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86 the importance of being synchronous cal synchrony with the plant species they visit than generalised visitors. At a given time and location, a specialised pollinator should use a relatively small fraction of all available flowering plant species. Moreover, the sets of plant species visited by a specialised pollinator at different sites should be similar. Thus, we expected to be able to identify specialists both by their local specialisation and the consistency of their visitation patterns across sites. Regarding phenology, according to our hypothesis a specialised pollinator should show a high degree of phenological overlap with the plant species it depends on at a given site. In addition, if the specialist occurs at more than one altitude, its phenology should closely track the phenological shift of the relevant plant species from one site to the next. In summary, we expected to find a positive relationship between local and inter-site specialisation and phenological synchrony. 5.3 methods 5.3.1 Data collection The data used in this paper were recorded in the National Park Berchtesgaden in the German part of the Alps (47 °32’ N, 12 °53’ E). Six grasslands in the central valley of the Park (“Wimbachtal”) at altitudes between 950 m and 2020 m a.s.l. were selected for data collection. These sites were neither mown nor grazed by cattle during the period of data collection. Only after the flowering season the three lowest sites were grazed extensively. Hence, the flowering phenologies recorded in this study are not influenced by human land use. At each of the six sites, five rectangular transects of 30 x 4 m were established. Transect locations were chosen so as to cover a representative sample of the local vegetation. Data collection at the lowest site took place from 8 May until 2 September 2010. Sampling at higher sites began as soon as they were free of snow and the first plants started to flower. Whenever possible, each site was visited once a week during dry weather to record open flowers and visiting insects. However, due to long-lasting rain and bouts of snowfall at higher altitudes, this was not always possible. As a result, between 13 (site 1: 950 m) and 9 (site 6: 2020 m) censuses were taken at each site over the course of the season. When visiting a site, all open flowers of insect-pollinated species (excluding grasses) were counted in 5 quadrats of 2 m²that were placed at equal distances along each transect. Thus, quadrats covered 5 x 2 m²x 5 = 50 m²or 1/12 of the total area of all transects at a site. Flowers of rarer plant species that were
5.3 methods 87 not found in at least one of the quadrats were counted separately. Diameters of flowers of all plant species found at a site were measured in the lab with a digital calliper to the nearest 0.1 mm, and converted to flower area by assuming a circular shape. Between 1 and 10 flowers per species were measured (mean: 7.1 flowers), and the mean of their diameters taken as a basis for the calculation of flower areas. For zygomorphic flowers, the mean of length and width of a flower was used as diameter of the circle. Strongly compact inflorescences (e.g. those of Asteraceae) were treated as single flowering units both in counting and measurement of diameters. For each plant species, the total flower area per site was calculated by multiplying the number of counted flowers in quadrats by the average area of a single flower or flowering unit, and by extrapolating from the quadrat samples to the total area covered by all transects at a site (600 m²). In addition to the monitoring of open flowers, transect walks were carried out for five to seven hours (mean: 6:12 h) between 9 a.m. and 6 p.m. at each sampling date. During transect walks, the observer walked along the middle line of the long side of a transect, and recorded flower-visiting insects within two meters to the left and to the right of this line. Only taxonomic groups comprising obligate flower visitors were included in insect sampling: Bees (Hymenoptera: Apidae), flies (Diptera: Brachycera), and butterflies and moths (Lepidoptera). Except for a few very common and easily identifiable species (e.g. Apis mellifera, Episyrphus balteatus), all recorded flower visitors were caught with a sweepnet and kept in individually labelled test tubes for later identification. Fly specimens were killed and preserved in 70% alcohol, while bees and lepidopterans were killed with ethyl acetate and stored in dry tubes. All captured insect specimens were later identified to species level with the help of taxonomists (see Acknowledgements). To examine the relationship between specialisation and floral morphology, we took measurements of the length of the floral tube from the same flowers used to determine flower areas (see above). The procedure was identical to the one described by Stang et al. (2006). 5.3.2 Statistical analyses 5.3.2.1 Phenological estimator For all statistical analyses of insect and plant phenology, we used the weighted mean day of occurrence (WMD) as a phe-
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L I N K I N G S P E C I A L I S AT
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E R K L Ä R U N G gemäß § 4 Abs
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D A N K S A G U N G Zuallererst mö
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xiv contents 3.3 The Model 43 3.3.1
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1 I N T R O D U C T I O N “Es ist
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1.3 ecological stability 3 vegetabl
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1.3 ecological stability 5 tions an
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1.4 specialisation 7 tween the fund
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1.4 specialisation 9 may be promote
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1.4 specialisation 11 ogy through h
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1.4 specialisation 13 tionships bet
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1.5 outline of this thesis 15 1.5.1
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1.5 outline of this thesis 17 2007)
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20 plant-pollinator dynamics: stabi
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Page 57 and 58: 3.2 introduction 41 the maximum num
Page 59 and 60: 3.3 the model 43 certain types of r
Page 61 and 62: 3.3 the model 45 time unit, summed
Page 63 and 64: 3.3 the model 47 Figure 3.1: Illust
Page 65 and 66: 3.4 results 49 difference in evenne
Page 67 and 68: 3.5 discussion 51 abundance 150 100
Page 69 and 70: 3.5 discussion 53 seed numbers betw
Page 71 and 72: 3.6 appendix 55 Despite the existen
Page 73 and 74: 3.6 appendix 57 mean number of visi
Page 75 and 76: 3.6 appendix 59 Table 3.2: Plant di
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Page 100 and 101: 84 the importance of being synchron
Page 116 and 117: 100 the importance of being synchro
Page 123 and 124: S Y N T H E S I S 6 The previous fo
Page 125 and 126: 6.1 mechanisms of diversity mainten
Page 131 and 132: 6.2 consequences of climate change
Page 137 and 138: S U M M A RY For most angiosperm pl
Page 139 and 140: summary 123 veloped in chapter 2. O
Page 141: summary 125 and intensity of extrem
Page 144 and 145: 128 zusammenfassung ten der Erhaltu
Page 146 and 147: 130 zusammenfassung wir den Zusamme
Page 149 and 150: R E F E R E N C E S Abrams, P.A. (2
Page 151 and 152: eferences 135 R., Thomas, C.D., Set
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eferences 137 Clavel, J., Julliard,
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eferences 139 role of trade-off str
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eferences 141 Gomez, J.M., Abdelazi
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eferences 143 Ives, A.R. & Carpente
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eferences 145 Leibold, M. & McPeek,
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eferences 147 Moonen, A. & Barberi,
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eferences 149 Pielou, E.C. (1975).
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eferences 151 Schemske, D.W., Mitte
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eferences 153 Visser, M.E. & Hollem
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L I S T O F P U B L I C AT I O N S
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