Total Prey Consumption Research Articles

Lethal and Sub-Lethal Effects of Organic-Production-Approved Insecticides and Fungicides on the Predator Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae).

In this study, the effects of paraffin oil, copper hydroxide, copper oxychloride, wettable sulfur, Beauveria bassiana and deltamethrin, as a toxic reference treatment, on the survival and predation rate of M. pygmaeus were investigated. In each treatment, the prey were classified as slightly, partially or fully consumed. The mortality rate after contact exposure was high (66.6%) when nymphs were treated with copper hydroxide but much lower after residual exposure (6.6%). B. bassiana caused 53.3% and 46.6% mortality via contact and residual exposure, respectively. The total prey consumption was significantly lower in the pyrethroid reference treatment control and B. bassiana treatments. The highest percentage of slightly consumed prey was recorded in the toxic reference and B. bassiana treatments, that of partially consumed prey in the copper hydroxide treatment and, finally, that of fully consumed prey in the paraffin oil treatment. Therefore, assessing the sub-lethal effects by separating the prey killed into slightly, partially and fully consumed is a sensitive approach to detect impacts which otherwise may remain unnoticed. The results provide information for the most appropriate use of M. pygmaeus in IPM programs and introduce more sensitive approaches in the detection of side-effects of pesticides on M. pygmaeus and other hemipteran predators.

Study of life table and predation efficiency of Typhlodromus bagdasarjani (Mesostigmata: Phytoseiidae) fed Eotetranychus frosti (Trombidiformes: Tetranychidae) reared on different apple cultivars

ABSTRACT The life table parameters and predation rate of Typhlodromus bagdasarjani Wainstein & Arutunjan (Phytoseiidae) fed on Eotetranychus frosti (McGregor) (Tetranychidae) nymphs reared on four apple cultivars Kohanz Golab, Imperial Gala, Lebanon Red, and Granny Smith were studied under laboratory conditions. The longest developmental time of immature stages in females was observed on Kohanz Golab, and the shortest one was on Granny Smith. The fecundity ranged from 27.28 eggs on Golab Kohanz to 41.98 eggs on Granny Smith. The highest and lowest intrinsic rate of increase (r) were obtained on Granny Smith (0.254 day-1), and Kohanz Golab (0.136 day-1), respectively. The total prey consumption by all immature stages on Kohanz Golab, Imperial Gala, Lebanon Red, and Granny Smith was 36.93, 29.93, 27.36, and 21.30 prey, respectively. The total prey consumption by adult females was 424.70±24.41 prey on Kohanz Golab, 327.39±18.50 prey on Imperial Gala, 289.77±17.42 prey on Lebanon Red, and 218.50±14.64 prey on Granny Smith. The lowest fecundity and intrinsic rate of increase as well as the longest total life span of the predator on the resistant cultivar (Kohanz Golab) to E. frosti showed that integrated use of resistant cultivars and phytoseiid mites for control of spider mites needs more investigations.

Neutral effects of turbidity across a gradient of vegetation density on the predation of juvenile mandarin fish (Siniperca chuatsi)

AbstractMandarin fish Siniperca chuatsi is a widespread piscivorous species in lakes of the Yangtze River basin. However, their wild population has drastically declined, and survival and growth rates of stocked populations are low. Anthropogenic activities have reduced submersed vegetation and increased turbidity in lakes containing S. chuatsi, thus, we hypothesize that reduced submersed vegetation and increased turbidity could inhibit the feeding efficiency of juvenile S. chuatsi, subsequently reducing their growth and survival. To test this hypothesis, we experimentally examined the effects of a range of vegetation density and turbidity on predation of S. chuatsi. Laboratory predation trials were performed with a common prey fish Carassius auratus offered simultaneously to S. chuatsi in clear or turbid water under five different levels of vegetation density (0, 20, 40, 80, and 120 stems/m2). The total prey consumption per day (in 24 hr) by S. chuatsi on C. auratus was significantly affected by vegetation density, with the consumption positively linearly related with increased vegetation density. The total prey consumption was unaffected by turbidity. Prey size selection was not significantly influenced by vegetation density or turbidity. These results indicate that turbidity does not appear to negatively affect the predation of S. chuatsi, but a reduction of vegetation can negatively influence feeding induced by decreased predation efficiency, and hence might hinder survival and growth.

Feeding potential of phytoseiid predator, Neoseiulus baraki Athias-Henriot on Coconut eriophyid mite, Aceria guerreronis Keifer

Experimental results showed that the overall daily prey consumption rate of individual larva, protonymph and deutonymphal stage of N. baraki were consumed 6.33 ± 0.50, 11.00 ± 0.75 and 13.45 ± 0.89 prey mites, respectively. Whereas, the consumption rate of adult male and female were 14.07 ± 0.56 and 15.91 ± 0.45 preys, respectively. The total prey consumption rate of larval, protonymph and deutonymphal stage of N. baraki were 12.65 ± 1.00, 22.00 ± 1.50 and 40.35 ± 2.69 preys, respectively. However, total consumption rate for adult male and female were 219.40 ± 5.86 and 477.97 ± 5.51 prey mites, respectively. The prey consumption rate during entire life period of male was 294.40 ± 14.09 preys, while female of 552.97 ± 14.09 prey mites. Thus, the present finding clearly suggest that N.baraki could be a highly efficient biological control agent of A. guerreronis.

Effects of Turbidity on Prey Selection and Foraging Rate of Hatchery‐Reared Juvenile Tiger Muskellunge

AbstractTiger muskellunge (Northern Pike Esox lucius × Muskellunge E. masquinongy) are stocked into aquatic systems across North America to control undesirable fish species or to create sportfishing opportunities. Because decreased water clarity can affect the poststocking foraging ability of an ambush predator like the tiger muskellunge, we evaluated the effects of turbidity on the foraging success of tiger muskellunge in a laboratory setting. We tested prey selectivity and total prey consumption by juvenile tiger muskellunge at four turbidity levels (Secchi depths of >84, 53, 26, and 18 cm) using three prey species: Goldfish Carassius auratus (a surrogate for Common Carp Cyprinus carpio), Gizzard Shad Dorosoma cepedianum, and Green Sunfish Lepomis cyanellus. Tiger muskellunge consumed significantly less prey at Secchi depths of 26 and 18 cm than at a Secchi depth of >84 or 53 cm. Selectivity for or against all prey types decreased as turbidity level increased, such that all three prey types had similar neutral selectivity at the highest turbidity level even though Gizzard Shad were positively selected and Goldfish were negatively selected in clearer water. Green Sunfish were neutrally selected at all turbidity levels tested. These results suggest that increasing turbidity levels will negatively impact prey encounters and consumption rates, which likely will reduce growth rates of tiger muskellunge, ultimately reducing fish survival and stocking success.

Experimental predatory behavior of the stone crab Eriphia verrucosa (Forskål, 1775) (Decapoda, Brachyura, Eriphiidae)

Abstract Predatory behavior of the crab Eriphia verrucosa (Forskal, 1775) on the oyster Magallana angulata (Lamarck, 1819), the mussel Mytilus galloprovincialis Lamarck, 1819, the limpet Patella depressa Pennant, 1777, the hermit crab Clibanarius erythropus (Latreille, 1818), the gastropod Phorcus lineatus (da Costa, 1778) and the sea urchin Paracentrotus lividus (Lamarck, 1816) was experimentally studied. Taken into account that the sampled population of E. verrucosa was infected with the parasitic barnacle Sacculina eriphiae Smith, 1906, four predator categories were established regarding crab sex and parasite presence: uninfected and infected males and females, respectively. These four crab categories were fed on the six preys offered, but prey remains suggest that the crab obtains the flesh of each prey using different methods of attack. Irrespective of the prey species, uninfected females consistently presented lower percentages of crab feeding and total consumption. On average, it was found that a significantly higher percentage of crabs feed on M. galloprovincialis, P. depressa and Ph. lineatus than on the other three prey species (chi-squared test, p < 0.05). In terms of mean eaten biomass, the preys most eaten were P. lividus and P. depressa and the least eaten was C. erythropus (ANOVA test, p < 0.05). For crabs feeding on M. galloprovincialis and Ph. lineatus there was a significant positive correlation (p < 0.05) between the predator size and prey size, as well as between the predator size and total prey consumption. According to these results, potential effects of this top predator on intertidal communities are also discussed.

Foraging behaviour and prey consumption by grey seals (Halichoerus grypus)—spatial and trophic overlaps with fisheries in a marine protected area

The roles of the marine national park of the Iroise Sea (France) are to maintain marine biodiversity, including the southernmost grey seal colony in the Eastern Atlantic, whilst managing sustainable human activities. This study compares the fish biomass taken by local seals and the landings by man in the Iroise Sea. Sixteen seals were satellite tracked from 1999 and 2003, providing location and behavioural (diving) data from which foraging locations were estimated. One individual spent a third of its foraging time in direct, long distance trips (200–350 km) across the English Channel, but most seals spent the majority (68.5%) of their foraging time in the Iroise Sea, making return trips within 30 km of their departure haulout sites. The energetic consumption of the seal colony, taking sex and age classes into account, was assessed and combined with seal abundance estimates and dietary data to assess the total prey consumption by seals, for each prey species. We estimated that during the study period, the grey seal colony in the Iroise Sea consumed around 115 tons of fish per year. The main source of uncertainty of this calculation came from the confidence intervals in total seal abundance estimates. This consumption comprised 13.6 tons of sea bass, 4.3 tons of pollack and 2.7 tons of sole, representing 16.4, 1.8, and 5.2% of landings in the same areas for these three fish species, respectively. Within the four ICES rectangles where grey seals foraged, overlap between seals and fisheries was greatest in rectangle 25E5 (72.7% of all foraging dives), where grey seals haul out, and less in rectangles 25E4 (11.7%), 26E5 (10.8%), and 26E4 (4.8%).

Age-stage predation capacity of Phytoseiulus persimilis and Amblyseius swirskii (Acari: Phytoseiidae) on susceptible and resistant rose cultivars

ABSTRACTPredation rate is basic to any investigation of prey–predator interaction. The predation rate of Phytoseiulus persimilis Athias-Henriot and Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) fed on the two-spotted spider mite (TSSM), Tetranychus urticae Koch, reared on the susceptible (Yellow) and resistant (Roulette) rose cultivars was determined under laboratory conditions at 25 ± 1°C, 60 ± 5% RH and a photoperiod of 16:8 (L:D) h. The value of total prey consumption in different life stages of both predators was higher on TSSM reared on the resistant rose cultivar than those on the susceptible one. In addition, the value of total prey consumption in different life stages of P. persimilis was higher than A. swirskii on both susceptible and resistant rose cultivars. The net predation rate (C0) of both predators on TSSM reared on the resistant rose cultivar was higher than those on the susceptible one. The stable predation rate (ψ) on the susceptible and resistant rose cultivars was 2.50 and 3.77 preys/predator for P. persimilis, respectively, and 2.24 and 2.76 preys/predator for A. swirskii, respectively. The finite predation rate (ω) in P. persimilis on the susceptible and resistant rose cultivars was 3.10 and 4.41, respectively, and in A. swirskii it was 2.58 and 3.10, respectively. The results revealed that the performance of both predators on the resistant cultivar (Roulette) was better than the susceptible one (Yellow), and based on the results of the finite predation rate, P. persimilis on both cultivars had higher performance compared with A. swirskii.

Effects of water-soluble fraction of petroleum on growth and prey consumption of juvenile Hoplias aff. malabaricus (Osteichthyes: Erythrinidae).

The influence of the water-soluble fraction of petroleum (WSF) on prey consumption and growth of juvenile trahira Hoplias aff. malabaricus was investigated. Juveniles were submitted to either WSF or Control treatment over 28 days, and jewel tetra Hyphessobrycon eques adults were offered daily as prey for each predator. Total prey consumption ranged from 16 to 86 individuals. Despite the initially lower prey consumption under WSF exposure, there were no significant differences in overall feeding rates between the two treatments. Water-soluble fraction of petroleum had a negative effect on the growth in length of H. aff. malabaricus juveniles. Although unaffected, prey consumption suggested a relative resistance in H. aff. malabaricus to WSF exposition and the lower growth of individuals exposed to WSF than the Control possibly reflects metabolic costs. The implications of the main findings for the individual and the food chain are discussed, including behavioral aspects and the role played by this predator in shallow aquatic systems.

Size matters: Body size determines functional responses of ground beetle interactions

Understanding patterns in predator:prey systems and the mechanisms that underlie trophic interactions provides a basis for predicting community structure and the delivery of natural pest control services. The functional response of predators to prey density is a fundamental measure of interaction strength and its characterisation is essential to understanding these processes. We used mesocosm experiments to quantify the functional responses of five ground beetle species that represent common generalist predators of north-west European arable agriculture. We investigated two mechanisms predicted to be key drivers of trophic interactions in natural communities: predator:prey body size ratio and multiple predator effects. Our results show regularities in foraging patterns characteristic of similarly sized predators. Ground beetle attack rates increased and handling times decreased as the predator:prey body-mass ratio rose. Multiple predator effects on total prey consumption rates were sensitive to the identity of the interacting species but not prey density. The extent of interspecific interactions may be a result of differences in body mass between competing beetle species. Overall these results add to the growing evidence for the importance of size in determining trophic interactions and suggest that body mass could offer a focus on which to base the management of natural enemy assemblages.

THE EFFECT OF TEMPERATURE ON DEVELOPMENT, FECUNDITY AND FOOD CONSUMPTION OF AMBLYSEIUS CYDNODACTYLON SHEHATA &amp; ZAHER

the present work was conducted to study the effect of temperature on development, fecundity and food consumpution of Amblyseius cydnodactylon (Shehata & Zaher) under laboratory conditions. The biology of A. cydnodactylon may be a considerable value for controlling P. tritici in Egypt. The results showed that the developmental period increased with temperature decrease. Fecundity, longevity and lifespan were longer at 25°C and lower at 35°C. At 25°C developmental period was short with higher fecundity and maximum longevity, where as it was the most suitable temperature for development of A. cydnodactylon , while 35°C was the least suitable.The results on food consumption showed a significant effect of temperature on developmental stages of A. cydnodactylon . The larvae of this predator did not feed during the experiment, and predation activity started just after the mites entered the protonymphal downloaded stage. Feeding capacities of protonymph and deutonymphal stages were in a similar trend. These were increased with increasing temperature from 20◦C to 25◦C, and then decreased at 30◦C and finally, increased again at 35◦C. The highest means for total prey consumption of females were recorded during oviposition, when they devoured an average of 103.0, 189.3, 109.0 and 79.0 prey at 20, 25, 30, and 35◦C, respectively. The highest and lowest values of the mean preyprey) and 20◦C (2.1 prey), respectively. During adulthood, the highest number of prey consumed was at 25◦C (201.9 prey), which decreased to 116.6, 110.8 and 86.9 individuals at 30, 20 and 35◦C، respectively. consumption by postoviposited females was observed at 25◦C (6.4

Top-down pressure on small pelagic fish by eastern Australian salmon Arripis trutta; estimation of daily ration and annual prey consumption using multiple techniques

Ecosystem-level models that trace flows of mass and energy to quantify species interactions are important tools in whole ecosystem-based approaches to managing marine resources. A critical input parameter for such models is an estimate of the consumption rates and biomasses of prey consumed by fish populations. Here we estimate the annual prey consumption of an abundant coastal piscivore, Arripis trutta, which may exert substantial top-down control on its prey over its broad latitudinal range (28–43°S) in the coastal waters off south-eastern (SE) Australia. Three independent techniques were used to estimate annual prey consumption at two environmentally-relevant temperatures, 15 and 20°C: experimental gastric evacuation experiments (coupled with stomach content analyses); bioenergetics modelling, and; empirical regression modelling. Each technique yielded a similar range of estimates with annual food consumed/biomass (Q/B) ranging from 3.20 to 4.02 at 15°C and 4.23 to 5.25 at 20°C. Using an estimated A. trutta stock biomass in SE Australia of 10,000t, total mean annual prey consumption was estimated to be 42,200t, consisting primarily (93%) of small zooplanktivorous teleosts, particularly Australian sardines Sardinops sagax (35%) and scads Trachurus spp. (30%). These results indicate that A. trutta do possess a top-down influence on the pelagic ecosystem of coastal SE Australia via consumption of considerable biomasses of small pelagic fish. However, despite the use of a maximum regional estimate of A. trutta abundance and the presence of at least two other ecologically similar predatory fish species with higher annual prey consumption rates in SE Australian coastal waters, A. trutta may remove only a small proportion (~15%) of the estimated spawning biomasses of its major prey species in this region annually. The multiple-technique approach used in this study has for the first time quantified the diet of A. trutta in SE Australia and provided broad and repeatable estimates of its annual prey consumption for use in ecosystem models designed to manage coastal fisheries resources in this region.

Feeding efficiency of planktivores under disturbance, the effect of water colour, predation threat and shoal composition

The consumption of phantom midge Chaoborus flavicans larvae by Perca fluviatilis showed clear response to water colour, predation threat and shoal composition with the most significant negative effect for water colour. In the case of Rutilus rutilus, no similar combined response was observed and the total prey consumption was significantly negatively affected by predation threat of Esox lucius. The results suggest that differences in life-history traits may result in disparity in species-specific responses to disturbance.

Stable isotope analysis as a tool to monitor dietary trends in little penguinsEudyptula minor

Long-term dietary monitoring of seabirds can be used to relate population fluctuations to at-sea events. Stomach flushing is a conventional dietary monitoring technique, but has a number of disadvantages. Stable isotope analysis (SIA) is a less invasive method that provides unbiased dietary information over a longer period. We evaluated stable isotope analysis as a potential tool for monitoring long-term little penguin Eudyptula minor diet. We determined diet composition during the chick feeding stage using stomach flushing and SIA at three separate colonies, using spatial variation in diet as a surrogate for potential temporal variation. Bayesian isotopic mixing models were generated for blood and feathers to evaluate their ability to discriminate broad-scale (fish, squid, crustaceans) and fine-scale (individual prey species) diet composition. Differences in stable carbon and nitrogen isotope ratios were found between colonies: broad-scale isotopic mixing models predicted different proportional contributions of broad taxa (fish, cephalopod, crustacean) to diet than was indicated by stomach samples, reflecting the bias incurred by one-off stomach contents analysis. Fine-scale isotopic mixing models predicted proportional contributions of prey items with less certainty. Blood isotopic mixing models had narrower confidence intervals than models for feathers, but trends in δ15N for feathers mirrored those for blood. Our results suggest that relying on stomach contents analysis to detect shifts in prey consumption in little penguins could be very misleading, resulting in a less-than-complete idea of total prey consumption. SIA of little penguin tissues could be used to monitor dietary shifts across dissimilar taxa that may affect population numbers, but would fail to detect shifts between fish species.

Two-spotted spider mite reared on resistant eggplant affects consumption rate and life table parameters of its predator, Typhlodromus bagdasarjani (Acari: Phytoseiidae)

The study of interactions between host plant cultivars and biological control agents is important in integrated pest management programs. In this study, the life table parameters and predation rate of Typhlodromus bagdasarjani Wainstein & Arutunjan were determined on two-spotted spider mites reared on a susceptible (Isfahan) or a resistant (Neishabour) eggplant cultivar. All experiments were carried out under laboratory conditions, at 25±1°C, 60±5% RH and a photoperiod of 16:8 (L:D) h. A significant difference was observed between mean developmental time of immature stages of T. bagdasarjani on the two eggplant cultivars: 6.6 versus 7.5days, on the susceptible and resistant cultivar, respectively. Net reproductive rate (R 0) of T. bagdasarjani did not differ between the cultivars. Doubling time on the susceptible and resistant cultivars was 3.48 versus 5.72days, mean generation time (T) was 10.13 versus 16.08days, respectively. Total fecundity was higher on susceptible than on resistant eggplants, the intrinsic rate of population increase (r) was 0.188 versus 0.119day(-1), respectively. Daily and total prey consumption of various life stages of T. bagdasarjani on two-spotted spider mite reared on susceptible versus resistant eggplant differed; total consumption was higher on spider mites reared on the resistant cultivar. However, the lower intrinsic rate of increase and higher mortality of the predator on the resistant eggplant (Neishabour) revealed that more attention should be devoted to integrated control of spider mites using resistant cultivars and phytoseiid mites.

The effects of turbidity on prey consumption and selection of zooplanktivorous Gasterosteus aculeatus L.

It is well documented that reduced visibility caused by elevated turbidity can affect feeding of fish, yet the extent to which selective zooplanktivory is altered in turbid conditions remains ambiguous. In this study, we examined the influence of natural sediment-induced turbidity on the overall prey consumption and selective predation of a common brackish water littoral zooplanktivore, the particulate feeding three-spined stickleback (Gasterosteus aculeatus L.). We hypothesized that the effects of turbidity on prey consumption and prey type selection would be pronounced due to the vision-oriented feeding of this species and that these effects would differ between genders. Using aquarium experiments with three different groups of cladocerans and copepods varying in size and behavior, we studied prey consumption and selectivity of this key planktivore in varying turbidity treatments. Our results indicated significantly decreased total prey consumption in the high turbidity treatments, as well as altered selective feeding on copepods and an enhanced preference for larger cladocerans. We found gender-dependent differences in prey consumption, which are consistent with observations of other visually feeding fish with sexual size dimorphism. We conclude that high turbidity, such as that occurring in shallow coastal areas, may affect selective feeding in vision-oriented zooplanktivores and that these effects may be gender-related.

Demographic parameters of Neoseiulus barkeri (Acari: Phytoseiidae) fed on Thrips tabaci (Thysanoptera: Thripidae)

Thrips tabaci Lindeman is a serious pest of cucumber and onion in field and greenhouse conditions in Iran. Neoseiulus barkeri Hughes is an indigenous biological control agent in west of Iran on cucumber and maize that preys on spider mites and T. tabaci and can prevent the outbreak of them. In this study, the demographic parameters of the Iranian population of N. barkeri were determined using 1 st instar larvae of T. tabaci as prey under laboratory conditions at 30±1°C,65±5% RH and photoperiod 8:16 h (D:L). The results showed that N. barkeri successfully developed on 1 st instars larvae of T. tabaci . The developmental times for egg, larva, protonymph, deutonymph and all immature stages were 1.37, 1.03, 1.54, 1.71 and 5.68 days, respectively. Also, 96.66% of eggs hatched and the survival rate for the movable immature stages were 100%. Total prey consumption by protonymphs, deutonymphs and adult female was 2.70, 3.57 and 75.85 individuals, respectively. Adult longevity of the male was recorded as 14.36 days while the females lived longer (20.17 days). The female ratio was 0.62%. The intrinsic rate of increase ( r m ) and the net reproductive rate ( R 0 ) were 0.252 day -1 and 18.70 female offspring, respectively. Our results showed that N. barkeri could be considered as a biological agent for the control of T. tabaci on cucumber. Expanding knowledge on the biological parameters of this predatory mite can help to increase the use of this indigenous biological agent for the control of T. tabaci on cucumber.

A bioenergetic assessment of the influence of stocking practices on rainbow trout (Oncorhynchus mykiss) growth and consumption in a New Zealand lake

Summary To investigate the carrying capacity and factors affecting growth of rainbow trout in Lake Rotoiti, we employed a bioenergetics model to assess the influence of stocking rates, timing of releases and prey abundance on growth and prey consumption. We hypothesised that stocking rates and prey abundance would affect growth and prey consumption by influencing per‐capita prey availability, and that the environmental conditions encountered by fish at the time of stocking would affect growth and consumption. Prey consumption of stocked rainbow trout was calculated with the Wisconsin bioenergetics model. We calculated growth trajectories of released trout based on data from stocked trout that were released in spring and autumn from 1993 to 2009 and then re‐captured by anglers. Diet, prey energy density, body mass lost during spawning and lake temperature were measured locally. Stocking timing had no effect on return rates to anglers or length or weight of caught fish. Although trout released in autumn were smaller than those released in spring, autumn‐released trout grew at a faster rate and had similar lengths and weights to spring cohorts after 2 years of growth in the lake. Modelled consumption parameters were negatively correlated with trout population size, suggesting that stocking rates (347–809 fish ha−1 year−1) caused density‐dependent effects on growth. Although common smelt (Retropinna retropinna) accounted for 85% of total prey consumption, no significant relationship was found between prey consumption by individual trout and adult smelt abundance, possibly because trout are targeting smaller smelt that our abundance estimate did not account for. Releasing trout in autumn appears to be advantageous for growth, possibly because (i) temperature is more suitable for growth in autumn–winter than in spring–summer and (ii) prey for small trout is abundant in autumn. Mild winter conditions appear to enhance overwinter survival and growth of rainbow trout in warm‐temperate lakes compared to higher latitudes. This implies that moderately productive warm‐temperate lake ecosystems are highly suitable for trout growth in winter, but less so in summer, when lake stratification and high nutrient levels may create conditions suitable for algal blooms and hypolimnetic deoxygenation. High growth rates of trout in warm‐temperate lakes can therefore be supported by timing releases to coincide with favourable winter conditions.

The floodplain food web mosaic: a study of its importance to salmon and steelhead with implications for their recovery

Although numerous studies have attempted to place species of interest within the context of food webs, such efforts have generally occurred at small scales or disregard potentially important spatial heterogeneity. If food web approaches are to be employed to manage species, studies are needed that evaluate the multiple habitats and associated webs of interactions in which these species participate. Here, we quantify the food webs that sustain rearing salmon and steelhead within a floodplain landscape of the Methow River, Washington, USA, a location where restoration has been proposed to restore side channels in an attempt to recover anadromous fishes. We combined year-long measures of production, food demand, and diet composition for the fish assemblage with estimates of invertebrate prey productivity to quantify food webs within the main channel and five different, intact, side channels; ranging from channels that remained connected to the main channel at low flow to those reduced to floodplain ponds. Although we found that habitats within the floodplain had similar invertebrate prey production, these habitats hosted different local food webs. In the main channel, 95% of total prey consumption flowed to fishes that are not the target of proposed restoration. These fishes consumed 64% and 47% of the prey resources that were found to be important to fueling chinook and steelhead production in the main channel, respectively. Conversely, in side channels, a greater proportion of prey was consumed by anadromous salmonids. As a result, carrying capacity estimates based on food were 251% higher, on average, for anadromous salmonids in side channels than the main channel. However, salmon and steelhead production was generally well below estimated capacity in both the main and side channels, suggesting these habitats are under-seeded with respect to food, and that much larger populations could be supported. Overall, this study demonstrates that floodplain heterogeneity is associated with the occurrence of a mosaic of food webs, all of which were utilized by anadromous salmonids, and all of which may be important to their recovery and persistence. In the long term, these and other fishes would'likely benefit from restoring the processes that maintain floodplain complexity.

Habitat overlap between predatory benthic fish and their invertebrate prey in streams: the relative influence of spatial and temporal factors on predation risk

Summary1. The spatial heterogeneity of ecosystems as well as temporal activity patterns of organisms can have far‐reaching effects on predator–prey relationships. We hypothesised that spatiotemporal constraints in mesohabitat use by benthic fish predators would reduce habitat overlap with benthic invertebrates and lead to mesohabitat‐specific predation risks.2. We analysed the spatiotemporal activity patterns of two small‐bodied benthivorous fishes, gudgeon (Gobio gobio) and stone loach (Barbatula barbatula), and of benthic invertebrates in a small temperate stream during three 24‐h field experiments. By applying a novel method of field video observation, we monitored the spatiotemporal foraging behaviour of the fish in their natural environment. A parallel analysis of invertebrate mesohabitat use by means of small area Hess sampling allowed a direct estimation of habitat overlap at a pool–riffle scale.3. Gudgeon showed a dominant spatial activity pattern preferring pools at all times of day, whereas stone loach used both mesohabitats but with a distinct temporal (nocturnal) activity pattern. The patterns of residence were not identical with those of active foraging. Invertebrate community composition differed significantly between mesohabitats but not between times of day. More than half of the total dissimilarity between pools and riffles was accounted for by six invertebrate taxa. Five of these were subject to higher fish predation in pools than in riffles. The total prey consumption of the two fish species together in pools was about three times as high as in riffles. Trophic niche breadth of stone loach and thus its predation range was broader than that of gudgeon.4. These results indicate that the potential predation risk for stream invertebrates depends on the combination of spatial and temporal patterns of both predator and prey. Given the distinct differences in predation risk found between pools and riffles, we conclude that spatial heterogeneity at the mesohabitat scale can influence mechanisms and consequences of selective predation. We also suggest that the analysis of spatiotemporal predator–prey relationships should not be based on the premise that the main residence habitat and active foraging habitat of a predator are identical.