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ZOBODAT - www.zobodat.at Zoologisch-Botanische Datenbank/Zoological-Botanical Database Digitale Literatur/Digital Literature Zeitschrift/Journal: Denisia Jahr/Year: 2002 Band/Volume: 0004 Autor(en)/Author(s): Niedringhaus Rolf Artikel/Article: Leafhoppers (Hemiptera, Auchenorrhyncha) from the perspective of insular biogeography 531-540 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 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 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 Frisian islands extends some 90 km along the be particularly reliable for sampling leafhop- Wadden Sea (Fig. 1). Some 2000 years ago the pers from herb and tree/shrub strata, respec- 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- subsequent formation of dunes aided by sand- of the North Sea. 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

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