Alan G. Hildrew

Queen Mary, University of London | QMUL · School of Biological and Chemical Sciences

This final chapter to the second edition of “Rivers of Europe” gives my personal reactions on reading the final or advanced drafts of all the other chapters—something perhaps few other people will do. This is actually my second look since my colleague Bernhard Statzner and I together wrote a personal perspective on the first edition of the book in...

Rivers of Europe, Second Edition, presents the latest update on the only primary source of complete and comparative baseline data on the biological and hydrological characteristics of more than 180 of the highest profile rivers in Europe. With even more full-color photographs and maps, the book includes conservation information on current patterns...

This final chapter to the second edition of “Rivers of Europe” gives my personal reactions on reading the final or advanced drafts of all the other chapters—something perhaps few other people will do. This is actually my second look since my colleague Bernhard Statzner and I together wrote a personal perspective on the first edition of the book in...

A personal summary of this latest scientific account of some of Europe's greatest rivers

• Stream ecosystems are supported by both green (i.e. based on grazing) and brown (i.e. detritus) food webs, whereas methane‐derived carbon is not considered generally to be important; here, we add circumstantial evidence for this potential third way. • Grazing cased‐caddis (Trichoptera) larvae in the family Glossosomatidae can be very abundant in...

Body mass–abundance (M‐N) allometries provide a key measure of community structure, and deviations from scaling predictions could reveal how cross‐ecosystem subsidies alter food webs. For 31 streams across the UK, we tested the hypothesis that linear log‐log M‐N scaling is shallower than that predicted by allometric scaling theory when top predator...

In the 'Excellence in Ecology" (EE) series published by the International Ecology Institute, Oldendorf, Germany, supported by the Otto Kinne Foundation. Shows how scientific natural history can play a role in the diagnosis of environmental problems and in suggesting remedies for them; and illustrates the pitfalls of predicting the future and the ea...

Methane oxidation produces biomass that is a potential source of particulate carbon for consumers, and is in addition to photosynthetic production. We assessed methanotrophy and photosynthetic production under differing conditions of light and methane concentration. We measured methane oxidation and photosynthesis in gravel sediments from adjacent...

Sedentary herbivores may improve the food resources available to them by 'gardening', and most obviously by fertilising primary producers with excreted nutrients such as nitrogen. In five English lakes, spanning a gradient of nutrient availability, we predicted that fertilisation of the larval retreat by the littoral, gallery-building caddisfly Tin...

The longitudinal distribution of many taxa in rivers is influenced by temperature. Here we took advantage of two older datasets on net-spinning caddisflies (Hydropsychidae) from contrasting European rivers to assess changes in species occurrence and relative abundance along the river by resampling the same sites, postulating that an increase in riv...

Many previous attempts to understand how ecological networks respond to and recover from environmental stressors have been hindered by poorly resolved and unreplicated food web data. Few studies have assessed how the topological structure of large, replicated collections of food webs recovers from perturbations. We analysed food web data taken from...

Imbalances between the supply of elements from resources and their demand from consumers may constrain key ecological processes, such as growth and production. Most previous studies have estimated such stoichiometric imbalances between consumers and resources by inferring the diet of the former from functional classifications rather than by direct...

The WHAM-FTOX model uses chemical speciation to describe the bioavailability and toxicity of proton and metal mixtures (including Al) to aquatic organisms. Here, we apply the previously parameterised model to 45 UK and Norwegian upland surface waters recovering from acidification, to compare its predictions of the maximum species richness of the ma...

This paper deals with the 20-year (1988–2008) record of macroinvertebrate sampling from the UK's Acid Waters Monitoring Network. At 12 of the 22 sites a significant temporal trend in the macroinvertebrate community is now evident. Indices of acidification suggest biological recovery at five of the 11 streams sites and at five of the lakes. All 10 s...

The use of species traits in basic and applied ecology is expanding rapidly because trait-based approaches hold the promise to increase our mechanistic understanding of biological responses. Such understanding could transform descriptive field studies in community ecology into predictive studies. Currently, however, trait-based approaches often fai...

The secondary production of culturally acidified streams is low, with a few species of generalist detritivores dominating invertebrate assemblages, while decomposition processes are impaired. In a series of lowland headwater streams in southern England, we measured the rate of cellulolytic decomposition and compared it with values measured three de...

1. Sedentary grazers can be numerous in fresh waters, despite the constraints on resource availability and the increased predation risk inherent in this lifestyle. The retreats of sedentary grazers have been assumed to provide protection to the resident (a ‘house’), but also may provide additional fertilised food for the grazer (i.e. a ‘garden’). I...

Acidity is a major driving variable in the ecology of fresh waters, and we sought to quantify macroecological patterns in stream food webs across a wide pH gradient. We postulated that a few generalist herbivore-detritivores would dominate the invertebrate assemblage at low pH, with more specialists grazers at high pH. We also expected a switch tow...

The significance of freshwaters as key players in the global budget of both carbon dioxide and methane has recently been highlighted. In particular, rivers clearly do not act simply as inert conduits merely piping carbon from catchment to coast, but, on the whole, their metabolic activity transforms a considerable fraction of the carbon that they c...

Pronounced stoichiometric imbalances (C∶N∶P) between consumers and resources reported from nutrient-poor systems potentially constrain key ecological processes, but such imbalances should be less marked when more nutrients are available. In a headwater stream rich in nutrients (total P = 208 µg/L; total oxidizable N = 7 mg/L), we determined the ele...

It is critical that the impacts of environmental stressors on natural systems are detected, monitored and assessed accurately in order to legislate effectively and to protect and restore ecosystems. Biomonitoring underpins much of modern resource management, especially in fresh waters, and has received significant sums of money and research effort...

An understanding of the consequences of long-term environmental change for higher levels of biological organisation is essential for both theoretical and applied ecology. Here, we present four decades of data from the well-characterised Broadstone Stream community, detailing biological responses to amelioration of acidification and the recent invas...

Flow in nine streams was examined in relation to refugia for invertebrates. Areas of bed maintaining low hydraulic stress throughout the discharge hydrograph could provide flow refugia for animals during spates. In one stream, near-bed shear stress and velocity were repeatedly measured in discrete patches. Three types were identified: "fast" patche...

Benthic macroinvertebrates were disturbed from stream substrata and caught in drift nets at various distances downstream. Four experiments were carried out at several discharges in each of four streams with contrasting hydraulic transport characteristics. The numbers of all invertebrates and of Plecoptera in the water column at each distance were f...

Recent attempts to include more ecological detail in connectance food webs have revealed strong relationships between food web structure, species abundance and body size. Few studies, however, have assessed these and other macroecological patterns in food webs in order to examine how network structure, dynamics and their determinants change across...

Sedentary species face a trade-off between the benefits of exploiting food close to their homes and the cost of defending it. In aquatic systems, it has been suggested that some sedentary grazers can increase the range of circumstances under which they are at an advantage over mobile grazers by enhancing food resources within their feeding territor...

Due to a combination of local methanogenesis and high background concentrations in the groundwater, water in the River Lambourn is 51 times supersaturated with methane (162 nmol CH(4) L(-1)). Pore-water concentrations of methane in the gravels of the riverbed were much lower throughout the year (71 nmol CH(4) L(-1)), suggesting significant methane...

Due to a combination of local methanogenesis and high background concentrations in the groundwater, water in the River Lambourn is 51 times supersaturated with methane (162 nmol CH4 L⁻¹). Pore-water concentrations of methane in the gravels of the riverbed were much lower throughout the year (71 nmol CH4 L⁻¹), suggesting significant methane oxidatio...

Evidence of chemical recovery from acidification in European freshwaters has emerged in recent years, with many previously damaged systems responding to decades of reduced acidifying emissions. Biological recovery, however, has often lagged behind, and this has been ascribed to several possible mechanisms, including inertia in the food web. We exam...

1. The fundamental importance of freshwater resources, the rapid extinction rate among freshwater species and the pronounced sensitivity of freshwater ecosystems to climate change together signal a pre-eminent need for renewed scientific focus and greater resources. Against this background, the Freshwater Biological Association in 2008 launched a n...

Recent attempts to include more ecological detail in connectance food webs have revealed strong relationships between food web structure, species abundance and body size. Few studies, however, have assessed these and other macroecological patterns in food webs in order to examine how network structure, dynamics and their determinants change across...

This paper describes an intensive study of an apparently ‘‘simple’’ stream community—a model system—placed in the context of an extensive study of a suite of progressively more diverse systems—a comparative approach. The main field sites were in the Ashdown Forest of southern England, where a combination of natural and anthropogenic factors produce...

Publisher Summary European Rivers: A Personal PerspectiveThis chapter presents first impressions of what this book about European rivers does and does not do. It gives a personal take on the state of the continent from a river ecologist's point of view, indicates what might be some policy lessons at this continental scale, and points out some scien...

We measured the delta(13)C values of dominant primary consumers and their potential food sources in a groundwater-fed lowland river. The delta(13)C of most consumers, such as Gammarus and Simulium, reflected that of the dominant forms of photosynthetic production, whereas the cased larvae of two caddis flies (Agapetus and Silo) were consistently (1...

We are probably familiar with the chemosynthetic ecosystems of the deep Pacific, where life in the dark is coupled to the oxidation of sulphur from `black smokers' rather than the sun, but few, if any, would suspect such a mode of life in the classic chalk rivers of southern England. We measured the delta13C values of dominant primary consumers and...

SYNOPSISEleven species of British Hydropsychidae are listed and characterised. The name H.siltalai Döhler 1963 is introduced and the identity of H.insta-bilis and H.fuhipes is discussed. A key to the adult males is given together with a key to the larvae with the exceptions of H.saxonica, H.exocellata, H.guttata. Notes on the distribution of the sp...

INTRODUCTION Although only a fraction of 1% of the world's fresh water is found in streams and rivers at any instant, running waters are a very valuable human resource: many of the world's rivers have acted as magnets for human settlement and there are now very few river catchments that are unaffected by people in some way. Rivers contain a rich an...

1. The apparent absence of a specialist herbivorous grazer guild from many acid streams suggests that algae-grazer linkages in acid-stream food webs are weak or absent. It has been hypothesized that the absence of herbivores is a consequence of the low quality and/or quantity of biofilms in acid streams. 2. We compared the taxonomic composition, bi...

1. In a region of south-eastern England, we investigated the hierarchical genetic structure of populations of two stream-dwelling caddisflies (Trichoptera: Polycentropodidae) with contrasting distributions: Plectrocnemia conspersa inhabits numerous small, patchily distributed seeps and streams, while the confamilial Polycentropus flavomaculatus is...

Ecologists have long struggled to predict features of ecological systems, such as the numbers and diversity of organisms. The wide range of body sizes in ecological communities, from tiny microbes to large animals and plants, is emerging as the key to prediction. Based on the relationship between body size and features such as biological rates, the...

1.The ecological recovery of streams from large-scale perturbations, such as acidification, requires aquatic insects to disperse between catchments. While adults can usually fly, dispersal is seldom observed directly. Catches of insects in transects of traps perpendicular from streams suggest that lateral adult dispersal is limited. This paper eval...

1. The emission of biogenic gases, particularly methane, is usually associated with wetlands rather than clean streams. Here, we investigated methane production from a southern English chalk stream, where increased sedimentation, compounded by extensive macrophyte growth, may have altered ecosystem function. 2. Cover of the channel by the dominant...

Ecologists have long struggled to predict features of ecological systems, such as the numbers and diversity of organisms. The wide range of body sizes in ecological communities, from tiny microbes to large animals and plants, is emerging as the key to prediction. Based on the relationship between body size and features such as biological rates, the...

Mini-piezometers were used to assess surface–subsurface hydrological exchange and biogeochemical processing in different patches on the river bed (coarse gravel, fine gravel/sand, silt/sand) at two sites on the River Lambourn (Berkshire, UK). Positive vertical hydraulic gradients (VHG) dominated the riverbed, indicating potentially upwelling subsur...

1. Despite a recent upsurge in interest, there remains remarkably little information about the dispersal and survival of the adults of most stream-dwelling insects, although this is a basic requirement for understanding their long-term population dynamics. 2. Using Malaise traps for a whole annual flight period, we captured adult stoneflies (Leuctr...

1. The relationship between microcrustacean abundance and flow habitat in three contrasting reaches of a single stream was examined. 2. Three methods of characterizing stream hydraulics (shear stress frequency distributions, Froude numbers and mean reach velocity) showed the same pattern among the three reaches, which were subsequently termed ‘fast...

SUMMARY1This paper focuses on the premise that the habitat provides the templet upon which evolution forges characteristic species traits. Alternative hypotheses are that there are historic and phylogenetic constraints on the match between organism and environment.2In our analysis of river systems, as one dimension of the templet we choose temporal...

SUMMARY1Based on information obtained from analysis of thirteen taxonomic groups of plants and animals occurring in the alluvial floodplain habitats of the Upper Rhône River, France, we synthesize results obtained on: (i) relationships among species traits; (ii) habitat utilization by species; (iii) the relationship between species traits and habit...

SUMMARY1. The retention characteristics of two moorland streams in mid-Wales were manipulated for 2 years by the addition of small traps which accumulated detritus. Leaf litter was also added to these essentially treeless streams at regular intervals to simulate natural inputs to a woodland stream.2. Leaf traps retained a significantly higher bioma...

1. The relationship between algal biomass accumulation, invertebrate colonization, and stream-water pH was investigated in seven streams in three regions of England and Wales. Possible nutrient limitation of algal production at all sites was examined with diffusion substrata. 2. Periphyton assemblages on experimental substrata after 30 days were do...

1Stone surface organic layers were investigated at five sites on small, acid streams in the Ashdown Forest, southern England. Sites differed in stream water pH (means 4.3–6.6) and some other physicochemical features.2Organic layers at the stream bed surface differed between sites in structure and in the amount of organic carbon present. Algae were...

1 Fliesswasserstammtisch (FST)‐hemispheres of identical size but different densities were exposed on a horizontal plane on the pebble‐covered bottom of a laboratory flume at streaming to shooting, turbulent and fully developed flow. The heaviest hemisphere moved was used as an indicator of shear stress, a flow force acting on the flume bottom. 2 Th...

SUMMARY 1. Predatory, net-spinning larvae of the caddis Plectrocne-mia conspersa (Curtis) were abundant in the acid headwaters of some southern English streams where fish were absent, but were scarce or absent downstream where brown trout (Salmo trutta L.) occurred. 2. Field enclosure experiments showed that both underyearling and older brown trout...

1. The results of a survey of thirty-four stream sites, differing in pH and invertebrate species richness, indicated that the pool of locally available, suitably adapted species was smaller in the acid streams. This plays a part in determining the general pattern of lower species richness at more acid sites.2. Diversity of feeding categories increa...

1. Invertebrates and fish were surveyed during October 1976 in thirty-four stony riffle stream sites in Ashdown Forest, Sussex. 2. A variety of physicochemical factors were also measured in an attempt to assess the importance of each in determining the distribution of species and the structure of communities. 3. Three analytical techniques—stepwise...

1. Ceilulolytic decomposition, measured by loss of tensile strength in strips of cellulose test cloth, was estimated in thirty-four stream sites in experiments in summer, autumn and winter.2. The results of multiple regression analyses showed that strength loss was most closely related to temperature in summer, when the model accounted for only 38%...

1. Micro-arthropods were surveyed during October 1986 at thirty stony, stream riffle sites in the Ashdown Forest, southern England. 2. The importance of a number of physicochemical variables in determining both the distribution of micro-arthropod taxa and community structure was assessed. 3. Acidic sites had an impoverished fauna. Total micro-arthr...

1. Dobson & Hildrew (1992) enhanced leaf litter retention in four streams by placing small plastic leaf traps in manipulated stretches. Litter standing crop and the local abundance of shredders was increased, relative to control stretches, in all sites save one which was naturally highly retentive. These results could indicate food limitation in th...

Acknowledgments,. ................ ................ ........... 129 References ................ ................ ................ .. 131 I. SUMMARY Previous studies were collated with new,data to produce,an exceptionally detailed connectance,web for Broadstone,Stream (UK) that contained,131 species, including the permanent meiofauna (i.e., species...

This report summarises the findings of the UK Acid Waters Monitoring Network (AWMN) 15 year data interpretation exercise. The AWMN is funded by the UK Department for Environment Food and Rural Affairs. The report also incorporates an analysis of data collated by the UK Acid Deposition Network (ADN) run by NETCEN.

We report biological changes at several UK Acid Waters Monitoring Network lakes and streams that are spatially consistent with the recovery of water chemistry induced by reductions in acid deposition. These include trends toward more acid-sensitive epilithic diatom and macroinvertebrate assemblages, an increasing proportional abundance of macroinve...

We examined the effects of acidification on herbivore-algal food web linkages in headwater streams. We determined the structure and abundance of consumer and benthic algal assemblages, and gauged herbivory, in 10 streams along a pH gradient (mean annual pH 4.6-6.4). Biofilm taxonomic composition changed with pH but total abundance did not vary syst...

1. Our objectives were to examine small-scale patterns in oviposition and genetic relatedness in a population of the stream-dwelling caddis Plectrocnemia conspersa and, in particular, to look for any evidence of the spatial proximity of close kin and, therefore, ‘patchy recruitment’. 2. In order to examine the distribution of related larvae at the...

We used microsatellite markers to examine the genetic relatedness of populations of two polycentropodid caddisflies over substantial areas of Great Britain. One (the small-bodied Polycentropus flavomaculatus) is found in large, continuous populations in larger streams and rivers, while the other (the large-bodied Plectrocnemia conspersa) is found i...

Studies on streams provide some of the most detailed and best resolved webs yet available, and provide a means to test food web theory. These systems can be used to test patterns in connectance webs and the effect of sampling on the patterns evident. The role of body-size in stream webs is reviewed. This chapter deals with attempts to quantify food...

Summary • We investigated abundance–size spectra and body size–density allometry using an exceptionally detailed data set from a stony stream. The body size distribution of the whole metazoan community was expressed in terms of both density and biomass over a 14-month survey, and the relationships of body size with population density and taxon rich...

The benthic communities of streams contain invertebrates of a wide range of body size and from many taxa. Owing mainly to methodological problems, however, the contribution of smaller and more obscure metazoans to community structure and dynamics, including production, is poorly known compared with that of larger size fractions and, particularly, i...

Summary • Many lowland rivers in Western Europe have been substantially modified to aid land drainage and support the intensification of agriculture. Although there have been many attempts at rehabilitation, few have been systematically evaluated on ecological criteria. • Macroinvertebrates were assessed in 13 UK lowland rivers containing instream...

Summary 1. There have been widespread changes in land use in the uplands of the UK but the implications for dispersal of adult stages of aquatic invertebrates are poorly known. We estimated the lateral dispersal of adult aquatic insects (Plecoptera, Trichoptera, Ephemeroptera) in seven small, upland streams draining catchments under three cat- egor...

The interstitial sediments of streams and rivers, the 'hyporheic zone', have a diverse and numerous fauna though the relative contribution of the subsurface and surface assemblages to total productivity remains poorly understood. Our main aim was to determine the contribution of hyporheic invertebrates to overall, reach-scale estimates of density a...

Summary • Empirical information about the intergenerational dynamics of stream insects is scarce, and most field experiments are conducted at small temporal and spatial scales that are inappropriate for assessing effects upon population dynamics. We performed a large-scale, intergenerational population manipulation of an abundant, stream-dwelling p...

1Spatial and temporal variation in the distribution and feeding of non-predatory macroinvertebrates was investigated in a first-order, acid stream in the Ashdown Forest, southern England.2Stonefly (Nemouridae) and chironomid (Orthocladiinae) larvae were abundant on the upper surfaces of mineral substrata of three sizes (small stones, large stones,...

1. Field experiments were carried out to determine whether animals move into areas of low shear stress during periods of peak flow and therefore avoid hydraulic disturbance.2. Flow at the scale of 0.05 m2 patches was reduced experimentally by creating artificial ‘refugia’. Invertebrate colonization of cages with 1.1 mm mesh sides, which provided su...

1. In each of twenty-six week-long experiments, the colonization by macroinvertebrates of boxes of natural sediment in a stony stream was measured. The experiments took place between February and November 1992 and environmental conditions prevailing during the weeks (particularly discharge and temperature) differed widely. 2. Colonization rate also...