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Fish Predation (fish + predation)

Distribution by Scientific Domains

Life Sciences	95%

Selected Abstracts

Subtle top-down control of a freshwater meiofaunal assemblage by juvenile fish

FRESHWATER BIOLOGY, Issue 9 2010
GERARD DINEEN
Summary 1. Top-down control of prey assemblages by fish predators has been clearly demonstrated in lakes (for zooplankton prey) and rivers (for macroinvertebrate prey). Fish predation can have a significant impact on the body size of prey assemblages; often large-bodied prey are reduced in abundance, and indirect facilitation of small-bodied prey occurs potentially initiating a trophic cascade. 2. Benthic communities in aquatic ecosystems also include a numerous and functionally important meiofaunal-sized component, but in freshwaters the impact of fish predation on meiofaunal assemblages is unknown. We used a laboratory microcosm study to explore the impact of juvenile fish predation on the abundance and size structure of a riverine meiofaunal assemblage. 3. The presence of fish in our microcosms had no significant effect on overall meiofaunal (temporary and permanent) abundance. However, for the Copepoda, we found the first evidence of top-down control of freshwater meiofaunal assemblages; in microcosms with juvenile fish, the abundance of large-bodied Copepoda was significantly reduced, whereas small-bodied Copepoda were significantly more abundant suggesting indirect facilitation. 4. We conclude that predation by juvenile fish can alter the structure of freshwater meiofaunal assemblages, although we do not yet know whether these relatively subtle changes are overwhelmed by large-scale events such as flow disturbances. [source]

Macrophyte refuges, prey behaviour and trophic interactions: consequences for lake water clarity

ECOLOGY LETTERS, Issue 2 2007
Motomi Genkai-Kato
Abstract Macrophytes may enhance grazing on phytoplankton by providing a refuge for zooplankton against fish predation. Loss of macrophytes can trigger sudden degradation of water clarity (regime shift) in lakes. However, the presence of piscivores may drive planktivorous fish to take refuge amongst littoral macrophytes. To address the possibility of regime shifts, I here constructed an empirically based model that combined population dynamics of organisms with game theory for optimal habitat selection, taking into consideration the trophic structure, lake size and eutrophication. The model showed that macrophytes generally acted as a refuge for zooplankton, rather than for fish. The model predicted that regime shifts were more likely in small, shallow lakes and that the presence of macrophytes raised the possibility of regime shifts. The present study demonstrated that the fast dynamics of animal behaviour could lead to regime shifts, in connection with slower variables such as nutrient loading. [source]

Rapid evolution and the convergence of ecological and evolutionary time

ECOLOGY LETTERS, Issue 10 2005
Nelson G. Hairston Jr
Abstract Recent studies have documented rates of evolution of ecologically important phenotypes sufficiently fast that they have the potential to impact the outcome of ecological interactions while they are underway. Observations of this type go against accepted wisdom that ecological and evolutionary dynamics occur at very different time scales. While some authors have evaluated the rapidity of a measured evolutionary rate by comparing it to the overall distribution of measured evolutionary rates, we believe that ecologists are mainly interested in rapid evolution because of its potential to impinge on ecological processes. We therefore propose that rapid evolution be defined as a genetic change occurring rapidly enough to have a measurable impact on simultaneous ecological change. Using this definition we propose a framework for decomposing rates of ecological change into components driven by simultaneous evolutionary change and by change in a non-evolutionary factor (e.g. density dependent population dynamics, abiotic environmental change). Evolution is judged to be rapid in this ecological context if its contribution to ecological change is large relative to the contribution of other factors. We provide a worked example of this approach based on a theoretical predator,prey interaction [Abrams, P. & Matsuda, H. (1997). Evolution, 51, 1740], and find that in this system the impact of prey evolution on predator per capita growth rate is 63% that of internal ecological dynamics. We then propose analytical methods for measuring these contributions in field situations, and apply them to two long-term data sets for which suitable ecological and evolutionary data exist. For both data sets relatively high rates of evolutionary change have been found when measured as character change in standard deviations per generation (haldanes). For Darwin's finches evolving in response to fluctuating rainfall [Grant, P.R. & Grant, B.R. (2002). Science, 296, 707], we estimate that evolutionary change has been more rapid than ecological change by a factor of 2.2. For a population of freshwater copepods whose life history evolves in response to fluctuating fish predation [Hairston, N.G. Jr & Dillon, T.A. (1990). Evolution, 44, 1796], we find that evolutionary change has been about one quarter the rate of ecological change , less than in the finch example, but nevertheless substantial. These analyses support the view that in order to understand temporal dynamics in ecological processes it is critical to consider the extent to which the attributes of the system under investigation are simultaneously changing as a result of rapid evolution. [source]

Assessing the potential for fish predation to impact zebra mussels (Dreissena polymorpha): insight from bioenergetics models

ECOLOGY OF FRESHWATER FISH, Issue 2 2004
M. A. Eggleton
Abstract,,, Rates of annual food consumption and biomass were modeled for several fish species across representative rivers and lakes in eastern North America. Results were combined to assess the relative potential of fish predation to impact zebra mussels (Dreissena polymorpha). Predicted annual food consumption by fishes in southern waters was over 100% greater than that in northern systems because of warmer annual water temperatures and presumed increases in metabolic demand. Although generally increasing with latitude, biomasses of several key zebra mussel fish predators did not change significantly across latitudes. Biomasses of some less abundant fish predators did increase significantly with latitude, but increases were not of the magnitude to offset predicted decreases in food consumption. Our results generally support the premise that fishes in rivers and lakes of the southern United States (U.S.) have inherently greater potential to impact zebra mussels by predation. Our simulations may provide a partial explanation of why zebra mussel invasions have not been as rapid and widespread in southern U.S. waters compared to the Great Lakes region. Resumen 1Modelamos la tasa de consumo anual de alimento y biomasa para varias especies de peces en una muestra representativa de ríos y lagos del este de Norte América. Combinamos los resultados para evaluar el potencial relativo que estas especies de peces pueden ejercer sobre la abundancia del mejillón asiático Dreissena polymorpha. Las predicciones sobre consumo para peces en lagos y ríos del sur fueron más del 100% comparadas con sistemas septentrionales. Esto se puede deber a las temperaturas anuales más altas y aumentos en la demanda metabólica de peces en ríos y lagos del sur de Norte América. 2La biomasa de varias especies claves de peces que consumen D. polymorpha no cambió apreciablemente con latitud. La biomasa de algunos peces que consumen D. polymorpha aumentó significativamente con latitud, pero este aumento no era de una magnitud suficiente para compensar la disminución en el consumo de alimento. 3Nuestros resultados apoyan generalmente la premisa de que los peces en ríos y lagos del sur de los Estados Unidos (EE.UU.) tienen un potencial inherente mayor para poder controlar D. polymorpha. Nuestras simulaciones proporcionan una explicación parcial de por qué las invasiones de D. polymorpha no han sido tan rápidas y ampliamente distribuidas en aguas sureñas comparado con la región de los Grandes Lagos. [source]

Subtle top-down control of a freshwater meiofaunal assemblage by juvenile fish

Cladoceran community responses to biomanipulation and re-oligotrophication in Lake Vesijärvi, Finland, as inferred from remains in annually laminated sediment

FRESHWATER BIOLOGY, Issue 6 2010
MIRVA NYKÄNEN
Summary 1. We studied the role of zooplankton in biomanipulation and the subsequent recovery phase in the Enonselkä basin of Lake Vesijärvi, using subfossil cladocerans in annually laminated sediment. Measures to restore the Enonselkä basin included reduction in external nutrient loading and mass removal of plankti- and benthivorous fish. Water clarity increased and the lake changed from a eutrophic to a mesotrophic state. However, some signs of increased turbidity were observed after 5,10 years of successful recovery. 2. Annual laminae in a freeze core sample were identified and sliced, based on the seasonal succession of diatoms. Cladoceran remains and rotifer eggs were counted, and Daphnia ephippia and Eubosmina and Bosmina ephippia and carapaces were measured. Annual changes in pelagic species composition were studied with principal component analysis. Individual species abundance, size measurements and various cladoceran-based indices or ratios (commonly used to reconstruct changes in trophic state and fish predation) were tested for change between four distinct periods: I (1985,1988) dense fish stocks, poor water quality; II (1989,1992) fish removal; III (1993,1997) low fish density, improved water quality; IV (1998,2002) slightly increased fish density and poorer water quality. 3. After the removal of fish, the mean size of Daphnia ephippia and Eubosmina crassicornis ephippia and carapaces increased significantly. In contrast, the percentage of Daphnia did not increase. When based on ephippia, the ratio Daphnia/(Daphnia + E. crassicornis) increased, but the interpretation was obscured by the tolerance of fish predation by small Daphnia and by the fact that bosminids were the preferred food of roach. Moreover, ephippial production by E. crassicornis decreased in recent years. 4. The abundance of Diaphanosoma brachyurum and Limnosida frontosa increased significantly after the fish population was reduced, while that of Ceriodaphnia and rotifers decreased. 5. The expanding littoral vegetation along with improved water clarity was clearly reflected in the concentration of littoral species in the deep sediment core. The species diversity index for the entire subfossil community also increased. 6. The period of faltering recovery was characterised by greater interannual variability and an increased percentage of rotifers. Nevertheless, the mean sizes of Daphnia ephippia and E. crassicornis ephippia and carapaces indicated a low density of fish. The deteriorating water quality was apparently related to multiple stressors in the catchment after rehabilitation, such as intensified lakeshore building, as well as to exceptional weather conditions, challenging the management methods in use. [source]

Weedbeds and big bugs: the importance of scale in detecting the influence of nutrients and predation on macroinvertebrates in plant-dominated shallow lakes

FRESHWATER BIOLOGY, Issue 3 2010
ANGELA L. BERESFORD
Summary 1. The scale of investigations influences the interpretation of results. Here, we investigate the influence of fish and nutrients on biotic communities in shallow lakes, using studies at two different scales: (i) within-lake experimental manipulation and (ii) comparative, among-lake relationships. 2. At both scales, fish predation had an overriding influence on macroinvertebrates; fish reduced macroinvertebrate biomass and altered community composition. Prey selection appeared to be size based. Fish influenced zooplankton abundance and light penetration through the water column also, but there was no indication that fish caused increased resuspension of sediment. 3. There were effects of nutrients at both scales, but these effects differed with the scale of the investigation. Nutrients increased phytoplankton and periphyton at the within-lake scale, and were associated with increased periphyton at the among-lake scale. No significant effect of nutrients on macroinvertebrates was observed at the within-lake scale. However, at the among-lake scale, nutrients positively influenced the biomass and density of macroinvertebrates, and ameliorated the effect of fish on macroinvertebrates. 4. Increased prey availability at higher nutrient concentrations would be expected to cause changes in the fish community. However, at the among-lake scale, differences were not apparent in fish biomass among lakes with different nutrient conditions, suggesting that stochastic events influence the fish community in these small and relatively isolated shallow lakes. 5. The intensity of predation by fish significantly influences macroinvertebrate community structure of shallow lakes, but nutrients also play a role. The scale of investigation influences the ability to detect the influence of nutrients on the different components of shallow lake communities, particularly for longer lived organisms such as macroinvertebrates, where the response takes longer to manifest. [source]

Seasonal trophic dynamics affect zooplankton community variability

FRESHWATER BIOLOGY, Issue 11 2009
BEATRIX E. BEISNER
Summary 1. The degree to which communities are variable may be affected by the ecological conditions to which they are exposed and can affect their propensity to form alternative states. We examined the influence of two common ecological factors, predation and seasonal successional stage, on the variability in community composition of herbivorous pond plankton. In a highly replicated, two factor, mesocosm experiment we determined whether beta diversity was affected by seasonal successional stage of the community (two levels), by fish predation (presence/absence) or by their interaction. 2. Several significant changes were found in the composition of the rotifer, cladoceran and copepod assemblages. Most cladoceran abundances showed sharp declines in the presence of fish, while some rotifers, as well as their assemblage species richness, responded favourably to fish. The copepod assemblage was composed of omnivorous and carnivorous species, which added invertebrate predation to the experiment and which intensified as the season progressed. Copepods showed responses to fish predation that depended on seasonal successional stage of the initial community, because of changes in their stage structure and edibility as they grew from nauplii to adults. 3. Community variability was consistently high at the end of each month-long experimental period for both cladoceran and rotifer assemblages, except under two conditions. In the early season treatments, the rotifer assemblages were more consistent (lower beta diversity) in the presence of fish. This was attributed to high population growth rates for rotifers under these ecological conditions because of reduced copepod predation on them through a trophic cascade from fish. Low community variability was also observed in the late season for rotifers when fish were excluded and, as a result, they were exposed to high invertebrate predation from cyclopoid copepods. 4. Results from the early season support theoretical predictions that when community size increases, variability in composition should decline because of an increase in competitive processes over stochastic ones. Late season results suggest that a second mechanism, specialist predation, can also reduce prey community variability. Our study demonstrates that plankton communities may be more predictable under certain trophic web configurations and challenges ecologists to find ways to incorporate such inherent variability into experiments and community theory. [source]

Predator,prey interactions in river networks: comparing shrimp spatial refugia in two drainage basins

FRESHWATER BIOLOGY, Issue 3 2009
ALAN P. COVICH
Summary 1.,Analysis of drainage networks provides a framework to evaluate the densities and distributions of prey species relative to locations of their predators. Upstream migration by diadromous shrimp (Atya lanipes and Xiphocaris elongata) during their life cycle provides access to headwater refugia from fish predation, which is intense in estuaries and coastal rivers. 2.,We postulate that geomorphic barriers (such as large, steep waterfalls >3.5 m in height), can directly limit the distribution of predatory fishes and, indirectly, affect the densities of their prey (freshwater shrimps) in headwater streams. 3.,We compared densities of shrimp in pools above and below waterfalls, in four headwater tributaries in two river basins of the Luquillo Mountains of northeastern Puerto Rico. We measured shrimp densities twice a year over 8 years (1998,2005) in Prieta, Toronja, Bisley 3 and Bisley 5 streams, which differ in drainage network positions relative to steep waterfalls in Río Espíritu Santo and Río Mameyes. 4.,Predatory fishes are absent in the Prieta and Toronja pools and present in Bisely 3 and in lower Bisley 5 pools. Atya lanipes and X. elongata rarely occur in the Bisley streams where predatory fishes are present but these shrimps are abundant in Prieta and Toronja, streams lacking predatory fishes. 5.,The mean carapace length of X. elongata is longer in pools where fish are present (Bisley 3 and lower Bisley 5) than in pools lacking fish (Prieta, Toronja, Upper Bisley 5). The increased body size is primarily due to significantly longer rostrums of individuals in stream reaches with fish (below waterfall barriers) than in those reaches lacking fish (above waterfall barriers). Rostrum length may be an adaptation to avoid predation by visually feeding fishes. 6.,Atya lanipes and X. elongata distributions and densities were predicted primarily by drainage network position relative to the presence or absence of predatory fishes. High, steep waterfalls effectively impeded fish from moving upstream and created a spatial refuge. Xiphocaris elongata may rely on size refugia (longer rostrum) to minimize predation where spatial refugia are lacking. [source]

Hide, rest or die: a light-mediated diapause response in Daphnia magna to the threat of fish predation

FRESHWATER BIOLOGY, Issue 1 2005
Miros, lusarczyk
Summary 1. In a laboratory batch culture experiment, a diapause response of Daphnia magna to a simulated threat of fish predation was tested at various light intensities, which under natural conditions determine potential vulnerability of Daphnia to visual planktivorous fish. 2. Under moderate light intensity (1.4 ,mol m,2 s,1) that allows effective predation by fish, the proportion of females producing dormant eggs was significantly higher than under dim light conditions (0.001 ,mol m,2 s,1) that are not favourable for visual detection of prey. Production of dormant eggs was not observed in complete darkness or in treatments missing fish kairomones, irrespective of tested light conditions. 3. The observed phenomenon is interpreted as a flexible response of prey to the conditional risk of predation assessed by Daphnia according to the presence of fish-derived cues on the one hand and the presence of dark refugia on the other. Irrespective of the presence of fish kairomones, Daphnia may not produce resting eggs as long as a safe, dark, bottom zone is accessible. [source]

Two hundred years of a diverse Daphnia community in Lake Naivasha (Kenya): effects of natural and human-induced environmental changes

FRESHWATER BIOLOGY, Issue 8 2004
Joachim Mergeay
Summary 1. We used fossil diapausing eggs extracted from 210Pb-dated sediment cores to reconstruct historical changes in the Daphnia community of Lake Naivasha, a climate-sensitive lake in Kenya which over the past 200 years has experienced a series of well-documented natural and anthropogenic environmental changes. 2. Contiguous sampling and analysis of four cores yielded ephippial capsules of eight Daphnia species. Only two of these had been recorded previously in live collections from Lake Naivasha, and one species is new to science. The four more common species (Daphnia barbata, D. laevis, D. magna, and D. pulex) show striking differences in abundance patterns and population dynamics through time. Four other species (D. lumholtzi, D. curvirostris, D. longispina s.l., and Daphnia sp. nov. type Limuru.) appear to have been present only occasionally. Nevertheless, between 1895 and 1915 seven species of Daphnia inhabited Lake Naivasha simultaneously. 3. Despite considerable natural environmental change associated with climate-driven lake-level fluctuations, the Daphnia community of Lake Naivasha has been severely affected by human activities over the past century, especially the introduction of exotic fishes and water-quality changes because of agricultural soil erosion. The recent reappearance of large-bodied Daphnia species (D. magna, D. barbata, D. lumholtzi, Daphnia sp. nov. type Limuru) after 20,110 years of absence can be explained by their release from fish predation, following a dramatic increase in turbidity caused by excess clastic sediment input from eroded catchment soils. The small-bodied species D. laevis has fared less well recently, presumably because the benefit of lowered predation pressure is counteracted by more pronounced negative effects of increased turbidity on this species and loss of submerged macrophyte beds which formerly served as predation refuge. 4. Our results suggest that, despite considerable environmental instability and the absence of specialised zooplanktivores, top-down control of fish on large zooplankton is important in Lake Naivasha. Predation pressure from fish has led to clear-cut shifts in local Daphnia species composition, but failed to drive the larger taxa to extinction. [source]

Growth and population size of crayfish in headwater streams: individual- and higher-level consequences of acidification

FRESHWATER BIOLOGY, Issue 7 2004
Steven M. Seiler
Summary 1. Environmental stress may have indirect positive effects on population size through modification of food-web interactions, despite having negative effects on individuals. Here we evaluate the individual- and population-level effects of acidification on crayfish (Cambarus bartonii) in headwater streams of the Allegheny Plateau (PA, U.S.A.) with field experiments and survey data. Median baseflow pH of 24 study reaches in nine streams varied from 4.4 to 7.4, with substantial variation found both among and within streams. 2. Two bioassays were conducted to evaluate the relationship between stream pH and crayfish growth rates. Growth rates were always higher in circumneutral reaches than in acidic reaches. Crayfish originating in acidic water grew less when transplanted into neutral water than did crayfish originating in neutral water, providing some evidence for a cost of acclimation to acidity. 3. Stream surveys showed that fish were less abundant and crayfish more abundant in acidified streams than in circumneutral streams. Crayfish density was sixfold higher in reaches with the lowest pH relative to circumneutral reaches. Large crayfish made up a higher proportion of crayfish populations at sites with high fish biomass, consistent with the hypothesis that fish predation on small individuals may be limiting crayfish population size at these sites. 4. Although individual crayfish suffered lower growth in acidified streams, increased acidity appeared to cause an increase in crayfish population size and shifts in size structure, possibly by relieving predation pressure by fish. [source]

Invertebrate communities associated with a native (Vallisneria americana) and an alien (Trapa natans) macrophyte in a large river

FRESHWATER BIOLOGY, Issue 11 2003
David L. Strayer
Summary 1. We used a corer and a Downing box sampler to sample macroinvertebrates living on and beneath the introduced Trapa natans and the native Vallisneria americana in the freshwater tidal Hudson River, New York. 2. Densities of macroinvertebrates were higher in Trapa than in Vallisneria, and higher in the interior of plant beds than at their edges. These effects were largely a result of high plant biomass in Trapa beds and in bed interiors (the plants have similar surface area per unit mass). 3. The composition of both epiphytic and benthic macroinvertebrates differed distinctly between Trapa and Vallisneria, and also seasonally. 4. These compositional differences were not easily interpretable as rising from possible differences in oxygen concentrations, fish predation, or water circulation in the two macrophytes. 5. Sida crystallina (Cladocera) collected from Trapa contained more haemoglobin than those collected from Vallisneria. 6. The replacement of Vallisneria by Trapa in the Hudson probably increased system-wide biodiversity and food for fish, although macroinvertebrates in Trapa beds may not be readily available to fish because of low oxygen concentration there. [source]

Phenotypic plasticity in pigmentation in Daphnia induced by UV radiation and fish kairomones

FUNCTIONAL ECOLOGY, Issue 4 2004
R. TOLLRIAN
Summary 1Planktonic organisms are exposed to harmful ultraviolet (UV) radiation. Pigmentation offers protection but at the same time increases visibility, and therefore vulnerability, to visually orienting predators such as fish. As an adaptation against fish predation, zooplankton should be transparent, though this would leave them less protected against UV radiation. Thus both adaptations would appear to be mutually exclusive. However, phenotypic plasticity in pigmentation could allow flexible adaptation to both environmental situations. 2We tested the hypothesis that Daphnia should be able to change their level of pigmentation in response to fish kairomone and/or UV radiation using four species of Daphnia. 3Daphnia hyalina Leydig increased pigmentation under UV radiation and D. pulex Leydig reduced pigmentation in the fish kairomone treatment. Both species live in habitats with variable UV and fish impact. 4Daphnia cucullata Sars and D. middendorffiana Fischer showed no reaction, probably because of their extreme adaptations: D. middendorffiana is strongly pigmented and seems to be adapted to high UV-B impact and an absence of fish in its arctic habitat. In contrast, D. cucullata has evolved in coexistence with fish. It can afford being nearly transparent because it lives in eutrophic lakes where UV-B is not relevant. 5Our data on four species suggest that plasticity in pigmentation might be common in Daphnia adapted to environments with contrasting or variable selection pressures. [source]

Leptodora kindti and Flexible Foraging Behaviour of Fish , Factors behind the Delayed Biomass Peak of Cladocerans in Lake Hiidenvesi

INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 1 2003
Laura Uusitalo
Abstract In the eutrophic L. Hiidenvesi, the spring biomass maximum of cladoceran zooplankton is missing and the highest biomass takes place in July,August. The factors behind the delayed biomass peak were studied in four different basins of the lake with concomitant data on cladocerans assemblages, density of the predatory cladoceran Leptodora kindti and food composition of fish. In all the basins, the abundance of Leptodora peaked in June, being highest (up to 800 ind. m,3) in the two most shallow basins (max depth < 4 m). The duration of the high population density was short and in July-August Leptodora density stayed below 200 ind. m,3, although the water temperature was still favourable. The collapse of the Leptodora population coincided with the change in the feeding habits of fish. In early summer, fish predation was targeted mainly on copepods and zoobenthos, while in high summer Leptodora was one of the main preys of perch, white bream and bleak. The biomass of herbivorous cladocerans was below 10 ,g C l,1 in June, and climbed to a maximum in August in the two most shallow basins (34 and 76 ,g C l,1), in July in the deepest basin (27 ,g C l,1), and in September in the intermediate basin (55 ,g C l,1). In the two most shallow basins, the death rate of the dominating cladoceran, Daphnia cristata, closely followed the food consumption rate by the Leptodora population. In the deeper basins, the agreement was not so close, smelts (Osmerus eperlanus) and chaoborids being important predators of herbivores. The duration of the period of high Leptodora density thus depended on the predation pressure by fish, while the increased fish predation on Leptodora in July,August allowed the elevation of the biomass of herbivorous cladocerans. [source]

The influence of nutrient loading, dissolved inorganic carbon and higher trophic levels on the interaction between submerged plants and periphyton

JOURNAL OF ECOLOGY, Issue 1 2002
J. Iwan Jones
Summary 1We studied the growth of a submerged aquatic plant in relation to periphytic and planktonic algae over a range of nutrient and dissolved inorganic carbon (DIC) availabilities. 2In consecutive years two factorial experiments were conducted in 48 artificial ponds (each 3.14 m3), comprising four concentrations of DIC (1.5, 2.5, 3.5 or 4.5 mm) each crossed with three separate nutrient loadings (10 µg L,1 P and 0.2 mg L N, 50 µg L,1 P and 1 mg L N, or 200 µg L,1 P and 4 mg L N). The second experiment differed by the inclusion of fish in the ponds. 3In the first year DIC had no effect on plant growth, but nutrient loading did. Plants failed to grow in treatments where phytoplankton density was high (> 100 µg L,1). Where phytoplankton was low, high numbers of invertebrates colonized the ponds, and periphyton abundance on the plants was low. In the second year, where phytoplankton never achieved the densities of the previous year, there was a significant effect of DIC concentration on plant growth but not of nutrients. Invertebrate abundance was lower and periphyton on the plants correspondingly higher. 4In both years increased nutrient loading had no effect on the abundance of periphyton growing on the surface of the plants. Periphyton abundance was determined by the density of grazing invertebrates in the ponds. 5There was a negative relationship between periphyton density and final plant density, which became significantly less steep with increasing DIC, indicating that periphyton and plants were competing for carbon. 6DIC concentration has the potential to influence community structure in shallow lakes, altering competitive interactions between periphyton and plants and rendering low DIC lakes more prone to loss of plants when nutrient loading increases. However, the expression of this competition between periphyton and plants will depend on the density of grazing invertebrates present, which is itself influenced by the intensity of fish predation on those invertebrates. [source]

Predator-induced life-history changes and the coexistence of five taxa in a Daphnia species complex

OIKOS, Issue 1 2000
Piet Spaak
Interspecific hybridization is common in water fleas of the Daphnia galeata species complex (e.g. D. galeata, D. cucullata, D. hyalina and their interspecific hybrids). We studied the effect of fish on the life histories of five taxa of this species complex originating from the Plußsee, northern Germany. Using four clones per taxon, we found that fish kairomones reduce size at birth and size at maturity significantly. For size at maturity larger taxa showed a significantly stronger reaction to fish kairomones than the smaller taxa. With respect to the intrinsic rate of increase, r, we compared two predation regimes (positive size selective and not selective). We found that under the fish predation regime most clones had a higher r when cultured with fish kairomones, leading to a higher r, and a stronger reaction for the smaller taxa. We conclude that fish predation might be an important factor influencing the co-occurrence of Daphnia parental taxa with their hybrids. [source]

Clay-Turbid Interactions May Not Cascade,A Reminder for Lake Managers

RESTORATION ECOLOGY, Issue 2 2005
Jukka Horppila
Abstract Food web management is a frequently used lake restoration method, which aims to reduce phytoplankton biomass by strengthening herbivorous zooplankton through reduction of planktivorous fish. However, in clay-turbid lakes several factors may reduce the effectivity of food web management. Increasing turbidity reduces the effectivity of fish predation and weakens the link between zooplankton and phytoplankton. Therefore, the effects of fish stock manipulations may not cascade to lower trophic levels as expected. Additionally, in clay-turbid conditions invertebrate predators may coexist in high densities with planktivorous fish and negate the effects of fish reductions. For instance, in the stratifying regions of the clay-turbid Lake Hiidenvesi, Chaoborus flavicans is the main regulator of cladocerans and occupies the water column throughout the day, although planktivorous Osmerus eperlanus is very abundant. The coexistence of chaoborids and fish is facilitated by a metalimnetic turbidity peak, which prevents efficient predation by fish. In the shallow parts of the lake, chaoborids are absent despite high water turbidity. We suggest that, generally, the importance of invertebrate predators in relation to vertebrate predators may change along turbidity and depth gradients. The importance of fish predation is highest in shallow waters with low turbidity. When water depth increases, the importance of fish in the top-down regulation of zooplankton declines, whereas that of chaoborids increases, the change along the depth gradient being moderate in clear-water lakes and steep in highly turbid lakes. Thus, especially deep clay-turbid lakes may be problematic for implementing food web management as a restoration tool. [source]

Decreasing trophic efficiency in cool-water aquaculture ponds: size-selective predation removes large prey

AQUACULTURE RESEARCH, Issue 5 2009
Chelsea O Bennice
Abstract Maximizing young-of-year (YOY) fish production in an aquaculture setting depends on matching predatory demand with prey availability. With a size-selective YOY fish species (saugeye: Sander vitreus Mitchell females ×S. canadense Griffith & Smith males) supplied with natural zooplankton prey (Bosmina sp. Baird), selective removal of larger individuals may decrease prey fecundity. However, increased nutrient fertilization may also ameliorate the top-down effects of fish predation. We tested these interactions in outdoor earthen production ponds (ca. 4000 m2; n=12) by measuring Bosmina sp. size at first reproduction (SFR), maximum size (MAX) and neonate size (NEO) in ponds that varied in YOY saugeye densities (18,50 saugeye m,3) and also differed in phosphorus maintenance levels (either 20 or 30 ,g PO4 -P L,1). We found that SFR decreased by 8% [from 0.298 mm±0.007 (mean±1 SE) to 0.275 mm±0.005], MAX decreased by 11% (from 0.367 mm±0.009 to 0.328 mm±0.009) and NEO decreased by 5% (0.198 mm±0.004 to 0.189 mm±0.003) over the range of saugeye densities, and that SFR increased by 4% (from 0.279 mm±0.004 to 0.290 mm±0.003) and MAX increased by 3% (from 0.336 mm±0.004 to 0.347±0.004) with increased fertilization. Further, prey offspring lengths strongly related to mother lengths and lengths differed from early to late in the production season. These results indicate that multiple factors affect prey sizes and emphasize that the removal of large prey individuals by size-selective YOY predators may decrease trophic efficiency, ultimately decreasing fish production. [source]

Extreme habitats are not refuges: poeciliids suffer from increased aerial predation risk in sulphidic southern Mexican habitats

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2010
RÜDIGER RIESCH
Extreme environments are often considered a predation refuge for organisms living in them. In southern Mexico several species of poeciliid fishes are undergoing incipient speciation in a variety of extreme (i.e. permanently dark and/or sulphidic) freshwater systems, and previous research has demonstrated reproductive isolation between populations from sulphidic and adjacent benign habitats. In the present study, we investigated bird predation rates (measured as successful captures per minute) in two sulphidic surface and several benign surface habitats, to test the hypothesis that extreme habitats are predation refuges. We found capture rates to be approximately 20 times higher in sulphidic environments: probably facilitated by extremophile poeciliids spending most of their time at the water surface, where they engage in aquatic surface respiration as a direct response to hypoxia. Even birds that are usually not considered major fish predators regularly engage in fish predation in the toxic habitats of southern Mexico. Our results demonstrate that extreme environments do not necessarily represent a refuge from predation, and we discuss the general importance of predation in driving incipient speciation in these systems. Finally, we hypothesize that natural selection via avian predation may play an important role in maintaining reproductive isolation between divergent poeciliid populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 417,426. [source]