Dudley Williams

• University of Toronto

Six of the 12 living orders of aquatic insects contain species engaged in entomophagy, but few are being harvested effectively, leading to overexploitation and local extinction. Existing practices range from including insects (e.g. dipterans) in the core diets of many indigenous peoples to consumption of selected insects as novelty food (e.g. caddi...

Of the 30 extant orders of true insect, 12 are considered to be aquatic, or semiaquatic, in either some or all of their life stages. Out of these, six orders contain species engaged in entomophagy, but very few are being harvested effectively, leading to over-exploitation and local extinction. Examples of existing practices are given, ranging from...

The ecological integrity of freshwater ecosystems is regularly examined through assessment of their macroinvertebrate assemblages. The various methods used in such biomonitoring all have one characteristic in common - the neglect of water mites. Even though this group perfectly fulfills all necessary requisites for successful bioindicators, these i...

Springs and seeps are common features of many global landscapes, representing points of emergence of the vast, underground resources of freshwater on our planet. Most are characterized by very low variability in their discharge, water temperature and chemical signature, resulting in benign environments that support a high number and diversity of ra...

Microbial communities are responsible for the bulk of biogeochemical processing in temporary headwater streams, yet there is still relatively little known about how community structure and function respond to periodic drying. Moreover, the ability to sample temporary habitats can be a logistical challenge due to the limited capability to measure an...

Background/Question/Methods Temporary woodland ponds in temperate forests and intermittent streams in deserts exhibit strong community responses to variation in hydrological properties. Climatic changes in temperature and precipitation events can alter the natural flow regime rending these habitats unsuitable for the invertebrates that rely on them...

Slight changes in climate, such as the rise of temperature or alterations of precipitation and evaporation, will dramatically influence nearly all freshwater and climate-related hydrological behavior on a global scale. The hyporheic zone (HZ), where groundwater (GW) and surface waters (SW) interact, is characterized by permeable sediments, low flow...

Ecosystem functioning is influenced by the flow of nutrients, detritus, and organisms. Variation in these flows, like that found in temporary ecosystems, affects temporal and spatial patterns of community diversity and secondary production. We evaluated the influence of hydroperiod and ecosystem size on the bi-directional flow of subsidies from int...

Identifying the ecological mechanisms that determine foodweb structure is critical for understanding the causes and consequences of diversity. Food-chain length (FCL) is a product of the biotic interactions within a community and the environment, but how environmental variation affects FCL is not well understood. We examined how gradients of ecosys...

The water and habitat quality in Panamanian streams and rivers are being degraded by agriculture, urbanization, industrial activities, mining, and other forms of development. Thus, the need for standards, especially those examining the biological attributes of lotic systems, are urgently required. We describe the development of a multimetric index...

1. Variation among individuals within size or age classes can have profound effects on community dynamics and food-web structure. We investigated the potential influence of habitat disturbance on intrapopulation niche variation. 2. Amphibians occupy a range of lentic habitats from short-hydroperiod intermittent ponds to long-hydroperiod permanent p...

The dynamics of in situ bacterial communities in the hyporheic zone of an intermittent stream were described in high spatiotemporal detail. We assessed community dynamics in stream sediments and interstitial pore water over a two-year period using terminal-restriction fragment length polymorphism. Here, we show that sediments remained saturated des...

Arrival of aerial insect colonizers was studied (from April to July) using traps (artificial pools) installed adjacent to two temporary ponds in southern Ontario, Canada. The two ponds differed in the length of their hydroperiod: Pond I held water for 98 days, whereas Pond II held water for 34 days. The duration of the study was 15 weeks, during wh...

Background/Question/Methods Habitats are open systems linked by the flow of nutrients, detritus, and organisms, all of which have the potential to influence ecosystem functioning in the recipient system. Yet few studies have comprehensively quantified the resource subsidies across discrete habitats. Here we examine energy flow between mixed decid...

Experiments on optimizing the use of benthos in a salmonid rearing channel are described. The cropping potential of invertebrates for use as fish food was measured by substrate recolonization which showed that 80,000 animals, weighing approximately 0.62 g (dry weight), could be liberated from 1 m2 of clean gravel substrate to a depth of 15 cm every...

Molecular methods were applied to explore the composition of hyporheic bacterial assemblages and their possible interaction with interstitial physicochemical variables. Hyporheic flows on a riffle were manipulated (a downwelling zone was converted to an upwelling zone and vice versa) in order to examine the influence of vertical flow patterns on mi...

The responses of nymphs of two species of perlid stoneflies to manipulation of some important features of their microhabitats were studied in laboratory stream tanks fitted with an infrared beam interruption system. The activity of both Paragnetina media (Walker) and Phasganophora capitata (Pictet) was significantly affected by current speed and su...

Overall level and type of activity of Gammarus pseudolimnaeus changed with current speed and pattern in laboratory stream tanks. With increasing current speed (15 to 28 cm/s) active and passive downstream transport increased whereas numbers of animals moving upstream decreased. Upstream movement increased in smooth and rough flow above 28 cm/s. Mea...

Stonefly (Paragnetina media) density was reduced in a rainbow trout (Oncorhynchus mykiss) enclosure by approximately 35%, whereas in a trout exclosure no significant changes in density occurred. Of the 35% reduction, approximately two-fifths and three-fifths were attributable, respectively to direct consumption of stoneflies by trout, and emigratio...

We demonstrate that prey (stoneflies), which are either solidly coloured or patterned, coordinate intervals of maximum daytime activity with periods when visually foraging predators (rainbow trout, Oncorhynchus mykiss) are least able to detect them. In this study, rainbow trout attacked solidly coloured stonefly nymphs (Paragnetina media) more freq...

Investigations into the vertical distribution of stream animals by means of a coring technique have demonstrated that they could be found many decimeters down in the gravel; a maximum of 17% was found in the top 5 cm.Sampling of arctic streams revealed that chironomid larvae comprised 70–80% of the numbers in the benthos and that their rate of drif...

In the Matamek River, Quebec, brook trout (Salvelinus fontinalis) and Atlantic salmon (Salmo salar) coexist. The trout alevins emerge from the redds in early June and the salmon ~1 mo later. The first diet of the trout consists primarily of small- to medium-sized invertebrates passing in the water column. Among the most common items are blackfly la...

When exposed to increases in current speed in a laboratory stream tank, crayfish altered their body posture to counteract the effects of drag, thus enabling them to maintain station at higher current speeds. Using a beam-type drag balance, direct drag measurements were made on live adults of eight Ontario crayfish species over a range of current sp...

Barbados is offset from the Lesser Antilles island chain and is subject to both ocean currents and prevailing winds that come from the east, making natural colonization by freshwater invertebrates difficult. Nevertheless, the island has an abundance of freshwater habitats, including deep-water wells that connect with an extensive aquifer lying bene...

The entire cuticular surface of Gammarus pseudolimnaeus Bousfield was examined by means of scanning electron microscopy and, to a limited degree, transmission electron microscopy and light microscopy. A large array of microstructures was found, including calceoli, microtrich arrays, aesthetascs, sensory spines (cone- and club-shaped), pores, type A...

In Duffin Creek, Ontario, nymphs of the predatory stonefly Paragnetina media (Perlidae) commonly feed on detritus and three prey types: hydropsychid larvae (Hydropsyche sparna and Hydropsyche slossonae), nymphs of the mayfly Baetis tricaudatus, and chironomid larvae belonging to subfamilies Tanypodinae and Orthocladiinae. This study examined tempor...

For over 80 years, chlorobenzenes were discharged into the Sebasticook River, Maine, from a woollen mill. Environmental conditions were assessed using invertebrate and bacterial techniques that were applied to river bed sediments at three contaminated and two reference sites. Invertebrate densities and species richness did not differ markedly among...

The relationship between the biology and habitat of larval mosquitoes was studied in a series of artificial ponds of differing characteristics established across a terrestrial vegetation gradient from open fields to deep woods. The ponds were uniformly colonized by two widespread species of Culex, both characteristic of small bodies of water, inclu...

This study examined key environmental cues used by Gammarus pseudolimnaeus during microhabitat selection, and cues and mechanisms used to evaluate and react to changing current conditions. Thigmotactic cues for complexity and texture were used independently during microhabitat selection. Neither the external leg sensilla nor the antennae appeared t...

Four species of Tetragnatha were found along the banks of Duffin Creek, Ontario: T. versicolor Walckenaer, T. elongata Walckenaer, T. laboriosa Hentz, and T. straminea Emerton. However, only the first two species were common; together they represented 91% of all species of spiders observed. Highest densities of T. elongata occurred in July, a time...

Experiments on site selection by aerially colonizing invertebrates showed that water current and food availability largely determine the qualitative and quantitative nature of the fauna that colonizes a body. New water bodies were rapidly colonized by a variety of species from nearby lotic and lentic habitats. After some time selection took place t...

The development of the invertebrate fauna in a man-made, permanent stream which replaced a natural, temporary stream was observed over a year. Species colonized the new stream through drift, upstream migration, migration from a nearby underground field drainage system, and from neighbouring water bodies. Community development was examined in terms...

Records of immature and mature stages of caddisflies found in lentic and lotic habitats or the Matamek River region of Quebec are presented. The species are related to their typical habitats and feeding preferences in this part of the boreal forest biome. Net-spinning families dominated the caddisfly fauna of the Matamek River and their populations...

Phryganea cinerea Walker is a member of one of the most primitive families of the tube-case-building caddisflies. The larva is well supplied with setae. The poor eyesight of caddisfly larvae is one indication that setae could play a significant role in their behaviour. This study records the responses of P. cinerea larvae to mechanical stimulation...

Members of the caddisfly family Helicopsychidae were present in the Upper Jurassic, and the present-day distribution of the genus Helicopsyche shows typical southern continent dispersion, suggesting that it was in existence before the breakup of Pangea. Most of the approximately 90 species of Helicopsyche are endemic to the tropics, indicating a tr...

A population of the aquatic oribatid mite Mucronothrus nasalis, living in a cold, hardwater springbrook near Toronto, Canada, was sampled monthly from July 1985 to July 1986 using a Surber sampler. Of nine sampling locations situated along the full 60 m length of the springbrook, the source had by far the highest density of mites. Mites were most a...

The arrival, establishment, and growth of a variety of algae were studied in a series of newly established, small (48.5 L) artificial ponds located at three sites of differing characteristics in southern Ontario, Canada: open field, edge of woods, and deep woods. Algal colonization was most rapid at the open site, within 4 days of the ponds being f...

Background/Question/Methods Headwater streams and hyporheic sediments serve as model systems for understanding ecosystem biogeochemistry across transitional aquatic-aquatic and aquatic-terrestrial environments. Moreover, varying hydroperiod length in headwater streams can illustrate the potential impacts of environmental change on nutrient cycling...

Background/Question/Methods Food webs depict consumer-resource interactions among species or individuals in a habitat. Food-chain length, the number of trophic transfers from the base to the top of a food web, is an important metric to describe food web structure because it influences ecosystem functions, community composition, and species divers...

Aquatic hyphomycetes play an essential role in the conditioning and breakdown of imported leaves, needles and other plant detritus in running waters. Most research on their diversity and function has been done in temperate regions and very little in South and Central America. Current knowledge suggests that fungal diversity in tropical streams is c...

Distinct boundaries, where biological and physicochemical environments change abruptly, occur in nature and, at least superficially, riverbanks appear to separate terrestrial from aquatic systems. However, at depth, catchment groundwater is linked to channel water via the hyporheic zone. Complex hydrological interactions between these two water mas...

Type II microtrichs are slender, peg-like sensilla found on the exoskeleton of amphipod crustaceans. Using scanning electron microscopy, the microtrichs and associated cuticular microstructures were compared in six species and two subspecies of Gammarus known to live in different habitats, ranging from freshwater lentic and lotic to marine intertid...

Food webs depict who eats whom in communities. Ecologists have examined statistical metrics and other properties of food webs, but mainly due to the uneven quality of the data, the results have proved controversial. The qualitative data on which those efforts rested treat trophic interactions as present or absent and disregard potentially huge vari...

The hyporheic zone of stream ecosystems is a critical habitat for microbial communities. However, the factors influencing hyporheic bacterial communities along spatial and seasonal gradients remain poorly understood. We sought to characterize patterns in bacterial community composition among the sediments of a small stream in southern Ontario, Cana...

The hyporheic zone is a region underneath streambeds that integrates surface and groundwater. Although its location is central to biogeochemical linkages between the riparian zone, dissolved nutrients, and benthic biota, the seasonal quality and likely sources of dissolved organic matter (DOM) in the hyporheic zone are not well understood. To inves...

The insects living in 27 coldwater springs in southern Ontario, Canada were analyzed using several permutation and ordination methods, in order to detect patterns in the composition of their communities. These patterns were compared against simulations using artificial landscapes. A Moving Window Mantel Correlogram indicated the presence of both a...

Uncertainty about predicted effects of global warming on freshwater ecosystems led us to manipulate the thermal regime of a shallow groundwater ecosystem. The study area was separated into a control and treatment block using a sheet-metal groundwater divide to a depth of 1m. Temperatures were increased according to General Circulation Model (GCM) p...

Small streams can serve as model systems for understanding the interactions between groundwater and surface water. Comparatively, small streams with permanent and intermittent hydroperiods can effectively illustrate the differences in nutrient exchange across the sediment-water interface. For example, when a streambed is dry, characteristics of gro...

The ciliates living in a shallow groundwater system in southern Ontario, Canada were subjected to an in situ temperature manipulation over 14 months. Ciliates were collected from the bed surface of a small springbrook and from interstitial water collected at five depths beneath its surface. Mean temperature elevations established at each depth (−20...

The immature stages of freshwater insects can sometimes be found in densities of up to 25,000 m -2 in saltwater- inundated regions of estuaries, however little is known of their condition there. The gut fullness and contents of larvae of two species of hydropsychid caddisfly (Hydropsyche siltalai and H. instabilis) from freshwater and saltwater-inu...

The role of predation in the regulation of freshwater communities is predicted to decrease along a habitat-duration gradient, from permanent to episodic waters. We tested the role of invertebrate predation in shaping the community structure in a fishless temperate intermittent pond with a three month long hydro-period by comparing the community str...

Freshwater wetlands are highly productive and important features of terrestrial landscapes, yet knowledge of their biotas and understanding of their function has lagged behind that of other ecosystems. Superficially, their communities are known to include bacteria, protists, algae, fungi, higher plants, and invertebrate and vertebrate animals that...

Rising temperatures are predicted to accelerate the decomposition of labile soil organic compounds such as proteins and carbohydrates, whereas biochemically resistant compounds, such as lipids from leaf cuticles and roots and lignin from woody tissues, are expected to remain stable on decadal to centennial timescales. However, the extent to which s...

Water-filled treeholes are temporally and spatially variable habitats that consist of communities of a limited number of insect orders, namely dipterans and beetles. Since these systems are largely heterotrophic, treeholes are dependent on the surrounding terrestrial ecosystem for their basal energy input. In this study, we observed a cyclic succes...

The taxonomic composition and functional feeding groups (FFG) of macroinvertebrate com-munities were characterized along a stream-size gradient of four streams in Trinidad, two being impacted by agricultural and urban activities (Arima and Guanapo Rivers) and two being relatively pristine (Marianne and Paria Rivers). The degree to which benthic ass...

Soil organic matter (SOM) contains two times more carbon than the atmosphere and the potential changes to SOM quantity and quality with global warming are a major concern. It is commonly believed that global warming will accelerate the decomposition of labile SOM compounds while refractory SOM constituents will remain stable. However, experimental...

Ochlerotatus triseriatus, the eastern treehole mosquito, reaches its northernmost range limit in the extreme southeast of Canada. As a known vector of West Nile and La Crosse encephalitis viruses and a potential vector of eastern equine encephalitis, its population biology is of interest. In southern Ontario, high larval densities occur in urban wo...

1. The hyporheic zone of a permanent first-order stream was divided into a treatment and a control section using a 1 m deep sheet-metal barrier. During a 4-month pre-treatment period, water temperatures in two transects of the two sections were not different. Upon heating, the water temperature in the treatment transect increased by an average of 4...

Habitat selection processes by organisms colonizing freshwater bodies have not been commonly studied, despite their obvious relevance to wetland ecology and management. We monitored, weekly, all organisms that appeared in tanks with different backgrounds (brown; white) and substrate/food availability treatments (control; added leaf litter; added al...

Three main hypotheses have been put forward to explain size-assortative pairing in gammarid amphipods: microhabitat separation, sexual selection and loading constraint. In order to determine which hypothesis best explains this phenomenon in the estuarine species Gammarus zaddachi, I first measured the body lengths and dry weights of precopula pairs...

1. Ciliated protozoans (Phylum Ciliophora) were collected from five sites in a shallow groundwater system in southern Ontario, Canada over a 13-month period: one at the spring source, two along the channel banks, and two in the stream channel. Ciliates and environmental data were collected from surface water and at five depths into the sediment, lo...

A population of Sphaerium occidentale (Lewis, 1856) was studied over a two-year period in an intermittent freshwater pond in southern Ontario, Canada. Sub-populations in control areas of the pond showed marked differences between the two years, which appeared to be related to different hydroperiods (34 days in 2001 vs. 94 in 2002), water temperatur...

Temporary waters are found throughout the world, including intermittent streams and ponds, episodic rain puddles, seasonal limestone lakes, and the water-retaining structures of plants, such as bromeliads and pitcher plants. They are populated by a variety of plant, animal, and microscopic communities ranging from the very simple to the highly comp...

Eight bimonthly sediment core samples (n = 6) were collected, to a depth of 64 cm, from the hyporheic zone of a springbrook in southern Ontario, Canada. Sediment cores were divided into three to four sections, and organic matter was subdivided into six different categories. Twigs were the most common substrate, followed by roots, cedar leaves, wood...

Considerable spatial and temporal variability was detected in the environmental conditions in 30 coldwater springs in southern Ontario, Canada. Using standard pyramidal emergence traps, a total of 86 insect species was recorded from these springs (not including the Chironomidae). These represented nine taxonomic groups, among which the Limoniidae (...

Valley Spring is a hardwater rheocrene consisting of a single point issue and a springbrook some 60 m long. The fauna consists of > 60 taxa, with insects and mites predominating. During 1985–86, benthic densities varied both along the springbrook and at single stations over time (range 58 to 756 animals 900 cm−2). A clear longitudinal zonation of m...

The chironomid larvae of the Rouge River, Ontario, Canada, showed a longitudinal zonation which may have been influenced by water temperature and substrate composition. Species of Orthocladiinae predominated in the cooler headwaters while species of Chironomini dominated the comparatively warmer water near the estuary. In the middle section the chi...

1. The life history of the small herbivorous stonefly Nemoura trispinosa Claassen was studied in a variety of small springs in southern Ontario, Canada. Nymphs generally were able to tolerate a wide range of environmental conditions and were found in 78% of habitats sampled, although population densities differed markedly. 2. Life‐cycle patterns va...

The vertical distribution of the benthic fauna of the Speed River, Ontario, was studied over a 13‐month period from October 1970 to October 1971. Various physical and chemical parameters of this interstitial environment were also measured. Several new techniques for sampling the interstitial environment of rivers wert devised. These methods and the...

1. A series of samples of interstitial water and fauna was taken along transects from the channel into the bank in two small rivers in southern Ontario, Canada. These were examined for any discontinuities which might indicate the position of the hyporheic/groundwater interface. 2. There were several chemical discontinuities in Duffin Greek, with “b...

1. Reactions of individual predatory stoneflies to contact by individual mayfly prey, and vice versa, were studied in the laboratory using two sets of species, one from a stream in southern Ontario. Canada, and the other from a stream in North Wales. 2. Based largely on information received via their antennae, the stoneflies were capable of disting...

The feeding behaviour of nymphs of the perlid stonefly Dinocras cephalotes when presented with two different mayfly prey types on different substrates was examined in the laboratory. Most of the evidence suggested that Dinocras cephalotes did not choose between Baetis rhodani and Rhithrogena semicolomta as, under identical circumstances: (i) the su...

1. Colonization of microhabitat implants by the amphipod Gammarus pseudolimmnaeus in a small southern Ontario stream was studied in order to analyses the factors controlling habitat selection. The variables substrate particle size, current speed, presence of food and light were used in an analysis of covariance, with percentage weight of organic ma...

Dissolved organic carbon (DOC) in marine and freshwater ecosystems represents an immense reservoir of organic matter with varied and significant ecological value. Global warming poses a significant threat in that it has the capacity to alter the concentration and distribution of DOC. Since groundwater constitutes approximately two-thirds of the ava...

The importance of top-down and bottom-up mechanisms in lentic systems has largely been explored in stable systems; however, their influence is likely to change along a habitat duration gradient. Using a case study of four intermittent ponds, we test the generality of these paradigms in systems nearing the extreme short end of this gradient. Intermi...

Pond physicochemical characteristics and bottom-up effects were more important than top-down effects in governing ciliate community structure in 2 adjacent intermittent ponds in Southern Ontario, Canada. The ciliates showed a bimodal seasonal pattern with abundances peaking early and late in the hydroperiods, and the communities showed a strong sea...

Chironomid (Diptera) larvae were collected between February 1997 and December 1998 from four Trinidadian rivers, two relatively impacted (the Arima and Guanapo Rivers), and two comparatively pristine (the Marianne and Paria Rivers), in order to assess community changes as a result of both land-use and the natural longitudinal gradient. Multivariate...

Our study site was composed of a spring that was divided lengthwise from its source into two equally wide channels, with water temperature in the experimental channel being increased by 2.0–3.5°C relative to that of the control channel. We examined sexual dimorphism in overall body size and eight morphological traits in the stonefly Nemoura trispin...

The purpose of this chapter is to briefly consider those temporary aquatic habitats that have been somewhat neglected by researchers even though they are commonplace. A few, such as treehole habitats and the chambers of insectivorous pitcher plants have recently received more attention and thus will be dealt with in more detail.

In this section we shall attempt to determine if there is such a thing as a community of organisms which can be readily identified as being universally characteristic of a temporary water body. To this end, in Table 4.1, I have listed the taxonomic groups recorded from temporary ponds in four well-separated regions of the world, eastern Canada, wes...

Odonates are obligate predators (Pritchard 1964), and the composition of their diet is reflective of their microhabitat and effectiveness in detecting and capturing prey (Griffiths 1973; Thompson 1978). In an intermittent woodland pond in southern Ontario, Canada, three species of Sympetrum (Odonata: Libellulidae) were found to coexist: S. internum...

Temporary waters, in general, are fascinating habitats in which to study the properties of species adapted to living in highly variable environments. Species display a remarkable array of strategies for dealing with the periodic loss of their primary medium that sets them apart from the inhabitants of permanent water bodies. Survival of individuals...

We examined the algal communities in an intermittent pond in southern Ontario, Canada, at one permanently wetted site and two that dried up. Samples were collected from decomposing leaves and from the water column from ice-out in April to late August. Most of the algae present were attached forms. While there were some differences at the genus leve...

Interactions between interstitial meiofauna and physicochemical parameters of the hyporheic zone were examined via an in situ experiment on the Speed River, Ontario. The manipulation comprised reversing upwelling and downwelling zones at the riffle scale, and was maintained for 1month. Significant differences in physicochemical parameters were dete...

Four individuals of the non-marine polychaete, Namanereis hummelincki, were collected from two deep (70-80 m) wells on Barbados; the largest specimen measured 2.2 cm long and 0.1 cm wide, and had 82 setigerous segments. These wells access the vast underground freshwater aquifer beneath the island, are 9 km apart, and are between 3.7 and 4 km from t...

1. Spatial relationships between hyporheic invertebrates and subsurface water flow patterns, sediment characteristics, water physicochemical parameters and several possible food sources were compared over three seasons at one site beneath a riffle. Measures of food sources included particulate organic matter (POM), bacterial activity (aerobic respi...

The distribution of nitrogen-transforming processes, and factors controlling their rates, were determined within the hyporheic zone of a lowland stream draining agricultural land. In the field, physicochemical parameters were measured along a 10?m-long hyporheic flow line between downwelling and upwelling zones. Sediment cores were retrieved from t...

This study describes a hyporheic zone that exists beneath a river-dominated estuary in North Wales, and which spans the freshwater/saltwater boundary. A series of 72 cores was taken from the Aber Estuary, in September, at depths from 10–60cm below the bed surface. Site 1 was above the extreme high water mark and therefore was never inundated by sal...

SUMMARY 1. The ciliate populations of two temporary ponds in southern Ontario were studied throughout their aquatic phases in 2001. Pond I (∼1 ha) held water for 98 days, whereas Pond II (∼0.25 ha) held water for 34 days. Populations were assessed both within the ponds themselves and within a series of enclosures in which invertebrate predator pres...