Spatial and temporal occurrence of invertebrates in a chalk stream,Berkshire, England

The invertebrate assemblages of the River Lambourn and its tributary, the Winterbourne stream, were investigated as part of a broad ecological study prior to water resource development in the catchment. The longitudinal distribution of the invertebrate fauna within the Winterbourne stream was examined in detail and supporting data for the R. Lambourn revealed that the upstream intermittent section of each water course had an invertebrate assemblage which was distinct from the fauna downstream where flow was permanent. Within the perennial zone taxon richness tended to increase downstream.A one-year programme of monthly quantitative sampling on five distinct biotopes (Ranunculus, Berula, Callitriche, gravel and silt) at two contrasted sites (shaded and unshaded) was undertaken in the lower perennial of the R. Lambourn below the confluence with the Winterbourne. On each study site, the taxon richness, numerical abundance and biomass of invertebrates were significantly higher on the three macrophytes than on gravel and silt. There were also statistically significant seasonal changes in the biomass of invertebrates on each site. Estimates of total biomass of invertebrates per site revealed a late spring peak (May/June) and a late autumn (November/December) peak, neither of which coincided with the summer peak biomass of macrophytes. This suggested that, in the lower perennial, the level of food resources (epiphytic algae in late spring and fallen tree leaves plus decaying macrophytes in autumn) rather than available habitat, were a major influence on population levels for most of the year.Quantitative sampling of each biotope on each site continued in June and December only for a period of 8 years (1971–78), during which time the river experienced a minor drought (1973) and a severe drought (1976). The Chironomidae showed a strong positive response to conditions of low flow in June of 1973 and 1976, when exceptionally high densities of larvae were recorded. Although further between-year differences were recorded in several other major components of the invertebrate fauna, which may have been related to conditions of low discharge, they did not have long-term consequences for the fauna in the lower perennial of the R. Lambourn.In contrast, in the upper perennial, the prolonged drought of 1976 resulted in the loss of wetted perimeter and macrophytes, coupled with deposition of silt, all of which had deleterious effects on the invertebrate assemblages. The following year, despite a normal discharge regime and the removal of silt, some submerged macrophytes were slow to return to their pre-drought condition. In the intermittent section, the drought of 1976 resulted in the total loss of flow for a 16 month period instead of a more typical four month period of water loss.Thus, chalk streams encompass within a single system both stable and extreme hydrological regimes which offer unique opportunities for investigating the processes of community formation and maintenance.     

Seasonal changes in biom ass of macrophytes on shaded and unshaded sections of the River Lambourn, England

SUMMARY. Monthly changes in the biomass of Ranunculus, Berula and Callitriche were recorded on two 50-m sites on the River Lambourn at Bagnor between March 1971 and October 1973. On the unshaded site. Ranunculus was the dominant macrophyte and characteristically its biomass changed from 20–40 g dry wt m^-2 in March to around 400 g dry wt m^-2 at the end of the growing season. On the shaded site, where Berula was the dominant macrophyte. the biomass of Ranunculus was lower than on the unshaded site. There was no significant difference between the mean biomasses of Berula on these two sites but Callitriche had a signifieantly higher biomass on the shaded site. Estimates of the total biomass of macrophyte on each site were calculated and the biomass of macrophyte removed during cutting operations each summer was also assessed.     

Growth and recession of aquatic macrophytes on an unshaded section of the River Lambourn, England, from 1971 to 1976

SUMMARY. The growth and recession of the macrophytes on an unshaded section of the R. Lambourn was documented by a mapping procedure from March 1971 to December 1976. The seasonal patterns were determined mainly by the dominant macrophytes. Ranunculus penicillatus var. calcareus and Ranunculus peltatus . Ranunculus grew rapidly in spring and early summer, mainly colonizing areas of gravel and reached a summer maximum. The greatest loss of plants was in August and September but losses continued through the winter to give minimum cover in March. Berula and Callitriche did not show regular seasonal growth patterns but their growth was largely confined to times when there was little growth of Ranunculus . Increase in area of Ranunculus in the spring was positively correlated with the mean discharge at that time. The growth of Ranunculus appeared to be restricted when shading was caused by turbid water due to dredging or by accumulation of epiphytic algae on the surface of the plants in years when discharge was low. Discharge also influenced the substrata underlying Ranunculus and the area of silt under Ranunculus beds was negatively correlated with discharge. The factors thought to influence growth of Ranunculus were used to develop a conceptual model of growth.     

Two commensals on a host: habitat partitioning by a ciliated protozoan and a chironomid on the burrowing mayfly, Ephemera danica

SUMMARY 1. Two taxonomically unrelated species, the ciliated protozoan Scyphidia sp. and the chironomid Epoicocladius flavens (Malloch), share a commensal mode of life on nymphs of the burrowing mayfly Ephemera danica Müller in a small river in eastern England.
2. Both commensals were present all through the year, with an average level of infestation of 25.1% and 54.7% for Scyphidia sp. and E. flavens , respectively, of the total E. danica population.
3. Scyphidia sp. occurred more frequently on younger, smaller nymphs of E. danica and was totally absent from hosts of more than 10 mm in length. In contrast, E. flavens preferred hosts of larger body size, usually more than 10 mm. Change in dominance of infestation between the two commensals occurred in the host size range of 6–8 mm and this pattern of habitat partitioning on the basis of host size was consistent throughout the study period.
4. Amongst E. danica individuals colonized by E. flavens , larger hosts supported heavier commensal load. A similar trend, though weak, was also observed among hosts harbouring Schyphidia sp.
5. Both commensals are considered to benefit from the association with E. danica in that they gain enhanced mobility and security in otherwise inhospitable habitats. Although plausible on an evolutionary time scale, competition alone cannot constitute a proximate cause for the clear partitioning of habitat observed in the two commensal species.     

Growth and recession of aquatic macrophytes on a shaded section of the River Lambourn, England, from 1971 to 1980

SUMMARY. The growth and recession of macrophytes on a shaded section of the R. Lambourn were documented by a mapping procedure. With the exception of Ranunculus spp., the changes in total cover did not indicate directly the pattern of growth and recession of the macrophyles. Analysis of gross changes, expressed as gains and losses on cover, indicated that colonization of gravel and silt by the dominant macrophyte, Berula erecta, did not vary seasonally. Colonization was at a constant rate of about 8% of the site each month throughout the year and this accounted for 50% of the total number of gains by Berula. Gains of Berula from Ranunculus showed an annual cycle with a maximum during the summer when Ranunculus was in recession. Gains of Berula from Callitriche spp. also varied annually but the maximum was during the autumn. Total losses of Berula were at a constant rate throughout the year but were to gravel and silt during the winter, to Ranunculus in spring and early summer and to Callitriche in late summer and autumn. Analysis of loss of Berula with time indicated that the position of the Berula carpet was constantly changing. The growth and recession of Berula could not be linked in a meaningful way to environmental variables. Callitriche and Ranunculus both showed an annual pattern of growth and recession. There was temporal separation of the two macrophytes with Ranunculus growing mainly in spring and early summer and Callitriche showing maximum growth in late summer and autumn, and some evidence of spatial separation. The observed differences between years in the growth of Callitriche could not be attributed to any of the environmental variables measured. Discharge was thought to be an important variable controlling the growth of Ranunculus since increase of Ranunculus in the spring was positively correlated with the mean discharge at that time. In years when discharge was low, the growth of Rununculus appeared to be restricted by shading from epiphytic algae which accumulated on the plant surfaces under these conditions.     

Population ecology of the commensal chironomid Epoicocladius flavens on its mayfly host Ephemera danica

SUMMARY. 1. Epoicocladius flavens (Diptera: Chironomidae) has a 1-year life cycle in the River Tud in eastern England. Pupation and adult emergence occurred from the end of May until the beginning of September. Larval growth was rapid during the summer but thereafter almost ceased until the following April.1 Unlike other chironomids, the population density of E. flavens was very stable and remained at around 1000m ⁻² all through the year.
2. Ephemera danica (Ephemeroptera: Ephemeridae), the host of E. flavens , has a 2-year life cycle. The proportion infested was about 90% for the older host year-class and less than 30% for the younger year-class from autumn until the following summer. A rapid increase in infestation occurred during the summer as a result of hatching of the E. flavens eggs. Of those infested, the older year-class hosts harboured two or three larvae, on average, whereas the younger ones had only one.
3. When host year-classes were treated separately, the frequency distribution of the number of E. flavens per host each month did not depart significantly from a Poisson distribution. Younger instars departed from a Poisson distribution more frequently than older instars.
4. The majority of E. flavens larvae attached to the gills of their hosts. As the instars progressed, increasing proportions were found on the thorax, legs and tails. The thorax was the preferred site for fourth instar larvae.
5. Enhanced chance of survival, rather than the supply of detrital food particles which collect on the host's body, is considered as an important benefit to accrue to E. flavens from this commensalism.     

Observations on the occurrence and maturation of the nematode Rhabdochona denudata (Dujardin, 1845) in Chub, Leuciscus cephalus (L.), of the Rokytná River, Czechoslovakia

From October 1985 until July 1987, the seasonal dynamics of Rhabdochona denudata in its principal definitive host, the chub (Leuciscus cephalus), was studied in the Rokytná River (the Danube basin), Czechoslovakia. Prevalence (overall prevalence 77%) and intensity of infection (1-59 nematodes per fish) in the fish were high all year, with both abiotic and biotic factors influencing the fluctuations. Maximum values of prevalence (82-87%) were found in the fish with body length exceeding 20 cm; the mean intensity was highest in the size-group of fish 20-25 cm long, whereas its values gradually decreased in larger fish, this being due to the choice of food by fish of different size-groups. In contrast to the situation in other localities, an annual maturation cycle was not evident and egg-producing female nematodes were present in fish throughout the year. New infections in fish were most common in summer but occurred all year round. This life history pattern seems to be mainly due to the availability of infected ephemeropteran intermediate hosts during all seasons, in this case the nymphs of Ephemera danica, a species noted for its two-year development. In this locality, specifically not determined Rhabdochona larvae were recorded from the mayfly nymphs Ephemera danica (0.4%), Ecdyonurus aurantiacus (7%), and Caenis macrura (10%). The diet of the chub included mayfly nymphs at all seasons.     

The chironomid larvae of a small chalk stream in Berkshire, England

Abstract. 1. The longitudinal distributions of larval Chironomidae (Diptera) were examined for 1 year in the intermittent and perennial sections of the Winterbourne, a small chalk stream in Berkshire, England.
2. Forty-nine chironomid taxa were recorded at ten major sites which were sampled on six occasions and four additional taxa were recorded at sites sampled only once.
3. Cluster analyses using data from the major sampling sites identified three groups of sites. A pond in the stream channel which had a distinct chironomid fauna was distinguished from all other sites before the remaining intermittent sites were separated from all perennial sites on the basis of the chironomid fauna.
4. In the perennial stream, a site heavily shaded by trees had low species richness compared with partially and unshaded sites further downstream. The lowest site, which was near to the confluence with a larger chalk stream, the River Lambourn, had the highest number of taxa (thirty-five), including several which were frequent in the Lambourn.
5. By recording the occurrence of prepupae, an indication of emergence periods was obtained and many taxa were shown to have extended periods of emergence.     

Spatial distribution of denitrifying activity in a stream draining an agricultural catchment

SUMMARY 1. A field study was made of the spatial distribution of denitrification activity in the sediment of the River Dorn, Oxfordshire, England.
2. An assay of denitrifying enzyme activity was used to examine the distribution of denitrification with depth in cores of sediment representative of the types found in the stream. The maximum activity recorded in a predominantly silt sediment core was 5 times greater than that recorded in a sandy gravel core. In both fine sand and silt cores, peaks in denitrifier enzyme activity were shown to correspond to the limit of the nitrate diffusion front. At this depth the redox potential dropped rapidly from + 300 mV to 0 or less. Denitrifying enzyme activity in the stream water was negligible.
3. In situ denitrification activity (I DA) measurements were carried out in an 800 m reach of the Dorn using the acetylene inhibition technique on small sediment cores. Concurrent measurements were also made of stream depth and velocity, nitrate concentration in the interstitial water, and the wet bulk density, loss on ignition, mineraliz- able carbon and total nitrogen contents of the sediment. Mineralizable carbon was the variable which showed the best correlation with I DA. Highest IDAs were associated with accumulations of fine-grained sediment at meander bends. Mean IDAs measured under flood conditions were significantly higher ( P <0.05) than those measured under baseflow. It was estimated that denitrification reduced the nitrate load in the River Dorn by 15% under summer baseflow conditions     

Microhabitat selection by a stream-dwelling amphipod: a muitivariate analysis approach

SUMMARY. 1. Colonization of microhabitat implants by the amphipod Gammarus pseudolimmnaeus in a small southern Ontario stream was studied in order to analyses the factors controlling habitat selection. The variables substrate particle size, current speed, presence of food and light were used in an analysis of covariance, with percentage weight of organic matter of silt and percentage interstitial space occluded by silt as the covariates.
2. Greatest numbers of amphipods settled on microhabitats featuring large substrate particles, no current and presence of food. There was also a positive relationship between total numbers and the volume of silt deposited on the microhabitats by the stream; small quantities of silt had a beneficial effect on colonization but larger quantities became detrimental.
3. The change from a positive effect occurred at approximately 25% occlusion of the interstitial space in large gravel ( diameter=3.2 cm) and at approximately 55% occlusion in small gravel ( diameter = 0.34 cm).
4. Large animals (6–16.0 mm long) were found predominantly in microhabitats featuring food and large substrate. Medium-sized animals (3–6.0 mm) were most commonly associated with no current and presence of food, and were positively affected by the amount of silt but, at the same time, were negatively affected by increasing occlusion of interstitial spaces by silt. Numbers of small Gammarus (<3.0 mm) were affected only by silt and in a similar manner to medium-sized animals.
5. Amphipod biomass was greatest in microhabitats featuring food and no current. Previous data on the behaviour of this species in laboratory stream-tanks are compared with the microhabitat selections seen.     

Life history of the gulf darter,Etheostoma swaini (Pisces: Percidae)

Synopsis Etheostoma swaini, the gulf darter, was collected from the Black Creek drainage in southern Mississippi (February 1978 – April 1979). The gulf darter generally inhabits small- to moderate-size creeks and occurs over a sand or sandy mud bottom, often in association with aquatic vegetation or a layer of organic debris. Larval dipterans were the most important food items, both numerically and volumetrically. Chironomids were found in 71–100% of the stomachs in all except the unusual March 16 collection. The length frequency distribution and the scale annuli analysis indicated there were three year-classes present in the population at any one time. Fifty-one percent of the specimens taken were less than 12 months old. During the mid-February to late March spawning season gulf darters were most often collected over clean gravel or gravelsand substrates. Laboratory observations suggest that the female burrows into the gravel where the demersal, adhesive eggs are deposited. Female gulf darters significantly outnumbered males at a ratio of 59:41.     

Feeding habits of the predaceous nymphs of Dolania Americana in Northwestern Florida (Ephemeroptera : Behningiidae)

Feeding habits of nymphs of the predatory mayflyDolania americana Edmunds & Traver in northwestern Florida were examined during 1971 and 1972. Larvae of Chironomidae (Diptera) formed the bulk of prey items. The size of the predaceousD. americana nymphs was correlated with the size of chironomid prey taken. Differential microhabit utilization allows partition of prey resources with the other major predator species present. The relationship between predator and prey biomass throughout the year is discussed.     

无定河流域不同地貌区径流变化归因分析

分析了无定河流域干流与其支流(黄土丘陵区的大理河和风沙区的海流兔河)的年径流变化(1960—2012)及其成因,并预测了其径流的变化趋势。结果表明:无定河及其不同地貌区支流海流兔河和大理河流域1960—2012年径流量均显著下降,但年降水量未发生显著变化;无定河和海流兔河流域年蒸散量未发生显著变化,仅大理河流域年蒸散量在1990s年代后期显著增加。无定河流域径流变化突变点发生在1979年和1996年,海流兔河流域径流变化突变点在1971年和1990年,而大理河流域径流突变点发生在1971年。人类活动对大理河流域1972—2012年径流减少的贡献大约占50%,对海流兔河流域1972—1990年和1991—2012年两个时期径流减少的贡献率分别为44.4%和82.4%。未来,无定河及其支流年径流量均呈持续下降趋势。归因分析表明大规模的水土保持治理措施减少了大理河流域侵蚀产沙量的同时,也在一定程度上减少了大理河流域的径流量,而过度的农田灌溉引水是海流兔河径流量下降的主要原因。因此,未来在大理河流域要优化现有植被建设布局,减少流域蒸散发,减缓径流下降;在海流兔河流域要进一步退耕还林(草),适当控制农田灌溉面积,提高灌溉用水效率,在减少灌溉用水的同时提高流域水源涵养能力。     

Macrobenthic community structure before and after pollution abatement in the Neches River estuary (Texas)

Macrobenthos and physicochemical conditions in the lower 39 km of the Neches River estuary were studied from August, 1984 to May, 1985. The results were compared with data collected in 1971–1972. Between 1972 and 1984 the permitted BOD waste load in the tidal Neches River was reduced from 123 125 kg d to 8717 kg d. River discharge and dissolved oxygen concentrations were consistently higher and salinity was lower, during the same seasons, during the 1984–1985 study. A total of 50 taxa of macrobenthos were collected in 1971–1972 and 104 taxa were collected in 1984–1985. The numbers of taxa per collection at each station in 1984–1985 were at least twice those found in 1971–1972. Minimum densities in 1984–1985 were much higher than the maximum densities in 1971–1972 at all stations. Patterns of dominance, Sorenson's similarity index, and diversity ( ) values indicated improved water quality in 1984–1985. Statistical analysis of macrobenthic diversity indicated significant differences between upper estuary and lower estuary stations in 1971–1972. No significant differences were found in 1984–1985. Significant differences in numbers of taxa, macrobenthos densities, and values between the two studies were found. Reductions of waste loads, increased river discharge, and deepening of the navigation channel were among the factors that probably contributed most to the changes in community structure of the macrobenthos observed.     

Abundance,structure, growth and origin of inshore clupeid populations of the west coast of Scotland

The abundance, structure, growth, and origin of clupeid populations in inshore waters of the west coast of Scotland were studied from April 1970 to October 1972. Clupeid populations in the area comprise mainly young fish. 0-group autumn-spawned herring, probably of Minch origin, move into the area about April and spring-spawned ones (Clyde origin) about June. The timing and the body length at which each group arrives in the area during the different years is the same. After the initial immigration, the distribution of both 0-group clupeids becomes localized.Herring populations in the sea-lochs and associated inshore waters are mainly 0-group fish, which are replaced each year by a new incoming brood. The sprat populations of the sea-lochs are dominated by the 0-group; in the more ‘open’ areas the populations comprise older individuals. Year-class distribution in the ‘open’ areas resemble that of the commercial fishery.The rate of increase of 0-group autumn-spawned herring is 3.68 mm/week and that of spring-spawned 0-group herring is 2.83 mm/week. The curves of growth of 0-group sprats of the 1970 and 1971 year-classes are different; the rate of increase in length, however, averages 3.55 mm/week for both year-classes and the differences are not significant.In sprats, after their first year of life a rapid increase in length takes place in the spring. This increase is thought to enable the majority of the population to reach the minimum size (88–90 mm) for initial gonadal maturation and thereby make them capable of reproducing in their second year of life.     

Heterogeneous selective pressures on egg-hatching time and the maintenance of its genetic variance in a Tetraneura gall-forming aphid

1. The performance of gall-forming aphids is largely dependent on the timing of egg hatch relative to host budburst. This study examined the mode of natural selection acting on egg-hatching time and the extent of its genetic variance in a Tetraneura aphid.
2. The budburst time of the primary host of the aphid varied greatly among individual trees. Egg hatch on a host tree was often asynchronous with host budburst.
3. Transplant experiments indicated that egg-hatching time was subject to heterogeneous selective pressures in heterogeneous host environments.
4. Hatching time was compared between half-sib families. Small nymphs in a half-sib family tended to hatch later, and this resulted in large within-family variance in hatching time.
5. Small nymphs that hatched late were likely to be selected out during the galling process. Thus, these nymphs may be produced not as bet-hedging but due to maternal effects. When such maladapted nymphs were not included in analysis, a significant amount of additive genetic variance was detected in hatching time.
6. Heterogeneous selection, coupled with density-dependent regulation of population on respective host trees, probably maintains additive genetic variance in this trait.     

Variation in chemical composition of the River Frome, England, from 1965 to 1972

This study covers a 7-year period from 1965 to 1972, and shows the variation in flow, water chemistry and throughput of nutrients. The annual discharge of the River Frome varied considerably from year to year, ranging from a mean value of 4.48 m³ sec⁻¹ in 1971 to one of 8.38 m³ sec⁻¹ in 1966. The mean annual nutrient losses calculated over all 7 years of study from the River Frome catchment were: Nitrate 11.4 kg ha⁻¹, phosphorus 0.49 kg ha⁻¹ and potassium 8.4 kg ha⁻¹. There has been an increase in annual throughput (in years of similar flow) of 21% in phosphate and 41% in nitrate from 1965 to 1972.     

Predation on mayfly nymph, Baetis rhodani, by native and introduced Gammarus: direct effects and the facilitation of predation by salmonids

1. In a series of laboratory experiments, we assessed the predatory nature of the native Irish amphipod, Gammarus duebeni celticus , and the introduced G. pulex , towards the mayfly nymph Baetis rhodani . We also investigated alterations in microhabitat use and drift behaviour of B . rhodani in the presence of Gammarus , and indirect predatory interactions with juvenile Atlantic salmon, Salmo salar .
2. In trials with single predators and prey, B. rhodani survival was significantly lower when Gammarus were free to interact with nymphs as than when Gammarus were isolated from them. The invader G. pulex reduced the survival of B. rhodani more rapidly than did the native G. d. celticus . Both Gammarus spp. were active predators.
3. In `patch' experiments, B. rhodani survival was significantly lower both when G. pulex and G. d. celticus were present, although the effect of the two Gammarus species did not differ. Again, active predation of nymphs by Gammarus was observed. Significantly more nymphs occurred on the top and sides of a tile, and per capita drifts were significantly higher, when Gammarus were present. Baetis rhodani per capita drift was also significantly higher in the presence of the introduced G. pulex than with the native G. d. celticus .
4.  Gammarus facilitated predation by salmon parr of B. rhodani by significantly increasing fish–nymph encounters on exposed gravel and in the drift. There were no differential effects of the two Gammarus spp. on fish – B . rhodani encounters or consumption.
5. We conclude that Gammarus as a predator can have lethal, nonlethal, direct and indirect effects in freshwaters. We stress the need for recognition of this predatory role when assigning Gammarus spp. to a `Functional Feeding Group'.     

Xylem feeding by periodical cicada nymphs on tree roots

Abstract. 1. Histological sections of tree roots on which periodical cicada nymphs of both the 17-year and the 13-year race arid various instars had fed showed that salivary sheaths made by the nymphs ended in xylem vessels.
2. Because no salivary sheaths were found in phloem cells, this observation indicates that cicada nymphs are xylem feeders throughout their developmental period.
3. The habit of feeding on xylem fluid, which is extremely dilute, may explain why periodical cicada nymphs require so many years (13 or 17) to mature. It may also explain why they excrete amino acids rather than sugars, as phloem feeders do.     

Habitat preferences of Ukrainian brook lamprey Eudontomyzon mariae ammocoetes in the lowland rivers of Central Europe

The pattern of microhabitat preferences of Ukrainian brook lamprey Eudontomyzon mariae ammocoetes was examined in two rivers of central Poland: the Pilica River (the Vistula River basin) and the Grabia River (the Odra River basin). A comparison of abiotic factors of the rivers revealed differences in water speed and principal components: PC1 (determining gradient from decreasing medium sand to the increasing share of three fractions of gravel), PC2 (a gradient from the declining share of very coarse and coarse sand fractions to the growing content of fine sand) and PC3 (correlated with an increasing proportion of silt). The sites did not differ significantly in terms of water depth. Relative abundance and frequency of ammocoete occurrence in the Grabia River were higher than in the Pilica River. Only speed, PC1 and PC2 made a significant contribution to the prediction of larval occurrence. Eudontomyzon mariae larvae preferred substrata with a reduced amount of medium sand and increased content of gravel (PC1) as well as with a lower content of coarse sand and higher proportion of fine‐grained sand (PC2). The ammocoetes also preferred areas with a water speed of 0·2 m s^?1 but avoided speeds ≥0·6 m s^?1. The abundance of E. mariae was affected by water speed, as well as by all PCs. The mean ± s.e. optimal current speed was 0·265 ± 0·007 m s^?1, while abundance decreased with increasing amounts of gravel (PC1) and increased with increasing amounts of fine sand and silt in the bottom substratum (PC2 and PC3). Comparison of ammocoete microhabitat use in the Pilica and Grabia Rivers showed the lack of differences in distribution in the preferred values of current speed, PC1 and PC2.