Baetis Research Articles

SEASONAL VARIATION IN DIET AND FEEDING STRATEGY OF THREE MAYFLY SPECIES

Understanding the feeding habits of aquatic invertebrates under reference conditions can contribute to our understanding of community assemblages in freshwaters. Here, seasonal changes in the diet of three species of Ephemeroptera from Irish high status rivers were investigated. A fluorescent dye, 4'6 diamidino-2-phenylindole, was used to differentiate the various types of gut contents and to allow bacteria and biofilm matrix to be visualised. Through interpretation of gut contents and feeding strategy plots, Baetis rhodani was found to have a generalist diet with detritus, algae and biofilm—the main food types. Two congeneric species, Ecdyonurus venosus and E. insignis, were found to be detritus specialists. Seasonal sampling indicated that biofilm can provide a valuable food source to E. venosus at times of high flow when detritus is not readily available. There was evidence of niche separation in summer when E. insignis and E. venosus co-existed. E. insignis fed on coccoid algae while E. venosus consumed no coccoid algae. B. rhodani consistently ingested a similar broad diet throughout the year. A detritus-based diet is likely nutrient poor leading to lower growth rates. These findings are discussed in the context of the behaviour of these species and sensitivity to nutrient enrichment.

Natural born killers: an invasive amphipod is predatory throughout its life-history

Introduced predators can have profound impacts on prey populations, with subsequent ramifications throughout entire ecosystems. However, studies of predator–prey interaction strengths in community and food-web analyses focus on adults or use average body sizes. This ignores ontogenetic changes, or lack thereof, in predatory capabilities over the life-histories of predators. Additionally, large individual predators might not be physically capable of consuming very small prey individuals. Both situations are important to resolve, as native prey may or may not therefore experience ontogenetic or size refuges from invasive predators. Here, we find that the freshwater amphipod invader, Gammarus pulex, is predatory throughout its development from juvenile through to adult. All size classes collected in the field had a common prey, nymphs of the mayfly Baetis rhodani, in their guts. In an experiment with predator, prey and experimental arenas scaled for body size, G. pulex juveniles and adults consumed B. rhodani in all size-matched categories. In a second experiment, the largest G. pulex individuals were able to prey on the smallest B. rhodani. Thus, the prey do not benefit from any ontogenetic or size refuge from the predator. This corroborates with the known negative population abundance relationships between this invasive predator and its native prey species. Understanding and predicting invasive predator impacts will be best served when interactions among all life-history stages of predator and prey are considered.

Loss of small glaciers will diminish beta diversity in Pyrenean streams at two levels of biological organization

ABSTRACTAim Small (< 1 km2) alpine glaciers are likely to disappear in this century, resulting in decreased regional habitat heterogeneity in associated streams. Both heterogeneity within and spatial isolation among glacier‐influenced streams can enhance beta diversity of stream‐dwelling organisms. We measured beta at both community and population‐genetic levels within and among streams currently influenced by small Pyrenean glaciers. We aimed to evaluate whether patterns are analogous between the two levels, to apply various approaches for characterizing beta, and to infer the outcome of future glacier loss on regional biodiversity.Location Four glacier‐fed basins in the Parc National des Pyrénées, France.Methods We classified each of 18 stream reaches across the basins into either high‐, mid‐ or low‐‘glaciality’ (glacial influence) groups according to four physicochemical characteristics. At each reach, we collected macroinvertebrate communities and evaluated mitochondrial DNA haplotypes for 11–13 individuals of Baetis alpinus Pictet. Using taxa/haplotypes as basic units, we evaluated community and population‐genetic beta diversity simultaneously. We measured beta diversity in three major ways: as multivariate (Sørensen's dissimilarity, Jost D) and ‘classical’ (gamma/alpha) variation to compare among glaciality groups, and as turnover along the glaciality gradient within each basin.Results For most approaches at both organizational levels, beta was greatest among high‐glaciality reaches, absolute values of variation of beta in high‐glaciality streams were strikingly similar between levels, and the steepest turnover within basins occurred between high‐ and mid‐glaciality reaches. Therefore, high‐glaciality reaches contained assemblages and populations that were unique both within that stream type (among basins) and compared with other stream types within basins.Main conclusions Parallel beta diversity patterns at population‐genetic and community levels suggested that environmental drivers influence these levels analogously. Extreme conditions (e.g. low temperature, high instability, isolation) in high‐glaciality streams probably enhance beta at both levels. Stream beta diversity is likely to decrease substantially with continued glacial reduction in this system.

Thiacloprid affects trophic interaction between gammarids and mayflies

Neonicotinoid insecticides like thiacloprid enter agricultural surface waters, where they may affect predator–prey-interactions, which are of central importance for ecosystems as well as the functions these systems provide. The effects of field relevant thiacloprid concentrations on the leaf consumption of Gammarus fossarum (Amphipoda) were assessed over 96 h (n = 13–17) in conjunction with its predation on Baetis rhodani (Ephemeroptera) nymphs. The predation by Gammarus increased significantly at 0.50–1.00 μg/L. Simultaneously, its leaf consumption decreased with increasing thiacloprid concentration. As a consequence of the increased predation at 1.00 μg/L, gammarids' dry weight rose significantly by 15% compared to the control. At 4.00 μg/L, the reduced leaf consumption was not compensated by an increase in predation causing a significantly reduced dry weight of Gammarus (∼20%). These results may finally suggest that thiacloprid adversely affects trophic interactions, potentially translating into alterations in ecosystem functions, like leaf litter breakdown and aquatic-terrestrial subsidies.

How river structure and biological traits influence gene flow: a population genetic study of two stream invertebrates with differing dispersal abilities

Summary1. Determined by landscape structure as well as dispersal‐related traits of species, connectivity influences various key aspects of population biology, ranging from population persistence to genetic structure and diversity. Here, we investigated differences in small‐scale connectivity in terms of gene flow between populations of two ecologically important invertebrates with contrasting dispersal‐related traits: an amphipod (Gammarus fossarum) with a purely aquatic life cycle and a mayfly (Baetis rhodani) with a terrestrial adult stage.2. We used highly polymorphic markers to estimate genetic differentiation between populations of both species within a Swiss pre‐alpine catchment and compared these results to the broader‐scale genetic structure within the Rhine drainage. Landscape genetic approaches were used to test for correlations of genetic and geographical structures and in‐stream barrier effects.3. We found overall very weak genetic structure in populations of B. rhodani. In contrast, G. fossarum showed strong genetic differentiation, even at spatial scales of a few kilometres, and a clear pattern of isolation by distance. Genetic diversity decreased from downstream towards upstream populations of G. fossarum, suggesting asymmetric gene flow. Correlation of genetic structure with landscape topography was more pronounced in the amphipod. Our study also indicates that G. fossarum might be capable of dispersing overland in headwater regions and of crossing small in‐stream barriers.4. We speculate that differences in dispersal capacity but also habitat specialisation and potentially the extent of local adaptation could be responsible for the differences in genetic differentiation found between the two species. These results highlight the importance of taking into account dispersal‐related traits when planning management and conservation strategies.

Systematics and phylogeny of the West Palaearctic representatives of subfamily Baetinae (Insecta: Ephemeroptera): combined analysis of mitochondrial DNA sequences and morphology

This study represents the first formal combined (morphological and molecular) phylogenetic analysis of the highly diversified subfamily Baetinae (sensu Kazlauskas 1972). Taxonomic sampling comprised the majority of different Palaearctic lineages within the subfamily recognised so far. The data set of 47 coded morphological characters was analysed together with the partial mitochondrial DNA cytochrome oxidase c subunit I gene (COI) sequences using parsimony and Bayesian inference. From the eight genera and species-groups investigated, three were supported as monophyletic in the analyses. The monophyly of another three genera/species-groups could not be tested because only a single species was included in the sampling. The remaining two subgenera/species-groups were recovered as paraphyletic at least using one methodological approach. A monophyletic group comprising the genera Labiobaetis + Nigrobaetis + Alainites was supported as a sister lineage to the genus Baetis s.str. Morphological characters were mapped on a cladogram, clade robustness was tested by multiple approaches and alternative views to the taxonomy of the subfamily were discussed. Intraspecific and interspecific divergences in the COI sequence were estimated for the species studied. The existence of a distinct ‘barcoding gap’ was not supported. Baetis rhodani and Alainites muticus exhibited unusually high values of intraspecific variability pointing to the possible existence of cryptic species.

Geographical and seasonal evidence of cryptic diversity in the Baetis rhodani complex (Ephemeroptera, Baetidae) revealed by means of DNA taxonomy

Previous phylogenetic investigations on the mayfly Baetis rhodani Pictet from several European countries, excluding Italy, strongly suggested the presence of cryptic species. Our paper reports a DNA-taxonomy phylogenetic analysis of B. rhodani with additional populations coming from Italian and UK sites, and aims to identify potential cryptic species with a coalescent-based method (GMYC model) and to understand the mechanisms of local coexistence of cryptic species. Twenty-five haplotypes of Italian samples and five haplotypes of UK samples were identified and added to a large European dataset. A total of 11 potential cryptic species have been recognised, and three of them co-occured in one Italian area. Such cryptic species seem to be phylogenetically over-dispersed on the tree and temporally segregated, and the seasonal substitution pattern of cryptic species could explain the apparently widespread distribution of the B. rhodani complex and its ability to adapt to different temperatures and food resources, justifying some of the differences observed in the relationship between water temperature, growth rates and phenology documented from field studies.

Longitudinal extent of acidification effects of plantation forest on benthic macroinvertebrate communities in soft water streams: evidence for localised impact and temporal ecological recovery

Plantation conifer forest can increase the risk of acidification in acid-sensitive catchments with consequences for macroinvertebrates and ecosystem functioning. This study compared headwater streams in forested and non-forested catchments to appraise the distance required for the acid effect on macroinvertebrates to diminish downstream. Strict criteria were followed in the selection of paired streams, including similarities in elevation, aspect, stream order, geographical proximity, geology and soil type, with no inflowing tributaries in the first 2.5 km and no major land-use other than plantation forest and moorland. Consequently two headwater streams (one forested, one non-forested) drained Ordovician sedimentary geology and two headwater streams (one forested, one non-forested) drained Old Red Sandstone (ORS) were selected. All streams drained peaty soils. Up to six sites at 500 m intervals were sampled in triplicate by multihabitat kick sampling. Ecological impact and recovery from acid effects involved the entire macroinvertebrate community, but varied between seasons. Acid-sensitive Ephemeroptera revealed marked effects of episodic acidification, with Baetis rhodani and Rhithrogena semicolorata found to be transient between seasons. The increase in acid-sensitive ephemeropteran species with increasing distance downstream indicates the finite effects of forest mediated acidification on soft water streams in Ireland. Ecological impact appears, therefore, to be localised within the catchment, with ecological recovery occurring a short distance downstream. This is the first study to have reported such results.

Effects of Rotenone Treatment on Lotic Invertebrates

AbstractTwo rivers in Norway were treated with rotenone in an effort to eradicate the salmon parasite, Gyrodactylus salaris. Rotenone induced an immediate catastrophic invertebrate drift, mainly of dead individuals. The response to rotenone with respect to degree and timing varied widely. Baetis rhodani, Isoperla sp. and Rhyacophila nubila displayed a strong increase in drift densities early in the treatment. Baetis niger, Ameletus inopinatus, Heptagenia sp. and Agapetus ochripes showed a delayed response. Ephemerella aurivillii, E. mucronata, Taeniopteryx nebulosa and Elmis aenea drifted at low densities throughout the treatment. Early larval instar tended to be more sensitive to rotenone than later instar, and the toxic effect of rotenone tended to increase with increasing water temperature. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental effects of sediment deposition on the structure and function of macroinvertebrate assemblages in temperate streams

AbstractFine sediment in streams and rivers is one of the most globally widespread of all freshwater pollutants. However, the ecological implications are still poorly quantified, and field experiments to assess likely functional and structural effects are scarce.We assessed the response of stream invertebrates to fine sediment (i.e. inert sand) added to trays (n = 65) containing otherwise natural substrata over a three‐week period in three replicate streams in the Usk catchment, Wales.Sediment addition to 0.6–18 kg m−2 affected both the structure and functional composition of invertebrate assemblages while also reducing overall abundance and in some common species (Baetis rhodani, Ecdyonurus sp. and Leuctra geniculata).Sediment also reduced richness and overall trait diversity (TD), while different life‐history traits were either favoured (polivoltinism, tegumental respiration and burrowing behaviour) or disfavoured (swimmers, attached taxa, gill respiration). Moreover, sediments appeared to promote a nested subset pattern in species composition, with generalists favoured at the expense of specialists either through exclusion or impaired colonization. Effects were due largely to the loss of five taxa that contributed to the significant nestedness across the sand gradient: B. rhodani, Ecdyonurus sp., Leuctra geniculata, Simuliidae and Ephemerella ignita.This short‐term experiment supports recent surveys in indicating how sedimentation can change the structural and functional composition of stream invertebrate assemblages even at low to moderate rates of deposition. In revealing direct effects on trait adversity, trait representation and nestedness, the data are also consistent with survey data in indicating that sediments have potentially important ramifications for conservation by removing organisms systematically according to life‐history features. Copyright © 2010 John Wiley & Sons, Ltd.

Drift and settlement of stream insects in a complex hydraulic environment

Summary1. The hydraulic and geomorphic characteristics of stream patches are often associated with distinctive assemblages or densities of stream invertebrates, and it is routinely presumed that these patterns reflect primarily species‐specific habitat requirements. An alternative hypothesis is that such patterns may be influenced by constraints on movement, such as the results of departure and settlement processes. We describe a manipulative experiment that examined how the hydraulic environments created by topographic bedforms influenced the drift behaviour and potential settlement sites for two species of mayfly (Baetis rhodani and Ecdyonurus torrentis). These species are common in the drift and often co‐occur in streams, but differ in their small‐scale distribution patterns, body shape and movement behaviour.2. Flume experiments were carried out to determine how the hydraulic environments conditioned by a step bedform influence the behaviour of mayflies in the drift (swimming, posturing, tumbling), and the consequences of those behaviours (drift distance and time), compared to drift over a plane bed. The ramped step in the flume mimicked step bedforms that are common in coarse‐grained, high‐gradient streams. In contrast to the plane bed, a zone of recirculating flow was created downstream of the step, above which flow was faster and more turbulent. Uniform flows are used in most flume studies of drift; our approach is novel in recreating a complex hydraulic environment characteristic of stream channels.3. Both species had some behavioural control over drift, and drift distances and times were shorter for live larvae than for dead larvae over the plane bed. The step had no impact on drift time or distance for live Baetis, but dead larvae were trapped in the flow separation eddy and drift time increased accordingly. Some Ecdyonurus also became trapped in the eddy, but live larvae drifted farther than dead larvae, and farther over the step than the plane bed.4. Whilst in the drift, larvae altered their behaviour according to the ambient hydraulic environment, but in a species‐specific manner. Over the plane bed, Baetis had occasional swimming bursts, but primarily postured (maintained a stable body orientation), whereas Ecdyonurus spent roughly equal time posturing and swimming. In the more turbulent flows generated by the step, Baetis spent proportionately more time swimming, whereas Ecdyonurus spent more time posturing and often tumbling as body orientation became unstable.5. In a high‐gradient stream, Baetis was more abundant close to steps than in plane bed patches with less complex flow, whereas the opposite pattern held for Ecdyonurus. Thus, the small‐scale distribution patterns of these species within streams correspond to their drift behaviours and ability to access various hydraulic patch types in our flume. These results are consistent with the hypothesis that constraints on movement and settlement may be important driver of distribution patterns within streams.

Primeiro levantamento da fauna de Ephemeroptera (Insecta) do Espírito Santo, Sudeste do Brasil

A partir de coletas realizadas entre 2008 e 2009 no Parque Nacional do Caparaó, Reserva Biológica de Sooretama, entre outras áreas do Espírito Santo, apresentamos o primeiro levantamento da fauna de Ephemeroptera do estado. A despeito do seu pequeno tamanho, pois a área do estado representa apenas 0,53% do território nacional, uma surpreendente diversidade de Ephemeroptera foi encontrada. Ao todo foram identificadas 76 espécies, 41 gêneros e nove famílias, que representam aproximadamente 25% das espécies brasileiras, 65% dos gêneros e quase todas as famílias ocorrentes no Brasil. Destes táxons, 17 espécies (a maioria de Baetidae e Leptophlebiidae) são novos para a ciência. Cinco espécies, coletadas apenas no estágio ninfal, não puderam ser identificadas. O presente trabalho demonstra que, como para muitos organismos, a diversidade de Ephemeroptera para o estado é alta e mais pesquisas sobre a composição faunística de insetos aquáticos no Espírito Santo devem ser incentivadas.

Low‐level effects of inert sediments on temperate stream invertebrates

Summary1. The delivery, entrainment and deposition of inert fine sediments are among the most significant contributors to stream and river impairment worldwide. Associated ecological effects have been observed frequently, but specific experiments to identify sensitivity and avoidance behaviour in stream organisms are few, particularly in headwaters.2. In a field‐experiment, we added fine sand at low levels (c. 4–5 kg m−2) to 10 m reaches of two replicate headwater streams in the Usk catchment (Wales, U.K.) over two periods (autumn and summer). Upstream reaches were used as control in a classic before‐after‐control‐impact design. Invertebrate drift and benthic composition were measured for 2 days before and 1 day after sediment impact.3. Sediment addition significantly increased overall drift density (by 45%) and propensity (by 200%), with effects largest on the night following addition rather than immediately (i.e. within 9 h). The mayflies Baetis rhodani, B. muticus and Ecdyonurus spp., simuliid and chironomid dipterans, and helodid beetles were the strongest contributors.4. There were no marked effects on benthic composition, but density declined in treated reaches by 30–60%, particularly in B. rhodani, Ecdyonurus spp. and Leuctra hippopus + L. moselyi.5. All effects were consistent between both seasons and streams.6. These data show how even low‐level, short‐term, increases in fine sediment loading to upland, stony streams can reduce overall benthic density through increased drift. We suggest that the likely cause of the delayed drift response was a change in habitat quality which prompted avoidance behaviour. Longer‐term experiments are required to assess whether these effects reduce fitness or explain the losses of some types of organisms observed recently in sediment‐impaired reaches of this and other catchments.

Influence of riparian cover on stream temperatures and the growth of the mayfly Baetis rhodani in an upland stream

This research aimed to assess whether stream temperature and the size of Baetis rhodani larvae (Insecta: Ephemeroptera) differed between sites with contrasting riparian vegetation cover. Stream temperatures and Baetis sizes were monitored at sites along a 5-km section of a small (30 km2) upland Scottish stream. Some sites had riparian tree cover dominated by mature broadleaved woodland, while others were located in areas of open Calluna moorland. The 13 month data period included two contrasting summers, one typical for the region and the other unusually warm. Daytime water temperatures were generally highest at the open moorland sites. The difference between moorland and broadleaved woodland sites was most apparent in the summer months, with the woodland shading apparently acting to reduce maximum temperatures and mediate temporal fluctuations. Size data suggest that Baetis has a bivoltine life-cycle in the stream. Significant differences in the mean size of Baetis were found between moorland and woodland sites, with differences occurring primarily during the summer months. Mean size of Baetis was significantly greater in the moorland during the time of summer adult emergence. During the months that followed (growth of the next generation), Baetis larvae in the woodland sites were significantly larger. Size distribution data for the population suggest earlier adult emergence in the moorland section and different egg-to-larvae hatch times. Overall, the results indicate that subtle differences in growth and life cycles, linked to differences in riparian cover and streamwater temperature, can occur over short distances in upland streams.

Short-Term Effects on Riverine Ephemeroptera, Plecoptera, and Trichoptera of Rotenone and Aluminum Sulfate Treatment to Eradicate Gyrodactylus salaris

ABSTRACT In Norway, attempts have been made to eradicate the salmon parasite Gyrodactylus salaris from infested rivers using solutions containing either rotenone or aqueous aluminum and sulfuric acid (AlS). When Steinkjewassdraget, a river system in central Norway, was being treated in summer 2007 with AIS and the rotenone formulation CFT Legumine, we investigated the immediate drift of Ephemeroptera, Plecoptera and Trichoptera in the River Rølla. The rotenone treatment induced catastrophic drift and caused mortality to the ephemeropterans Baetis fuscatus/scambus, Baetis muticus, Baetis niger, Baetis rhodani, Heptagenia dalecarlica, Heptagenia sp., and Ecdyonurus joernensis; to the plecopterans Amphinemura borealis, Amphinemura sp., Capniidae indet., Leuctrafusca, Leuctra sp., Nemoura avicularis, Perlodidae indet., Protonemura meyeri, and Taeniopteryx nebulosa; and, to the tichopterans Hydropsyche sp., Polycentropodidae indet., Polycentropus flavomaculatus, and Rhyacophila nubila. The AlS treatment induced catastrophic drift and had negative effects on the trichopteran Rhyacophila nubila, and the ephemeropterans B. rhodani, B. niger, and possibly B. fuscatus/scambus, although its effects on these species were less pronounced than those from the rotenone treatment. No effects on drift densities or mortalities were recorded for any of the plecopterans during the AIS treatment.

Life cycle shifts in Baetis rhodani (Ephemeroptera) in the Norwegian mountains

The life cycle of the widely distributed mayfly, Baetis rhodani, was investigated in Øvre Heimdalen, in the Jotunheimen Mountains of central southern Norway. B. rhodani displayed a shift in life cycle from univoltine below the lake, Øvre Heimdalsvatn (1090 m a.s.l.) to a two-year life cycle in the inflowing stream, Brurskardbekken (1100–1300 m a.s.l.). The day degree sum for the univoltine life cycle was 950 compared to 1500–1550 for the two-year life cycle. Larvae of B. rhodani grew rapidly during the ice-free period (June–October) with growth rates of 2.1–8.1% (mg/day), while growth rates were low during winter (0.3–0.5%). There was a positive correlation between growth (mg/day) and temperature (r 2 = 0.34, p = 0.02). Although larval growth and voltinism were influenced by water temperature, other factors such as food resources are likely to be important in mountain areas. The life cycle plasticity exhibited by B. rhodani has undoubtedly contributed to its success in colonising a wide range of running water habitats throughout Europe.

Community structure and distribution of Ephemeroptera and Plecoptera larvae in lowland karst rivers in Slovenia

Mayfly and stonefly larval community compositions were investigated in lowland karst rivers. From January to December 2005, 49 benthos samples were taken using a multi-habitat approach. Environmental variables were measured in about monthly intervals. Altogether, 26 mayfly taxa (20 species) and 17 stonefly taxa (13 species) were recorded. Eight species were common, whereas 16 taxa were rare. Only Baetis rhodani and Ephemerella ignita occurred frequently at all sites. Significant differences were observed among sampling sites in diversity and richness metrics but neither in abundance nor in values of index of biocenotic regions. Spatial and seasonal differences amongst assemblages were determined by NMS. The relationship between mayfly and stonefly assemblage structure and seasonally varied environmental factors were investigated using canonical correspondence analysis (CCA). Mayfly and stonefly larval taxa distribution was best correlated to an eutrophication gradient represented by conductivity, nitrate concentration and dissolved oxygen concentration.

The Ephemeroptera fauna of the Meurthe River in north-eastern France

Since 1987, 20 years of investigations on the river Meurthe from its springs to its confluence with the river Moselle have revealed at least 43 species of Ephemeroptera, i.e. almost two-thirds of the regional diversity. The typical assemblages occurring in upper and middle courses are described; these parts of the river can be considered as “reference streams” for the region, the rest of the river being more degraded by human activities. The upper rhithral section pertains to the Vosges Mountain, and has escaped the acidification which affects many surface waters in this crystalline massif. The middle course is a typical epipotamal section on silicious alluvions. The most remarkable species found in the upper course are Ameletus inopinatus, Baetis alpinus, B. melanonyx, Rhithrogena gr [hercynia], Rh. cf carpatoalpina, Ephemerella mucronata. In the middle course Baetis liebenauae, Baetis vardarensis, Caenis lactea, Ephemera lineata, Heptagenia coerulans, H. fuscogrisea, H. longicauda, Rhithrogena beskidensis were found. Both upper and middle sections are partly included in the “Natura 2000” European network.

Degrees of polarization of reflected light eliciting polarotaxis in dragonflies (Odonata), mayflies (Ephemeroptera) and tabanid flies (Tabanidae)

With few exceptions insects whose larvae develop in freshwater possess positive polarotaxis, i.e., are attracted to sources of horizontally polarized light, because they detect water by means of the horizontal polarization of light reflected from the water surface. These insects can be deceived by artificial surfaces (e.g. oil lakes, asphalt roads, black plastic sheets, dark-coloured cars, black gravestones, dark glass surfaces, solar panels) reflecting highly and horizontally polarized light. Apart from the surface characteristics, the extent of such a ‘polarized light pollution’ depends on the illumination conditions, direction of view, and the threshold p* of polarization sensitivity of a given aquatic insect species. p* means the minimum degree of linear polarization p of reflected light that can elicit positive polarotaxis from a given insect species. Earlier there were no quantitative data on p* in aquatic insects. The aim of this work is to provide such data. Using imaging polarimetry in the red, green and blue parts of the spectrum, in multiple-choice field experiments we measured the threshold p* of ventral polarization sensitivity in mayflies, dragonflies and tabanid flies, the positive polarotaxis of which has been shown earlier. In the blue (450 nm) spectral range, for example, we obtained the following thresholds: dragonflies: Enallagma cyathigerum (0% < p* ≤ 17%), Ischnura elegans (17% ≤ p* ≤ 24%). Mayflies: Baetis rhodani (32% ≤ p* ≤ 55%), Ephemera danica, Epeorus silvicola, Rhithrogena semicolorata (55% ≤ p* ≤ 92%). Tabanids: Tabanus bovinus, Tabanus tergestinus (32% ≤ p* ≤ 55%), Tabanus maculicornis (55% ≤ p* ≤ 92%).

Knowledge-based versus data-driven fuzzy habitat suitability models for river management

Aquatic habitat suitability models have increasingly received attention due to their wide management applications. Ecological expert knowledge has been frequently incorporated in such models to link environmental conditions to the quantitative habitat suitability of aquatic species. Since the formalisation of problem-specific human expert knowledge is often difficult and tedious, data-driven machine learning techniques may be helpful to extract knowledge from ecological datasets. In this paper, both expert knowledge-based and data-driven fuzzy habitat suitability models were developed and the performance of these models was compared. For the data-driven models, a hill-climbing optimisation algorithm was applied to derive ecological knowledge from the available data. Based on the available ecological expert knowledge and on biological samples from the Zwalm river basin (Belgium), habitat suitability models were generated for the mayfly Baetis rhodani (Pictet 1843). Data-driven models appeared to outperform expert knowledge-based models substantially, while a step-forward model selection procedure indicated that physical habitat variables adequately described the mayfly habitat suitability in the studied area. This study has important implications on the application of expert knowledge in ecological studies, especially if this knowledge is extrapolated to other areas. The results suggest that data-driven models can complement expert knowledge-based approaches and hence improve model reliability.