Table Of Content2002. The Journal of Arachnology 30:389-402
ON THE NATURE OF AGROBIONT SPIDERS
Fereec Samu: Plant Protection Institute, Hungarian Academy of Sciences, RO. Box
102, Budapest, H-1525 Hungary, E-mail: [email protected]
Csaba Szieetar: Berzsenyi College, P.O.Box 170, Szombathely, H-9701 Hungary
ABSTRACT. Results from a 10 year survey of spiders in Hungarian arable and natural grassland habitats
We
are cumulated in order to reveal the key characteristics of agrobiont species. define agrobionts as
species that reach high dominance in agroecosystems. The most dominant species, Pardosa agrestis, on
average accounted for 40% of the total spider population in Hungarian arable fields. The presence of
agrobionts led to a strong skew in arable spider community species distriibution. Regardless of the over-
dominance by agrobionts, arable spider communities had a potential for very high species richness. The
agrobiont segment of arable spider communities showed very little field-to-field or regional variation, i.e.
the same agrobiont species occurred in all fields. Agrobionts were indicators of arable habitats, and were
rare in other habitat types, but in many species preferences for specific natural habitat types could be
shown. These natural habitat types were often strongly abiotically driven, frequently disturbed habitats.
The life cycle of agrobionts showed synchronization with the arable crop-growing season. While many
closely related non-agrobiont species had maturity and reproductive periods either earlier or later than the
main crop vegetation period, agrobionts invariably reached adulthood and reproduced during that period.
Association with frequently disturbed natural habitats and phenological synchronization with the annual
arable disturbance regime are such traits that support the theory that agrobiont species are adapted to
predictably ephemeral habitats.
Keywords: Community structure, arable fields, cyclic colonization, life history strategy
Agricultural habitats are artificially created a few super-abundant species often dominate
and maintained by periodic disturbances to be these systems. The dominating species, since
more uniform than most natural habitats. Ag- the seminal paper by Luczak (1979) are called
ricultural systems have been present for only ‘agrobiont’ species. The dominance of agro-
a short evolutionary time period. Thus they bionts has been established in various crops
are likely to lack co-evolved animal commu- and geographical areas (Richman et al. 1990;
nities. Many ‘empty niches’ may offer them- Nyffeler & Breeee 1992; Blick et al. 2000)
selves for colonization both by herbivorous but many questions about the ecological strat-
and predatory animals from natural habitats. egies of agrobionts are still open. Duffey
It is still debated as to what degree these hab- (1978) and Luczak (1979) predicted that agro-
itats are recolonized repeatedly, or to what ex- bionts are habitat generalists, “eurytopic”
tent they are self-perpetuating systems, at least species, that occur sometimes in quite con-
at the metapopulation level (Duffey 1978; trasting habitats. Recently Wissinger (1997)
&
Bishop Riechert 1990; Wissinger 1997). To proposed that agrobionts are species with an
study the community assembly rules in agri- “adaptation to predictably ephemeral habi-
APEH
cultural areas, and to study the ecological tats” (APEH). According to the hy-
characteristics of the individual species should pothesis agrobionts are not generalist species,
be revealing for the basic ecological phenom- rather they evolved a specific strategy, called
ena, and may provide opportunities to shift the the “cyclic colonization” strategy. Through
balance in agricultural communities towards cyclic colonization, agrobionts can escape the
beneficial organisms, and thus promote bio- regularly occurring disturbances by dispersing
logical control. to permanent refugia. The strategy requires
Considering comm.unities of predatory ar- specific life history adaptations, with special
thropods in agricultural areas, and those of regard to synchronization with the periodic
spiders in particular, it has been observed that disturbances through the timing of reproduc-
389
390 THE JOURNAL OF ARACHNOLOGY
—
Table 1 . Sampling locations that provided data for the meta-analysis. (A = alfalfa, C = cereal, G =
grassland (No. of sub-types), P = pitfall, D = suction sampling.)
No. of
County Settlement sites Habitats Method
Baranya Nagyharsany G(2) P
1
Csongrad Kiralyhegyes 2 A, G(2) P, D
Heves Hatvan C P
1
Heves Recsk G(l) D
1
Nograd Bank C D
1
Nograd Diosjeno A D
1
Nograd Paszto C D
1
Nograd Retsag 1 C, G(l) D
Nograd Romhany A, G(l) D
1
Pest Kartal 2 C P
Pest Nagykovacsi 3 A, C, G(2) P, D
D
Pest Paty 3 A, C, G(l)
D
Pest Budapest 1 G(l) P,
Tolna Decs A, C D
1
Tolna Felsonana 5 A, C P, D
Tolna Szekszard A, C D
1
Tolna Tevel 1 A, C P, D
Vas Szombathely 2 C P
Veszprem Somlovasarhely G(l) P
1
tion, and the presence of various colonizer and dominance structure of the whole spider com-
overwintering stages. Other ecological char- munity, as compared to natural grassland
acteristics, such as competitive ability (Mar- communities; (iii) how agrobiont composi-
&
shall Rypstra 1999), tendency for cannibal- tions vary field-by-field and regionally; (iv)
&
ism and intraguild predation (Wagner Wise what the original natural habitats of the agro-
1996; Hodge 1999; Samu et al. 1999b), and bionts are; and (v) what commonalties can be
colonization power (Richter 1970; Sunderland found in their life cycles, and how do these
&
Topping 1993; Marshall et al. 2000) are ad- relate to the disturbance regime of arable
ditional features that might be important char- fields?
acteristics of the agrobionts’ ecological per-
METHODS
sona. Although the importance of life history
characteristics has been stressed in earlier Arachnological results from various faunis-
studies (Duffey 1978; Toft 1989), no compre- tic and agro-ecological projects on arable
&
hensive comparisons of regional agricultural fields (Samu et al. 1996; Toth Kiss 1999;
spider faunas and those occurring in natural Szinetar & Miltenyi 2000; Samu et al. 2001)
habitats has been made, to date. were accumulated into a common database
The present paper tries to reveal the eco- (Samu 2000). The present paper provides a
logical nature of the agrobiont species in Hun- meta-analysis of these data, focused on the
garian arable fields. We hope to find common ecology of agrobiont species.
ecological features of agrobiont species, and The sampling methods were pitfall trapping
in this way get closer to their secret of being and hand-held suction sampling. Original sur-
successful in human influenced habitats. vey datasets contained information on c.
Agrobionts are characterized through a meta- 110,000 individuals, but we restricted the
analysis of 10 years of survey data on spider scope of the analysis by the following criteria:
assemblages of Hungarian arable fields. In the (i) only adults were considered; (ii) only those
meta-analysis we seek to clarify (i) which are data sets were included in which sampling
the main agrobionts in Hungarian arable lasted for at least one year for the given field/
fields; (ii) how the presence of these super- habitat patch and for the given method, and
dominant species affects the diversity and (iii) the total catch of spiders was greater than
—
( .
SAMU AND SZINETAR-ON THE NATURE OF AGROBIONT SPIDERS 391
of
2
out
o
present ,4.^-c-(dS c-2cd doo 0m0CN00 rrin4n (N V(qO2 imqOnv 0q0 V'1dO^- ccqnn foqMd Vq(O2 Od-V VO Ov Of—v 0r=0H
00 ON 00 r- «N in CN CN
2
g
eS
was
species
2
c
d o
a .o2 d PVO do c0n0 drr--- d q q00 in q00 OCnv| q00 q00 m— o mo00 VO
sto 22. 0000 o ViOn 00 00 O(VN ri—n( VdO’ iVnO (VMO crn- in’ VO^ r- c0n0
fields
a
of cG3O
percentage COD
m m o O
C3 VO VO ov ov VO d’ CM in (N
.a ^^ O) q q CN q qd q q q q 0d0 0d0 dr- VdO VdO idn q
00 cn VO p_i f—
the a cn
Q
indicate
o m m
d VO OCM Ov VdO dVO CM ov 00 VO VO O(N CM VO 0d0 00
columns 2o dCM qP00 qP V0O0 Ccnn| in cn CcMn CrM- VCMO CCMM C<Mi CM r- VO CPPM 26,752
o'
+-I
e2
two
Last
species.
(U <D
cd
2 'O 0) D D
(^u dCd 0) t! dcd (D CO
spider t0£u3 d2COQo><O3D> 2dcoed. 2ac I+S&_S)D .d:d2DaSm 2'222OSS o'dcCOd^Hd2oC«C-Od ’22dC^agGOj 22df2>ci>d% 22dc2cd 2<SWSCD 0C2§O 2.22Cad .22dc3a^s2o«2CO
alfalfa)
and
(cereal 'a
o
0)
a r-
00
arable
<u m ^
dominant .*ooai<C_CzuD)i 2CO 2'0^C&d0D VC<^^oO3OO0. i^2ac>yo?dd 0dd^Ce>0D 0^0 oC01=con~0dI( m02'^FCO»0=D-i( C0N0l 2irrun-- .SoMXcCWeC2-h)dD) 2202c^q0d 2D^00da1O00 CO0^<=wON013 00^2p^gl0\.l00^01oe000 2Si02con0d
most X-)d ‘(auU CO eg ^ d U uVWh d PQ a ^ O Co
T12h6.—e '2acccq/d«i. 00 •»=g«s.4 5s; <sc3j- ^Oo = -K 2sslso -^dHVO(B.UI ~Cg5 '•S^CSgQ*Iad 22*CssG1,o^ 2tSg2o 3^ sas '2s^Gs^ 'ata3a!>o« CCc.DD«
Table t(eU ^ sGo ^s^ 22to tCSoD tta»2 2Vaoj g<d3o Ctio.) ^a ~2a t«
C) •^§ (SO ^^ Cj a o .2 a ;C.DH
2 ^ O 2^ 2"C 2 Q- >< 2 2O ^C ^ I "a 2 *o_1 Total
—
392 THE JOURNAL OF ARACHNOLOGY
Species richness b) Alpha diversity
100
15
75
10
O
50
03 <
5
25
0
Alfalfa Cereals Grassland Alfalfa Cereals Grassland
Figure 1. a. Species richness (estimated by first order Jacknife estimator) and b. alpha diversity of
spider communities of habitat patches/fields belonging to the main habitat types investigated.
100 adult individuals for the field; (iv) results (fields were typically 30 ha, ranging between
&
were included from samples taken between 1.5 250 ha), or the natural equivalent, a
1990 and 2000. Since species composition is “habitat patch”. Samples conforming to the
dependent on trapping method, and pitfall above criteria were taken in 47 field/habitat
trapping yielded many more adults, commu- patches at 30 sites. The sites were in 19 lo-
nity structure and field-by-field comparisons calities in eight counties in Hungary (Table 1).
were made relying on pitfall trap data only. The main sampled habitat types were cereal
The spatial unit of the analysis was a field fields, alfalfa fields and natural or semi-natural
grassland areas. Grasslands could be classified
into five different sub-types: secondary, me-
70
60 sophile, saline, rock grasslands, and moist
50 meadows. Secondary grasslands developed
40
30 mainly on sites previously occupied by agri-
20
cultural fields or intensive pastures, later aban-
10
0oc) 0 doned but might receive occasional distur-
70
CcO 60 bances. They are colonized by numerous
E 50
o pioneering, introduced or ruderal species, but
D 40
0 30 a natural regeneration has already started. The
Dj 20
TO disturbance-induced simplified stratification is
C 10
0O 0 typical for the structure. Mesophile grasslands
!0_ 70
60 are a category for dense perennial grasslands
Q_
50
of lowlands and hills, fertilized and well-
40
30 drained. They are species rich grasslands with
20
10 23456789 a complex structure. Light disturbance, such
0 as occasional grazing or using them as hay
1 10 others
meadows is possible. Saline grasslands are
Species in dominance rank order comprised of salt steppes and saltmarsh mead-
—
Figure 2. The dominance structure of spider ows (and all the continuum between them) of
communities of habitat patches/fields belonging to the Pannonic plain. Large expanses of salt
the main habitat types investigated. steppe form an open landscape of short-grass
SAMU AND SZINETAR-ON THE NATURE OF AGROBIONT SPIDERS 393
RndField RndField
A) B)
cer-28
alf-30
alf-12
cer-27
cer-1 1
04 alf-21
W
s.
cer-11
cer-27 alf-30
cer-28 cer-20
alf-21
cer-20 alf-58 alf-58
1
Axis 1 Axis 1
—
Figure 3. Non-Metric Scaling (NMS) ordination plots, representing the Soerensen similarity structure
of selected arable fields, when A) the first eight dominant species; and B) the second eight dominant
species are considered. The random field was generated by shuffling mean dominances of the first 16
dominant species, (alf-x denotes alfalfa field; cer-x stands for cereal field, where x is identifier number of
the given field; RndField denotes the hypothetical field where spider community was created by random-
ization [see text for details].)
swards on slightly elevated ground and of inant and non-dominant species should he to
rills, eroded shallow depressions with bare or be arbitrary, but considering a rather conser-
sparsely vegetated saline soils. Because of vative 1% minimum dominance limit (i.e. an
poor drainage, the rills experience yearly agrobiont species should be represented by
flooding in springtime, but dry out completely more than 1% of all the individuals in the
by summer. The structure is simple and open. sampled assemblage) seems to be practical. It
Rock grasslands are xero-thermophile grass- is also important to consider how widespread
lands, on rocky areas or on rendzinas on hilly is the occurrence of a species in the consid-
or montaneous areas. They occupy sites with ered crop(s). The rest of the analysis concen-
a warmer, drier microclimate, in particular trates on the species listed in Table 2 and re-
south-facing slopes with extreme conditions fers to species that occur on more than 75%
of insolation, temperature variation and evap- of the fields and are above the 1% dominance
oration. They are rich in plant species, but the threshold as “agrobionts”. Species that are
structure is dominated by low grasses. Moist below this limit, but still common in fields are
meadows develope on moderately to very nu- called “agrophile” species after Luczak
trient-rich, alluvial or fertilized, wet or damp (1979).
soils, often inundated at least in winter, and Given the overwhelming dominance of
relatively lightly mowed or grazed. They in- agrobionts in arable fields, it is of interest to
clude a large number of distinctive and often see how overall community structure is af-
species-rich communities, many of which har- fected by them, what room is left for other
bor specialized and rare species of plants. species, and how agricultural spider commu-
nity structure compares to the closest natural
RESULTS AND DISCUSSION
systems, grassland habitats. Species richness
Agrobio—nts and agricultural spider com- of cereal, alfalfa and grassland field/habitat
munities. Taken together all arable (cereal patches was estimated from pitfall trap data
and alfalfa) data sets, a very distinctive list of with the first-order Jackknife richness esti-
the most dominant species arises (Table 2). mator (Fig. la) using Estimates (Colwell
The most dominant species are, by our defi- 1999), which gives a rather conservative es-
We
nition, the agrobiont species. regard any timate of species richness. Alpha diversity
delimitation where a borderline between dom- (Magurran 1988) for the same data set was
394 THE JOURNAL OF ARACHNOLOGY
s 5^ s
0fl) fQci,
40-)1 o A&CI •A2 ^Q
P
P 'I S' .3
s
5
O e O
'a
o
"§ o I
o
(U o o o
a.
•iM
bO 6,
s
cd
^ .2 ^ A=s
cereal alfalfa secondary saline mesophile rock moist O ^-2 6, A > A&0 ^
Arable/grassland habitattype m •t-l •S' Q,
> Oo a Q
— 0) s;
o
Figure 4. Percentage representation of agro= Q s c bo
M 2 s y o g 3
biont spiders (first eight species in Table 2) in var- "«o A^ N
ious habitat types in Hungary, A ^ o s
0) s N AQ -K, O^ ^ A
0) O§ ^ F 3
.a
also calculated (Fig, lb). Variation for both s ^ 'S
species richness and diversity values was high cu« ^ ^
a
(mean = 54,0%, mean ^ tQoo
CVri^^ness CVdiversity
43.3%, where CV = coefficient of variation), 5 Q
e
and no significant difference could be shown I Ago S^ N Q
among the different habitat types in either Q. A ^ A O A U
measure (one way ANOVA, richness: F —
= F =
0.015, df 2, 15, ns; diversity: 0.649, df
=
2, 15, ns).
e
While agricultural spider communities were 32 o
not different in terms of species richness and o cd c«
.2 ooGsor-ODOo
diversity from the natural grassland commu- fWe.), .a2 ‘ao
nities, the dominance structure of the agricul- 4-o1
tural and natural communities showed a d
marked difference (Fig. 2). The first most
dominant species of each field/habitat patch o
had a significantly higher dominance value in o .2 PIT)
tithaetsar(aobnleewhaabyitAatNsOtVhAan:iFn t=he1g0r.a0s3s1l,anddf h~ab2-, •4oS_ “So o o CNi CcS-l cNi in VCOV r-
19, P < 0.005, Tukey HSD test at P = 0.05: d “ A
cereal and alfalfa ns, grassland significantly
different from both). The descent of the dom-
inance curves also differed significantly be-
5o_i
tween arable and grassland habitats, being less 9
(ANCOVA o Acfl ACO ACO
steeply descending in the later on C d d
log transformed dominance, habitat type*rank "O e 3 A i=< cd .ed cd 3
interaction: F = 12.477, df ~ 2, 214, P < •cOt-di <JUh DO5G-1 4'3-Am e4«O5-d)1 C2O ^2CO2^ CCcmOOd
'a
0.0001). W c
(Zi
The high species richness and diversity
found in some of the studied agricultural fields
contradicts the traditional viev/ of the impov-
erishment of these habitats (Nyffeler et al.
1994). While arable fields clearly have the ca- ACdO CeO 'WdaD
pacity for high diversity, maybe it is even cd cd 3 3
D. 4-1 CO CO
more important to point out large between eo A43-1 m Cc5m-dO1 CcmOd
U
field variability. Toft (1989) reported that two 3I 3 cId 3I
cereal fields were as diverse in Denmark as 0) G 43-1 3
i«n G5-1 43-1 cd
the best natural habitats; in Poland only about o o
« >'
SAMU AND SZINETAR-ON THE NATURE OF AGROBIONT SPIDERS 395
d d
o ^ O O O X
summed e3 -^(VmONavvDvo—ri- — Xc3 X m m(N mCnI fC4o G3 (N Ov m(N m cN
Xi VO
< I < <
were
s
values
+a«>
o
CO CO
0) CSo S 03
dCO w3.
(Abundance 5 C<aO3 CSo 3G d CSPo d CGDOm
a(e1l99t.5). “oQ§) X3 u00)) SSbd0PGX)3) uXT3W«3CCC/S3/5D) m00)) u-coc<epod«D d,40wCaub00-NIx3oO33() Q5 IX*cc—S3d1 'm4s0so_p3l ^QCC3ubXOO) d>O30S033 dxb0X3)£d^0C^o3bX3O3)u^d330GCCSb^3X)OO) GCv5)u 3X+33=> ^uG0o3 3dd3uG(C3!b0G>-OO3<X),ki3u-4G0>-s3^3i dr'dd0^N«^p3^^.d3CG0kGG3sMO3 3m3IoS
individuals.) 05 c/5
Hanggi
=10
d d
-o m — m X — X
from cp VPOh O VO C(ON O^r- 0C0O Gp V^O 0^0 I r-- VO c3 crN- cn m m' —< V—O
< «N O<) cn (N ^ ' -<O
Common
obtained
5,
Data = s
bo
oOn CO
wo '5t> 03 s
CD p U3i s
bcJO • 4_» +-> k.
species. common (3aZ) C3aO
<3 d
S d
spider •sS; 3 <0u •(NdD ?P cd d0N3 CO 3cCO OS -C) 3 -rt ^ CO
agrophile F1a=i,rly I IX+-S> -t(d/UT q_CW0S-Z,D3() CO0/)3 0<.3 3Xcd 3 't0"+3SH doCm dCb0XO3) 'cO0S_Gd3 ^!a«fP2e0i Cj 3Kcd 1gCMCOO oCbiO)b^mO3Ql dOG0s3 3
Rare U o 0g1; b'X) "OG u0S-3N b^'X) .S+Se2 U Ck0M3O JkOH Mc^GCrt "c3GS/5 Q^fc^da 03 SmCOPO U0033
00 t/5 qq (X k. PQ
and
follows:
agrobiont
d d
as ^ o o O O o X X
e d’ O r- cNi c VO ^ cn VO G (oN IT) OV GO ^
p 00 CNl VO VO IT) 3 VO —I r' VO 3 ov »d in
04 CN --H X5 cn cn (N (N ’-v X) C4
< < <
some categories
of
Cx,
-G
p
oo CO
preferences abundance (X1 (U s 03
'3 JP=i k3^ CSo m id5
+_i e
Co o3ao CcaOd .P •GG ^G
HT4aabib.t—laet vagtafiltvuoeiersng Icat. IS u3(w(uiU dddu—c03!M<>-0uil m(0U4 4ddUNCCcUM<^hOOdtu gdmpa(u3G3^jU sCP0cU0eoO33i) kob5j^o 3X+3c-d> d3.GCC3ub0msXOO3) U\u Ud3d*GCCsb0>^-OO3»X)dr^0CC3kb0N^G.IX3OO343> IJCaC'vO) Co 34GG-i duC0GG3O3 dGGOk0sM3 V’S00Gb3Ck0G”M33O3 Qd0^kCC2bk>)3HXHOO;) UCG20O3 U3ddMCCGkb0GpG>—iH3OO)
OC c/^ Pd PQ CQ C/5
396 THE JOURNAL OF ARACHNOLOGY
Lycosidae cycles
life
Aaricultural solecies
o
Ct3
C 50 P 23
O
2
<
CD P
"3 25
Q, P
qj
c
CD
E
<
c
CD
3
CO
<
CD
"B
2
.CD
O
CO
S
CL
C3O
8
h-’
1 2 3 4 5 6 7 8 9 10 11 12
month month
—
Figure 5. Life cycle of natural habitat vs. agrobiont and agrophile species belonging to the Lycosidae.
The histograms indicate the occurrence of adult individuals as percentage of all adults caught from the
given species. Species as in Table 2. Those not listed there: Alopecosa piilvenilenta, A. cursor, A. mariae,
A. siilzeri, Pardosa hortensis, P. bifasciata, Hogna radiata, Trochosa robusTa, T. ruricola.
half of that richness was found (Luczak 1975). patterns. To study the magnitude of similarity,
Both in the US (Richman et al. 1990) and 8 fields with large enough sample sizes were
Hungarian (Samu et al. 1996) alfalfa fields selected (4 cereal, 4 alfalfa), and, relying on
there were also high between field and re- pitfall trap data, the spider community of the
gional differences in spider species richness. first 16 most dominant species was considered
A
The establishment of the causes for this vari- (Table 2). ‘random field’ was also gener-
ation is an important task for both agricultural ated, in which the average dominance values
ecologists and conservationists. There is like- of the first 16 species were shuffled. The fields
ly to be multiple causation, including struc- were ordinated by non-metric scaling (NMS)
&
tural diversity (Sunderland Samu 2000), (Clarke 1993), first by the first eight most
management intensity, pesticide use (Altieri dominant species, then by species of domi-
1994; Jenser et al. 1999), field size, and land- nance rank 9-16. The ordination plots show
&
scape structure (Nyffeler Breene 1992; (Fig. 3), that regarding the first 8 dominant
&
Samu et al. 1999a; Toth Kiss 1999). species, fields were similar to each other
Variation in agrobiont composition of ar- (mean Soerensen similarity ± SD = 0.61 ±
—
able fields. Unlike species richness, very lit- 0.145), and dissimilar to the random field,
tle variation was found in the agrobiont com- while for species of dominance rank 9-16
position of the different arable fields sampled. similarity to each other was much lower
The first 8 species were virtually ubiquitous, (mean Soerensen similarity ± SD = 0.35 ±
and dominance orders showed very similar 0.140), and they were not as distinctly sepa-
SAMU AND SZINETAR-ON THE NATURE OF AGROBIONT SPIDERS 397
Linyphiidae cycles
life
month month
—
Figure 6. Life cycle of natural habitat vs. agrobiont and agrophile species belonging to the Linyphiidae.
The histograms indicate the occurrence of adult individuals as percentage of all adults caught from the
given species. Species as in Table 2. Those not listed there: Centromerus sylvaticus, Lepthyphantes nanus,
Minicia marginella, Simula spiniger, Trichoncus hackmani.
rated from the random field (Fig. 3). The So= limited geographical area, such as Hungary.
erensen similarity, also known as Bray-Curtis In this study only “arable agrobionts” are
or Czekanowski similarity, is a proportion co- considered, but the identity of “agrobionts” is
efficient in city-block space. As compared to also strongly crop dependent. Different agro-
Euclidean distance it retains sensitivity in bionts can be found in structurally or other-
more heterogeneous data sets and gives less wise radically different systems, such as or-
&
weight to outliers (McCune Mefford 1999). chards (Jenser et al. 1999) or rice
Considering the first 10 dominant species (unpublished data), but within a range of only
in cereal fields, the distance between fields in broadly similar crops, such as in alfalfa and
terms of species composition (1-Soerensen cereals in the present study, no difference in
similarity) showed no significant relationship the agrobiont composition could be shown.
to the geographical distance for either sam- The agrobiont nature of individual species
pling methods (Mantel test, suction sampling: also shows geographical variation. Comparing
n = A, R = 0.19, ns, pitfall: n = 6, R = 0.35, the present data set with data of agrobionts in
ns, McCune & Mefford 1999), thus no re- other European studies (Hanggi et al. 1995),
gional effect on agrobiont composition can be for Central-Europe, four core arable agro-
inferred. bionts could be identified: Meioneta rurestris
The uniformity of agrobiont composition (C.L. Koch 1836), Pachygnatha degeeri Sun-
seems to be a generality that is valid for a devall 1830, Oedothorax apicatus (Blackwall
398 THE JOURNAL OF ARACHNOLOGY
Theridiidae cycles
life
AaricuHtural soecies
i
1 2 3 4 5 6 7 8 9 10 11 12
month month
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Figure 7. Life cycle of natural habitat vs. agrobiont and agrophile species belonging to the Theridiidae.
The histograms indicate the occun'ence of adult individuals as percentage of all adults caught from the
given species. Species as in Table 2. Those not listed there: Enoplognatha thoracica, Neottiura bimaculata,
N. suaveolens, Dipoena melanogaster, Episinus truncatus, Thehdion impressiim.
1850) and Erigone dentipalpis (Wider 1834). fields. In secondary grassland habitat patches
Other species, like the most abundant in Hun- they represented a modest portion (13.6%) of
gary, Pardosa agrestis (Westring 1861), show the total spider fauna, and their overall pres-
a strong North-West South-East geographical ence was minimal (6%) in all studied natural
gradient in their association with agricultural grassland habitat types (Eig. 4). The indicator
systems (Blick et al. 2000). One of the major species analysis showed, that agrobiont spe-
agrobionts of North-West Europe, Lepdty- cies are not widespread generalists, that would
phantes tenuis (Blackwall 1852) shows an op- occur in a wide range of habitat types. If agro-
posite gradient, and can be listed only as an bionts were wide-tolerance, eurytopic gener-
agrophile in Hungary. Pardosa agrestis has a alists, then they should not be indicators of
shift in life cycle along the same gradient; it either of the considered main habitat types.
has one generation per year in Northern Eu- This hypothesis was falsified by finding that
rope (S. Toft pers. comm.), and has two gen- in all arable-grassland comparisons nearly all
erations in Hungary (Samu et al, 1998). This agrobionts showed up as indicators of the ag-
parallel change in life cycle and agrobiont ten- ricultural habitat (Table 3). On the other hand,
dency suggests again the importance of life indicator species analysis, by not providing
history characteristics for being successful in any agrobiont as an indicator in the alfalfa-
agricultural systems. cereal comparison, reinforced the finding of
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Habitat preference of agrobionts. In the field-by-field comparison, that the same
Hungary agrobionts (first eight species of Ta- dominant species occurred in all arable fields,
ble 2) were virtually only dominant in arable irrespective of crop type.
