Prey selectivity of Piona exigua,a planktonic water mite

Summary Females, males and nymphs of Piona exigua were observed during prey capture and ingestion. The encounter radius of the mite was very small, allowing the escape of some crustaceans, such as the calanoid copepod Boeckella. Cladocerans, such as Bosmina or Chydorus, with little or no pre-contact escape response were the most vulnerable to mite predation. Preference values in size-selection experiments varied widely between individual mites. Adult mites presented with two sizes of Daphnia carinata generally preferred the smaller prey. When four sizes were presented simultaneously, however, the preferences of female mites for each size were not significantly different. Patterns of prey selection varied with predator age and sex; for example, female mites preferred Daphnia to Simocephalus, Ceriodaphnia and Chydorus, while nymphs showed a strong preference for Chydorus over Ceriodaphnia. When two prey types were present in equal proportions, differences in total prey density (range 5 or 10/1 – 30 or 50/1) did not alter preferences between the prey species. The preference of female mites for a particular prey type generally increased with increasing relative abundance of the prey type in each of three experiments (Daphnia: Ceriodaphnia, Ceriodaphnia: Chydorus, and Daphnia: Simocephalus). These results imply switching behaviour in these mites. Our results indicate the value of direct observation of predatory behaviour as an adjunct to prey selection experiments. It is also apparent that predatory behaviour in the presence of more than one prey type may not be predictable from that observed in single-prey situations. Predation rates on particular prey species were sometimes reduced in the presence of another species. The relative proportions of prey eaten when two species were present could not be predicted from the number of each species eaten when they were presented separately.     

Effects of temperature and food level on growth and development of a planktonic water mite

We analysed the relative effects of food availability and temperature on rates of growth and development of a predatory planktonic water mite, Piona exigua. Growth in length of mites fed Daphnia, Ceriodaphnia and Chydorus was analysed by Gompertz or von Bertalanffy curves; these curves were compared by parallel curve analysis. Growth rates of nymphs and adult female mites increased with temperature; the duration of the imagochrysalis stage decreased. Females grown at 10 °C were smaller at final size than females grown at 15 °C, 18 °C or 22 °C. Females reared at food levels of 15 or 30 prey l⁻¹ grew more slowly and were smaller than those provided with 60 or 120 prey l⁻¹. Nymphs grew more slowly when Daphnia were the only prey, than when smaller prey were available. Food level did not affect nymph growth at 10 °C or 15 °C, but growth at 18 °C or 22 °C may have been slowed at the lowest food levels. Synergistic effects of temperature and food level on nymph growth were apparent only from analysis of growth curves and not from stage duration data.     

Measuringin situ predation byMysis relicta and observations on underdispersed microdistributions of zooplankton

Described are a method and apparatus that allowin situ measurement of predation on zooplankton byMysis relicta. The method, which can be generalized to other predators, involves lowering paired large-volume (30-1) plankton traps to the depth of interest, with subsequent trapping of the ambient zooplankton assemblage in each trap and release of predators into one of the traps. The statistical adequacy of the method was shown by error propagation theory to depend on the percentage of available prey consumed, on the number of prey captured by the traps, and on the distribution of zooplankton within the volume of water captured by the traps. Repeated casts of the apparatus showed that, in contrast to other studies of zooplankton distribution, various zooplankton categories were statistically underdispersed (evenly dispersed in space) or at least not more statistically dispersed (clumped) than was a random distribution at a space scale of 1 m. An error analysis of many replicated feeding experiments showed that the errors obtained were reasonably small and that they conformed with or were less than those predicted by error propagation theory that assumed random distribution of zooplankton. Thus, these results supported the practical application of the method and corroborated the conclusion of random dispersion or underdispersion drawn from the experiment of repeated casts of the apparatus.     

The food preference of vendace (Coregonus albula) in South Swedish forest lakes including the predation effect on zooplankton populations

Vendace (Coregonus albula, L.) is in the southern part of its distribution area during the summer period restricted to hypolimnion. Food is dominated by Bosmina coregoni and Daphnia sp. The selectivity index is highest for large cladocerans and large copepods.The pelagic crustacean fauna in vendace lakes is dominated by small species like Bosmina coregoni, Daphnia cristata, Thermocyclops and Mesocyclops sp. and Eudiaptomus sp. During periods of maximum vendace abundance only Bosmina coregoni is left of the cladocerans, while the abundance of cyclopoid copepods increases.     

Evaluation ofChaoborus predation on natural populations of herbivorous zooplankton in a eutrophic lake

Hydrobiologia - The effect ofChaoborus predation on natural zooplankton communities was tested in enclosure experiments during June, July and August in the eutrophic Frederiksborg Slotssø,...     

Changes in abundance of the icefish Neosalanx pseudotaihuensis Zhang (Salangidae) and the impact on the zooplankton community of Xujiahe Reservoir,central China

The icefish Neosalanx pseudotaihuensis Zhang is a small and commercially exploited zooplanktivorous fish in Xujiahe Reservoir (central China). Data of catch per unit effort (CPUE) from June 1995 to December 1997 show that the abundance of the icefish varied dramatically, which is reflected in the populations of the dominant cladocerans. The densities of Leptodora kindti, Daphnia galeata and Diaphanosoma dubia were the highest in 1997 when the abundance of the icefish was the lowest, and the reverse was the case for Boimina spp. These results document that the population of this annual fish is very variable and high biomass of the fish could exert a pronounced effect on the zooplankton community.     

Impact of selective predation by Mesocyclops pehpeiensis on a zooplankton community: experimental analysis using mesocosms

Predation by cyclopoid copepods is an important factor affecting zooplankton communities in freshwater habitats. Experiments provide strong evidence of the role of selective predation by cyclopoid copepods in structuring zooplankton communities. To assess the predation impact of a cyclopoid copepod, Mesocyclops pehpeiensis, we conducted a mesocosm experiment using 20-l polyethylene tanks in which the density of the predator and the food available to herbivorous zooplankton varied. M. pehpeiensis had a notable but selective effect on the zooplankton community. The population of a small cladoceran, Bosmina fatalis was affected negatively, but M. pehpeiensis did not have any apparent impact on the population dynamics of another Bosmina species, B. longirostris. On the other hand, the population of small rotifers responded positively to the presence of M. pehpeiensis, and their densities increased in mesocosms with a high density of M. pehpeiensis. It seems that suppression of B. fatalis by M. pehpeiensis predation indirectly affected rotifers by releasing them from competition with B. fatalis. The results suggest that copepod predation is a powerful factor regulating zooplankton communities directly and indirectly.     

Predation on soft-shell clams (Mya arenaria) by the nemertean Cerebratulus lacteus in Atlantic Canada: implications for control measures

The nemertean, Cerebratulus lacteus Verrill (Nemertinea: Heteronemertini), has been identified as an important threat to soft-shell clam (Mya arenariaL.) populations in Atlantic Canada. The biology of this species, however, is still largely unknown. Field and laboratory studies were undertaken in 1998 and 1999 in Prince Edward Island, Canada, to test certain control measures to reduce predation on soft-shell clam populations and to better describe the relationship between C. lacteus and M. arenaria. Field abundance of C. lacteus, M. arenaria and Nereis virens Sars were evaluated in relation to particular habitat modifications that were used as control measures. Sediment manipulations tested were: (1) addition of shells and (2) use of a hydraulic rake. No difference was observed on the abundance of C. lacteus, M. arenaria and N. virens after treatments were applied. In the laboratory, C. lacteus was shown to be an efficient predator of M. arenaria. Clam mortalities reached 100% in the presence of C. lacteus while 0% mortality was observed in its absence. A complementary set of experiments was carried out to see if the sympatric polychaetes N. virens and Glycera dibranchiata Ehlers had any impact on the relationship between C. lacteus and M. arenaria. N. virens showed no impact on C. lacteus predation on clams. The presence of G. dibranchiata significantly reduced the nemertean predation rate. Analysis of clam size selection revealed no significant preference by C. lacteus. Other experimental studies revealed that high predator densities did not impede predation on clams and that C. lacteus preferred soft-shell clams among other commercial bivalve species presented (Mercenaria mercenariaL., Crassostrea virginica Gmelin and Mytilus edulisL.). This study should provide a better understanding of the relationship between C. lacteus and M. arenaria and lead to the development of improved nemertean control measures.     

Predation of Arternia cysts by water-tiger larvae of the genus Anacaena (Coleoptera,Hydrophilidae)

Artemia cysts are preyed upon by the larvae of Anacaena (Coleoptera, Hydrophilidae) in the wet supralittoral of the hypersaline Solar Lake near Elat. The larvae are specialized feeders of the cysts, as shown by laboratory experiments.     

Low fish predation pressure in London reservoirs: II. Consequences to zooplankton community structure

The 1992 survey of zooplankton structure in fourteen London supply reservoirs showed the overall dominance of large-bodied zooplankton, mainly species of Daphnia. These reservoirs can be considered as ‘anti-fish’ by virtue of their steeply sloping concrete or brick sides. The average biomass of large Daphnia spp (retained on a 710 μm sieve) in the total zooplankton biomass was higher than 20% for twelve out of fourteen reservoirs. The cladoceran-copepod ratio was inversely correlated with both dominance of large-bodied Daphnia magna and cladoceran body-size structure. Parallelly, there were tendency of more efficient utilization of lowered algal crops in reservoirs dominated by large-bodied Daphnia spp. A graphical model is presented which relates daphnid species composition and zooplankton size structure to a presumed gradient of fish biomass in these reservoirs.     

Potential impact of size-selective planktivory on phosphorus release by zooplankton

A laboratory model of phosphorus release by Daphnia rosea was implemented for published zooplankton data from lakes characterized by different abundances of size-selective planktivores. Size-selective feeding reduces average prey size and increases P release per unit biomass. At the system level, decreased prey standing crop associated with higher planktivore abundance could balance the size dependent increase in P release rate. However, estimates of both net reduction and net increase in rate of P release from zooplankton resulted from model application. Size-selective feeding might be important not only in energetic or evolutionary relationships between predator and prey but also in determination of the relative importance of different pathways of phosphorus flow through pelagic systems.     

The feeding behaviour of Leptodora kindti and its impact on the zooplankton community of Neusiedler See (Austria)

Leptodora kindti is a very efficient invertebrate predator. Its searching mode of preying is tactile. The setae of the first thoracic limb act as mechanoreceptors, the other thoracic limbs, thorax and head together form the shape of an open basket in which after encounter the prey is pushed in by the aid of the first thoracic limbs and the furca. In Neusiedler See, small individuals of Diaphanosoma brachyurum (0.6–0.9 mm) are the preferred prey, rarely copepods are taken. The predation rate is influenced by temperature, prey density and predator size and varies between less than one and 12 prey items per predator per day. At high predator densities, Leptodora will have a substantial effect on the Diaphanosoma population of Neusiedler See.     

Effects of temperature on the rate of development of eggs of a planktonic water mite, Piona exigua

SUMMARY. 1. The eggs of a planktonic, predatory water mile Piona exigua Viets were reared in the laboratory at constant temperatures ranging from 10°C to 280C. Egg development rates increased with increase in temperature.
2. Five models describing the effect of temperature on egg development times were fitted to the data.
3. The variances of the egg hatching times at each temperature differed widely, but these variances were not made more equal by In-transformation.
4. A simple power curve, fitted to the raw data, accounted for ≥.97% of the variation in the data. Two further models, both of which included a third parameter, provided a better fit at the temperature extremes.
5. Close examination of the patterns of variance at difference temperatures may provide information relating to the pattern of emergence of aquatic poikilotherms.
6. At temperatures below 230C. eggs of Piona exigua developed more rapidly than eggs of Piona constricta , from Heney Lake. Quebec (Riessen, 1982)     

Ambush Predation by the Ponerine Ant Ectatomma ruidum Roger (Formicidae) on a Sweat Bee Lasioglossum umbripenne (Halictidae), in Panama

An individual ambush predation is used by huntresses of the ponerine ant Ectatomma ruidum to capture halictid bees (Lasioglossum umbripenne) in the Panamanian mountains. Workers, which use this strategy and originated from a colony (A) situated within a nest aggregation of halictid bees, capture almost four times more prey than colony (B) with a foraging area which does not include this type of bee's nest. Forty-eight percent of the prey of colony (A) are halictid bees, demonstrating the local importance of this predatory strategy in E. ruidum. A close examination of the behavioral sequence of predation shows that ambush is successful in only 4.8% of cases, a very low success rate in comparison to other predatory strategies described in this species. Nevertheless, due to the high repetition (16.1 ± 5.9 times on average) of very short waiting phases (6.3 ± 1.9 s), the true success rate (i.e., according to the number of individual trips) can reach up to 80%. A review of ambush predation among ant species allows us to distinguish approaches between jumping, long stealth approaches, and true ambushes. Implications of learning and expectation processes are also discussed.     

Impacts of mosquitofish (Gambusia affinis) predation on plankton communities

An investigation of the effects of mosquitofish (Gambusia affinis) predation was conducted in 12 experimental ponds in southern California over a period of 10 months.Gambusia essentially eliminatedDaphnia pulex andCeriodaphnia sp. populations, reducedDiaptomus pallidus andKeratella quadrata populations, had little impact onCyclops vernalis, and caused large increases inK. cochlearis, Polyarthra sp.,Synchaeta sp., andTrichocerca spp. populations and in total phytoplankton.Gambusia caused a decrease in the PIE (probability of interspecific encounter) of the planktonic crustaceans and an increase in the PIE of the planktonic rotifers. Hemiptera, such as neustonicMicrovelia sp. and nektonicBuenoa sp. andNotonecta sp., andHyla regilla tadpoles were absent from fish ponds but sometimes abundant in control ponds.Gambusia caused higher pH and oxygen levels, presumably via its effect on the phytoplankton. The impact ofGambusia on the pond ecosystems was less in winter, when fish numbers and feeding rates were low, than in summer. Results of other fish-plankton studies are summarized in tabular form. A model is proposed to account for variation in the calanoid/cyclopoid ratio; evidence is summarized suggesting that in general calanoids are more susceptible to predation by predaceous zooplankters while cyclopoids are more susceptible to fish predation. Some parallels are drawn between the effects ofGambusia predation and those of insecticide treatments.     

Effectiveness of phytoplankton control by large-bodied and small-bodied zooplankton

Employingin situ enclosures containing inocula of the lake zooplankton (mainlyDaphnia galeata, Daphnia cucullata andBosmina spp.) from a moderately eutrophic Lake Ros (Northern Poland) or large-bodiedDaphina magna, the following observations on succession of phytoplankton were made: 1) whereasD. magna could control the density of all the photoplankton size classes, the lake zooplankton could not suppress the large-sized phytoplankters or net phytoplankton; 2) the lake zooplankton was able to control the density of small algae (< 50μm), but its effect on large algae may be opposite: a promotion of net phytoplankton growth by removing small-sized algae which can out-compete net phytoplankton for limited PO₄-P resources (<5μg P l⁻¹). Since efficiency of phytoplankton density control byD. magna decreased with an increase in net phytoplankton abundance, biomanipulation could not be successful without introducing or maintaining a high population of large-bodied cladoceran species before high densities of large algae would make the control of phytoplankton inefficient.     

Prey preference and utilization by Mesostoma lingua (Turbellaria,Rhabdocoela) at a low arctic site

The rhabdocoel Mesostoma lingua is a common inhabitant of rock bluff ponds in the area of Churchill, Manitoba. Unlike most flatworms it has the ability to prey actively on zooplankton. Among the zooplankton, Mesostoma prefers Daphnia pulex, Simocephalus vetulus, and Diaptomus tyrrelli. Larger calanoid copepods are difficult to capture and take much longer to consume. Growth in Mesostoma is maintained when individuals consume 0.5 Daphnia day^–1 and is maximal at 4 Daphnia day^–1. In comparison, Mesostoma maintained growth only when offered the copepod Diaptomus victoriaensis at the rate of 8–10 individuals-day^–1. Mesostoma may be an important agent in structuring pond zooplankton communities in the arctic, producing a shift in dominance away from cladocerans such as Daphnia toward larger calanoid copepods.     

Mesocosm experiment on the impact of invertebrate predation on zooplankton of a tropical lake

Invertebrate predation on zooplankton was investigated in mesocosms in the shallow tropical Lake Monte Alegre, São Paulo State, Brazil, in the summer of 1999. Two treatments were applied: one with natural densities of prey and the predators Chaoborus brasiliensis and the water mite Krendowskia sp. (Pr+), and another without predators (Pr-). Three enclosures (volume: 6.6 m³ of water per enclosure) per treatment were installed in the sediment of the deepest area of the lake (5.0 m). At the beginning, Chaoborus larvae were present in Pr- enclosures, because of technical difficulties in preventing their entrance, but they virtually disappeared in the course of the experiment. Water mites were almost absent in Pr- enclosures. Chaoborus predation negatively influenced the Daphnia gessneri population, but not the populations of the copepods Tropocyclops prasinus and Thermocyclops decipiens and the rotifers Keratella spp. Death rates of Daphnia were generally significantly higher in the Pr+ treatment; Daphnia densities increased after the disappearance of Chaoborus in Pr-. Copepod losses to predation in the experiment may be compensated by higher fecundity, shorter egg development time, and lower pressure on egg-bearing females, resulting in a lower susceptibility to Chaoborus predation. The predation impact of water mite on microcrustaceans and rotifers in the experiment was negligible.     

Influence of predation by fish and water turbidity on a Daphnia gessneri population in an Amazonian floodplain lake,Brazil

The population behavior of Daphnia gessneri Herbst, 1967 in a floodplain lake (Lago Grande) of the lower Rio Solimões was investigated between April 1979 and March 1980 with regard to 1) predation by the fish called tambaqui (Colossoma macropomum, Characidae), 2) water level fluctuation and 3) water transparency. Zooplankton density samples were collected at two sites near mid-lake, where water depth and Secchi disc transparency were measured. In addition, qualitative samples of zooplankton and fish collections were taken at several sites in the adjacent floodplain areas. The author concludes that fluctuations in Daphnia gessneri populations correlate most with intense predation by fish and water turbidity.     

Predation on and by pelagic Turbellaria in some lakes in Brazil

Planktonic Turbellaria are of common occurrence in both natural and man-made lakes in Brazil. Experiments were performed in 1987 and 1989 to determine which zooplankton species are consumed by predatory Mesostoma sp. from three natural lakes in the Rio Doce Valley. Experiments were also performed in 1989 with a yet unidentified flatworm from Barra Bonita reservoir. Both predators consumed Daphnia and Ceriodaphnia at a high rate: 4 individuals per day in the case of Mesostoma sp., a large species and 1.5 ind day^–1 in the case of the smaller species from Barra Bonita reservoir. Consumption of copepod nauplii, copepodids and adults was much lower, and Ostracoda were not consumed at all. Experiments on food selectivity showed a clear preference by the flatworms for cladocerans.In the lakes studied, flatworms are heavily preyed upon by larvae of Chaoborus and by Mesocyclops species.Turbellaria densities in the natural lakes were around 300 individuals per cubic meter, whereas in Barra Bonita reservoir, 1000 individuals per cubic meter was a mean value in a fifteen days study.Federal University of São Carlos - Laboratory of LimnologyUniversity of São Paulo - Canter of Water Resource and Applied EcologyPost-graduate student - University of São Paulo