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Fish assemblages in reservoirs and lakes are mainly assessed by multiple sampling gear. The challenge exists in how to combine all the data from the different types of gear to develop a fish-based index. In this paper, we describe a novel approach to this challenge in reservoirs in Flanders. The developed approach can also be used for natural lakes in the same eco-region and for any combination of fishing methods. In a first step, we defined a reference list of fish species occurring in man-made Flemish reservoirs. To compile this reference list, we adapted the reference for Dutch lakes with recent data from freshwater reservoirs in Flanders. This reference list contains guild-specific information needed to define metrics. To pre-classify the reservoirs, a habitat status for each reservoir was set using abiotic parameters (pressures). Fish gear-dependent metrics were selected according to their response to these pressures. Threshold values for metrics were determined based on the species reference list and occasionally on the calculated metric values. The ecological quality ratios derived from the index calculation were validated with an independent set of data. The developed index proved to successfully assess the ecological status of the reservoirs in Flanders. [ABSTRACT FROM AUTHOR]

Background: Gene flow and adaptive divergence are key aspects of metapopulation dynamics and ecological speciation. Long-distance dispersal is hard to detect and few studies estimate dispersal in combination with adaptive divergence. The aim of this study was to investigate effective long-distance dispersal and adaptive divergence in the fen orchid (Liparis loeselii (L.) Rich.). We used amplified fragment length polymorphism (AFLP)-based assignment tests to quantify effective long-distance dispersal at two different regions in Northwest Europe. In addition, genomic divergence between fen orchid populations occupying two distinguishable habitats, wet dune slacks and alkaline fens, was investigated by a genome scan approach at different spatial scales (continental, landscape and regional) and based on 451 AFLP loci. Results: We expected that different habitats would contribute to strong divergence and restricted gene flow resulting in isolation-by-adaptation. Instead, we found remarkably high levels of effective long-distance seed dispersal and low levels of adaptive divergence. At least 15% of the assigned individuals likely originated from among-population dispersal events with dispersal distances up to 220 km. Six (1.3%) ‘outlier’ loci, potentially reflecting local adaptation to habitat-type, were identified with high statistical support. Of these, only one (0.22%) was a replicated outlier in multiple independent dune-fen population comparisons and thus possibly reflecting truly parallel divergence. Signals of adaptation in response to habitat type were most evident at the scale of individual populations. Conclusions: The findings of this study suggest that the homogenizing effect of effective long-distance seed dispersal may overwhelm divergent selection associated to habitat type in fen orchids in Northwest Europe. [ABSTRACT FROM AUTHOR]

National or regional conservation strategies are usually based on available species distribution maps. However, very few taxonomic groups achieve a full coverage of the focal region. Distribution data of well-mapped taxonomic groups could help predict the distribution of less well-mapped groups and thus fill gaps in distribution maps. Here, we predict the distribution of five heathland butterflies in Flanders (north Belgium) using typical heathland bird distribution data as predictor variables. We compare predictions with those using only biotope or a combination of both biotope and bird data as variables. In addition, we test the transferability of 'bird', biotope and combined models to the Netherlands, an ecologically similar region. Transferability was tested in three separate sandy regions in the Netherlands at different distances from the region in which the models were built. For each of the five heathland butterflies, we applied logistic regressions on ten random model sets and tested the models on ten random evaluation sets within Flanders. We used the area under the curve (AUC) of the receiver-operating characteristics (ROC) plots to estimate model accuracy. Overall, bird models performed significantly better than biotope models but were not significantly different from the combined models in Flanders. In the Netherlands, the transferred biotope and the combined models performed better than the transferred 'bird models'. We conclude that on a local scale, birds can, to some extent, serve as proxies for biotope quality, but that biotope models are more robust when transferred to another region. [ABSTRACT FROM AUTHOR]

Abstract: We studied the effects of heavy metal exposure on host plant choice and performance of the grass miner Chromatomyia milii (Diptera, Agromyzidae). Cadmium decreased plant growth in a dose-dependent way. C. milii preferred the control to the cadmium-exposed plants for feeding and oviposition. Moreover, preference for the control plants increased with increasing cadmium exposure of the alternative choice. Adult and offspring performance decreased with increasing plant cadmium exposure. This suggests that, at least under our laboratory conditions, host choice of C. milii is adaptive under pollution stress. Foliar cadmium concentration increased and the soluble sugar concentration decreased with increasing cadmium exposure. Regression analysis showed that both latter components might be responsible for the decrease in performance of C. milii on cadmium-exposed plants. The protein and amino acid concentration of the leaves, the amount of structural defenses, and water concentration were not affected by the cadmium treatment. [Copyright &y& Elsevier]

The plant stress hypothesis predicts that environmental stress increases the suitability of plants as food for herbivores, especially for senescence feeders. Yet, performance is enhanced only at moderate stress intensities in several herbivores. Even more paradoxically, a large number of insect species prefer and perform better on vigorously growing plants. In order to test plant stress theory, we conducted a laboratory experiment in which the influence of plant water stress on host preference and the performance of the grass minerChromatomyia miliiwas studied. We imposed a gradient of stress intensities, i.e. 25, 50, 75, 150, and 300-ml weekly-administered water per grass pot, in order to study the full range of responses ofC. miliito water stressed plants. Plant stress intensity was quantified by measuring individual plant mass, foliar water content and the concentration of the photosynthetic pigments chlorophyll a and b. Plant mass had decreased from the 150 and 300-ml treatments to the lowest water treatment at the end of our experiment, which was mainly a result of a reduction in leaf area and leaf number. Foliar water content was clearly negatively affected by water shortage. Chlorophyll a and b also decreased with water shortage. Finally, the stress intensity measurements showed that plants acclimated to water stress conditions throughout the experiment. Feeding and oviposition preference ofC. miliiwas positively related to water supply. No larvae survived on two lowest water treatments and only 38% survived on the 75-ml treatment, while more than 80% survived on the 150 and the 300-ml treatments. Offspring development time was longer on the 75-ml treatment than on the 150 and the 300-ml treatments. We also evaluated the mechanisms that could explain the response ofC. miliito water stressed plants. Although no relationship between water treatment and foliar amino acid concentration was found, we observed significantly higher foliar protein concentrations in the 25 and the 50-ml treatments. This supports the hypothesis that abiotic stress causes an increase of nitrogenous compounds in plants. Leaf senescence following self-pruning, a process by whichH. lanatusplants acclimate to drought conditions, was responsible for the dramatically high offspring mortality on the water stressed plants. The shape of the plant stress intensity–herbivore response relationship showed strong variation and depended both on the type of plant stress intensity measure and herbivore response variable involved. Yet, all relationships showed a monotonic increase of herbivore preference and performance with decreasing plant stress intensity. This indicates thatC. miliiprefers and performs better on vigorously growing plants. We found no support for an increased herbivore performance on moderately or severely stressed plants. [ABSTRACT FROM AUTHOR]

We studied the relationship between plant stress intensity and herbivore response in the grass miner Chromatomyia milii (Kaltenbach) (Diptera: Agromyzidae) on nutrient stressed plants. We subjected the host grass Ifukus lanatus (Poaceae) to a range of nutrient treatments (0%, 25%, 50%, 100%, and 200% Hoagland nutrient solution) and recorded plant stress intensity (plant growth and foliar chlorophyll a and b levels) and offspring performance of C. milii. Plant growth and foliar chlorophyll a and b levels decreased from the 25% treatment to the 200% treatment. The plant stress intensity from the 0% treatment was equal to or only slightly higher than the 25% treatment. Offspring survival of C. milii was lower on the 100% and the 200% treatments than on the other treatments. Offspring development time and pupal mass did not differ between the nutrient treatments. Offspring survival of C. milii showed a monotonic non-linear increase with decreasing plant stress intensity. These results clearly show that an excess of nutrients may result in plant stress and reduced herbivore performance. [ABSTRACT FROM AUTHOR]

Journal of Ecology (2004) 92 , 5–14 [ABSTRACT FROM AUTHOR]

We investigated the relative importance of environmental factors versus host phenotype in determining parasite prevalence in Eurasian red squirrels ( Sciurus vulgaris). One hundred and forty-three fecal samples of 116 different squirrels collected in 2000 and 2001 from five study areas in the Italian Alps, were examined for intestinal protozoans. Two species of Eimeria were present with a medium to high prevalence in both years and in all areas, while two other species were rare, occurring only in some areas and not in all years. Cryptosporidium parvum had a high prevalence in the two study areas of the Western Alps, while in the three areas of the Central Alps it was recorded only once. The prevalence of Eimeria sciurorum and C. parvum fluctuated in parallel with squirrel density, suggesting a possible correlation between the presence of these protozoans and host density. A gender effect on E. sciurorum prevalence at low density could be explained by different space use patterns and social organization of males and females. C. parvum occurred more frequently in young squirrels, suggesting an acquired immunity in adults, but age-related susceptibility was not found for eimerian species. The coccidian community was more similar within than between regions, and study area and year were key parameters in predicting coccidia infection. There was no evidence of competition between coccidian species, but one positive interaction between E. sciurorum and E. andrewsi was observed. Our results suggest that the effects of geographic region, area features, and year effects probably related to fluctuations in host population density, were more important than individual phenotypic host characteristics in structuring the coccidian assemblage and determining levels of parasite prevalence in red squirrel populations. [ABSTRACT FROM AUTHOR]

We studied the effect of potassium on the uptake of radiocesium from sediment by larvae of the midge Chironomus riparius. Sediment ingestion rate was determined for one week. After 24 h the gut content remained constant, indicating that equilibrium was reached between sediment ingestion and sediment elimination. These data were used to account for radiocesium present in the gut in subsequent uptake experiments. Reference sediment was equilibrated with solutions containing different concentrations of potassium: 1, 10, 100, and 1,000 µM. Adsorption of 137Cs to the sediment was investigated. Three different radiocesium levels (0.3, 0.6, and 1.2 KBq/ml) were applied at the four different potassium levels. In all cases more than 94% of all radiocesium was adsorbed to the sediment within 48 h. The sediment, equilibrated with the four different potassium levels, was spiked with a constant amount of 296 Bq/ml 137Cs. Accumulation by midge larvae was followed for one week, and subsequently elimination was followed for another week. No significant differences in radiocesium levels in midge larvae among the treatments were found after one week of exposure. However, using a one-compartment accumulation model, a small but significant effect of potassium in water and sediment on the uptake and elimination rate constants (ka and ke) was found. These results indicate that although differences were rather small, radiocesium accumulation decreased with increasing potassium level in the sediment. [ABSTRACT FROM AUTHOR]

Investigates the relationship between host plant choice and plant nutritional quality in two oligophagous grass miners Chromatomyia milii and C. nigra. Demonstration that fitness parameters are differentially related to host chemistry; Suggestion that chemically mediated host suitability for adult performance is an important determinant of host choice in this species.

We studied population dynamics of red squirrels in a group of small forest fragments, that cover only 6.5% of the total study area (4664 ha) and where distances to the nearest source population were up to 2.2 km. We tested effects of patch size, quality and isolation and supplementary feeding on patch occupation during 1995-99. Larger patches and patches with supplementary feeding had a higher probability of being occupied. No patch < 3.5 ha was ever occupied. No effects of isolation were found, suggesting that the forest habitat in the study area is not sufficiently fragmented to influence red squirrel distribution across patches. For medium sized patches (3.7-21 ha), that were occupied some years, there was an increase in patch occupation over the years, even though overall population size tended to decrease. These patches had a high turnover, especially of males. Patches in which the squirrel population went extinct were recolonized within a year. For patches that were at least some years occupied, squirrel density depended on patch quality only. No effects of patch size, isolation and winter temperature on population density were found. These data suggest that in our study area habitat fragmentation has no effect on local squirrel density and that the random sample hypothesis explains the distribution pattern across patches. [ABSTRACT FROM AUTHOR]

Many parthenogenetic species are geographically more widely distributed than their sexual relatives. Their success has been partly attributed to the existence of general purpose genotypes (GPGs). Darwinula stevensoni is an ostracod species, which has persisted for >25 million years without sex, and is both ubiquitous and cosmopolitan. Here, we test the hypothesis that this ancient asexual species may possess a highly generalised (or general purpose) genotype. The ecological tolerance of D. stevensoni was compared with asexual populations of Heterocypris incongruens, a common cypridinid species with mixed reproduction, as well as with that of another ancient asexual darwinulid species with a limited geographic and ecological distribution, Vestalenula molopoensis. The unusually wide tolerance range for both salinity (0–30 g/l) and temperature (10°C, 20°C and 30°C) of the freshwater species D. stevensoni, supports the hypothesis that this ancient asexual has indeed developed a GPG. This coincides with its wide geographic and ecological distribution and might explain its persistence as an obligate asexual in its long-term evolution. The more restricted salinity tolerance of V. molopoensis (maximum at 12 g/l) shows that not all species of the ancient asexual family Darwinulidae have a GPG. D. stevensoni has a much broader tolerance than the asexuals of H. incongruens. We argue why a GPG is most likely to develop in long-term asexuals. [ABSTRACT FROM AUTHOR]

Focuses on the role of top-down forces in host choice evolution of phytophagous arthropods. Analysis on the nature of third trophic level effects; Elimination of species vulnerability; Clarification of the evolutionary role.

Environmental stresses affect plant growth and performance in nature. Host plant quality in turn affects herbivore performance and population dynamics. In view of these interactions, two major hypotheses were formulated. The plant stress hypothesis proposes that physiologically stressed plants become more susceptible to herbivores. The plant vigour hypothesis proposes that plants that grow vigorously are favourable to herbivores. Here we test the plant stress/plant vigour hypotheses for a leaf miner, Agromyza nigripes (Diptera; Agromyzidae), on the grass Holcus lanatus. We assessed larval performance (survival, developmental time, pupal mass) on grasses growing under different levels of nutrients (Hoagland solution) and drought stress, under controlled field and greenhouse conditions. Plant vigour and nutrient content were high on soils with an intermediate nutrient concentration and lower under drought stress and soil nutrient shortage and overdose. Larval performance was also highest on wet soils with intermediate nutrient supply. The results of the mining flies support the plant vigour hypothesis (density, survival and development better on vigorous plants). Herbivore performance is higher on leaves with a higher protein content. [ABSTRACT FROM AUTHOR]

We focused on male harassment on different female color morphs of the damselfly Ischnura elegans and on variation in morph-specific mating avoidance tactics by females. In I. elegans, one of the female morphs is colored like the conspecific male (andromorphs) while the other morphs are not (gynomorphs). Our first goal was to quantify morph-specific male mating attempts, hence male harassment, in populations with manipulated population parameters (densities, sex ratios, and proportion of andromorphs). Second, we examined the female's perspective by looking for potential differences in morph-specific mating avoidance tactics and success of those tactics in a natural population. Differences in population conditions did influence the number of male mating attempts per morph. The less frequent female morph was always subject to fewer mating attempts, which contradicts earlier hypotheses on mimicry, but supports those that assume that males learn to recognize female morphs. Gynomorphs occupy less open habitat and often fly away when a male approaches, while andromorphs use more open habitat, do not fly large distances and directly face approaching males. Female morphs did not differ in the proportion of successful mating-avoidance attempts. Our results suggest that the maintenance of the color polymorphism is most probably the result of interactive selective forces depending on variation in all population conditions, instead of solely density- or frequency-dependent selection within populations. [ABSTRACT FROM AUTHOR]

The role of vegetation and soil factors on the biodiversity of two soil dwelling, saprophagous, fly families (Sphaeroceridae and Lonchopteridae) in a heathland ecosystem were investigated. The fly community is primarily affected by soil humidity and the amount of organic matter while the vegetation structure and species composition only indirectly influence the fly communities. There was no correlation between plant species richness and the fly diversity indices. Based on our results and literature data, we hypothesise that the direct effects of the vegetation is more evident for herbivorous insects than for species that do not feed on plants. The investigated families show a clear response to microhabitat differences in the soil factors, which makes them promising indicators for soil health and as tool for monitoring environmental changes. [ABSTRACT FROM AUTHOR]

We studied the costs of lamellae autotomy with respect to growth and survival of Lestes sponsa damselfly larvae in field experiments. We manipulated predation risk by Aeshna cyanea dragonfly larvae and lamellae status of L. sponsa larvae in field enclosures and compared differences in numbers, size and mass of survivors among treatments. In the absence of a free-ranging A. cyanea larva, about 29% of the L. sponsa larvae died. This was probably due to cannibalism. The presence of a free-ranging A. cyanea reduced larval survival by 68% compared to treatments in which it was absent or not permitted to forage on L. sponsa damselflies. Across all predator treatments, lamellae autotomy reduced survival by about 20%. The mean head width and mass of survivors was lower in the enclosures with a free-ranging A. cyanea compared to the other two predator treatments. This suggested that larvae grew less in the presence of a free-ranging predator, indicating that increased antipredator behaviours were more important in shaping growth responses than reduced population density. Mass, but not head width, of survivors was also reduced after autotomy. The fitness consequences of these effects for the adults may be pronounced. In general, these field data strongly suggest that lamellae autotomy affects population regulation of damselflies. [ABSTRACT FROM AUTHOR]

Previous allozyme analyses of the hermaphroditic terrestrial slugs Arion fasciatus, A. circumscriptus and A. silvaticus (subgenus Carinarion) have suggested that in North America these species are each single monomorphic strains. However, new data on 18 putative enzyme loci show that in western Europe the three taxa, respectively, consist of at least three, two and 12 homozygous multilocus genotypes (strains), which regularly co-occur. The current opinion that American and European Carinarion populations are similarly structured, and that colonization events did not affect the population genetics of North American Carinarion, should therefore be readdressed. The present data also provide the first indication of heterozygosity and possible outcrossing in Carinarion. Nevertheless, uniparental reproduction is confirmed as the main breeding system in West European Carinarion, although the high incidence of multistrain populations in A. silvaticus and A. fasciatus appears at variance with the current model of population genetic structuring in selfing terrestrial pulmonates. Finally, the systematic status of the three Carinarion spp. is tentatively questioned. [ABSTRACT FROM AUTHOR]

The balance between costs and benefits is expected to drive associations between species. While these balances are well understood for strict associations, we have no insights to which extent they determine facultative associations between species. Here, we quantified the costs of living in a facultative association, by studying the effects of red wood ants on the facultatively associated isopod Porcellio scaber. Porcellio scaber frequently occurred in and near hostile red wood ant nests and might outnumber obligate nest associates. The facultative association involved different costs for the isopod. We found that the density of the isopod decreases near the nest with higher ant traffic. Individuals in and near the nest were smaller than individuals further away from the nest. Smaller individuals were also found at sites with higher ant traffic. A higher proportion of wounded individuals was found closer to the nest and with higher ant traffic. We recorded pregnant females and juveniles in the nest suggesting that the life cycle can be completed inside the nests. Lab experiments showed that females died sooner and invested less in reproduction in presence of red wood ants. Porcellio scaber rarely provoked an aggression response, but large numbers were carried as prey to the nest. These preyed isopods were mainly dried out corpses. Our results showed that the ant association incurred several costs for a facultative associate. Consequently, red wood ant nests and their surrounding territory act as an alternative habitat where demographic costs are offset by a stable resource provisioning and protection. [ABSTRACT FROM AUTHOR]

Bats exhibit a variety of life‐history traits that can serve as valuable surrogate metrics of terrestrial ecosystem health. Here, we investigate how sonotype activity of hipposiderid bats covaries with habitat structure at finer spatial scales. We recorded passive echolocation calls and measured key habitat attributes in six rainforests in the Lomami and Yangambi landscapes, Democratic Republic of the Congo. Using bat passes as a measure of sonotype activity, we clustered echolocation calls based on call structure similarity to control for within‐sonotype variation in activity. Over 432 h of recording, we detected 370 passes matching a hipposiderid sonotype in three subgroups, recovering eight potential species. Open habitats negatively affected sonotype activity in the Hipposideros subgroup, which was associated with higher echolocation frequencies. Indeed, activity peaked in the early evening when mean post‐sunset temperature was above the nocturnal average and declined until early morning when mean temperatures dropped below the nightly average. All habitat variables were marginally correlated with the activity of the Doryrhina subgroup, whereas Macronycteris was more active in open habitats. Our findings indicate a probable flexibility of habitat use in lower echolocating bats and point to three possible foraging guilds that modulate hipposiderid bat responses to habitat structure. [ABSTRACT FROM AUTHOR]