Altitudinal Gradients of Generalist and Specialist Herbivory on Three Montane Asteraceae

Acta Oecologica 24 (2003) 275–283 www.elsevier.com/locate/actoec Original article Altitudinal gradients of generalist and specialist herbivory on three montane Asteraceae U. Scheidel, S. Röhl, H. Bruelheide * Department of Ecology and Ecosystem Research, Albrecht-von-Haller-Institute for Plant Sciences, University of Goettingen, Untere Karspuele 2, 37073 Goettingen, Germany Received 23 August 2002; accepted 12 September 2003 Abstract Different functional types of herbivory on three montane Asteraceae were investigated in natural populations in central Germany to test the hypothesis that herbivory is decreasing with altitude. Generalist herbivory was assessed as leaf area loss, mainly caused by slugs, and, in Petasites albus, as rhizome mining by oligophagous insect larvae. Capitules were found to be parasitized by oligophagous insects in Centaurea pseudophrygia and by the specialist fly Tephritis arnicae in Arnica montana. Only the damage to leaves of P. albus showed the hypothesized decrease with increasing altitude. No altitudinal gradient could be found in the leaf and capitule damage to C. pseudophrygia.In A. montana, capitule damage increased with increasing elevation. The data suggest that abundance and activity of generalist herbivores are more affected by climatic conditions along altitudinal gradients than specialist herbivores. In all probability, specialist herbivores depend less on abiotic conditions than on their host’s population characteristics, such as host population size. © 2003 E´ ditions scientifiques et médicales Elsevier SAS. All rights reserved. Keywords: Arnica montana; Centaurea pseudophrygia; Flower head parasitization; Geographical distribution; Leaf damage; Petasites albus; Seed predation 1. Introduction duce the fitness of the highland species. Grime (2001) pre- sumed that herbivory decreases with increasing environmen- Plant range boundaries are the result of various abiotic and tal harshness. The most important climatic variable that biotic factors that prevent the successful completion of the causes the harshness at higher altitudes is temperature which life cycle of a plant species outside its geographical range. decreases with elevation. Molluscs as important consumers This is also true in the case of montane and alpine species of plants may be affected negatively by decreasing tempera- which do not occur in the lowlands. The hypothesis that the tures (e.g. Baur and Rabaud, 1988), but may also benefit from warmer lowland climate leads to higher respiratory losses of increasing precipitation and reduced evapotranspiration at storage carbohydrates has often been referred to, but has high elevations. The hypothesis that the abundance of slugs is been tested in only a few plant species (e.g. Stewart and generally lower in harsher climatic regions has yet to be Bannister, 1974; Graves and Taylor, 1988; Larigauderie and proved (Keller et al., 1999). Körner, 1995; Atkin et al., 1996; Arnone and Körner, 1997; We are also aware of only a few studies on herbivores Bruelheide and Lieberum, 2001). However, the results of other than molluscs along altitudinal gradients that could these studies generally showed a great acclimation potential demonstrate a decrease in herbivore activity with increasing of plants from higher altitudes. Most other abiotic site factors altitude. The damage to Polemonium viscosum by aphids and become more favourable for plant growth with decreasing ungulates was lower at 4000 m than at 3530 m in the Rocky altitude and therefore cannot directly cause range limits of Mountains (Galen, 1990). Predispersal seed predation by highland plants at lower altitudes. oligophagous lepidopteran and dipteran larvae in Swedish However, lowland conditions may disproportionately Bartsia alpina populations was lower at 900 m than at 400 m favour competitors, herbivores or pathogens which then re- (Molau et al., 1989). Herbivory damage to Sanguisorba tenuifolia in Japan reached clearly lower levels at 980 m than * Corresponding author. at 4 m (Suzuki, 1998). Kelly (1998) found decreasing aphid E-mail address: [email protected] (H. Bruelheide). damage to Solidago macrophylla between 800 and 1550 m in ©2003E´ ditions scientifiques et médicales Elsevier SAS. All rights reserved. doi:10.1016/j.actao.2003.09.004 276 U. Scheidel et al. / Acta Oecologica 24 (2003) 275–283 the White Mountains (New Hampshire). Transplant experi- (Mt. Brocken). They cover an area of more than 2000 km2 ments with several Asteraceae in the Harz Mountains, Ger- with a maximum extension of about 90 km from northwest to many, revealed decreasing levels of leaf area loss from the southeast. There are clear altitudinal climatic gradients lowlands to montane and subalpine sites (Bruelheide and (Glässer, 1994). The mean annual temperature is at about Scheidel, 1999; Scheidel and Bruelheide, 2001). 8 °C at the western foothills of the mountain range at 200 m However, there are also studies that found no increasing and decreases by 0.55 K per 100 m altitude resulting in 2.8 °C herbivory with decreasing altitude. Olofsson (2001) reported at the top of Mt. Brocken. The growing season with mean similar densities of mammalian herbivores in a meadow at daily temperatures>8°Cisabout 200 days at the western 450 m and in a snowbed at 600 m. However, without herbi- border of the Harz Mountains and 97 days on Mt. Brocken. vore exclosure, the biomass of transplanted tall herbs de- The annual precipitation amounts to 840 mm at the western creased during 3 years in the snowbed but not in the meadow. border and 1600 mm on Mt. Brocken. In natural populations of Arnica montana (Scheidel and Bruelheide, 1999) and Senecio sp. (Scheidel and Bruelheide, The plant populations studied were located mainly in the 2001) in the Harz Mountains, no altitudinal gradient in the south-western part of the mountain range between their leaf damage could be detected. Other observations indicated lower altitudinal range limit (about 300 m) and an upper limit that there was no linear altitudinal trend in herbivory. For at about 700 m. Most investigations were carried out in 1999. example, Diemer (1996) found no altitudinal gradient (2600–3310 m) in leaf and flower damage to the alpine Ranunculus glacialis. In England, Randall (1986) reported 2.2. Study species maximum attack rates on seed capsules of Juncus squarrosus at 300 m where nearly all of the seeds were eaten by the 2.2.1. Petasites albus (L.) Gaertn larvae of the moth Coleophora alticolella. Above 300 m, Petasites albus occurs in Europe from Spain to Russia and seed predation decreased because of low larval densities due further east to the Altai Mountains. In central Europe, except to more unfavourable climatic conditions. Below 300 m, for the Baltic Sea coast, most populations are found at alti- there was also a decrease due to an increasing parasitoid tudes higher than 200 m. The species is widespread in the attack to the larvae. Similarly, Virtanen and Neuvonen (1999) Harz Mountains. Here the lowest stands grow at about 300 m. found that the parasitoid attack to the larvae of the moth Most populations are found in montane forests, tall-herb Epirrita autumnata changed with altitude, however, one communities, road verges and riverbanks and have a large parasitoid species was most abundant at lowest altitudes and extension due to clonal fragmentation of the rhizomes. The one species preferred the highest altitudes. plant is functionally dioecious and flowers in March–April, The present contribution is based on the hypothesis that i.e. before leaf expansion. Seeds are dispersed by wind in higher herbivory at lower altitudes causes the absence of May. In summer, P. albus forms dense stands due to its large montane plant species in the lowlands. To test whether or not 15–30 cm tall leaves. there is a changing herbivory pressure even over a relatively small altitudinal gradient (300–700 m), observational studies 2.2.2. Centaurea pseudophrygia C.A. Meyer were conducted in natural populations of three Asteraceae Centaurea pseudophrygia occurs from central Europe to (Arnica montana, Centaurea pseudophrygia, Petasites al- the southern Ural Mountains. In central Germany, most bus) in the Harz Mountains. The plant species were wide- populations are found at submontane and montane altitudes, spread over the studied altitudinal gradient. Leaf area losses in mown or abandoned meadows and at road verges. In the were mainly caused by polyphagous slugs; whereas the rhi- southern parts of the Harz Mountains, the lowest populations zomes of P. albus and the capitules of P. albus and C. are located at about 300 m. The shoots of this hemicrypto- pseudophrygia were parasitized by oligophagous insects. In phyte attain a height of more than 1 m. Flowering period contrast, the flower heads of A. montana were exclusively starts at the beginning of July and continue until the first attacked by the monophagous fly Tephritis arnicae. autumn frosts. Seeds are dispersed from the beginning of The main hypothesis of our study was that the damage by August onwards. invertebrate herbivores decreases with increasing altitude. Another hypothesis was that this trend differed between 2.2.3. Arnica montana L. polyphagous and oligophagous herbivores. Arnica montana grows in Europe from France to Russia. In central Europe, a large proportion of the lowland populations have disappeared during the last 50 years, mainly due to 2. Materials and methods more intensive land use. In the Harz Mountains, the species is found in submontane and montane meadows above 350 m. 2.1. Study area The hemicryptophyte produces numerous rosettes. However, only a minor fraction develops a flowering shoot of about The Harz Mountains in central Germany are mainly built 50 cm height in June and July, with 1–5 flower heads. Seed up by palaeozoic rocks and rise from about 200 to 1142 m dispersal is finished in mid-August. U. Scheidel et al. / Acta Oecologica 24 (2003) 275–283 277 2.3. Leaf damage one sample comprising of at least 12 capitules or capitules- cences was taken at a site.

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