Life table responses and population dynamics of four cladoceran zooplankton during a reservoir flood

The life table responses and population dynamics of four cladocerans(Ceriodaphnia lacustris, Daphnia parvula, Diaphonosoma leuchtenbergianumand Moina micrura) were measured during a flood of a large turbidreservoir (Lake Texoma, Oklahoma-Texas). Mean recruitment andlongevity of Ceriodaphnia and Daphnia in life table experimentswere reduced during the flood when abundant silt particles andpicoplankton (<2 µm) replaced algal particles in thewater column. Individual growth rates measured in the life tableexperiments were slower for Ceriodaphnia during the flood. Fieldcollections revealed that Ceriodaphnia and Daphnia populationsdeclined immediately after the arrival of turbid water, andremaining females carried fewer eggs. Populations of Moina andDiaphanosoma increased during the flood, and life table experimentsshowed that these species were able to grow well in silt-ladenwater.     

The coexistence of Bosmina and Ceriodaphnia in a south Andes lake

1. The coexistence of Bosmina and Ceriodaphnia was studied in relation to phytoplankton succession in a small lake (Laguna Ezquerra) in the araucanian region of Argentina. 2. The study involved field sampling and single species cultures of each of the two cladocerans in lake water under laboratory conditions. 3. Ceriodaphnia showed a unimodal cycle while Bosmina had a bimodal pattern during 4 months of coexistence. Ceriodaphnia exhibited a direct relationship between clutch size and biovolume of edible algae, whereas Bosmina's fecundity was related to the density of flagellates. 4. We found that the fecundity of these species responded differently to laboratory and field conditions. The fecundity of Ceriodaphnia followed the same pattern in both the field and laboratory, whereas Bosmina showed higher fecundity values in laboratory experiments. 5. Our results are in good agreement with predictions derived from Northern Hemisphere studies, indicating that food-limited populations of daphnids and Bosmina can coexist for extended periods in spatially homogeneous environments. 6. The variation in food availability, measured as biovolume of edible algae, determines the loss of Ceriodaphnia and the persistence of Bosmina.     

Effect of competition on the demography of planktonic cladocerans — Daphnia and Diaphanosoma

Summary Isolated and mixed continuous cultures of Daphnia hyalina and Diaphanosoma brachyurum in lake water were maintained under laboratory conditions to elucidate demographic effects of competition. Population dynamics curves were obtained. Interspecific competition was revealed by the decrease in the average density of animals in the mixed versus isolated cultures and by the extinction of one species in the presence of the other. Within the first 50 days either Diaphanosoma (4 cases) or Daphnia (1 case) was the superior competitor, depending on the initial conditions. Further cultivation resulted in the extinction of Diaphanosoma in the mixed cultures. There were no statistically significant differences between the maximum rates of population increase (r _m ) in Daphnia and Diaphanosoma at the concentration of edible algae about 2·10⁵ m³ml^-1(0.293 and 0.286 days^-1, respectively). Time lags for density-dependent parameters of the populations were evaluated by means of rank cross-correlations. Regardless of the species identity the time lags of fecundity, birth rate, and the rate of population growth were significantly higher in the superior competitor. The initial conditions of culturing affected the time lags which in their turn influenced the outcome of the interaction. Enhanced competitive ability due to the maximized time lags in Daphnia was not associated with the loss of population stability. Conversely, it brought about destabilization of Diaphanosoma populations which seemed to be the ultimate cause of its extinction observed in the end of the experiment. Time lag of the population growth rate was well predicted based on the half-sum of time lags in birth and death rates (r²=0.80, P<0.001). Daphnia responded to competition with a sharp shortening of the time lags of fecundity, birth rate, and the population growth rate. It increased clutch size and showed inverse relationship between the fecundity time lag and average fecundity even though it was strongly suppressed by Diaphanosoma. The competitive ability was not related to the percentage of adults in the populations. In contrast to the current belief the major result of interspecific competition in the experiment was not a decrease in the rate of population growth but was a reduction in population time lags.     

Influence of phytoplankton composition and stratification degree on gut pigment content of Ceriodaphnia sp. at dawn

Very short-term feeding activity of the cladoceran Ceriodaphniasp. was investigated in situ in a eutrophic reservoir in thesouth of Spain, using fluorimetric analysis of the gut pigmentcontent in periods when the water column was relatively mixedor strongly stratified. The results obtained in the mixed watercolumn showed a clear increase in gut pigment content at dawn,a period sampled with high frequency. The accumulation of thecladoceran at the depth of maximum concentration of phytoplankton,and the high gut pigment concentration in cladocerans at thatdepth just after dawn, suggested active feeding of Ceriodaphniaon phytoplankton at that time. During stratification, the abundanceof Ceriodaphnia was higher, but the gut pigment contents werevery low and they did not reflect any clear feeding patterns,with either time or depth. Changes in phytoplankton concentrationand composition between the relatively mixed and the stratifiedwater column suggest a shift in feeding activity from herbivorousto.     

Food and feeding habits of Mesocyclops leuckarti (Claus) in Lake Kinneret (Israel)*

SUMMARY. The diet and feeding habits of natural and cultured populations of Mesocyclops leuckarti were studied. Nauplii and copepodid stages I–III are herbivorous. Copepodid stages IV–V and adults preferentially preyed upon Ceriodaphnia and Diaphanosoma whereas Bosmina was not preyed upon. Rate of predation on Ceriodaphnia and newborn Artemia nauplii was higher between 15–22°C than between 22–27°C. Under starvation conditions, the survival time for males was shorter than for females.     

Zooplankton community grazing in a hypertrophic lake (Hartbeespoort Dam, South Africa)

Seasonal abundance as total biomass and specific densities ofthe main herbivorous zooplankton (>60 µm) in hypertrophicHartbeespoort Dam from 1981 to 1983 are described. After springzooplankton biomass maxima each year there followed a mid-summerdecline in the Daphnia population and a shift to a smaller bodiedcladoceran community dominated by Ceriodaphnia concomitant witha change from largely edible phytoplankton species to abundantcolonial Microcystis. In situ community grazing rates were measuredthroughout 1983 using a ¹⁴C-labelled unicellular alga. Integratedcommunity grazing rates measured in the aerobic water columnwere highest in December (260.2%/day) when Daphnia was abundantand the edible component of the phytoplankton was diminishing.Lowest integrated community grazing rates occurred in January–February(19.8–35.3%/day) and July (28.3%/day) when the phytoplanktonwas composed almost entirely of Microcysris, and Ceriodaphniadominated the zooplankton community whilst food availabilitywas low. Feeding in Ceriodaphnia was not hindered by abundantlarge Microcysris colonies; total biomass specific grazing ratewas high when Ceriodaphnia dominated and low when Daphnia dominatedthe zoo-plankton community. Results indicate that in hypertrophicconditions it is unlikely that large filter-feeders such asDaphnia are able to retard or limit the development of Cyanophyceaeblooms by high grazing pressure.     

Life history strategies of cladocerans: comparisons of tropical and temperate taxa

We review recent works on different life history variables of cladoceran taxa in tropical and temperate freshwater bodies, comparing the strategies that cladocerans have evolved to adapt to contrasting environmental conditions in the two geographical regions. These life-history parameters relate to age and size at maturity, survival, fecundity, life-expectancy at birth, lifespan, gross, and net reproductive rates, generation time, the rate of population increase, peak population density and day of peak abundance. We also discuss the role of photoperiod and temperature on some of these life history parameters. We found a general paucity of experimental work and field data in tropics on cladocerans. There is very limited information on the few Daphnia species found in the tropics. The misconception of low species diversity of cladocerans in the tropics arose due to several reasons including lack of extensive and intensive field collections. Higher water temperatures apparently promote permanent infestation of tropical waters with toxic cyanobacteria, which reduce the zooplankton diversity. In addition to higher temperatures in the tropics, the year-round high predation pressure of planktivorous fish probably causes the tropical species, particularly in pelagic habitats, to reach maturity earlier (< 3 days) than in temperate regions. Species of Daphnia in temperate regions are particularly adapted to living at food concentrations that are much lower and seasonably more variable than those for tropical genera such as Diaphanosoma. This is further corroborated by the more than an order of magnitude higher threshold food concentration (TFC) for tropical Cladocera than for their temperate counterparts. Fecundity patterns differ between tropical and temperate cladoceran taxa: cultured under optimal temperature regimes, tropical taxa have fewer eggs than temperate species of a comparable body size. Predation pressure may act differently depending on the size of the cladoceran neonates and thus on their population size structure. Global warming and climate changes seem to affect the behaviour (migration), distribution, and abundance of cladocerans. Apparently, in direct response to these changes, the possibility of encountering the tropical cladocerans in the northern, temperate hemisphere (bioinvasions) is on the rise.     

Growth and reproduction of three cladoceran species from a small wetland in the south-eastern U.S.A.

SUMMARY 1. Growth, reproduction and life‐history parameters were measured for three cladoceran species from a small south‐eastern wetland, U.S.A. Simocephalus serrulatus, Diaphanosoma brachyurum and Scapholeberis mucronata juveniles were reared at temperatures between 10 and 25 °C on natural food resources. 2. Growth rate increased with temperature and decreased with individual size for all three species. Maximum somatic growth rate was higher for Simocephalus (49–72% day^?1) and Diaphanosoma (21–91% day^?1) than for Scapholeberis (11–45% day^?1). Multiple regression equations were developed which predict temperature‐ and mass‐specific growth rates for each species. 3. Scapholeberis egg production was positively related to temperature; however, maximum egg production occurred at intermediate temperatures for Simocephalus and Diaphanosoma. Mean cumulative egg production was higher for Scapholeberis (28–92 eggs per female) than for Simocephalus (18–25 eggs per female) and Diaphanosoma (1–41 eggs per female), and was related to differences in reproductive strategy and survival. 4. Survival was inversely related to temperature in most cases. For all three cladocerans, the intrinsic rate of increase (r) and net reproductive rate (R₀) increased with temperature, whereas generation time (G) decreased. Greater egg production by Scapholeberis compared with the other two cladocerans was consistent with higher R₀ values for Scapholeberis at any given temperature. Although r was very similar among species, G was typically longer for Scapholeberis than for Simocephalus and Diaphanosoma. 5. This analysis provides basic information about the population parameters of these coexisting wetland species, and the growth rate models can be applied to field data to determine production dynamics.     

GROWTH AND DEMOGRAPHY OF POPULATIONS OF BIOMPHALARIA PFEIFFERI (GASTROPODA, PLANORBIDAE) IN THE LABORATORY

The growth and demography of the freshwater snail Biomphalariapfeifferi, an intermediate host of the parasitic worm Schistosomamansoni in Eastern Zaire, were investigated in the laboratoryunder two conditions of crowding. Both individual and populationgrowth were depressed by crowding. Crowding reduced growth rateand all the variables and parameters related to reproduction(fecundity, instantaneous birth rate, net reproduction rate),but did not affect maximum size, survivorship, instantaneousdeath rate and life expectancy. The mechanism involved in theseeffects is likely to be exploitation competition for especiallyprofitable food items such as diatoms. (Received 10 November 1986;     

Resource limitation and food quality for cladocerans in a tropical Brazilian lake

Food quality of the natural food (seston) from Lake Monte Alegre was evaluated throughout a series of life-table experiments with cladocerans from the same lake carried out in summer and autumn. Experiments were performed using cohorts of newborns originated from ovigerous females cultured for several generations in the lab or taken directly from the lake. For these tests of food limitation, juveniles of different species were submitted to one of the following treatments: (1) lake seston and (2) lake seston + green algae. The age at first reproduction, mean clutch size, total offspring and the intrinsic rate of natural increase (r) were estimated. Cladocerans responded to both seasonal changes in food resources and to additions of green algae. In summer, food levels were higher and cladocerans grew better than in autumn. The low fecundity and population growth rates of Daphnia gessneri, together with high C:P ratios (>500) in the seston in summer, suggested P limitation. The other cladocerans (Moina micrura, Ceriodaphnia cornuta and Simocephalus mixtus) were apparently less sensitive than D. gessneri to P-limitation in summer. However, energy limitation cannot be disregarded even in summer, although in a lower degree compared to autumn. In this season, the predominance of large diatoms and dinophyceans of low nutritional value and the low food concentration suggested both quantitative and qualitative food limitation. Phytoplankton composition, nutritional value and particle size appeared to be important factors in determining cladocerans reproduction rates with seston diets.     

Zooplankton community size structure and taxonomic composition affects size-selective grazing in natural communities

The body size of an individual zooplankton is well related to its grazing rate and to the range of particle sizes it can ingest, and since cladocerans and copepods feed differently, they follow different relationships. Based on these general patterns in individual organisms, we tested whether the size structure and taxonomic composition of more complex natural zooplankton communities are related to their in situ grazing rate and to the range of algal sizes they graze. We compared community grazing rates on individual algal taxa in two communities dominated by small cladocerans, three communities dominated by large cladocerans and three copepod-dominated communities. Small algae were usually grazed most intensively, but grazing rates were poorly related to algal size alone. The range in size of grazed algae increased with increasing mean zooplankton body size, but differed systematically with their taxonomic composition. Communities dominated by Ceriodaphnia or Holopedium grazed a narrower size range of algae [maximum greatest axial length dimension (GALD)=16–36 μm)] than communities with large biomasses of Bosmina or Daphnia (maximum GALD=28–78 μm). Copepod-dominated communities followed the same general relationship as cladocerans. Daphnia-dominated communities grazed the broadest range of algal sizes, and their total grazing rates were up to 2.4 times their grazing rates on small (<35 μm) “highly edible” algae, a difference of similar magnitude to those found in successful trophic cascade biomanipulations. Received: 31 March 1998 / Accepted: 19 October 1998     

MICROEVOLUTION AND PHENOTYPIC PLASTICITY IN DONAX SERRA RODING (BIVALVIA: DONACIDAE) ON HIGH ENERGY SANDY BEACHES

Morphological differences between populations of the wedge clamDonax serra inhabiting two different coasts and biogeographicregions of South Africa were investigated. Both adults and juvenilesoccupied different positions along the beach gradient dependingon the coast: on the southeast coast adults occurred in themid intertidal and juveniles and recruits were low intertidalto subtidal; on the west coast the zonation pattern was reversed.Not only adults but also juvenile clams had shapes differingsignificantly between the two coasts; west coast clams werethinner, rounder and had a higher body density than the southeastones-recruits were less dense in the former coast. Differencesin shell shape between coasts are probably the result of directionalselection on the adults with the microevolutionary changes beingmaintained by geographical isolation. Shell density, on theother hand, seems to be environmentally determined through physiologicalcontrol of shell calcification, i.e. more mobile intertidalclams having lower shell density than less mobile subtidal clams.Ontogenetic changes in shape and density are presumably adaptiveand appear to be related to mobility, i.e. the larger, heavierand denser adults being more stable in the substrate, and thesmaller, thinner and less dense juveniles being more mobileand dispersive. Phenotypic plasticity in present D. serra populationsis an important factor that enabled this species to occupy differenthabitats and biogeographic regions and to survive 5 millionyears of environmental changes. ¹ Present address: Laboratory for Ecology and Aquaculture, ZoologicalInstitute, Katholic Universiteit, Leuven, Naamsestraat 59 B-3000,Leuven, Belgium. E-mail: agsoares{at}eudoramail.com (Received 15 October 1997; accepted 5 January 1998)     

Interference from a game theoretical perspective: shore crabs suffer most from equal competitors

In virtually all natural systems, interference competition amongindividuals is asymmetric. Here, we used game theoretical modelson contest behavior to predict how time lost in agonistic interactionscould affect strength of interference under asymmetric competition.We hypothesized that interference through time lost in agonisticinteractions would result in a greater reduction in availableforaging time and overall feeding rate under symmetric competitionthan under asymmetric competition. We tested this hypothesisfor male shore crabs (Carcinus maenas) that foraged on mussels(Mytilus edulis) in an experiment where prey levels were keptconstant. We varied absolute size of crabs (juveniles, smalladults, large adults), mussel density (4, 16, 32 per 0.25 m²),and competitor size (smaller, equal, larger). Large adults spentmore time in aggressive behaviors than juveniles or small adults,possibly because large adults were more persistent in interferingor because large adults were intrinsically more aggressive,as the experiment was conducted in the mating season. When handlingprey, crabs mostly avoided competitors, but juveniles and smalladults did so more than large adults. When searching for prey,crabs mostly displaced smaller competitors but threatened oravoided size-matched or larger competitors. By avoiding a competitor,the focal crab lost time but the competitor often did not, andthis asymmetry in agonistic behavior is not yet incorporatedin models on contest behavior. However, overall, negative effectsof others were strongest with size-matched competitors, in linewith our hypothesis.     

Effect of vertebrate predation on the spatio-temporal distribution of cladocerans in a temperature eutrophic lake

We analysed the spatio-temporal distribution of zooplankton along a profile of 10 stations from the shore to the pelagic zone from April to September 1988, the period when the larvae and juveniles Rutilus rutilus, the most abundant species in the Lake, are in the littoral zone. The digestive tracts of the young roach were analysed. They fed essentially on rotifers and on cladocerans. For comparison, zooplankton was also analysed at one littoral area without fish fry. There was an increase of cladoceran density from the vegetated nearshore zone to the offshore zone. Considering the density of Bosmina longirostris, Daphnia longispina, Chydorus sphaericus and Ceriodaphnia quadrangula, we observed a different distribution pattern in the course of the year. In the nearshore zone, the relative abundance of small species, Bosmina and Chydorus, was much higher than that of the larger Daphnia. From April to September, predation pressure mainly affected the smallest species: in contrast to the inshore station without fish fry, the density of Bosmina decreased in May in the littoral with fish. Chydorus was concentrated in the littoral between February and April, then grew into the pelagic zone, where predation pressure obviously was low during the warm season. The number of Daphnia, which was eaten by the fish fry at any time, remained low in the nearshore zone, which suggests that the presence of fish may cause Daphnia to avoid this zone. Ceriodaphnia which was not affected by this predation, was scarce in the nearshore zone during mid-summer. The low density of the cladocerans in the nearshore zone is likely associated with vertebrate predation by roach fry and juveniles, the result of such a process being either a depletion in density of the prey, or an avoidance behaviour.     

Interactions between year classes in the benthic amphipod Monoporeia affinis: effects on juvenile survival and growth

Summary The effect of 1-year-old Monoporeia (=Pontoporeia) affinis on the survival and growth of young of the year was studied in laboratory experiments. Amphipods were kept in jars with sediment and a continuous supply of cooled water for 3 months. Adults or juveniles were added to a control density of juveniles. Juvenile mortality increased at higher total densities, and was greater when adults were present. The mean length and dry weight of juveniles decreased at higher densities, but adults did not have a greater effect than juveniles. These density-dependent effects are probably caused by competition for food within and between year classes. Thus, a high abundance of juveniles or adults could reduce the recruitment of juveniles into the adult year-class the following year, and the suppression of juvenile growth could lower fecundity. The results of this experiment support the hypothesis, inferred from field data from the Baltic Sea and Swedish lakes, that intraspecific interactions contribute to fluctuations in the abundance of populations of M. affinis.     

Reproductive effort in viscous populations

Abstract.— Here I study a kin selection model of reproductive effort, the allocation of resources to fecundity versus survival, in a patch-structured population. Breeding females remain in the same patch for life. Offspring have costly, partial long-distance dispersal and compete for breeding sites, which become vacant upon the death of previous occupants. The main result is that the evolutionarily stable reproductive effort decreases as offspring dispersal rate increases. The result can be understood as follows: In a well-mixed population with global competition, neither adults nor juveniles compete with relatives, but in a patch-structured population with dispersal restricted to the juvenile phase, juveniles experience relatively less competition with relatives than adults, thus making juveniles relatively more valuable. Because this asymmetry between adults and juveniles decreases with the dispersal rate, so does the evolutionarily stable level of allocation to fecundity.     

OTHER PAPERS: INTERFERENCE AND RESOURCE COMPETITION IN TWO LAND SNAILS: ADULTS INHIBIT CONSPECIFIC JUVENILE GROWTH IN FIELD AND LABORATORY

Interference and resource competition by adults inhibited growthrates of conspecific juveniles of the land snail species Mesodonthyroidus and Neohelix albolabris in separate field and laboratoryexperiments, but not in laboratory experiments on Anguispiraalternata. In 1 m² field cages at near-natural densities underambient food and water conditions, juvenile M. thyroidus apparentlycompeted with adults for food or water or both resources, growingmore slowly when living with two conspecific adults, but beingunaffected by adult presence when food and water were augmented.Neohelix albolabris juveniles were similarly unaffected in fieldcages by presence of two adults when food and water were augmented.In contrast, interference, not resource competition, apparentlyexplained growth inhibition in laboratory cages at densitiesconsiderably greater than natural densities, with non-limitingfood and moisture; both M. thyroidus and N. albolabris juvenilesgrew more slowly as conspecific adult number increased fromzero to three. (Received 17 July 1995; accepted 11 November 1996)     

A laboratory study of the effect of non-phytoplankton diets on the reproduction of Calanus helgolandicus

The effect of five non-phytoplankton and one phytoplankton dietson reproduction is described for the copepod Calanus helgolandicusand compared to field fecundity estimates. A fecundity increasefollowed ingestion of larvae of the sea urchin Sphaerechinusgranularis (LSU) and the oyster Crassostrea gigas (OYS) by copepodfemales, whereas a decrease followed ingestion of eggs of thecopepods Acartia and Temora spp. (COP), as a function of proteinconcentration in diets. With larvae of the sea urchin Paracentrotuslividus (SSU) and the dinoflagellate Prorocentrum minimum (PM;standard phytoplankton diet), fecundity was identical. Althoughprotein concentrations differed greatly from one food treatmentto the other, mean fecundity values were rather low. For unknownreasons, and despite their very high protein concentrationsin comparison to in situ, none of these diets could improvefemale fecundity or reach maximum egg production rates reportedin C.helgolandicus. Hatching rates were >80%, stable andsimilar with both PM and COP diets. With SSU, LSU and OYS diets,egg viability was lower than in situ and with PM, showing astrong and mild decrease with time with LSU and SSU, respectively.Ingestion of zygotes of the brown alga Fucus spiralis (ZYG)led to the death of females. These results suggest that denseblooms of zygotes of macroalgae and invertebrate embryos andlarvae, occurring in the continental shelf as part of copepoddiets, could have different effects on the demographic responseof C.helgolandicus.     

Seasonality,Population Dynamics and Production of Daphnia longispina in the Subtropical Lake Bhimtal (U.P.), India

Seasonal variation in population density, birth rate, mortality and production of a daphnid was studied in a high, altitude sub-tropical lake. A bimodal growth curve with maxima during summer and autumn was observed. A positive correlation was reported between fecundity and death rate, probably due to a difference in age specific death rate combined with a high relative frequency of juveniles in a growing population. The production of Daphnia longispina correlates better with temperature than with food. The P/B ratio was higher during summer and autumn months.     

Production of Penilia avirostris in Kingston Harbour, Jamaica

The cladoceran Penilia avirostris is one of the more abundantand widespread members of the crustacean zooplankton in nearshoretropical and subtropical waters. Its abundance, biomass, fecundity,development rate and production were estimated in Kingston Harbour,Jamaica, during an 18 month period. Mean annual abundance ofPenilia was 1821 m^–3, while biomass (excluding eggs/embryos)was 2.87 mg ash-free dry-weight (AFDW) m^–3 (43.1 mg AFDWm^–2), accounting for 13% of the copepod community biomass.Fecundity increased with body size. There was no clear seasonalpattern of abundance, size or fecundity, nor were physical orbiological variables correlated to these variations. Developmenttime averaged 20.5 h for juveniles and 41.4 h for adult femalesduring incubations; there was no clear evidence of a diel patternto molting. Growth rate appeared to be exponential, with correspondingsomatic growth rates, averaging 0.27 day^–1 for juveniles,and 0.34 day^–1 for somatic plus reproductive growth inadult females. Annual production was estimated as 173 kJ m^–2year^–1,