Population dynamics of phototrophic bacteria in three basins of Lake Banyoles (Spain)

The annual dynamics of the phototrophic bacterial populations developing in the anoxic layers has been monitored in three basins of the northern area of Lake Banyoles (Spain). Although two of the studied basins are meromictic and one is holomictic, chemical properties of the water are almost identical. Therefore, differences in both the spatial and temporal distribution, as well as in the composition of phototrophic bacterial communities, dominated by Chlorobium phaeobacteroides and Chromatium minus, are discussed on the basis of the structural and morphometric characteristics of each basin. Both species showed the same physiological adaptations to light intensity changes by modifying the carotenoid/bacteriochlorophyll ratio. Light reaching the oxic-anoxic boundary appears to be the most important factor controlling the growth of phototrophic bacteria in Lake Banyoles. The oxic-anoxic boundary becomes shallower as summer advances, until enough light is available for bacterial photosynthesis.     

Population dynamics of Limnothrix redekei,Oscillatoria lanceaeformis,Planktothrix agardhii and Pseudanabaena limnetica (cyanobacteria) in a shallow hypertrophic lake (Spain)

Populations of Limnothrix redekei, Oscillatoria lanceaeformis, Planktothrix agardhii and Pseudanabaena limnetica were found in a hypertrophic, gravel-pit lake near Madrid (Spain), throughout a one year sampling at weekly intervals. Physico-chemical factors, phytoplankton biomass and net growth rates were measured. Oscillatoria lanceaeformis was only observed a few weeks, probably being related to phosphorus limitation. Planktothrix agardhii biomass was related to PhAR irradiances, light attenuation coefficient in the water, Brunt-Väisäla frequency and decrease of soluble reactive phosphorus. Limnothrix redekei and Pseudanabaena limnetica biomass values were related to a decrease of inorganic nitrogen and temperature. A different lag response of populations was observed in relation to the environmental features.     

The physical, chemical and biological characteristics of the holomictic sulphated Lake Arcas-2 (Cuenca, Spain)

The main limnological features of Lake Arcas-2 were followed through two consecutive stratification periods. Its morphometrical characteristics, such as the high relative depth (31%) and steep basin walls, enhance the sharp water stratification with the formation of an oxic-anoxic boundary at 8.8–9 m and a sulphide-rich hypolimnion during the thermal stagnation. The ionic sequence was SO ₄ ^2- >Alkal.>Cl^- and Ca²⁺>Mg²⁺>Na⁺>K⁺ and the mineralization was high, with water conductivity higher than 2500 S cm^-1. It is mesotrophic with epilimnetic chlorophyll a concentrations of 2–5 g l^-1 and metalimnetic of 8 g l^-1. The depth of the euphotic zone was established at around 8 m. Phosphorus concentration in the oxic waters was low but largely accumulated in the anoxic hypolimnion, together with other compounds such as ammonium, silicate, sulphide, etc. Nitrate was abundant in the oxic waters and is related to the use of fertilizers in the surrounding fields. A fine-layer sampler was used to study the oxic–anoxic interface where a dense plate of Chromatiaceae developed. The dominant species, Chromatium weissei, reached a maximum integrated biomass of 121 gWW m^-2 during August. Thiocapsa sp., representing less than 1% of total purple bacteria, had an integrated biomass of 0.8 gWW m^-2 and Amoebobacter sp. (1%) had 1 gWW m^-2. Other populations were sharply stratified i.e. Oscillatoria cf. ornata and Cryptomonas erosa. Those organisms, and mainly the cyanobacterium, accounted for the high chlorophyll a concentrations (>100 g l^-1) recorded in the anoxic waters of the hypolimnion. Green bacteria were scarcely developed due to the shadowing effect caused mainly by the purple bacterial bloom.     

Population dynamics of two small cichlid fish species in a tropical man-made lake (Lake Kariba)

The population dynamics of two small cichlid fishes (Pharyngochromis darlingi andPseudocrenilabrus philander) were studied in Lake Kariba, a very large African man-made lake. They are of no economic importance but make up about 14% and 7% respectively of the inshore fish population and are the major components of the diet of fish-eating birds on the lake.P. darlingi isthe larger species (L = 156.5 mm) and is found on both shelving and steep, eroding shores. Its mortality rate differs in each habitat (Z = 0.44 and 0.72 month^–1 respectively), only 0.79% survive for 12 months and its % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiuaiaac+% cadaqdaaqaaiaadkeaaaaaaa!384D!\[P/\overline B \] ratio is 5.45 (on shelving shores).Ps. philander is smaller (L = 83.9 mm) and is restricted to shelving areas with abundant vegetation. Its monthly mortality rate was high (Z = 7.69), only 0.05% survive to 12 months whilst its % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiuaiaac+% cadaqdaaqaaiaadkeaaaaaaa!384D!\[P/\overline B \] ratio was very high (7.69). The estimates of growth obtained forP. darlingi differ considerably from those given in an earlier study in Lake Kariba and some possible reasons for this are discussed. In suitable habitats, the combined production of both species could be 40 kg ha^–1 yr^–1 which indicates their potential importance to the ecology of the lake.     

Population dynamics of Bosmina longirostris (Crustacea: Cladocera) in Lake Kariba,Zimbabwe

The population dynamics of Bosmina longirostris in a large tropical reservoir, Lake Kariba, Zimbabwe, are described. Population density showed two peaks associated with periods of high nutrient fluxes. Fecundity was always low. Two eggs per female was the maximum ever recorded. Instantaneous rates of birth, death and population growth calculated from field data using the egg ratio method are discussed. The rate of biomass change fluctuated in a regular pattern, probably linked to food availability or predation by a clupeid, Limnothrissa miodon.     

Population dynamics of Panonychus osmanthi (Acari: Tetranychidae) on two Osmanthus species

Panonychus osmanthi is a non-diapausing species of spider mite that superficially resembles P. citri. It infests Osmanthus species, which are evergreen roadside and garden trees. The population dynamics of P. osmanthi were studied on Osmanthus aurantiacus and O.×fortunei during a three-year period. Seasonal changes in P. osmanthi populations were fundamentally the same in each year, although their density differed greatly from year to year. TheP. osmanthi population was bimodal, with one peak in spring (May–June) and another in winter (November–January). Populations abruptly declined after the spring peak. Predators showed a delayed density-dependent response to changes in spider mites from spring to summer, whereas in autumn and winter, predators were few because they had entered diapause. To determine the effect of predators on the rapid decline of spider mites just after the spring peak, the predators were removed by treating the trees with a synthetic pyrethroid. As a result, spider mite density did not decline after the spring peak and remained at a high level during the June-August period when spider mite density is usually very low. This suggests that predators play an important role in the drastic decline of P. osmanthi density just after the spring peak. This revised version was published online in July 2006 with corrections to the Cover Date.     

Population dynamics of Stylaria lacustris (Linnaeus, 1767) (Oligochaeta,Naididae) in Los Talas,Argentina

Population dynamics of Stylaria lacustris were analyzed over 2 years in a pond located at Los Talas, Argentina. In both years, the peak in abundance, due to intense asexual reproduction, fell at the end of winter, and was followed by mature individuals. The species was not collected during summer. Temperature was the main factor regulating the population through both sexual and asexual reproduction. In the second year, density was lower and correlated with a lower water level and a reduced vegetation development. Individuals were randomly distributed in periods of high abundance and contagious when density was low. Generation time was 15 days.     

Burrowing beetles of the genus Bledius (Staphylinidae) as agents of bioturbation in the emergent areas and shores of an athalassic inland lake (Fuente de Piedra,southern of Spain)

Bledius (Elbidus) bicornis (Germ.) and B. (Eucerotobledius) furcatus (Oliv.) (Coleoptera: Staphylinidae) are the most important burrowing species in the emergent areas and shores in the athalassic lake of Fuente de Piedra (Málaga, S. of Spain). A first estimate of the importance of these organisms in this system is presented. These insects kick out sediment during their burrowing activity, which accumulates on the surface near the burrows as tumuli which can be easily eroded. The lake perimeter (17 km) is densely colonized (usual densities from 1700 to 2500 ind m⁻²). The amount of granulated material that can be potentially kicked out was 46.22 g dry wt m⁻² day⁻¹. At the same time, the material that constitutes the tumuli shows different characteristics from the compact ground below the surface. Thus, it is relatively enriched with organic matter (6.15 g per square meter), soluble phosphate (406.5 μg m⁻²) and ammonium (4856 μg m⁻²), whereas it lacks nitrate. Results of a transect from uninhabited areas to zones of maximum population density also show a similarity between the higher ground level of ammonium and phosphate concentrations and population density.     

Population dynamics of alien gammarid species in the River Odra estuary

During the period of 1988–2000, three alien gammarid species, i.e. Gammarus tigrinus Sexton, 1939, Pontogammarus robustoides G. O. Sars, 1894, and Dikerogammarus haemobaphes (Eichwald, 1841) were recorded in the Odra estuary. This study, the first record of G. tigrinus and P. robustoides in Poland, focuses on the distribution, abundance, and biomass as well as on population structure of the three new species found in the coastal zone of the estuary. G. tigrinus and P. robustoides were first sampled in the Szczecin Lagoon (mid-part of the estuary) in 1988. The densities of both species were high from the time they were first recorded and exceeded 10 000 ind. m^–2, while the biomass was 25 and 140 g m^–2, respectively. G.tigrinus occurred at higher densities in northern and eastern parts of the Lagoon, while P. robustoides was particularly abundant in the south-eastern part, most heavily affected by River Odra discharge. In 1999, the third gammarid, D. haemobaphes, was recorded in the southern part of the estuary. Both in 1999 and 2000, the species was found in qualitative samples (dredge collections of Dreissena polymorpha) taken from the western branch of the river. As estimated from quantitative samples, densities and biomass in the eastern branch were rather low and did not exceed 150 ind. m^–2 and 2.7 g m^–2, respectively. The Szczecin Lagoon population of G. tigrinus produces at least two generations within a year: a summer one and an overwintering one. The latter is dominated by older and larger specimens. The species may reproduce in the Lagoon from April until November.     

Population dynamics of Barbus barbus plebejus (Valenciennes) and Leuciscus cephalus cabeda (Risso) in the middle River Po (Italy)

Scales from 427 Barbus barbus plebejus and 406 Leuciscus cephalus cabeda from the middle River Po were examined. The last annulus was formed between April and May 1977, except the 0–1 age-group of L.c. cabeda which developed its first year-ring between March and April 1977. The survival (S) and annual mortality (A) rates were equivalent in both fish populations; the same was true of both sexes of Leuciscus, but S in Barbus males was lower than in females. The sex ratio showed a preponderance of females in both species.Growth rate from June to September 1976 was higher than in the rest of the year. Annual growth in Barbus females was higher than in males, whereas both sexes in Leuciscus showed equivalent growth rates; growth rate was higher in Barbus than in Leuciscus. The P/B ratio of both species was higher in the young age-groups.Presented at the XLVII Congress of the Italian Zoological Union, Bergamo (Italy), September 1979.Presented at the XLVII Congress of the Italian Zoological Union, Bergamo (Italy), September 1979.     

Population dynamics of daphnia pulex and utilization by the rainbow trout (salmo gairdneri)

The effect of rainbow trout (Salmo gairdneri) predation on the population dynamics of the water flea,Daphnia pulex, was examined during 1976 and 1977 in Becker Lake, a small, shallow, productive reservoir in northeastern Arizona.Rainbow trout were size-biased feeders, utilizing daphnids which were 1.3 mm in size or larger. Trout predation uponDaphnia pulex occurred mainly during winter and early spring when their numbers were relatively low but their clutch size high, suggesting that trout selectedDaphnia on the basis of brood pigmentation. By far the greatest proportion ofDaphnia mortality was due to nonpredatory sources, since generally less than 6% could be attributed to trout predation.TheD. pulex population exhibited a bimodal seasonal abundance curve which was attributed to ephippial egg production and trout predation during the winter and poor food quality/quantity during the summer.This work was supported in part by the Arizona Department of Game and Fish. The authors wish to thank Jim Novy and Joe Stone of that department for their invaluable assistance in the field collecting segment of this study.     

Population dynamics of Microtus arvalis in a weed strip

A population of Microtus arvalis Pallas, 1779, living in a weed strip was studied by capture–recapture method over a 2-year period. Weed strips are characterized by their linear shape and high vegetation cover, and are not comparable to the habitats examined in most previous studies on M. arvalis.Abundance of voles was found to be high in the strip with a maximum of 410 voles/ha known to be alive in the first year and 641 voles/ha in the successive year. Abundance was minimal in spring and increased until July. A decrease in population size at the beginning of August was followed by a new increase in both years. One difference between the 2 years was a pronounced peak abundance at the end of June in the second year. The peak may be related to a shift in sex ratio in favour of females in this year (ratio of males:females of 1:8). Also the time of residency of females was significantly longer in the second year than in the year before, and the survival rate of females was greater than in males.The turnover was generally very high and reached maximum values of 80% renewal of population every 2 weeks.     

Population dynamics and population structure ofFerrissia wautieri (Mirolli, 1960) (Gastropoda,Ancylidae) in a pond near Nijmegen (The Netherlands)

Ferrissia wautieri, a freshwater limpet, is a widely distributed species in The Netherlands. In a pond near Nijmegen samples were taken twice a month over the year to study the population size and structure of this species in relation to the water temperature. Only ancyloids were found. Production of juveniles is temperature-dependent; peak numbers occurred in July and August. Just-hatched juveniles (shell length 0.6–1.0 mm) occurred over a lengthy period in the year, but were absent in March and April. During these months the collected numbers of specimens were very low. The largest specimens were collected during March, April and May.     

Reproduction, population dynamics, growth and production ofScrobicularia plana da costa (pelecypoda) in the Bidasoa estuary, Spain

The breeding cycle, recruitment, population dynamics, growth and production ofScrobicularia plana were studied at one station in the Bidasoa estuary (SE of the Biscay Bay, Spain) during a period of 3 or 4 years. To complete this study, the reproduction for a period of 1 year was analysed at two other sites of the estuary. At none of the stations important differences in spawning activity were observed between the different years. The animals reproduced for the first time when they reached the age of two years. The histological data and the recruitment analysis showed only one spawning period between June and mid-September, with a peak in July-August. This breeding pattern differs from those shown by other southern European populations. The recruitment of spat (0.25–0.50 mm) occurred from June–July to October–December in different years. The population showed different annual patterns of density and population structure, depending on recruitment success. Growth was most rapid in spring and summer. The bivalves reached a mean length of 21.8 mm at the age of approximately 16 months; in the following year they grew to 30 mm. The growth during the life span fitted the theoretical growth equation of Von Bertalanffy. Annual production was in the range of 59.0–83.4 g AFDW m^–2 year^–1. The P/B ratios of the population varied between 0.84 and 1.48 (1.06 ± 1.36; ¯x ± 95% C.I.).     

Vertical distributions of zooplankton and population dynamics of Daphnia in a meromictic lake

Vertical distributions of zooplankton were studied in relation to profiles of temperature, oxygen and chlorophyll a in Roi Lake, a small meromictic lake in central Alberta. Zooplankton were distributed fairly evenly through the oxygenated part of the water column in early summer, but a gradual descent of several species became evident in June. The vertical distribution of chlorophyll was dominated by a huge peak at the 8- to 9-m-deep chemocline. the location of a plate of photosynthetic sulfur bacteria. Ambient concentration of chlorophyll was a poor predictor of the numbers of zooplankton and the fecundity of Daphnia pulicaria at different depths, and per capita birth rates of Daphnia were usually highest in the surface waters. The reproductively disadvantageous restriction of daphnids to deep water by late summer and their catastrophic decline in the face of high ambient concentrations of chlorophyll suggest that factors other than temperature and food supply are important in influencing the dynamics and distribution of zooplankton in this lake.     

Population growth dynamics of the rotifer Brachionus plicatilis cultured in non-limiting food condition

Population growth parameters in batch culture of Brachionus plicatilis under a continuous supply of freeze-dried microalgae powder have been determined. Two B. plicatilis strains (L- and S-types) and four microalgae species (Nannochloropsis oculata, Nannochloropsis gaditana, Nannochloris oculata and Tetraselmis suecica) have been tested, establishing the dynamics of growth at different daily food rations. Cultures showed a short lag phase, an exponential growth phase, a long post-exponential growth phase and long decline with episodic increases. In both rotifer strains, the best growth was obtained with Nannochloropsis oculata and the poorest with Nannochloris oculata.     

Comparative study of two meromictic basins of Lake Banyoles (Spain) with sulphur phototrophic bacteria

The annual limnological dynamics of two meromictic basins of Lake Banyoles (C-III and C-IV) have been studied and compared on the basis of their physical, chemical and biological characters. Stability values calculated for both basins gave 865 g cm cm⁻² and 495 g cm cm⁻² for C-III and C-IV respectively. These values are in agreement with the fact that C-IV was almost completely mixed during winter. In this basin, during stratification, the monimolimnion increased in thickness as the stability increased. Isolation of the respective monimolimnia resulted in the development of anoxic conditions and the accumulation of sulphide in both C-III and C-IV, which favoured the development of dense populations of sulfur phototrophic bacteria. The purple sulphur bacterium Chromatium minus and the green sulphur bacterium Chlorobium phaeobacteroides were identified as the main components of these photosynthetic populations. The different depths at which the O₂/H₂S boundary was situated in both basins (and consequently the different light intensity reaching this zone) determined the growth of these bacteria. Light intensities at the chemocline of C-IV reached values up to 5% of surface incident light. In contrast, in C-III this variable was sensibly lower, with values depending on season and seldom reaching 1%. Phototrophic bacteria were consequently found earlier in C-IV than in C-III, where no significant concentrations were found until August. Finally stability is discussed as an important factor controlling chemical and biological dynamics in meromictic lakes.     

Reproductive isolation of two sympatric subspecies ofJuniperus phoenicea (Cupressaceae) in southern Spain

The phenology, reproductive cycle and cone crop of two sympatric subspecies ofJuniperus phoenicea (Cupressaceae) were studied during three consecutive years in southern Spain. The flowering pattern of each subspecies was constant during this period: inJ. phoenicea subsp.turbinata flowering was always in October–November, whileJ. phoenicea subsp.phoenicea flowered in February–March. There was no overlap between the flowering periods of the two taxa. The reproductive cycle of the two subspecies was similar, though there were some important differences because of their flowering times. Male cone development in both subspecies occurred in autumn, but the male cones ofJ. phoenicea subsp.phoenicea did not shed pollen until the end of February. InJ. phoenicea subsp.turbinata, the gap between pollination and fertilisation was seven months while inJ. phoenicea subsp.phoenicea it was only three months, fertilisation taking place at the same time in the two taxa. Post-fertilisation events were similar in the two subspecies, leading to a cycle of two years inJ. phoenicea subsp.turbinata and a shorter one of about 20 months inJ. phoenicea subsp.phoenicea. Alternating good and slight seed cone crops were found in both taxa during the three years studied, the good crops of one subspecies coinciding with the slight crops of the other one. Although the proximity of the two subspecies and method of pollination could make hybridisation between the taxa possible, the different flowering seasons prevent hybridisation isolating them reproductively.