The spider assemblages (Araneae) of exposed riverine sediments in Scotland and northern England

8 Pages·2002·0.39 MB·English

by  Eyre, M D

Bull.Br.arachnol.Soc.(2002)12(6),287–294 287
The spider assemblages (Araneae) of exposed Pajunen et al., 1995). These studies were carried out
riverine sediments in Scotland and northern using pitfall trapping as the sampling technique.
England* ERS are highly disturbed habitats by rivers with
varying compositions and vegetation covers. Compo-
M. D. Eyre sition varies from boulder- and cobble-dominated sedi-
ments, found by fast-flowing stretches of rivers, to
DepartmentofAgricultural&EnvironmentalScience,
TheUniversity,NewcastleuponTyne,NE17RU;and sediments of fine sand with silt found where both the
EntomologicalMonitoringServices(EMS), river flow and sediment deposition are slow, while
13ManorGrove,NewcastleuponTyne,NE77XQ some sediments are a mixture of different particle sizes.
GenerallyERStendtobeunvegetatedafterwinter,with
J. C. Woodward and M. L. Luff
thecoarsersedimentsbythefasterriversremainingbare
DepartmentofAgriculturalScience,
while sand and silt sediments acquire varying amounts
TheUniversity,NewcastleuponTyne,NE17RU
ofvegetationcoverthroughouttheseason.However,all
sites are prone to disturbance at any time by river
Summary scouring, depending on flow conditions. In the present
paper a standardised pitfall sampling approach
Asurveyofspidersusingpitfalltrapsonexposedriverine
sediments (ERS) by rivers and tributaries in four catch- (Luff, 1996) was applied to ERS in four catchments in
mentsinScotlandandnorthernEnglandyielded105species Scotland and northern England to assess spider
and lists from 149 sites. These data were analysed using assemblage distribution and the variables influencing
ordination and classification techniques to identify the
distribution.
species assemblages present within and between catch-
ments and the factors affecting the distribution of these
assemblages. There were major differences between
Material and methods
assemblagesonERSinhighlandandlowlandcatchments,
butthemajorfactorwithincatchmentswastheamountand Sites
type of vegetation. The distribution of sites within habitat
groups tended to be related to site location within catch- Exposed riverine sediments (ERS) in the catchments
ments, but sediment composition also had a limited effect oftheRiversCarron,NithandSpeyinScotlandandthe
onassemblagedistribution.FewspecialistERSspecieswere
Tweed, which straddles the Scotland-England border,
recorded,whilstavarietyofspeciesfoundonotherhabitats
were sampled in 1996 and 1997. The 10km squares
such as unmanaged and agricultural grasslands, wetlands
andbareground,werefoundonsedimentsthroughoutthe containing sites in the four catchments are shown in
four catchments. Fewer spider assemblages were identified Fig. 1. The 1996 sampling was restricted to sites on the
onriverinesedimentsascomparedwithotherinvertebrate main rivers, whilst sampling was expanded in 1997 to
groupsrecordedfromthesamesites.
Introduction
Invertebrate research work on exposed riverine sedi-
ments (ERS) has tended to be concentrated on the
distributionandhabitatpreferencesofbeetlespeciesand
assemblages(e.g.Eyre&Lott,1997;Eyreetal.,2001a,b)
but there have also been a number of investigations of
spidercommunitiesonERS(Boumezzough,1983;Bigot
& Favel, 1985; Droschmeister, 1994; Smit et al., 1997;
Manderbach&Framenau,2001)andsomeintoecology
of single spider species on ERS (Albert & Albert, 1976;
Framenau et al., 1996). Sadler & Petts (2000) investi-
gated the presence of a number of invertebrate groups
onERS,includingbothspidersandbeetles,whilstother
work has concentrated on other riparian habitats
(Moring&Stewart,1994;Greenwoodetal.,1995;Malt,
1995; Hendrickx et al., 1998; Wenninger & Fagan,
2000).
Research on spider species assemblage distribution
using epigeal species has been carried out on a number
of different habitats. There are reports from grasslands
of various types (e.g. Rushton & Eyre, 1992; Corey
et al., 1998; Pozzi et al., 1998) and agricultural eco-
systems (e.g. Rushton & Eyre, 1989; White & Hassall,
1994;Feberetal.,1998),withsomeworkonforests(e.g.
*Correspondingauthor:DrM.D.Eyre,DepartmentofAgricultural Fig. 1: Map showing the 10km national grid squares in the Carron
& Environmental Science, The University, Newcastle upon Tyne, (northwest), Spey (northeast), Nith (southwest) and Tweed
NE17RU. (southeast)catchmentscontainingsitessampledinthesurvey.
288 Spidersofexposedriverinesediments
takeinboththemainriversandtheirtributaries.Atotal the index, and the scores were generated for all sites
of 149 sites were sampled, made up of 29 sites in the together and for the sites in individual catchments. The
Carron, 26 in the Nith, 40 in the Spey and 54 in the indexscoresweresmallforsilt/sandsedimentsandlarge
Tweed catchments. The sampling rationale was to trap for cobble/boulder sediments in all five examples. An
in the widest variety of ERS, covering differences in estimateofriverorstreamsizewasmadeusingbandsof
sediment particle size and vegetation cover with sites width in non-spate conditions. Each band was given a
from all parts of the four catchments. value: 1=1–5m, 2=6–10m, 3=11–15m, 4=16–20m,
5=>20m.Thethirdvariablewasanestimateofvegeta-
tion cover on each site. Each vegetation cover type was
Sampling
assigned a value: 1=bare, 2=ruderal, 3=rank, 4=shrub
Spiders were sampled using pitfall traps (8.5cm cover,5=treecover.Fortheanalysisdealingwithallthe
diameter,10cmdeep),partlyfilledwithethyleneglycol. sites,categoricalvalueswereassignedtoeitherhighland
Tentrapswereusedateachsiteinalineat1mintervals, catchments (Carron and Spey) or lowland catchments
asoutlinedbyLuff(1996).ThetrapsweresetinMayof (Nith and Tweed). There was therefore differentiation
each year and sampling continued until August, with between the northerly catchments, with base-poor,
collections carried out at three-weekly intervals. There mainly igneous, geology and the southern catchments
wassomedisruptionofsamplingcausedbyriverspating with more productive coal measures and sandstone
buttrapswereresetasrapidlyaspossible.Samplesfrom geology.
thetentrapsineachcollectionwerepooledandtakento
the laboratory for sorting.
Results
All catchments
Analyses: ordination and classification
A total of 105 spider species were recorded from the
The multivariate techniques of ordination and classi- ERSsitesandafulllist,withthenumberofsitesineach
ficationhaveconsistentlybeenusedtoassessdifferences catchment from which each species was recorded, is
in invertebrate species assemblages, including in a given in the Appendix.
number of spider investigations (e.g. Rushton & Eyre, The variation along axis 1 (eigenvalue 0.377) of the
1989, 1992; Downie et al., 1995). These techniques ordination of all site lists was from ERS by the small
produce results which can be interpreted in the light of tributaries of the Spey near the origin to sites by the
known environmental variables and habitat types, and downstream Tweed and Nith at the other end of the
grouptogethersimilarsitesbasedonspeciesassemblage axis. The sites near the origin of axis 2 were open, dry,
composition. cobble-dominatedsedimentswithlittlevegetationonthe
In order to investigate the variation in the distri- Nith,CarronandTweed,whilstthesitesattheotherend
bution of the spider species assemblages, the data were weredampsandandshingleERSwithmorevegetation.
ordinated using detrended correspondence analysis Sites shaded by trees by the streams of the Carron and
(DECORANA—Hill, 1979). No transformation of the theNithwereneartheoriginofaxis3,andopensitesby
datawascarriedoutandthenumberofsegmentsusedin the Nith and Tweed with sparse vegetation were at the
therescalingwas26.Thepresence/absenceofspecies,in other end.
lists containing five or more species, was used in the Fourgroupsweregeneratedintheclassificationofall
ordinations,asinotherworkwithspiders(e.g.Rushton the sites in the four catchments, and the frequency of
&Eyre,1989,1992).Classificationwascarriedoutusing occurrence of species in the groups is shown in Table 1.
fuzzy set clustering (Bezdek, 1981) based on the ordina- Group 1 included 44 sites, 15 from the Carron, mainly
tion, as in work on other invertebrate groups (e.g. Eyre by the upstream river and by streams, two from
et al., 2001a,b). The site scores on the first three axes of tributaries of the Nith, 16 from the upstream Spey and
theordinationwereusedfortheclassificationofsitesin tributaries, and 11 from tributaries of the Tweed. These
all catchments, but with the sites in individual catch- ERS had mixed particle sizes usually with sand, were
ments the scores from the first two axes were used mainly dry and had sparse vegetation. This group had
because the third axis could not be explained. the highest incidence of Trochosa terricola Thorell,
In addition to the ordination by DECORANA, con- Drassodes cupreus (Blackwall), Alopecosa pulverulenta
strainedordination(CANOCO—TerBraak,1987)was (Clerck), Xysticus cristatus (Clerck) and Pachygnatha
also used with a number of environmental variables. degeeri Sundevall. Group 2 included 38 sites, 11 from
Both DECORANA and CANOCO analyses were the Carron, four from the upstream Nith and
carried out using the CANOCO software. A sediment tributaries,16fromtheSpeytributaries,andsevenfrom
index was generated using a DECORANA ordination the Tweed tributaries. These were bare sites on larger
of an estimate of particle size at each ERS site. The areas of mixed dry sediment than those in group 1,
particles and their approximate sizes were: silt generally further down the catchments. They had the
(<0.2mm), sand (0.2–2mm), shingle (2–10mm), mostOedothoraxretusus(Westring),butwereotherwise
pebbles(10–50mm),cobbles(50–100mm)andboulders similar in species occurrence to group 1 (e.g. Pardosa
(>100mm). The percentage of each particle size was agricola(Thorell)andP.pullata(Clerck))butwithmore
estimated, to the nearest 5%, as used by Eyre et al. Oedothorax apicatus (Blackwall). There were 37 sites in
(2001a,b).Theaxis1siteordinationscoreswereusedas group3,twofromthedownstreamCarron,14fromthe
M.D.Eyre,J.C.Woodward&M.L.Luff 289
Species Group sites of group 2, with these sites also being opposite the
1 2 3 4 vegetation cover variable, indicating bare, open sedi-
Haplodrassussignifer(C.L.Koch) 45 11 — — ments. Group 3 and 4 sites were situated along the
Xysticuscristatus(Clerck) 52 13 — 3 positiveaxis1,withthelowlandvariableindicatingsites
Drassodescupreus(Blackwall) 70 53 8 3 in the Nith and Tweed catchments. The sites in group 3
Pardosapullata(Clerck) 41 37 3 3 weremainlydownstreamsites,asindicatedbythewidth
Robertuslividus(Blackwall) 39 11 — 3
variable, whilst the sites in group 4 had the most
Tisovagans(Blackwall) 25 8 3 3
vegetation, as shown by the cover variable.
Alopecosapulverulenta(Clerck) 59 39 14 7
Piratapiraticus(Clerck) 5 21 11 —
TrochosaterricolaThorell 73 53 19 20
Individual catchments
Trochosaruricola(DeGeer) 30 3 8 17
Diplocephaluscristatus(Blackwall) 25 21 — 7
River Carron
Pardosaagricola(Thorell) 75 79 62 13
PachygnathadegeeriSundevall 52 32 35 13 TheordinationoftheCarrondataproducedanaxis1
WalckenaeriaacuminataBlackwall 25 21 — 17 (eigenvalue 0.442) with open, bare ERS by the down-
Oedothoraxretusus(Westring) 48 74 59 57
stream river near the origin and tree-shaded sediments
Erigonedentipalpis(Wider) 43 63 84 63
by streams at the other end. Axis 2 also had the open,
Pardosaamentata(Clerck) 84 97 92 73
Oedothoraxapicatus(Blackwall) 27 58 97 63 baresedimentsneartheorigin,withthesmall,upstream
Oedothoraxfuscus(Blackwall) 14 26 27 33 river ERS next to moorland at the other end. The
ErigoneatraBlackwall 25 53 86 73 classification of the Carron data yielded three groups,
Dicymbiumtibiale(Blackwall) 9 3 — 27 and the frequency of occurrence of species in these
PachygnathaclerckiSundevall 16 16 49 80
groups, and in the groups generated by the classifica-
LepthyphanteszimmermanniBertkau 7 — 3 47
tions of the other catchments, is shown in Table 2.
Leptorhoptrumrobustum(Westring) 2 5 8 50
Gongylidiumrufipes(Linnaeus) — — 3 23 Group 1 included 10 sites, all by the upstream river.
Bathyphantesgracilis(Blackwall) — 5 5 33 These small areas of sediment were open and dry, with
mainly small particles, and were next to moorland.
Table1: Thefrequencyofoccurrence(%)ofspiderspeciesinthefour There was a high incidence of Pardosa pullata, P.
groupsgeneratedfromtheclassificationofallsitelistsfrom amentata (Clerck), Trochosa terricola and Oedothorax
the four catchments (minimum >20% in one group). The retusus. There were 14 sites in group 2, 12 by the mid
speciesorderisasforthefirstaxisoftheordination.
and downstream river and two by streams. These were
mainly on large areas of sediment with a mixture of
particle sizes, from boulders to sand, and were bare or
Nith, seven from the Spey, and 14 from the upstream
with sparse vegetation. Erigone dentipalpis, Pardosa
Tweed. These ERS were a mixture of dry and damp
agricola and P. amentata were all numerous. Group 3
particle sizes, and were by the main rivers with either
included five sites, all by streams with small particles,
ruderal or rank vegetation. There was the highest inci-
andallshadedbytrees.Therewasthehighestfrequency
dence of Erigone dentipalpis (Wider), E. atra Blackwall
of Robertus lividus (Blackwall) and Walckenaeria
and Oedothorax apicatus, and few or no species in
acuminata Blackwall, and several species, including
genera such as Xysticus, Drassodes and Haplodrassus.
Lepthyphantes zimmermanni and Neriene clathrata
Group 4 included 30 sites, one by a stream of the
(Sundevall), were found only in this group.
Carron, six from the Nith, one from the Spey, and 22
fromlargetributariesandthedownstreamTweed.These
were either sand and shingle or sand and silt ERS, and
weredampwitheitherrankorshrubvegetationorwere
shaded by trees. The species in this assemblage were
similar to those of group 3, but with the highest fre-
quencyofPachygnathaclerckiSundevall,Lepthyphantes
zimmermanni Bertkau and Leptorhoptrum robustum
(Westring).
The constrained ordination biplot (Fig. 2) indicated
that the major factor affecting spider assemblage distri-
bution was differences in the catchment types, with the
highland sites split from the lowland sites. The river
width and vegetation cover variables had a similar
amount of influence, but the sediment variable was less
important.Thesitesingroups1and2wereconcentrated
along the negative axis 1, with sites in group 1 spread Fig.2: Constrainedordinationbiplotshowingthedistributionofsites
along most of axis 2 and sites in group 2 generally inthefourgroupsgeneratedfromtheclassificationofallthe
limited to the negative axis 2. There was considerable sites, the sediment index (sediment), river width (width) and
vegetationcover(vegetation),shownbyarrows,andthehigh-
overlapofsitesingroups1and2,andtheyweremainly
land(high)andlowland(low)catchmentvariables,shownby
highlandsitesinthecatchmentsoftheCarronandSpey.
dots. Polygons enclose the sites in each group, indicated by
The sediment variable indicated larger particles in the numbersinitalics.
290 Spidersofexposedriverinesediments
TheconstrainedordinationbiplotfortheCarronsites, sediments with rank vegetation, by the main river and
together with those of the other three catchments, is tributaries,wereneartheoriginofaxis2.Thesitesatthe
shown in Fig. 3. The most important variable was veg- otherendofthisaxiswerealsomainriverandtributary
etation cover, with sites in group 3 by streams with tree ERS, but were damp with less dense vegetation. Only
shading having an assemblage distinct from the assem- twogroupsweregeneratedfromtheclassificationofthe
blagesintheothertwogroups.Riverwidthandsediment Nith sites. Group 1 included 19 sites, 15 by the main
had a similar influence on species assemblage distribu- river and four by tributaries. There was a mixture of
tion,withwidthrelatedtothedownstreamsitesingroup sediment types, from cobble-dominated to sand ERS,
2andthesedimentvariablerelatedtositesingroup1. and the sites were bare or with sparse vegetation. There
was a high incidence of Oedothorax apicatus, Pardosa
amentata,P.agricolaandErigoneatra,andanumberof
River Nith
species occurred only in this group, including Pachy-
Axis1(eigenvalue0.604)oftheordinationoftheNith gnatha degeeri and Trochosa terricola. There were seven
sites had sites with small particles and sparse vegetation sites in group 2, all by the main river. These were also
by streams near the origin and downstream main river composed of a mixture of particles, but had either rank
sites shaded by trees at the other end. Dry, open vegetation or were shaded by trees. They had the most
Species Carrongroup Nithgroup Speygroup Tweedgroup
1 2 3 1 2 1 2 3 1 2 3
Zeloteslatreillei(Simon) — — 38
Agynetadecora(O.P.-Cambr.) — 21 —
Steatodaphalerata(Panzer) 7 47 38
Micariapulicaria(Sundevall) — 6 38
Haplodrassussignifer(C.L.Koch) 40 14 40 7 41 63
ClubionacomtaC.L.Koch — — 40 — 12 38
Antisteaelegans(Blackwall) — — 25
Xysticuscristatus(Clerck) — 41 63 — 7 73
Drassodescupreus(Blackwall) — 43 20 26 — 20 76 100 — 20 93
Pardosapullata(Clerck) 90 14 — 20 29 75 — 7 47
Robertuslividus(Blackwall) 60 7 100 — 18 50
Tisovagans(Blackwall) 4 20 60
Microlinyphiapusilla(Sundevall) — 43 20
Alopecosapulverulenta(Clerck) 30 43 40 21 — 20 59 38 — 27 87
Piratapiraticus(Clerck) 32 — — 6 25
Agynetaolivacea(Emerton) 30 7 —
TrochosaterricolaThorell 80 64 40 37 — 20 53 50 25 33 80
Trochosaruricola(DeGeer) — 40 53
Diplocephaluscristatus(Blackwall) — 36 60 — 29 — 8 7 27
Pardosaagricola(Thorell) 30 86 40 63 14 93 94 50 29 33 93
PachygnathadegeeriSundevall 50 14 60 58 — 13 24 25 21 40 80
WalckenaeriaacuminataBlackwall — 7 80 — 18 25 — 40 40
Walckenaerianudipalpis(Westring) — — 38 4 33 7
Lepthyphantestenuis(Blackwall) 14 40 20 — 27 13
Hypommabituberculatum(Wider) 10 14 40 8 47 20
Oedothoraxretusus(Westring) 90 50 60 74 29 53 71 — 58 73 53
Monocephalusfuscipes(Blackwall) — 7 40 — 27 7
ClubionareclusaO.P.-Cambr. 4 27 —
Nerieneclathrata(Sundevall) — — 60 — 43 — 6 25
Erigonedentipalpis(Wider) 30 79 40 74 43 67 29 13 88 80 73
Pardosaamentata(Clerck) 100 93 80 79 43 93 76 75 92 100 100
Oedothoraxapicatus(Blackwall) 10 36 40 89 43 80 65 25 92 33 27
Oedothoraxfuscus(Blackwall) 60 7 — 26 29 25 53 40
ErigoneatraBlackwall 40 50 — 79 71 73 53 — 88 67 27
Dicymbiumtibiale(Blackwall) 8 40 7
Troxochrusscabriculus(Westring) — 43 4 33 20
Arctosacinerea(Fabricius) 26 —
Diplostylaconcolor(Wider) — — 40
PachygnathaclerckiSundevall 30 7 — 37 100 40 6 — 67 80 13
Linyphiatriangularis(Clerck) — 29
LepthyphanteszimmermanniBertkau — — 60 — 29 33 20 —
Leptorhoptrumrobustum(Westring) 58 33 7
Gongylidiumrufipes(Linnaeus) 5 43
Bathyphantesgracilis(Blackwall) 11 43
Diplocephaluslatifrons(O.P.-Cambr.) — 29
Table2: Thefrequencyofoccurrence(%)ofspiderspeciesinthegroupsgeneratedfromtheclassificationsofsitesinthefourindividualcatchments
(minimum>20%inonegroupineachclassification).Thespeciesorderisasforthefirstaxisofanordinationofthecompletedata.
M.D.Eyre,J.C.Woodward&M.L.Luff 291
PachygnathaclerckiandalotofErigoneatra,aswellas Alopecosa pulverulenta and Oedothorax retusus. There
thepresenceofspeciesassociatedwithtrees,e.g.Neriene were eight sites in group 3, three by small streams and
clathrata and Linyphia triangularis (Clerck). five by large tributaries. These were stable ERS with
Vegetation cover was shown by the constrained ordi- patchy, short vegetation. They had the most Drassodes
nation to be the most important variable affecting cupreus and a high incidence of Pardosa pullata and
species assemblage composition, with the split between Xysticus cristatus.
thetwogroupsmainlydependentonthisvariable.River The constrained ordination of the Spey data showed
widthandsedimentcompositionhadalimitedinfluence that vegetation cover and river width had a similar
on species assemblage distribution (Fig. 3). amount of influence, with the sediment variable less
important. The distribution of sites in the three species
assemblage groups was less clear than with the other
River Spey
catchments,butsitesingroups1and3,withvegetation,
Axis 1 (eigenvalue 0.436) had sandy ERS with rank were generally different from those in group 2, where
vegetation by the downstream main river near the there was little vegetation. The other main difference in
origin, with stable sediments with short, patchy vegeta- assemblage distribution was between sites by the main-
tion by small tributaries at the other end. Dry ERS by stream river and large tributaries in groups 1 and 2 on
largetributarieswithamixtureofsedimentparticlesand theonehand,andsitesbysmallertributariesingroup3
sparsevegetationwereneartheoriginofaxis2.Thesites on the other.
at the other end of this axis were the sandy main river
sites with rank vegetation. Three groups were generated
River Tweed
by the classification. Group 1 included 15 sites, nine by
themainriver,fourbylargetributariesandtwobysmall The ordination of the spider data from the Tweed
tributaries. These were sites with a mixed composition, catchment produced an axis 1 (eigenvalue 0.416) with
some sandy and some dominated by cobbles and downstream river sites with sand and silt ERS and
pebbles,withmosthavingeitherruderalorrankvegeta- considerable vegetation near the origin. The sites at the
tion. There was a high incidence of Pardosa amentata, otherendofthisaxiswerebytributaries,withsandand
P. agricola and Erigone atra, although this group had shingle and sparse vegetation. Axis 2 had sand and
thefewestspecies.Group2included17sites,fourbythe shinglesiteswithrankvegetationbytributariesnearthe
upstream river, 12 by large tributaries and one by a origin, and sites by the main river with mixed sediment
small tributary. These sites also varied in sediment compositionandsparsevegetationattheotherend.The
compositionbutweremoreopenthanthoseingroup1, classification of the Tweed sites produced three groups.
with only sparse vegetation if any. They again had a Group 1 included 24 sites, 23 by the main river, occur-
lot of Pardosa agricola and the highest frequency of ringallthewaydown,andonebyatributary.Therewas
Fig.3: Constrainedordinationbiplotsshowingthedistributionofsitesinthegroupsgeneratedfromtheclassificationofsitesinthefourindividual
catchments,andthesedimentindex(sediment),riverwidth(width)andvegetationcover(vegetation),shownbyarrows.Polygonsenclosethe
sitesineachgroup,indicatedbynumbersinitalics.
292 Spidersofexposedriverinesediments
a mixture of sediment types, from cobble-dominated to such as Oedothorax apicatus and Trochosa terricola
sandandsilt,mostwithsparsevegetationbutsomewith which prefer dry, open and sandy substrates, including
rank vegetation. There was a high incidence of Erigone grasslands (Rushton & Eyre, 1992), were found in
atra, E. dentipalpis, Oedothorax apicatus and Pardosa groupswheresedimentsprovidedtheseconditionsinall
amentata. There were 15 sites in group 2, four by the four catchments. These species of open, bare sites con-
main river, six by large tributaries and five by small trasted with those such as Neriene clathrata found on
tributaries. Most had sediments with small particles, vegetated sediments in group 3 of the Carron and Spey
especiallysand,andweredampwithrankvegetation.As and group 2 of the Nith catchments. Vegetation archi-
well as Pardosa amentata at all these sites, they had the tecture has long been understood to be an important
most Pachygnatha clercki and Oedothorax retusus. factor affecting spider species assemblage distribution
Group 3 included 15 sites, 14 by small tributaries and (e.g. Rushton & Eyre, 1992; Downie et al., 1995). One
one by a large tributary. These were sand and shingle obviousdifferencebetweentheassemblagesonERSand
ERS, mainly dry, and either bare or with sparse vegeta- those reported from grasslands and moorlands (Rush-
tion. Pardosa amentata again occurred at all sites and ton & Eyre, 1989, 1992; Downie et al., 1995) was the
there was the highest frequency of Trochosa terricola, paucity of species on ERS. These sediments appear to
Pardosa agricola, Alopecosa pulverulenta, Drassodes have considerably fewer species than less disturbed and
cupreus and Xysticus cristatus. more vegetated habitats, with Zulka et al. (1998) also
The constrained ordination of the Tweed data indi- recording only eight species from a gravel ERS.
cated that river width was the most important variable, There were major differences in the species assem-
with vegetation cover and sediment composition having blages between the highland and lowland catchment
lessinfluence.Thisisincontrasttotheothercatchments types, with two groups of the classification of all sites
where vegetation cover was more important. The distri- being dominated by highland ERS and two by lowland
bution of species assemblages was primarily related ERS. The secondary variation in the ordination of
to site location in the catchment, with sites in group 1 all-site data was mainly related to site position in the
being mainly by the downstream main river, those in catchment, as reflected by river width, and the amount
group 2 by the mid river and larger tributaries, and ofvegetationonsites.Thevegetationcovervariablewas
thoseingroup3mainlybythesmallertributaries.There the most influential factor in explaining the distribution
were some differences in vegetation cover, with more of assemblages on ERS in the individual catchments of
vegetationonthegroup2sitesthanonsitesingroups1 the Carron, Nith and Spey, whilst river width was most
and 3. importantintheTweedcatchment.Vegetationcover,or
the lack of it, was shown to be a factor in all the
classifications where the major differences between sites
Discussion
inthehabitatgroupstendedtobereflectedinaprogres-
Whilst a considerable amount of previous work on sion from bare sediment, through sparse and rank
spider species assemblages next to rivers has been con- vegetation, to tree-shaded ERS. Sediment composition
cerned with various floodplain and other habitats hasbeenfoundtobeanimportantvariableaffectingthe
(Greenwoodetal.,1995;Gajdosˇ,1996;Hendrickxetal., distribution of ground beetles on ERS (Eyre & Lott,
1998; Bell et al., 1999), other recent work has concen- 1997)butitappearstobelessimportantforspiders.The
trated on the spiders found on sediments (Smit et al., vegetationonERStendstoberelatedtothepositionof
1997, Sadler & Petts, 2000; Wenninger & Fagan, 2000). the site in the catchment, with the distribution of sites
One aspect of the results presented here, and in other in the habitat groups grouped in distinct bands limited
surveyssuchasthatofSadler&Petts(2000),isthelarge to, for instance, tributaries or downstream main river
number of species recorded which are not specific to stretches. However, it was interesting that the vegetated
riverine sediments. Pardosa agricola was the only ERS in the Carron catchment were by the stream
specialist ERS species (Albert & Albert, 1976) recorded tributaries and the upstream river, whilst they were
fromsitesinallcatchments,andtheonlyotherspecialist distributed on the mid and downstream stretches of the
ERSspeciesintheUK,Arctosacinerea(Fabricius),was rivers of the other three catchments.
recorded only from its usual habitat of dry, cobble- This survey shows that there were distinct spider
dominatedERSwithsomesand(Framenauetal.,1996), assemblagespresentonERSbyriversandtributariesin
by the River Nith. Scottish and northern English catchments. Other inver-
Species usually recorded from short and agricultural tebrate assemblages, such as ground beetles and rove
grasslands, such as Erigone atra and E. dentipalpis beetles (Eyre et al., 2001a,b), show similar patterns of
(Rushton&Eyre,1989,1992),wererecordedfrequently distributiononERSbutitappearsthatnumbersofboth
from sites in group 1 of the Nith, Spey and Tweed spider species and assemblages found on the Scottish
catchments, whilst those of unmanaged grasslands (e.g. and northern English sediments were smaller than for
Pachygnatha clercki) were found at a number of sites in the beetle groups. There were also fewer habitat groups
group 1 of the Carron, Spey and Tweed and group 2 of in a classification of spider grassland habitats in north-
the Nith classifications. The wetland species Pirata east England (Rushton & Eyre, 1992) than in a corre-
piraticus and Leptorhoptrum robustum were found at sponding ground beetle classification (Luff et al., 1992).
sitesingroup1oftheNithandTweedrespectively,and In surveys of epigeal invertebrates covering the same
P. piraticus also in group 3 of the Spey, whilst species range of sites, it appears that different numbers of
M.D.Eyre,J.C.Woodward&M.L.Luff 293
habitattypestendtobeidentifiedfordifferentgroupsof Environmental monitoring, surveillance and conservation using
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and prediction of grassland habitats using ground beetles
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MALT, S. 1995: Epigeic spiders as an indicator system to evaluate
WewouldliketothankDrPMerrettandtworeferees biotope quality of riversides and floodplain grasslands on the
forconsiderablehelpinimprovingthispaper.Thework RiverIlm(Thuringia).InV.Ru˚žicˇka(ed.),Proceedingsofthe
was carried out as part of a survey of ERS for Scottish 15thEuropeanColloquiumofArachnology:136–146.Instituteof
Entomology,C{eskéBudeˇjovice.
Natural Heritage.
MANDERBACH,R.&FRAMENAU,V.W.2001:Spidercommu-
nities of riparian gravel banks in the northern parts of the
EuropeanAlps.Bull.Br.arachnol.Soc.12:1–9.
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294 Spidersofexposedriverinesediments
Familyandspecies Carron Nith Spey Tweed Familyandspecies Carron Nith Spey Tweed
Liocranidae Walckenaeriakochi(O.P.-Cambr.) — — — 1
Agroecaproxima(O.P.-Cambr.) — — 1 — WalckenaeriaacuminataBlackwall 5 2 5 11
Dicymbiumnigrum(Blackwall) — — — 2
Zoridae
Dicymbiumtibiale(Blackwall) 2 — 1 9
Zoraspinimana(Sundevall) 1 — — —
Gnathonariumdentatum(Wider) — 2 1 1
Thomisidae Gongylidiumrufipes(Linnaeus) — 4 — 4
Xysticuscristatus(Clerck) 2 3 13 12 Dismodicusbifrons(Blackwall) 1 1 1 —
XysticusbifasciatusC.L.Koch — — 2 — Hypommabituberculatum(Wider) 5 2 2 12
Ozyptilatrux(Blackwall) 1 1 3 4 Baryphymapratense(Blackwall) — — — 6
Baryphymatrifrons(O.P.-Cambr.) — — — 1
Philodromidae
Gonatiumrubens(Blackwall) 1 — — 2
Tibellusmaritimus(Menge) — — — 1
Gonatiumrubellum(Blackwall) 1 1 — —
Salticidae Pocadicnemispumila(Blackwall) 1 — — 1
Salticusscenicus(Clerck) — — — 1 Oedothoraxgibbosus(Blackwall) 1 2 3 2
Heliophanusflavipes(Hahn) — — 1 — Oedothoraxfuscus(Blackwall) 7 7 2 19
Oedothoraxretusus(Westring) 19 16 19 33
Lycosidae
Oedothoraxapicatus(Blackwall) 8 20 25 31
Pardosaagricola(Thorell) 17 13 34 26
Trichopternathorelli(Westring) — — — 3
Pardosapalustris(Linnaeus) — — 1 3
Pelecopsismengei(Simon) — — — 1
Pardosapullata(Clerck) 11 1 14 8
Pelecopsisparallela(Wider) 1 — 2 —
Pardosaamentata(Clerck) 27 18 33 52
Silometopuselegans(O.P.-Cambr.) — — 1 —
Pardosanigriceps(Thorell) — — — 3
Tisovagans(Blackwall) 1 1 1 13
Alopecosapulverulenta(Clerck) 11 4 16 17
Troxochrusscabriculus(Westring) — 3 3 9
Trochosaruricola(DeGeer) 1 3 4 14
Monocephalusfuscipes(Blackwall) 3 — 1 5
TrochosaterricolaThorell 19 7 16 23
Micrargusherbigradus(Blackwall) 2 — — 3
Arctosaperita(Latreille) — — 1 —
SavigniafrontataBlackwall 3 1 — —
Arctosaleopardus(Sundevall) — 1 — —
Diplocephaluscristatus(Blackwall) 8 1 4 7
Arctosacinerea(Fabricius) — 5 — —
Diplocephaluspermixtus(O.P.-Cambr.) 1 — — —
Piratapiraticus(Clerck) 2 6 3 3
Diplocephaluslatifrons(O.P.-Cambr.) — 2 — 2
Agelenidae Araeoncuscrassiceps(Westring) 1 — — 1
Cryphoecasilvicola(C.L.Koch) 1 — 4 — Millerianainerrans(O.P.-Cambr.) 1 — 1 —
Erigonedentipalpis(Wider) 16 17 16 43
Hahniidae
Erigonepromiscua(O.P.-Cambr. 1 — — —
Antisteaelegans(Blackwall) 1 — 2 3
ErigoneatraBlackwall 11 20 20 34
Hahnianava(Blackwall) — 1 — —
Leptorhoptrumrobustum(Westring) — 1 — 20
Mimetidae Hilairaexcisa(O.P.-Cambr.) 1 — — —
Erofurcata(Villers) — — — 1 Haloratesdistinctus(Simon) — 1 — 4
Porrhommaconvexum(Westring) — 1 — —
Theridiidae
Agynetasubtilis(O.P.-Cambr.) — — 1 —
Steatodaphalerata(Panzer) — 2 12 2
Agynetadecora(O.P.-Cambr.) 4 — — —
Steatodabipunctata(Linnaeus) — 1 — —
Agynetaolivacea(Emerton) 4 — — —
Robertuslividus(Blackwall) 12 1 7 2
Meionetasaxatalis(Blackwall) 1 — — —
Nesticidae Centromeritaconcinna(Thorell) — — 1 1
Nesticuscellulanus(Clerck) — — 1 — Saaristoaabnormis(Blackwall) 2 — — —
Bathyphantesgracilis(Blackwall) — 5 1 7
Tetragnathidae
Bathyphantesparvulus(Westring) — — — 4
PachygnathaclerckiSundevall 4 14 7 30
Bathyphantesnigrinus(Westring) — 1 — —
PachygnathadegeeriSundevall 10 11 8 22
Kaestneriapullata(O.P.-Cambr.) — 1 — 1
Metellinamengei(Blackwall) 1 1 1 1
Diplostylaconcolor(Wider) 2 — — 3
Linyphiidae Stemonyphanteslineatus(Linnaeus) — — 1 —
Ceratinellabrevipes(Westring) 1 — 1 — Bolyphantesluteolus(Blackwall) — — — 2
Ceratinellabrevis(Wider) 2 — — 1 Lepthyphantestenuis(Blackwall) 6 — — 6
Walckenaerianudipalpis(Westring) 2 — 3 7 LepthyphanteszimmermanniBertkau 3 2 2 11
Walckenaeriavigilax(Blackwall) — 1 — — Lepthyphantespallidus(O.P.-Cambr.) — — — 2
Walckenaeriaantica(Wider) — — — 1 Linyphiatriangularis(Clerck) 1 2 2 1
WalckenaeriacuspidataBlackwall 1 — 2 1 Nerieneclathrata(Sundevall) 3 3 3 5
WalckenaeriaunicornisO.P.-Cambr. 1 — — — Microlinyphiapusilla(Sundevall) 7 — 2 —