periods. However, due to industrial activities, river water, sediments and soils are often contaminated with metals which may have adverse effects on the ecosystem's structure and functioning. Additionally, salinity may greatly affect the bioavailability and toxicity of metals present or imported into these systems. The effect of contaminated soils under different flooding and salinity exposure scenarios on the growth, reproduction and metal accumulation in the oligochaete Tubifiex tubitex (Muller, 1774) were examined. In these bioassays metal contaminated soils were flooded with water of different salinities (0 and 3 psu), and tested after 0, 6 and 12 months of permanent inundation. We indeed found that inundation time had significant decreasing effects on Cu and Zn accumulation; although initial accumulation of Cu and Zn was higher in the previously unflooded soil at the start of the flooding treatment, these differences seem to disappear after 6 months of permanent inundation. Moreover, the complex interaction between substrate type and salinity suggests that redox potential is probably of major importance. (C) 2006 Elsevier B.V. All rights reserved.
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Intensification of agriculture, landscape composition and wild bee communities: A large scale study in four European countries
- The impacts of agricultural practices and landscape composition on bee communities were investigated in 14 sites located in four Western European countries (Belgium, France, the Netherlands and Switzerland). Standardized interviews with farmers assessed agricultural practices in terms of agricultural inputs (nitrogen fertilization and pesticides), livestock density and crop types. The proportion of semi-natural habitats was calculated for each site. We showed negative effects of agricultural intensification on species richness, abundance and diversity of wild bees. By contrast, bee species richness increased with the amount of semi-natural habitats in the landscape. Using a co-inertia analysis, we found an opposition between two types of agricultural specialization: towards crop production or towards animal husbandry. Species richness, abundance and diversity of wild bees were greater in sites turned towards crop production. In these sites, flowering crops provided abundant food resources for bees whereas, in the other group of sites, intensive animal husbandry led to landscapes dominated by forage crops rather than flower-rich permanent grasslands. We also showed that bumblebees seemed to be less sensitive to agricultural intensification than solitary bees. (C) 2010 Elsevier B.V. All rights reserved.
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Is the hairy groove in the gibbosus male morph of Oedothorax gibbosus (Blackwall 1841) a nuptial feeding device?
- Oedothorax gibbosus (Blackwall 1841) (Erigoninae, Linyphiidae, Araneae) is a dwarf spider characterized by dimorphic males. There is a "gibbosus" male morph characterized by a hunch on the posterior third of the carapace, anterior to which is a hairy groove, and a "tuberosus" morph without these features. We observed several gustatorial courtship interactions by a gibbosus male morph and a conspecific female as well as a by a gibbosus male and a male of the closely related species, Oedothorax fuscus (Blackwall 1834). These interactions suggest that the hairy groove in the gibbosus male morph is a nuptial feeding device possibly under the influence of sexual selection. The interspecific interactions can possibly be interpreted as 'robbings' of the nuptial feeding. The interspecific interactions indicate that the cephalic structure of gibbosus probably does not function as a "lock and key" mechanism.
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Isolation and characterization of microsatellite loci in the dark bush cricket, Pholidoptera griseoaptera (Tettigoniidae)
- Twelve novel polymorphic microsatellite loci are presented for the dark bush cricket, Pholidoptera griseoaptera. All loci are polymorphic, with up to 37 alleles per locus. These microsatellites will be useful tools for studying the influence of landscape structure and land use intensity in agricultural landscapes on genetic diversity within and among populations of P. griseoaptera.
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Larval presence prediction through logistic regression: an early warning system against Mytilopsis leucophaeata biofouling
- Mytilopsis leucophaeata is a biofouling bivalve causing major problems in the cooling water system of BASF, Antwerp NV, Belgium, a large water-using industrial facility. This study aimed to develop a statistical model to predict the response of M. leucophaeata larvae to environmental conditions in estuarine ecosystems. Multiple logistic regression, taking into account temporal autocorrelation, was applied on a large dataset allowing the prediction of the probability of occurrence of M. leucophaeata larvae at BASF NV as a response to the environmental variables. The final model made it possible to predict larval presence in the water column solely by monitoring water temperature. The results from subsampling indicated that the model was stable. The model was tested with 2005 data, demonstrating a 98\% precise prediction of the occurrence of M. leucophaeata larvae in the water column, with a sensitivity of 100\% and a specificity of 97\%, even though autumn 2005 was exceptionally warm, which led to an extended presence of the larvae.
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Life cycle, reproductive patterns and their year-to-year variation in a field population of the wolf spider Pirata piraticus (Araneae, Lycosidae)
- Patterns of growth, phenology and reproduction were studied in a field population of the wolf spider Pirata piraticus from November 1997 until October 1998 and in June 1999 to unravel the intrapopulation variation and co-variation of these traits. Individuals of P. piraticus overwinter as juveniles of different instars while adults were found from the end of April until September. Strong year to year variation in the age and size of overwintering juveniles was present, resulting in a corresponding difference in adult size in the subsequent breeding season. The main period of reproduction occurred from May until August with larger individuals breeding earlier in the season. The size at which adults breed was also significantly different in the successive years. Clutch mass (cocoon mass), clutch volume and fecundity are dependent on the size of the female according to a weakly negative allometric relationship. The differences in those reproductive traits between the succesive years are therefore proportionate to the differences in female size. This was in clear contrast to egg size, a life history trait that shows much less variation and appears to be independent of female size. Therefore, egg size was not significantly different between spring 1998 and spring 1999. There is, however, some variation in fecundity due to egg size and number independent of female size. When corrected for female size, females with larger eggs produce relatively fewer eggs indicating a trade-off between these two reproductive characters.
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Local extinction processes rather than edge effects affect ground beetle assemblages from fragmented and urbanized old beech forests
- Local extinction of specialist species due to fragmentation is one of the major causes of biodiversity loss. Increased extinction rates in smaller fragments are expected to result from both smaller local population sizes, which increase the effect of environmental or demographic stochasticity, and increased edge effects. However, the relative effect sizes of these two factors are still poorly investigated. We attempt to disentangle these effects on ground beetle communities of temperate broadleaved woodland fragments situated in one of the most urbanized regions in Belgium. Assemblages were sampled along transects that extended from 30 m outside to 100 m inside both small and large historic forest fragments. Although species assemblages within the forest were highly distinct compared to those sampled outside the forest, species turnover along these transects was less pronounced within forest fragments indicating only weak edge effects. The magnitude of edge effects did not differ significantly between large and small fragments. However, larger differences in species composition were observed with respect to fragment size, wherein highly specialized species persisted only in the largest fragment. In sum, increased local extinction processes in smaller fragments, which led to a strong reduction of specialized and wingless forest species, appeared to be the most important factor that drives changes in species composition in this historic and fragmented woodland complex.
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Loss of genetic diversity and increased genetic structuring in response to forest area reduction in a ground dwelling insect: a case study of the flightless carabid beetle Carabus problematicus (Coleoptera: Carabidae)
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Metal accumulation in some terrestrial arthropods and its ecological and microevolutionary consequences in the wolf spider Pirata piraticus (Lycosidae, Araneae).
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Nematode communities of small farmland ponds
- The nematofauna of 14 farmland ponds, selected according to a gradient of surrounding agricultural land-use intensity, from five regions in North-West of Belgium were studied. The total nematode density (9-411 ind./10 cm(2) per pond), and especially the number of species (4-12 species per pond) was especially low in these ponds. In total, 17 genera of free-living benthic nematodes, belonging to 15 families, are identified. Tobrilus gracilis and Eumonhystera filiformis were the most common species and were found in 13 and 12 of the 14 sampled ponds, respectively. The genera Tobrilus and Eumonhystera jointly comprise 77\% of the total nematofauna. Consequently, the investigated water bodies were dominated by deposit feeding Monhysteridae and/or by chewing Tobrilidae. Diplogasteridae and Rhabditidae, normally related with eutrophic habitats, were almost absent. In order to explain the variation of total density, diversity, feeding-types composition and the individual density of the six most important species within ponds as well, sets of environmental variables were statistically selected. It was demonstrated that morphologically very similar species can show highly different ecological properties. The presence of a substantial mud layer and of an overall high level of eutrophication as well as the presence of possibly associated anaerobic conditions are put forward as the main factors explaining the observed low density and diversity. Total phosphate concentration and sediment characteristics seem to be the most important variables to explain the nematode community structure. However, a clear pattern of environmental variables, agricultural land use and nematode assemblages was not observed.
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Nematode communities of small pools in an agricultural landscape
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Parallel habitat specialization within the wolf spider genus Hogna from the Galapagos
- Within most island archipelagos, such as the Galapagos, similar ecological gradients are found on geographically isolated islands. Species radiations in response to these ecological gradients may follow different scenarios being (i) a single habitat specialization event followed by secondary colonization of each ecotype on the different islands or (ii) repeated and parallel habitat specialization on each island separately. This latter scenario has been considered less likely as gene flow might hamper such ecotypic differentiation. At least for the Galapagos, the extent to which this process is involved in species radiations remains yet poorly understood. Within the wolf spider genus Hogna, seven species are described that can be divided into three different ecotypes based on general morphology and habitat preference i.e. species that inhabit the pampa vegetation in the highlands, species that occur in coastal dry habitats and one generalist species. Comparison of the species phylogeny based on one mitochondrial (COI) and one nuclear (28S) gene fragment convincingly demonstrates that 'pampa' and 'coastal dry' species evolved in parallel on the islands Santa Cruz and San Cristobal. Despite the observation that allozymes analysis indicated that each species forms a distinct genetic cluster, phylogenetic divergence within these species complexes was very low and paraphyletic and most likely due to hybridization rather than incomplete lineage sorting, as demonstrated for the Santa Cruz species complex. This suggests that within-island speciation occurred under low levels of gene flow. Species phylogeny in general did not follow the progression of island emergence as a molecular clock analysis suggested that island endemic species may have diverged after as well as before the emergence of the islands. This represents the first clear example of parallel and within-island speciation because of habitat specialization on the Galapagos and that such divergence most likely occurred under historic gene flow.
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Patterns of habitat occupancy, genetic variation and predicted movement of a flightless bush cricket, Pholidoptera griseoaptera, in an agricultural mosaic landscape
- Habitat fragmentation has been generally regarded detrimental to the persistence of many species, especially those with limited dispersal abilities. Yet, when exactly habitat elements become functionally disconnected very much depends on the dispersal ability of a species in combination with the landscape's composition in which it occurs. Surprisingly, for many small and ground-walking generalists knowledge at what spatial scale and to what extent landscape structure affects dispersal is very scarce. Because it is flightless, the bush cricket Pholidoptera griseoaptera may be regarded susceptible to fragmentation. We applied habitat occupancy surveys, population genetic analyses and movement modelling to investigate the performance of P. griseoaptera in an agricultural mosaic landscape with suitable habitat patches of varying size and isolation. Despite its presumed dispersal limitation we could show that P. griseoaptera occupied the majority of suitable habitats, including small and isolated patches, showed a very low and non-significant genetic differentiation (F (ST) = 0.0072) and, in the model, managed to colonize around 73\% of all suitable habitat patches within one generation under weak and strong landscape-effect scenarios. We conclude that P. griseoaptera possesses the behavioural attributes (frequent inter-patch dispersal) necessary to persist in this landscape characterized by a patchy distribution of habitat elements. Yet, sound recommendations to landscape planning and conservation require more research to determine whether this represents a general behaviour of the species or a behavioural adaptation to this particular landscape.
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Pervasive effects of dispersal limitation on within- and among-community species richness in agricultural landscapes
- Aim To determine whether the effect of habitat fragmentation and habitat heterogeneity on species richness at different spatial scales depends on the dispersal ability of the species assemblages and if this results in nested species assemblages. Location Agricultural landscapes distributed over seven temperate Europe countries covering a range from France to Estonia. Methods We sampled 16 local communities in each of 24 agricultural landscapes (16 km(2)) that differ in the amount and heterogeneity of semi-natural habitat patches. Carabid beetles were used as model organisms as dispersal ability can easily be assessed on morphological traits. The proximity and heterogeneity of semi-natural patches within the landscape were related to average local (alpha), between local (beta) and landscape (gamma) species richness and compared among four guilds that differ in dispersal ability. Results For species assemblages with low dispersal ability, local diversity increased as the proximity of semi-natural habitat increased, while mobile species showed an opposite trend. Beta diversity decreased equally for all dispersal classes in relation to proximity, suggesting a homogenizing effect of increased patch isolation. In contrast, habitat diversity of the semi-natural patches affected beta diversity positively only for less mobile species, probably due to the low dispersal ability of specialist species. Species with low mobility that persisted in highly fragmented landscapes were consistently present in less fragmented ones, resulting in nested assemblages for this mobility class only. Main conclusions The incorporation of dispersal ability reveals that only local species assemblages with low dispersal ability show a decrease of richness as a result of fragmentation. This local species loss is compensated at least in part by an increase in species with high dispersal ability, which obscures the effect of fragmentation when investigated across dispersal groups. Conversely, fragmentation homogenizes the landscape fauna for all dispersal groups, which indicates the invasion of non-crop habitats by similar good dispersers across the whole landscape. Given that recolonization of low dispersers is unlikely, depletion of these species in modern agricultural landscapes appears temporally pervasive.
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Prediction uncertainty of environmental change effects on temperate European biodiversity
- Observed patterns of species richness at landscape scale (gamma diversity) cannot always be attributed to a specific set of explanatory variables, but rather different alternative explanatory statistical models of similar quality may exist. Therefore predictions of the effects of environmental change (such as in climate or land cover) on biodiversity may differ considerably, depending on the chosen set of explanatory variables. Here we use multimodel prediction to evaluate effects of climate, land-use intensity and landscape structure on species richness in each of seven groups of organisms (plants, birds, spiders, wild bees, ground beetles, true bugs and hoverflies) in temperate Europe. We contrast this approach with traditional best-model predictions, which we show, using cross-validation, to have inferior prediction accuracy. Multimodel inference changed the importance of some environmental variables in comparison with the best model, and accordingly gave deviating predictions for environmental change effects. Overall, prediction uncertainty for the multimodel approach was only slightly higher than that of the best model, and absolute changes in predicted species richness were also comparable. Richness predictions varied generally more for the impact of climate change than for land-use change at the coarse scale of our study. Overall, our study indicates that the uncertainty introduced to environmental change predictions through uncertainty in model selection both qualitatively and quantitatively affects species richness projections.
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Present conservation status of red wood ants in north-western Belgium: Worse than previously, but not a lost cause
- The number of colonies of red wood ants (Formica rufa group) in the north western part of Belgium has declined by more than half over the past 20 years. In the study area of 20 x 50 km there are currently only 36 colonies of two species of red wood ants (Formica rufa and F. polyctena). Both species form both monodomous and polydomous colonies. Monodomous F. rufa colonies occur in large areas of open woodland dominated by Pinus sylvestris. The other three types of red wood ant (F. rufa polydomous, F. polyctena mono-and polydomous) occur in clearings or along the margins of small areas of deciduous or mixed woodland. The extinction of red wood ants cannot be attributed to a loss of their main habitat. Their decline in abundance, however, appears to be due to the deterioration in their habitat caused by several factors. Shading by overgrowing shrubs and the closure of the tree canopy, nearby intensive agriculture, urbanisation and use of the forest for recreation are the more important factors threatening and ultimately leading to the extinction of colonies. At poor quality sites there are no or very few nests of Serviformica ants, which initially serve as host ants and are necessary for recolonization by red wood ants. Thus, it is unlikely that these sites will be recolonized. To conserve red wood ants and maintain populations there is an urgent need to undertake certain measures, especially in areas outside nature reserves. For this there is a need to create clearings in the woodland, reduce shading due to overgrowing shrubs and closure of the tree canopy, and mitigate the effects of intensive agriculture, urbanisation and recreation. It is important that the effects of these measures should be monitored.
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Quantifying the impact of environmental factors on arthropod communities in agricultural landscapes across organizational levels and spatial scales
- 1. In landscapes influenced by anthropogenic activities, such as intensive agriculture, knowledge of the relative importance and interaction of environmental factors on the composition and function of local communities across a range of spatial scales is important for maintaining biodiversity. 2. We analysed five arthropod taxa covering a broad range of functional aspects (wild bees, true bugs, carabid beetles, hoverflies and spiders) in 24 landscapes (4 x 4 km) across seven European countries along gradients of both land-use intensity and landscape structure. Species-environment relationships were examined in a hierarchical design of four main sets of environmental factors (country, land-use intensity, landscape structure, local habitat properties) that covered three spatial scales (region, landscape, local) by means of hierarchical variability partitioning using partial canonical correspondence analyses. 3. Local community composition and the distribution of body size classes and trophic guilds were most affected by regional processes, which highly confounded landscape and local factors. After correcting for regional effects, factors at the landscape scale dominated over local habitat factors. Land-use intensity explained most of the variability in species data, whereas landscape characteristics (especially connectivity) accounted for most of the variability in body size and trophic guilds. 4. Synthesis and applications. Our results suggest that management effort should be focused on land-use intensity and habitat connectivity in order to enhance diversity in agricultural landscapes. Since these factors are largely independent, specific conservation programmes may be developed with regards to socio-economic and agri-environmental requirements. Changes in either of these factors will enhance diversity but will also result in specific effects on local communities related to dispersal ability and the resource use of species.
