Life cycle and population dynamics of Trochosa terricola Thorell (Araneae: Lycosidae) in a Norfolk grass heath

Abstract. 1. The population of the lycosid Trochosa terricola Thorell was sampled from April 1973 to August 1975 at Weeting Heath NNR, a Breckland grass heath.
2. Four sampling methods were compared for efficiency. Hand searching gave density estimates between 38.3 and 70.1% of heat extraction.
3. The temperature range in the sward at +1 cm was –5°C to 39°C with January and July means of 3.2°C and 17.4°C.
4. Eight male and nine female instars were determined and the life cycle extended over 2 or 3 years.
5. Adults were nocturnal but the juveniles diurnal. An annual diplochrone activity pattern was observed for adult males.
6. The horizontal distribution within the sward was aggregated, the structure and microhabitat being important determining factors. The population density was greater in moist, young Festuca spp. tussocks. An equation relating population density to habitat characteristics was derived.
7. The overall population density ranged from 14.0 m^-2 to 76.0 m^-2 and was maximal in autumn after breeding. The population biomass was greatest during autumn (291.2 mg d.wt m^-2).
8. Mean number of juveniles emerging from an egg sac was 77.3 (first sac) and 38.0 (second sac). The natality in 1973 was 66.8 individuals m^-2.
9. The survivorship curve until maturity varied between types I and III in different years.
10. The population dynamics were compared and are discussed in the light of other data. The variable population characteristics suggested that Den Boer's "spreading of risk" theory applied to the T.terricola population.     

Population dynamics and production of Sialis lutaria L. (Megaloptera) in the Danish River Suså

SUMMARY. 1. Populations of Stalls lutaria L. were sampled quantitatively at about monthly intervals during 3 years at two localities in the macrophyte rich River Suså, Denmark.
2. The life cycle was univoltine. The larvae hatched in June-July, and the initial S. lutaria population densities varied between 10 and 370 ind. m⁻². These differences were probably due to extreme variations in stream discharge during the period of recruitment, high velocities preventing the small swimming larvae from reaching the sediment.
3. The S. lutaria rate of elimination varied between 0.11 and 1.47% d⁻¹at the two localities. The high rate of elimination was possibly due to fish predation.
4. The growth rates varied between 0.54 and 15% d⁻¹. Growth rates differed between localities and years.
5. Numbers of potential prey organisms were not higher in sample units with S. lutaria than in sample units without S. lutaria . Numbers of leeches, which were potential competitors, did not differ significantly in sample units with and without S. lutaria .
6. Production of S. lutaria varied between 0.16 and 2.49 g ash free dry weight m⁻² y⁻¹, and the P/ ratios varied between 3.0 and 7.3 y⁻¹. The P/ ratios increased significantly with increasing rate of elimination.     

Energetics of a population of Asellus aquaticus (Crustacea, Isopoda): respiration and energy budgets

SUMMARY. Respiration of Asellus aquaticus was determined on tiine occasions throughout the year using a Gilson differential respirometer. On each occasion the determination was made at the lake temperature, which ranged from 2 to 18°C, Linear regressions were derived for log oxygen uptake against log dry weight. There was a significant difference between mean rates of oxygen uptake at the various temperatures but the slopes of the regression lines, which varied from 0,62 to O.85 with a mean of 0,76, were not significantly different.
The temperature of the lake was monitored throughout the year. Using the relationship of oxygen uptake against temperature, and estimates of population density obtained previously, the total annual respiration of the population was calculated as 4571 ml O₂ m^-2, equivalent to an energy loss of 92.3 kj m^-2 year^-1 from a mean biomassof 752 mg m^-2.
Consumption of decayed Alnus glutinosa leaves and faecal production rates, and thus assimilation efficiency, were determined by gravimetric methods in the laboratory at 10°C, close to the mean temperature of the lake (10.rC), In the four size classes investigated, larger animals consumed more food per individual, but less on a weight specific basis. However, it was shown that consumption was greater if the leaf material was more highly decomposed, Assimiliation efficiency was calculated as 23%.
Using data for respiration, population density and the assimilation efficiency, the annual population energy budget was estimated as (kJ m^-2year^-1): consumption, 568.9 (100%); production, 38.5 (6.8%); respiration, 92.3 (16.2%); faeces, 438.1 (77%). The significance of these energy values, and the ecological efficiencies calculated from them, are discussed in relation to other published work.     

Ecology of an Indian grassland millipede Streptogonopus phipsoni (Diplopoda: Polydesmoidea)

Each of stadia II-VII and adults (stadia VIII) of Streptogonopus phipsoni (Pocock) can be distinguished by segment numbers, length, breadth and paired legs. Sexes are separate from stadium IV and sex ratios in immature stages were more or less 50% throughout the year, but high proportions of adult females are noted from June to September. High ratios of immature to adult were related to the breeding periods, from May to October, and in other months adults increased in proportion as a result of heavy mortality of immatures.
Adults were aggregated in distribution from April to October while solitary individuals were common in other months of the year.
Population density of S. phipsoni varied from 0.25 to 98 m^-2 on the soil surface and 1 to 11.75 m^-2 in the lower layer (0–7 cm deep). Biomass ranged from 12.25 to 2253 mg^-2 on the surface and 50.75 to 424.75 mg^-2 in the lower layer (0–7 cm deep).
A positive and significant correlation was found between mean monthly population density and mean monthly rainfall.
Streptogonopus phipsoni appears to complete its life cycle in one or two years     

Peat respiration and decomposition in Antarctic terrestrial moss communities

Oxygen uptake by the peat of two Antarctic bryophyte communities (a moss turf and a moss carpet) is converted to organic matter loss and used to derive the rate of decomposition. The decay rates obtained in this way are evaluated in two mathematical models which simulate the accumulation of dead organic matter (DOM) in the communities from the litter production and decomposition rate. Litter production, the extent of DOM accumulations at present on the sites and mean decomposition rates (i.e. fraction of standing crop lost per year) were 409 g m^-2 year^-1, 33.5 kg m^-2 and 0.017 g g^-1 year^-1 in the moss turf and 392 g m^-2 year^-1, 29.6 kg m-² and 0.010 g g^-1 year^-1 in the moss carpet respectively (all weights expressed as dry weight). Aerobic decomposition rate declined with depth in both communities. From the model's predictions it is suggested that the observed decay rate was too high in the moss turf and too low in the carpet. Possible reasons for this are discussed and suggestions made for future work.     

A carbon budget for nematodes, rotifers and tardigrades in a Swedish coniferous forest soil

Nematodes, rotifers and tardigrades from a Swedish pine forest soil were investigated in a monthly sampling programme lasting for one year. The monthly mean values of number, biomass and oxygen consumption were estimated. All groups fluctuated rather much over the year with a summer minimum (1.1 ˙ 10⁶ animals m^-2) and a winter maximum (6.3 ˙ 10⁶ animals m^-2) for the nematodes. The reasons for these fluctuations are discussed in relation to fluctuations of water content and temperature of the soil. On an annual basis a carbon budget was calculated which gave the following values for this fauna; consumption 4.3, production 0.6, respiration 0.9 and defecation 2.8 g carbon m^-2.     

Growth and production of five species of Ephemeroptera larvae from an experimental recirculating stream

SUMMARY. The production and growth of the larvae of five species of Ephemeroptera in an experimental recirculating stream-channel are described. The most abundant species were Baetis rhodani , which achieved a maximum population density of c. 29,000 m^-2 in August, and Ephemerella ignita which reached a density of c. 13,000 m^-2 in the spring. Three other common speeies, Paraleptophlebia submarginata, Centroptilum luteolum and Caenis rivulorum were present at lower densities (< 1000 m^-2). B. rhodani had five cohorts in a year whilst C. luteolum had two or possibly three. E. ignita, C. rivulorum and P. submarginata were univoltine. Mean speeifie growth rates were calculated for each species, the maximum being 3.26±0.49% length day^-1 for E. ignita (3 April—15 May). Production of each of these five species of Ephemeroptera was calculated giving a total annual production of 10.2 g dry wt m^-2 (computational method).     

Studies on feeding, growth and production of a recruited inshore population of Pleuronectes platessa (L.) at East Anglesey, North Wales

Trawl surveys in an area of 237 km² to the east of Anglesey (Irish Sea) indicated a population of recruited plaice ( c . 480000 fish) between 2 and 15 years old. Seasonal growth began in early April and annual growth in the dominant cohorts was analysed for males and females separately. Net annual production was estimated to be 0.17 g m^-2 from a standing crop of 0.3 g m^-2; c . 50% of the production is removed by fishing. The annual consumption (2.5 g m^-2) of Abra and Pectinaria was converted with 6.8% efficiency by weight (8.0% in energy units).     

Leaf Gas Exchange Characteristics in Relation to Leaf Canopy Position of Myrica faya in its Native Environment (Tenerife, Canary Islands)

Abstract: Diurnal courses of gas exchange were measured throughout one year in fully expanded current-year leaves in the uppermost canopy (sun leaves, 18 m above ground) and in the lower canopy (shade leaves, 12 m above ground) of Myrica faya Ait., a dominant component of the Canarian laurel forest in Tenerife, Canary Islands, Spain.
M. faya showed large differences between sun and shade leaves in gas exchange characteristics (about 50 % of maximum carbon assimilation rate (A_max) reduction in shade leaves, but this reduction can be higher on specific days) that were modulated by strong light attenuation and high leaf area index (LAI) of the stand. This species presented low A_max, about 10 μmol m^-2 s^-1, high maximum transpiration (E, 8 mmol m^-2 s^-1) and stomatal conductance (g_s, 750 mmol m^-2 s^-1) and very low instantaneous water use efficiency (WUE, mean maximum 1.1 mmol mol^-1) and A/g_s (mean maximum 23.5 μmol mol^-1). M. faya responded to high air vapour pressure deficit (VPD), decreasing its g_s but maintaining relatively high values of A and E during the studied period. Stomatal response to VPD showed a higher sensitivity than its congeners, M. cerifera, and Laurus azorica, tree species co-occurring in the Canarian laurel forest. In general, all these gas exchange characteristics lead us to consider this species more similar to subtropical plants of humid regions than to species of the Mediterranean region.     

Litter decomposition by slugs in mixed deciduous woodland

For the one year period considered, it is calculated that 683.5 g m^-2 plant litter entered the study area site. Of the six slugs studied, Arion intermedius Normand, the smallest species, had the highest overall consumption rate on the nine test foods (29.1 ± 0.9 mg dry wt g live wt^-1 d^-1) and the highest overall mean assimilation efficiency (72.0 + 0.9%). The mean faecal production for each of the six slug species was very similar, ranging from 8.4 to 9.9 mg dry wt g live wt^-1 d^-1. Using regression equations of food consumed on faeces produced, it is estimated that the slug fauna each year consumes 8.4% of the leaf litter input and 6.5% of the total available plant litter. Of the plant material consumed, 13.8 g dry wt m^-2 are deposited annually as faeces. The role of slugs in decomposition processes is discussed and compared with that of other soil organisms.     

Production of a stream shredder, Peltoperla maria (Plecoptera: Peltoperlidae) in disturbed and undisturbed hardwood catchments

SUMMARY. (1) The average benthic density of Peltoperla maria in an undisturbed southern Appalachian stream was more than twice that of a nearby stream draining a previously clear-cul catchment in its tenth year of natural secondary succession.
(2) Peltoperla production estimates, using three methods, do not show a significant difference in production between streams draining the two catchments. We attribute these results to quicker growth and slightly higher densities of larger nymphs in the disturbed stream. Production estimates for the disturbed stream ranged from 498 to 560 mg (ash free dry weight) m⁻²y⁻¹ while those for the undisturbed stream were 41–4–515 mg m⁻² y⁻¹.
(3) Our results reinforce the view that conclusions based solely upon numerical densities may lead to erroneus interpretations about the roles organisms play in ecosystems.
(4) Annual frass production by this shredder is about 20 times (10 g m⁻² y⁻¹) the secondary production of P. maria.     

Effects of light and temperature on the cell size and some biochemical components in two freshwater cryptophytes

The effects of light and temperature on cell size and cellular composition (chlorophyll, protein, carbohydrate) of two freshwater cryptophytes were studied with batch cultures. Neither of the species had a constant cell size but the size varied with growth conditions. At each temperature the smallest cells were recorded at the lowest experimental photon flux density. The smallest cells of Cryptomonas 979/67 had an average volume of 232 μm³ and the largest ones 1 020 μm³. In Cryptomonas 979/62 the smallest and largest cells measured 4 306 μm³ and 12 450 μm³. Both species increased their cellular chlorophyll content when PFB dropped below 110–120 μmol m^-2 s^-1. The highest and lowest chlorophyll contents of 979/67 were 7.45 fg μm^-3 and 0.55 fg μm^-2 respectively. For 979/62 the corresponding values were 10.23 fg μm^-3 and 0.93 fg μm^-3. In both species the protein content remained stable at PFDs higher than 110–120 μmol m^-2 S^-1. The highest content of protein measured in 979/67 was 638 fg μm^-3 and the lowest 147 fg μm^-3. For 979/62 these values were 1 036 fg μm^-3 and 148 fg μm^-3 respectively. The carbohydrate results were less clear and no pattern either in response to photon flux density or temperature was obvious. The lowest and highest contents recorded for 979/67 were 62 fg μm^-3 and 409 fg μ^-3 and for 979162, 36 fg μm^-3 and 329 fg μm^-3     

Life history and production of Paranephrops zealandicus in a forest stream, with comments about the sustainable harvest of a freshwater crayfish

1. Life history and production were assessed for the crayfish Paranephrops zealandicus in three reaches of a headwater stream with a catchment of regenerating coniferous-broadleaf forest in the south-east of the South Island of New Zealand.
2. Crayfish density ranged from 3 to 4 m⁻² in riffles and 4–12 m⁻² in pools, depending on reach. Crayfish biomass (4–33 g AFDW m⁻²) and annual production (2–11 g AFDW m⁻²) were high compared with values reported elsewhere, while P:B ratio was low (0.33–0.43). This substantial production was dependent primarily upon high biomass rather than high growth rate.
3. The crayfish of this population rank amongst the longest lived and slowest growing ever recorded. Individuals estimated to be 16+ year of age were not uncommon. Females became reproductively active at 6+ year. Fewer than 4% of females carried eggs, and young remained attached to females for at least 15 months.
4. We propose that characteristics of this population are the consequence of a cool thermal regime (mean daily stream temperature = 7.0 °C, range 1.8–11.9 °C), and that low biomass turnover and poor reproductive rate precludes any sustainable commercial harvest of crayfish from streams in New Zealand with similar thermal regimes.     

A modified drop-net method for sampling mobile epifauna on marine shallow sandy bottoms

The seasonal variations in numbers and biomass of the mobile epifauna of a shallow, sandy bay in Gullmar Fjord (Sweden) was investigated during 1976–1977 using the drop-net technique. Juvenile plaice, Pleuronectes platessa L., sand goby, Pomatoschistus minutus (Pallas), and brown shrimp Crangon crangon L. are the dominant epifaunal species. A net enclosing an area of 100 m² was used, and the organisms captured were collected with a small trawl. Three stations with a water depth≤ 1 m were regularly sampled with a total number of 73 drops. Maximum abundance was for plaice in June (6 ind m^-2), for the shrimp in July-August (61 ind m^-2), and for sand goby in September (2 ind m^-2). Standing stocks (dry wt) were 0.2, 1.5 and 0.2 g m^-2 respectively. Production estimates were based on seasonal changes in size frequency and information on specific growth rates. The production rate was for plaice (0-group) 0.3 g m^-2 yr^-1, for the shrimp 1.5, and for sand goby 0.2 g m^-2 yr^-1. Reliable estimates of the absolute abundance can be derived from the mean catch per unit area only when the efficiency of the fishing gear is known. After 6 hauls with the trawl in the drop-net enclosure more than 85% of the shrimps were caught and after the fifteenth haul less than 1% were still left. The fishing efficiency of a push-net in relation to the drop-net was for the shrimp 50%, for plaice 35% and for sand goby 17%.     

Carbon Dioxide Exchange Between the Atmosphere and an Alpine Shrubland Meadow During the Growing Season on the Qinghai-Tibetan Plateau

Abstract: In the present study, we used the eddy covariance method to measure CO₂ exchange between the atmosphere and an alpine shrubland meadow ecosystem (37°36'N, 101°18'E; 3 250 m a.s.l.) on the Qinghai-Tibetan Plateau, China, during the growing season in 2003, from 20 April to 30 September. This meadow is dominated by formations of Potentilla fruticosa L. The soil is Mol-Cryic Cambisols. During the study period, the meadow was not grazed. The maximum rates of CO₂ uptake and release derived from the diurnal course of CO₂ flux were -9.38 and 5.02 μmol·m^-2·s^-1, respectively. The largest daily CO₂ uptake was 1.7 g C·m^-2·d^-1 on 14 July, which is less than half that of an alpine Kobresia meadow ecosystem at similar latitudes. Daily CO₂ uptake during the measurement period indicated that the alpine shrubland meadow ecosystem may behave as a sink of atmospheric CO₂ during the growing season. The daytime CO₂ uptake was correlated exponentially or linearly with the daily photo synthetic photon flux density each month. The daytime average water use efficiency of the ecosystem was 6.47 mg CO₂/g H₂O. The efficiency of the ecosystem increased with a decrease in vapor pressure deficit.
(Managing editor: Ya-Qin HAN)     

The life cycle, population dynamics, growth and secondary production of the snail Xeropicta arenosa Ziegler (Gastropoda: Pulmonata) in northern Greece

The life cycle, population dynamics and secondary production of the xerothermophilic land snail Xeropicta arenosa were studied in northern Greece. The study of biology and the demographic analysis of the populations of X. arenosa revealed that it is a semelparous annual species. Reproduction takes place in autumn and the majority of the adults die after egglaying. Growth is continuous throughout the year and no seasonal fluctuations occur. Estimation of annual secondary production with the Hynes' size frequency method revealed a mean standing crop ( aa ) of 0.075 g m^-2 year^-1 and a productivity ( P ) of 0.267+ 0.043 gm^-2 year^-1. The annual turnover ratio ( P/ ) was equal to 3.56.     

Energy partitioning in the Antarctic collembolan Cryptopygus antarcticus

Abstract. 1. Consumption, production and assimilation rates were determined for two age groups of Crypropygus antarcticus to give an estimate of energy utilization, and to investigate low temperature adaptation in its energy partitioning.
2. Feeding selectivity shown in laboratory preference tests was supported by gut analysis of field animals from contrasting sites. Although moulting rate was not significantly affected by food type, rates of growth were slowest and mortality highest when fed on a non-preferred substrate.
3. Both a radio labelling and a more direct method for measuring dry weight consumed gave similar results for Cvpropygus feeding on algae. The consuniption rate for animals when feeding on algae was lower than that on moss peat. The assimilation efficiency for immature animals feeding on algae was 46% and for mature animals was 19%; the values when feeding on moss peat were 7% and lo%, respectively, The net production efficiency ranged from 35%(inimatures) to 13% (matures) and was similar on both substrates.
4. Food consumption exceeded assimilation over the range 2.5–10°C, but the two converged from 2.5 to 0°C. Immature Cryptopygus maintained a net positive energy balance over 0–10°C, whilst below 1S°C respiration exceeded assimilation for mature individuals.
5. An estimate of the annual dry matter consumption (7 g m^-1 y^-1) by Ctypropygus in a moss turf at Signy Island agrees with one based on respiration data alone (Davis, 1981). The consumption at an alga-dominated site was c . 26 g m^-2 y^-l, and Crypropygus may have a locally limiting effect on net priniary production at such sites.     

The life history and production of the leech Helobdella stagnalis (Hirudinea:Glossiphonidae) in the River Ely, South Wales

SUMMARY. A population of the glossiphonid leech Helobdella stagnalis was studied over a period of 16 months in the organically polluted River Ely, South Wales. There were two generations each year. The overwintering population released young (the spring-brood) in June. The spring-brood in turn produced their own offspring (summer-brood) in August.
Seasonal patterns of mortality were related to flow, temperature and life-cycle stage. Individual growth rates were dependent upon both temperature and life-cycle stage.
Annual population production (P) was 7.56 g wet wt m^-2, mean annual population biomass (B) was 1.43 g wet wt m^-2 and the annual P/B ratio was 5.29.     

The growth rate of eel in tributaries of the lower River Severn, England, and its relationship with stock size

The growth rate of 1980 eel Anguilla anguilla from 15 sites in the Severn system varied between 16·4 and 27·9 mm year^-1, density from 0·12 to 1·14 m^-2 and biomass from 2·56 to 25·24 g m^-2. There was no significant relationship between growth rate and density or biomass ( P > 0·05).     

Mode of interference of chlorosis-inducing herbicides with peroxisomal enzyme activities

In rye leaves ( Secale cereale L. cv. Petkus "Kustro") bleached in the presence of the chlorosis-inducing herbicides aminotriazole, haloxidine, San 6706 or difunone in white light of 54.2 W m^-2 (5000 lx), catalase activity was very low. In addition, the activities of glycolate oxidase and hydroxypyruvate reductase were strongly diminished in treatments with San 6706 and difunone. The lowering of the peroxisomal enzyme activities was observed in red, but not in blue light and did not occur after treatment with the non-bleaching pyridazinone derivative San 9785. The deficiencies of the peroxisomal enzymes did not appear to be involved in the initiation of the chlorosis. Instead they are probably produced as secondary consequences of the bleaching. Low peroxisomal enzyme activities were also obtained without herbicide treatment by growing the leaves in an atmosphere of 2% O₂ and 3% CO₂, but in this case were not accompanied by an increased sensitivity of the Chl to photooxidative bleaching. The peroxisomal enzymes reached as high activities as in untreated controls when the herbicide-treated leaves were grown at a low light intensity of 0.106 W m^-2 (10 lx). After transfer of herbicide-treated leaves grown under 0.106 W m^-2 to 306 W m^-2 (30 000 lx), catalase was strongly inactivated, even at 0°C. In treatments with San 6706 and difunone the increase of the activities of glycolate oxidase and hydroxypyruvate reductase was either stopped, remaining unchanged, or the enzymes were slightly inactivated after exposure to 306 W m^-2 (30 000 lx). The observations suggest that the inactivation of peroxisomal enzymes results from photooxidative events in the chloroplasts.