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Leafhoppers (Hemiptera, Auchenorrhyncha)
from the perspective of insular biogeography
R. NlEDRINGHAUS
Abstract
Distribution and abundance of leaf- stics, including (1) degree of habitat spe-
hoppers (Hemiptera: Auchenorrhyncha) cialization; (2) preference for special
were investigated on the chain of the East groups of host plants; (3) preference for
Frisian dune islands situated in the particular stages of landscape develop-
Wadden Sea from 3 to 13 km off the north ment; (4) degree of niche overlap; (5)
western German coast in order to explore abundance in the recruitment area. It is
the absence or presence of species on the demonstrated that the specific characteri-
islands and to explain differences in colo- stics of each potential colonist species
nization success of species. - A total of combine to a "disposition" regarding their
172 leafhopper species was assessed from prevailing colonization chances: high dis-
the islands by standardized sweepnet position values render a high colonization
samplings from 1982 to 1988. Species rate, low disposition values render a low
numbers found on the 7 old islands are colonization rate.
roughly on level (110 to 139 species), but Key words: Auchenorrhyncha, North
differences in species composition are con- West Germany, East Frisian Islands, insu-
siderable. The species-abundance relations lar biogeography.
of the leafhopper assemblages show great
similarities to those of dynamic and insta-
ble communities. The leafhopper data of
the East Frisian islands fit the "habitat-
diversity hypothesis" more closely than
the "area-per-se-hypothesis" of insular
biogeography theory. Colonization success
of the potential colonists correlates positi- Denisia 04,
vely or negatively with certain characteri- zugleich Kataloge des OÖ. Landesmuseums,
Neue Folge Nr. xx (2002),
531
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Introduction results fit current theories of "insular biogeo-
graphy"?
Islands are particularly suited for analysing
(3) Which role do "organisms-related"
distribution patterns of species assemblages
factors (dispersal ability, body size, hiberna-
and their dynamic in space and time. Impor-
tion, generation cycle, habitat requirements,
tant factors such as size, isolation and age of
feeding specificity, etc.) play? Which charac-
development are easily determined. Islands
teristics can be related to increasing or decrea-
are often "more simple" in structure and their
sing colonization chances?
communities of organisms are more easily to
(4) Does the specific set of characteri-
survey.
stics of each potential colonist convey a
It was not until the sixties of the last
specific "predisposition" in relation to its colo-
century when islands were brought to the
nization chances?
attention of ecologists by the "equilibrium
(5) How far does this explain a species'
theory of insular biogeography" of Robert
colonization success or failure?
MACARTHUR and Edward WILSON (1963,
1967). Their concept, which seeks to explain Due to their biology and distribution leaf-
species numbers of organismic assemblages by hoppers are well suited for ecofaunistic studies
the parameters size and degree of isolation of on different spatial scales as well as for analy-
an island in first place, provoked lively debate ses of colonization processes:
and extensive conceptual advances that have
- They form diverse assemblages in
precipitated in a plethora of publications to
virtually all terrestrial habitats. On the East
the present day (for reviews see CONNOR &
Frisian islands they are only absent from the
MCCOY 1979, WILLIAMSON 1981).
glasswort fields and barren beaches.
The chain of East Frisian dune islands
- Leafhoppers complete their life cycle
situated off the central European mainland
within the same habitat. Compared to other
offer all advantages as study sites:
groups of arthropods population density is
The islands emerged independently from mostly very high. Hence, leafhopper assembla-
the mainland, so that all organisms had - and ges can be sufficiently surveyed in terms of
still have - to immigrate. The islands share quantity and quality.
many features, but do also differ in size, degree - More than 90% out of a total of 380 spe-
of isolation, landscape structure as well as age
cies recorded from north western Germany are
and state of development. The islands show a
restricted to distinct habitats. Strong preferen-
characteristic set of well distinguishable habi-
ces for single host plant species for oviposition
tats on a small scale which themselves can be
or feeding (more than 85% are mono- to
viewed as "islands", due to their mosaic-like
oligophagous) is in many cases coupled with a
distribution ("habitat patches").
strong preference of a distinct microclimate
In the present contribution, which is lar- and, hence, of a distinct habitat (more than
gely based on research conducted from 1982 70% are classified stenotopic). In this way, a
to 1988 (NlEDRINGHAUS 1991), the coloniza- reliable alignment of habitat data and potenti-
tion success of leafhoppers (Hemiptera: al species composition data can be achieved.
Achenorrhyncha) on the dune islands is ana-
- Notwithstanding a certain "homing
lysed by comparing potential colonist and
behaviour" and a comparatively small range of
assessed species. The following questions are
vagrancy of individuals, the dispersal ability of
addressed in particular:
populations can be regarded as fairly strong:
(1) How many and which species have Population waves which occur at times and in
successfully colonized the islands and different places provide a steady proportion of migra-
habitats? ting or drifting individuals to render coloniza-
(2) Which role do "area-related" factors tion from more or less remote areas within a
like size, isolation, habitat diversity, age and comparatively short period (e.g. RAATIKAINEN
stage of development of an island play in the 1972, RAATIKAINEN & VASARAINEN 1973,
process of colonization? How do the present WALOFF 1973).
532
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Study area Material and methods
Situated in the southern part of the North Primarily employed was the method of
Sea off the German mainland the arc of East quantitative sweepnet sampling that proved to
be particularly reliable for sampling leafhop-
Frisian islands extends some 90 km along the
pers from herb and tree/shrub strata, respec-
Wadden Sea (Fig. 1). Some 2000 years ago the
tively (see e.g. EMMRICH 1966, SCHIEMENZ Fig. 1:
dune islands emerged independently from the Geographical position of the East
1969, NlEDRINGHAUS & BRÖRING 1986, 1989;
mainland from a process of sedimentation and Frisian islands along the southern coast
WlTSACK 1975; for details on sampling effi-
of the North Sea.
subsequent formation of dunes aided by sand-
cacy see NlEDRINGHAUS 1991).
binding plants and since then have been sub-
ject to considerable changes in position, size
and structure (STREIF 1990). In addition to
these 7 "old" islands the investigations were
extended to the two smaller islands of Mem-
mert and Mellum which were only formed
about a century ago.
On the 7 old islands there are larger villa-
ges of several thousand inhabitants each.
Increased tourism and related activities has
encroached upon the whole natural environ-
ment. This appears the more serious, since
these islands are part of one of the last pristi-
ne landscapes of northern central Europe.
Since 1985 the chain of East Frisian islands is
largely part of the Niedersächsisches Watten-
meer (Lower Saxon Wadden Sea) National
Park. surface area isolation landscape- number of plant
(km*) km diversity species
Due to similar conditions during their
Borkum 25.6 10.5 2.747 594
history and their linear position along the Memmert 1.7 13.0 2.560 388
edge of the Wadden Sea, the 7 old islands Juist 9.2 8.0 2.713 455
Nordernev 17.8 3.0 2.542 342
developed characteristic sea-land clines of
Baltrum 4.7 4.5 2.617 384
landscape elements and, thus, show a similar Lanqeooq 14.3 5.0 2.565 359
basic landscape pattern. In contrast, landscape Spiekerooq 9.6 6.5 2.571 363
Wanqerooqe 5.9 6.5 2.000 135
elements developed to a much lesser degree on
Mellum 3.0 6.0 1.615 200
the two younger islands. The largely patchy
distribution and conspicuous variation of The quantitative sweepnet samplings were Tab. 1:
habitats on a small scale leads to an extremely repeatedly conducted in representative sam- Surface area (irrespective of beach
areas and glasswort mud flats),
high heterogeneity and a high potential of pling sites under suitable weather conditions
degree of isolation (distance from
resources which is unrivalled in most main- (not too hot, dry, slight wind) about every four mainland), diversity of landscape ele-
land areas. weeks from end of May until mid September ments (number of habitats per 25ha
fields) and number of plant species of
With respect to size (notwithstanding of the years 1982 to 1988 (for details see the islands under investigation (see
beach areas and glasswort mud flats) and NlEDRINGHAUS 1991). Selection of sampling NIEDRINGHAUS 1991 for further details).
degree of isolation from the mainland the sites was guided from considering (1) surface
islands show considerable differences (Tab. 1): area and distribution of habitat classes;
Area of the smallest island (Memmert) is (2) achieving as much area coverage as possi-
merely 7% of the largest (Borkum); the most ble with sampling sites most randomly distri-
remote islands are 4 times farther off mainland buted; (3) sufficient representation of hetero-
than the nearest. Habitats and plant life are geneity within habitat classes; (4) in single
most diverse on both of the largest islands of cases potential habitats or certain host plants
Borkum and Norderney, but least rich on the of expected leafhopper species were particular-
two smallest islands of Memmert and Mellum. ly surveyed.
533
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A total of 927 sampling sites (including Some 25% of the species recorded from
264 permanent plots) and 2098 single sam- the islands (nearly 40 species) are less abun-
plings were analysed. In addition, pitfall traps dant to rare in the remaining parts of north
were used on each island and in all habitats to western Germany, but are mostly indigenous
assess the primarily ground-dwelling (epigeic) and partly common on the islands. Within
species. The material analysed includes north western Germany 9 species are exclusi-
210.000 specimens. Nymphs were usually con- vely found on the islands or in the adjacent
sidered from 3. stage onwards. coastal area, namely Gravesteinietta boldi. Ana-
ceratagallia frisia, Aphrodes aestuannus, Psam-
Catch efficiency on the level of individual
motettix mantimus, Psammotettix sabulicola in
islands is very high and lies between 89 and
coastal dunes and Anoscopus limicola, Eupteryx
94% (according to trend-analysis/forecasting
artemisiae, Macrosteles horvathi, Psammotettix
procedure and jackknife procedure after
putoni in salt marshes.
HELTSHE & FORRESTER 1983).
The East Frisian islands harbour an extre-
mely rich fauna of more than 10.000 species
Results and discussion
(BRÖRING et al. 1991), including a high
proportion of rare and endangered as well as
The leafhopper fauna of the East
Frisian islands highly specialized thermophilic species. For
terrestrial bugs indigenous to these islands the
A total of 172 leafhopper species has been proportional representation out of the north
assessed from the chain of islands (species list western German fauna is 46% (BRÖR1NG
in NlEDRINGHAUS 1991). This amounts to 1991), even exceeding 70% for aquatic and
nearly 50% of all leafhopper species known semi-aquatic bugs (BROR1NG & NlEDRlNGHAUS
from the north western German lowland 1988). Aculeate Hymenoptera and sawflies
(NIEDRINGHAUS & OLTHOFF 1993). The two are represented with 40 %, each (HAESELER
largest and structurally most diverse islands of 1985, RlTZAU 1995), and spiders with 51%
Borkum and Norderney are also most diverse (SCHULTZ 1995). However, the question
in species, harbouring 129 and 139 native spe- remains, whether and to which extend the
cies, respectively. Species numbers of the species characteristic to the islands become
remaining old islands are more or less on a endangered irrespective of the proclamation
level (Juist 106, Baltrum 110, Langeoog 114, of the National Park, in that they are banished
Spiekeroog 112, Wangerooge 118). Irrespec- by organisms being directly (e.g. plantations of
tive of great similarities in their resource various trees and shrubs) or indirectly favou-
potentials, the islands differ conspicuously in red by human activities. With respect to leaf-
species composition (Fig. 2) and dominance hoppers such species already contribute one
pattern. In the much smaller and - in terms of third of the present assemblage.
landscape elements and resources - less diver-
Fig. 2: se islands of Memmert and Mellum 67 species Leafhoppers as indicator orga-
Species diversity and distributional
(62 indigenous) and 59 species (53 indg.), res- nisms of insular dynamics
pattern of leafhoppers of the East Fri-
sian islands. pectively, were recorded.
Even 2000 years after their formation the
islands in parts are still subject to a strong
180
T dynamic. On the one side, this is due to natu-
160
ral processes (dislocation of sand by the action
140
y
H of seawater and wind, periodic and non-peri-
£ 120 1 • 1 H • • 1 sint^e island
odic floodings of certain insular parts etc.),
• 2-» islands
| 100
I " • ^«islands but, on the other side, is further occasioned by
II 1 1 1 II
• all 7 old islands human activities (punctual and large-scale
n.
g 60 alterations of the landscape) which greatly
40 increased during the last decades.
• 1 1 1 1 1 1 1
20 This situation is reflected by the present
0 I 8 results on the leafhopper fauna from the East
I
I Frisian islands. The frequency distributions
(species - abundance pattern) of the islands
534
© Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at
and biotopes show parallels to those found in colonizing plant and animal species had to
species assemblages of unstable and dynamic immigrate from outside. With distances of 1 to
ecosystems (e.g. BAZZAZ 1975): 11 kilometres off mainland and between each
The observed distribution patterns in other their degree of isolation is fairly low.
some cases (islands and biotopes) approxima- Although most investigations on insular bio-
te the so-called log-series distribution (more geography focus on the bird life of islands of
or less linear graph, FlSHER, COLBERT & much greater isolation (of up to several thou- Fig. 3a-c:
WILLIAMS 1944, Fig. 3a) which is assumed to Distribution patterns of the leafhop-
sand kilometres), the available analyses of
per assemblage (represented from
be largely governed by chance effects. This
arthropod assemblages usually pertain to most common to the rarest species).
pattern is found at the beginning of a colo-
nization phase when the successively immigra-
100000
ting species are each exploiting a maximum
Mellum
proportion of a given resource, thus, leaving 10000
only "leftovers" for later colonists. Interspeci-
1000
fic relationships are supposed to play no role at
100
this stage.
"*
Most islands and biotopes show a distribu- 10
••••
tion pattern intermediate between log-normal 1
distribution (slightly S-shaped graph, cf. 0 20 40 60 80
PRESTON 1948, 1962, Fig. 3b) and broken stick order of rank 1-52
distribution (distinctly S-shaped graph repre-
senting many medium-common species, cf. 100000
MACARTHUR 1957, 1960, Fig. 3c). Log-nor- 10000 •
mal distribution patterns are often found in Langeoog, sattmarshes
1000
areas where succession has reached a more or
less mature state, but which are still subject to 100
moderate dynamic processes. A broken-stick 10
distribution appears where competition
1
between the species of an assemblage prevails
20 40 60 80
over other more or less independent abiotic order of rank 1-43
factors and resource partitioning and niche
separation have advanced. 100000
In most cases the distribution patterns 10000
Wangerooge, dune area
appear "torn", i.e. there are more or less irre-
1000
gular deviations from the theoretically expec-
100
ted pattern (particularly regarding the medi-
—•% .^
um-common species). These indicate conspi- 10
cuous qualitative and especially quantitative 1
fluctuations within the species assemblages. 20 40 60 80
Permanent changes in the availability of order of rank 1-80
resources (caused by natural and human
impact) impede the formation of distinct and
stable species assemblages. islands as little isolated as those in the present
study (e.g. As 1984, NiEMELÄ et al. 1985,
Leafhoppers from the per-
BOOMSMA et al. 1987, NlLSSON et al. 1988). In
spective of insular biogeo-
graphy some cases distances to the source areas amo-
unted to a few to some hundred meters, only
Colonization success of the leaf-
(e.g. WILSON & SIMBERLOFF 1969, REY 1981).
hoppers from the East Frisian
islands Leafhoppers, as a comparatively vagrant
Since - unlike the North Frisian "Geest- group of insects, are not impeded to bridge
core" islands - the East Frisian dune islands distances of a few kilometres (cf. e.g. STEARNS
were never connected to the mainland, all & Me CREARY 1938, HOLZAPFEL & PERKINS
535
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1969, WOLF et al. 1986), at least within a lon- tion rates found on the younger islands of
ger colonization period. It should, therefore, Memmert and Mellum (67 and 70%) are in
not surprise that no relation could be establis- first line attributable to a high proportion of
hed between numbers of species and degree of eurytopic species and species being common
isolation (Fig. 4a), nor between colonization within the recruitment area which, therefore,
success and dispersal ability (Fig. 4b). experience higher colonization chances.
Fig. 4:
(a) Relation between numbers of spe- Naturally, not all of the 380 leafhopper Whether such colonization rates are to be
cies and degree of isolation, considered high or low and which conclusions
species known from the north western Ger-
(b) relation between colonization suc-
to draw cannot be settled here in want of fur-
cess and dispersal ability. man lowland are able to establish themselves
ther studies on additional animals groups.
2.4 .
90 Factors affecting the colonization
22 F oo - • - -
success
~ fc 70
° 2 —•—-___^ c
S1 —— »g f5in0 Leafhopper species numbers of the East
Frisian islands are more closely related to their
Ji Q. 30 habitat diversity (R = 0,974, p < 0.01) than
1«
o size (R = 0,835, p < 0.01; Fig. 5a,b). Hence,
•M0S» M. r = -0.402 tiobc ,0 I 1I 1 the present data do better fit the "habitat-
Qtn. Q. diversity hypothesis" (WILLIAMS 1964: species
1.2 2
numbers of isolated areas dependent on its
diversity of landscape elements) than the
04 0.6 0.S 1 12
degree of Isolation (logl 0) I • dispersal ability high Q dspersal ability bw "area-per-se-hypothesis" (MACARTHUR &
WILSON 1963, 1967: species numbers of isola-
ted areas dependent on its size).
2,4 Conversely, species numbers of bugs from
22 NO the East Frisian islands are more closely rela-
Ol 2 bb 10) BA WM SP ^^**^ ted to island size than diversity of landscape
a 1.6 . ML _ rp =. 00,9 0714 mber (log 1,8 • M.T ML r p=< 00,3.0315 esilzeem eexnptsla (iBnRs ÖmRoINreG t h1a9n9 17)2: %In othfi st hger ovuapr iiasnlacneds
u of deviation (partial correlation with diversity
i/i 1.4 s n 1,4 maintained constant), but merely 23% in leaf-
e
ci
i hoppers (NlEDRINGHAUS 1991:86). Diversity
Q.
1 . 1 of landscape elements explains only 56% in
1,5 2 2.5 3 2,5 3 3T5 bugs, but 82% in leafhoppers. These findings
habitat diversity area (Iog10)
may be explained by the following argument:
Fig. 5: on the chain of islands. Considered as poten- 1. Compared to bugs leafhoppers generally
(a) Relation between species number tial colonists are only those species from the show higher population densities and repro-
and island habitat diversity (a) and recruitment area (i.e. roughly the mainland ductive rates and presumably also a greater
island area (b).
region within a radius of some 150 km from vagrancy particularly as to larger distances.
the islands; see NlEDRINGHAUS 1991 for This ultimately renders a faster and more
details) the resource requirements of which "complete" colonization of potential habitats.
are sufficiently met on the islands. Given this, 2. There are comparatively numerous
236 species are regarded as potential colonists members of leafhoppers exerting minimal
for the chain of islands as a whole (between areas of a few square meters, only. Since the
212 and 236 spp. each for the old island, 92 potential habitats are usually much larger on
and 76 spp., respectively, for the young islands the islands, insufficient habitat size would not
of Memmert und Mellum). Hence, the "colo- play a role as a prerequisite for a successful
nization rate" is about 71%, in other words, colonization in such cases.
29% of the potential colonists currently failed 3. On all old islands the potential of
to establish themselves. For the old islands resources increased through human activities
colonization rates range between 49 % (Juist) (e.g. shrub and tree plantations) within the
and 59 % (Norderney). The higher coloniza- last decades. In this way, species spectra of
536
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leafhoppers increased considerably on the are characterized by very low disposition
islands (by some 50 to 60% each). These new- values (CD 25 to < 28; very small colonizati-
habitats being independent of island size are on chances), 56 species (24%) by low (CD 28
fast colonized by leafhoppers (see point 1.). to < 31), 46 species (20%) by high (CD 34 to
While according to the area-per-se < 37) and 13 species (6%) by very high
approach exclusively quantitative aspects (CD >37) disposition values. 109 species are
Tab. 2:
have an effect (island area and species num-
indifferent in this respect, i.e. their colonizati- Relation between colonization success
bers of colonists), the importance of qualitati- and various factors (deviations of cha-
on chances appear to be neither increased nor
ve aspects (number and specificity of potenti- racteristics-fractioned rates of success
decreased (Fig. 6). from mean rates).
al habitats, species numbers of colonists and
composition of species assemblies) is stressed
2. preference for grasses sedges/rushes herbs woody plants
by the habitat-diversity approach. Thus, the special groups of 8±3 -1 ±9 3± 5 -10 ±5
analysis of colonization success of the species host plants
under study demands the evaluation of those 6. degree of habitat highly eurytopic eurytopic stenotopic highly stenotopic
specialization 29 ±7 3*2 -23 ±6 8±5
characteristics which may affect the coloniza-
7. potential length of very long long short very short
tion process, particularly with respect to the colonization period (ca. 2000 years) (ca. 100 years)
questions: "Why are certain species absent 27 ±5 11 ±2 -9 ±3 31 ± 5
8. degree of niche high medium low
from the islands ?" and "Why are certain colo-
overlap -11 ±4 -1 ±9 11 ±9
nist species more successful than others?"
9. abundance in the very abundant abundant rare very rare
For the group of leafhoppers the following recruitment area 35 ± 14 10 ±9 -12 ±6 -10 ±10
characteristics were considered as potentially
affecting the colonization chances:
1. dispersal ability; 2. preference for speci- 100 -, * *t <e r,*• t* *
al groups of host plants; 3. feeding specificity
• •,y *» * m
in terms of host plant taxa; 4- hibernating sta- 80 -
\ •
ge and number of generations per season; #
! 60- •
5. body size; 6. habitat preference; 7. preferen- • «
JO
ce for particular stages of the landscape deve-
N 40 -
lopment on the island (potential duration of •o5 « * • •
the colonization period; 8. degree of niche ° 20 -
overlap; 9. abundance in the recruitment area. R = 0,6!7, p «0.000
0 -
Whether these characteristics are strictly cau-
25 28 31 34 37 40
sal or merely "observed effects" being linked to
cdorizaton cfsposffion
other characteristics cannot be decided at pre-
sent.
The relation between colonization success Fig. 6:
Five characteristics (2, 6, 7, 8, 9) are more
Relation between colonization „dispo-
(proportion of successfully colonized versus
or less related to the colonization success on sition" and colonization success.
available islands) and colonization disposition
the islands (Tab. 2). All other components
seem negligible in this respect. is highly significant, although its explanatory
value is not particular high because of the
Corresponding to its specific combination
many indifferent species (R = 0,627,
of characteristics each potential colonist spe-
cies appears more or less "qualified" for succes- p « 0.0001). After deleting these indifferent
sfully colonizing an islands. Each species is species this relation increases to R = 0,805,
distinguished by a certain "disposition" which p « 0.0001. For the 127 potential colonist
raises or reduces its colonization chances. In species showing a determined disposition the
order to facilitate further analysis, for each expected and observed colonization success
potential colonist a specific "colonization dis- match to 90%. Nevertheless, 14 species (10%)
position" (CD) value has been calculated for do not meet this expectation. These include
each potential colonist by summing up the potential colonists with low disposition values
various factor values (for details see NlEDRlNG- experiencing a colonization success higher
HAUS 1991). than expected, on the one side, and colonists
11 species (5%) out of the total of 235 spe- with high disposition values yielding a low
cies regarded as potential colonists (see above) colonization success or none at all, on the
537
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other. Whether these findings are indicative of landschaftlichen Diversität als durch die der
chance phenomena or further unknown fac- Flächengröße erklären. Die Daten zur Zika-
tors remains to be settled. denfauna dieser Inseln sind insofern eher mit
der "habitat-diversity-Hypothese" als mit der
In contrast to the approaches and models
"area-per-se-Hypothese" in Einklang zu brin-
of insular biogeography relying on purely
gen. Die Gründe dafür sind sowohl in spezifi-
quantitative parameters (numbers of species of
schen Eigenheiten der Zikaden zu finden (z.T.
isolated areas as a variable to be explained) the
starke Lebensraum-Spezialisierung und damit
present study aims at the individual species
zusammenhängend effiziente und schnelle
and their biological-ecological characteristics
Besiedlung potentieller Habitate, z.T. sehr
as a starting point of reasoning. The focus lies
geringe Minimallebensräume) als auch in spe-
on qualitative aspects (the specific combina-
zifischen Eigenheiten der Inseln (permanente
tion of species as a variable to be explained)
Dynamik hinsichtlich der landschaftlichen
and, thus, on the uniqueness of the studied
Entwicklung, Entkopplung von Inselgröße und
species assemblage.
Anzahl potentieller Habitate durch künstliche
Diversifizierungen der Inseln).
Acknowledgements
Es besteht ein Zusammenhang zwischen
Special thanks are due to Dr. Michael dem Kolonisationserfolg und bestimmten
Struck-Gerbaulet, Phyllobolic Institute, Dan- Merkmalen der potentiellen Kolonisten; ent-
nenberg/Elbe, for substantially improving the scheidende Komponenten dabei sind: der Spe-
English text and helpful comments on an ear- zialisationsgrad hinsichtlich Lebensraum, die
lier draft of the manuscript. Nahrungspräferenz für bestimmte Pflanzen-
gruppen, die Präferenz für bestimmte land-
Zusammenfassung schaftliche Entwicklungsstufen auf den Inseln,
die Einnischungsfähigkeit gegenüber Konkur-
Von 1982-1988 wurden auf den im renten, die Häufigkeit im Rekrutierungsareal.
Wattenmeer der südlichen Nordsee gelegenen Weitere mögliche Komponenten wie Disper-
7 alten Ostfriesischen Inseln Borkum, Juist, sionsfähigkeit, Grad der Nahrungsspezialisation,
Norderney, Baltrum, Langeoog, Spiekeroog Überwinterung, Generationszyklus oder Kör-
und Wangerooge sowie auf den beiden jungen pergröße spielen hinsichtlich der Kolonisa-
Inseln Memmert und Mellum inselbiogeogra- tionschancen keine nennenswerte Rolle.
phische Untersuchungen zur Zikadenfauna
Jeder einzelne potentielle Kolonist verfügt
(Hemiptera, Auchenorrhyncha) durchgeführt.
aufgrund seiner spezifischen Merkmalskombi-
Auf der Inselkette wurden insgesamt nation über eine bestimmte „Disposition",
172 Arten nachgewiesen. Die Artenzahlen der gemäß der seine Kolonisationschancen steigen
alten Inseln liegen annähernd auf gleichem oder fallen. Die Quantifizierung dieser „Kolo-
Niveau (110-139 Arten). Die Artenzusam- nisationsdisposition" ergibt: 3% der potentiel-
mensetzungen zeigen trotz starker Ähnlichkei- len Kolonisten zeichnen sich durck sehr nied-
ten der Ressourcenpotentiale der Inseln aller- rige Dispositionswerte (stark verminderte
dings erhebliche Unterschiede. Die Muster der Kolonisationschancen), 22% durch geringe,
Häufigkeitsverteilungen zeigen in vielen 21% durch hohe und 9% durch sehr hohe Dis-
Fällen ausgeprägte Parallelen zu Artenzusam- positionswerte aus. Fast die Hälfte aller poten-
mensetzungen dynamischer und nicht ausge- tiellen Kolonisten (46%) erweist sich als
reifter Landschaften. m.o.w. neutral, so daß bei ihnen weder von
Der Isolationsgrad der Inseln ist zu gering, erhöhten noch von verminderten Kolonisa-
als daß der Kolonisationserfolg der Zikaden tionschancen auszugehen ist. Ist die Kolonisa-
tionsdisposition jedoch gerichtet, so werden -
davon beeinflußt wird: Weder zwischen
wie die Prüfung der tatsächlichen Erfolgswerte
Artenzahl und Isolationsgrad noch zwischen
ergibt - für 90% der entsprechenden potentiel-
Kolonisationserfolg und Dispersionsfähigkeit
len Kolonisten die Erwartungen hinsichtlich
ergeben sich Korrelationen. Die Zikaden-
ihres Kolonisationserfolges bzw. Mißerfolges
Artenzahlen der Ostfriesischen Inselkette las-
auf der Inselkette erfüllt.
sen sich besser durch die Variablen der
538
© Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at
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Address of the author:
Dr. Rolf NlEDRlNGHAUS
Department of Biology, Earth and
Environmental Sciences
University of Oldenburg
P.O. Box 2503
26111 Oldenburg
Germany
540
