On Some Population Parameters of Drosophilids in Switzerland (Diptera, Drosophilidae)

On Some Population Parameters of Drosophilids in Switzerland (Diptera, Drosophilidae)

Bächli, G; Schatzmann, E; Haring, E (2008). On some population parameters of drosophilids in Switzerland (Diptera, Drosophilidae). Mitteilungen- Schweizerische Entomologische Gesellschaft , 81:243-260. Postprint available at: http://www.zora.uzh.ch University of Zurich Posted at the Zurich Open Repository and Archive, University of Zurich. Zurich Open Repository and Archive http://www.zora.uzh.ch Originally published at: Mitteilungen- Schweizerische Entomologische Gesellschaft 2008, 81:243-260. Winterthurerstr. 190 CH-8057 Zurich http://www.zora.uzh.ch Year: 2008 On some population parameters of drosophilids in Switzerland (Diptera, Drosophilidae) Bächli, G; Schatzmann, E; Haring, E Bächli, G; Schatzmann, E; Haring, E (2008). On some population parameters of drosophilids in Switzerland (Diptera, Drosophilidae). Mitteilungen- Schweizerische Entomologische Gesellschaft , 81:243-260. Postprint available at: http://www.zora.uzh.ch Posted at the Zurich Open Repository and Archive, University of Zurich. http://www.zora.uzh.ch Originally published at: Mitteilungen- Schweizerische Entomologische Gesellschaft 2008, 81:243-260. MITTEILUNGEN DER SCHWEIZERISCHEN ENTOMOLOGISCHEN GESELLSCHAFT BULLETIN DE LA SOCIÉTÉ ENTOMOLOGIQUE SUISSE 81: 243–260, 2008 On some population parameters of drosophilids in Switzerland (Diptera, Drosophilidae) GERHARD BÄCHLI1, ERNST SCHATZMANN2 & ELISABETH HARING3 1 Zoological Museum, Winterthurerstrasse 190, CH-8047 Zürich; [email protected] 2 Hofwisenstrasse 3, CH-8317 Tagelswangen; [email protected] 3 Museum of Natural History, 1. Zoological Department, Molecular Systematics, Burgring 7, A-1010 Vienna; [email protected] Based on a collection of Drosophilidae in western Switzerland, the counts of flies were analyzed to get coordinated information about population parameters such as aggregation, succession, sex ratio, association and diurnal activity. The results are in conformity with data from literature. Keywords: Population parameters, aggregation, succession, sex ratio, association, diurnal frequency. INTRODUCTION It is the general experience made by all collectors of drosophilids that sample size and species content vary in time and space, and in particular, that the method of collecting has an important influence on the result. Beside certain effects of chance, it has been shown that collecting by net sweeping and by baiting yields quite different results. This can be explained by the type and quality of the bait (e.g. Birch & Battaglia 1957; Johnston & Heed 1975; Beppu & Toda 1976; Atkinson 1977; Watabe et al. 1980; Atkinson 1981; McInnis 1981; Hoenigsberg et al. 1982; Sene et al. 1981; Carson & Heed 1983; Spence et al. 1984; Bächli et al. 1991; Mitsui & Kimura 2000), but mainly by characteristics of the habitat (e.g. Dobzhansky & Epling 1944; Crumpacker & Williams 1973; Sabath 1974; Toda 1974; Begon 1975; Shorrocks 1975; Atkinson & Shorrocks 1977; Begon & Shorrocks 1978; Taylor & Powell 1978; Atkinson & Miller 1980; Shorrocks & Nigro 1981; Begon 1982; Atkinson 1983; Bélo & Banzatto 1984; Shorrocks 1996). The typical method for collecting drosophilids is using different kinds of baits which have provided information concerning various aspects, such as diurnal dif- ferences (e.g. Nozawa 1956; Wakahama et al. 1963; Hoenigsberg et al. 1977; Bélo & Lemos 1978; Rocha Pité 1978; Bächli et al. 1985; Argemí et al. 2000; Krav- chenko et al. 2006), sex ratio differences (e.g. Mather 1956; Paik 1957; Burla 1961; Kaneko et al. 1966; Martin & Stevenson 1967; Kaneko et al. 1968; Hunter & Navarro 1969; Bächli 1973; Reddy & Krishnamurthy 1973; Begon et al. 1975; Toda 1976; Begon 1978; Bélo & Lemos 1978; McInnis et al. 1982; Gómez & Nájera 1987; Band 1993; Burla & Bächli 1993; Burla 1995; Argemí et al. 2002), associ- ations of species, guilds (e.g. Watabe 1984; Shorrocks & Rosewell 1987; Shorrocks et al. 1990; Shorrocks & Sevenster 1995), aggregations (e.g. Shorrocks & Begon 1975; Shorrocks et al. 1979; Atkinson & Shorrocks 1984; Shorrocks & Rosewell 1988; Shorrocks 1990), successions of species (e.g. Bächli 1972; Atkinson 1977; 243 GERHARD BÄCHLI, ERNST SCHATZMANN & ELISABETH HARING Bächli & Schatzmann 2006), niche characteristics (e.g. Hummel et al. 1979; Jae- nike 1974; Shorrocks 1974) and other trends, e.g. influence of climatic factors (Ste- venson & St. Clair 1953; Rocha Pité 1977) or absolute population size (Gromko 1981). Because most of the reports mentioned are based on the different backgrounds of the respective projects, we have decided to combine in one study as many aspects as possible, in order to get information on some population parameters, giving a possibility to answer the following hypotheses: — some species are aggregated over baits — the aging process of the bait has an influence on the species composition — males and females are differently distributed over baits — some species are associated, forming a guild — there are diurnal differences (morning/evening) As it may be difficult to include several hypotheses in one study, we have tried to standardize the sampling procedures as well as possible, in order to avoid exces- sive effects of habitat choice of the involved species and other unwanted parameters. Anyway, it was not possible to evaluate the habitat structure etc. in detail; there- fore, the following data are empirical and descriptive, and we were unable to pro- vide a causal argumentation for the findings. METHODS Baiting A collection of drosophilids was made by two of us (GB, EH) in the almost homogeneous, protected, extensive Scots Pine (Pinus sylvestris) woodland area Pfynwald, about 500 m above sea level, in the center of the canton Wallis, Switzer- land, from August 2 to 5, 1999. In addition to the pine trees, occasionally a ground layer of certain bushes and herbaceous plants also existed (not recorded). As bait we used mashed, fermenting bananas put on the ground, in form of open plates. They were arranged in two parallel lines each of 10 plates in a distance of about 100 m, leaving in each line at least 10 m from plate to plate. The distance of the plates was considered large enough to provide as much independence of the in- dividual bait as possible; we have to admit that this independence is not fully guaranteed. The baits were brought out in the late morning of August 2. Collecting was made by net sweeping over the plates, beginning in the evening of August 2, then every morning and evening of August 3 to 5; on each occasion, the flies were sampled in three successive turns, allowing additional flies to be attracted and/or occasion- ally escaped flies to join the bait again. During the collection time the weather conditions were favorable (warm, mostly sunny), but rather dry, to the effect that the bait suffered from an aging pro- cess, its condition changing successively from fresh bait to a compact, almost dried out version (with smell of acetic acid), with an obvious loss of attraction capabil- ities. The baits were slightly irrigated on August 4. The flies were immediately identified and afterwards stored in ethanol. 244 ON SOME POPULATION PARAMETERS OF DROSOPHILIDS (DIPTERA, DROSOPHILIDAE) Tab. 1. Overview. Counts per species and day and daytime, including some population parameters. August: 2334455 Daytime:EM EM EM E Species Code Totals Amiota alboguttata AG 1 1 Chymomyza amoena AO 2 1 3 Drosophila ambigua AM 1 1 2 Drosophila funebris FU 1 1 2 Drosophila helvetica HE 2 8 23 34 22 5 94 Drosophila hydei HY 1 312 7 Drosophila immigrans IM 7 8 27 21 11 5 79 Drosophila kuntzei KU 2 107 191 387 248 459 209 1603 Drosophila limbata LI 1 1 2 Drosophila littoralis LT 115213044357 153 Drosophila melanogaster ME 14 41 167 61 67 9 28 387 Drosophila obscura OB 84 20 104 38 82 9 337 Drosophila phalerata PH 104 93 227 94 338 109 965 Drosophila subobscura SO 30 521 516 552 675 281 170 2745 Drosophila testacea TE 305 345 981 574 1123 581 3909 Drosophila transversa TR 1451974589247336 Drosophila tristis TT 11844 18 Leucophenga maculata MA 1 2 3 Lordiphosa fenestrarum FE 1 1 Phortica semivirgo SE 1 3 1 5 Scaptodrosophila rufifrons RU 1124 Scaptomyza pallida PA 1 3 3 1 4 12 Totals 50 1234 1396 2481 1866 2461 1180 10668 Number of Species 7 13 14 16 17 14 16 22 Indices: Diversity H' 1.59 2.39 2.45 2.49 2.47 2.31 2.22 2.51 EXP (H') 3.02 5.25 5.46 5.61 5.55 4.95 4.66 5.68 Simpson's D 0.56 0.74 0.76 0.08 0.75 0.72 0.69 0.76 Equitability 0.57 0.65 0.64 0.62 0.61 0.61 0.55 0.56 Data analysis Parameters For some population parameters, the indices mentioned by Bächli & Schatz- mann (2006) were calculated. Statistics The aim of the study was to investigate the distribution of drosophilid flies over similar baits over a few days. The design led to 3 evaluable days with 2 day- times each, morning and evening, and 20 baits. The baits can be seen as not fully independent repetitions. Most analyses were applied on the square roots of the original counts. This is a widely used transformation applied on count data (e.g. Osborne 2002). Only the data of August 3, 4 and 5 were statistically evaluated. On August 2 there was a test run to examine whether the location of the baits was suitable. This 245 GERHARD BÄCHLI, ERNST SCHATZMANN & ELISABETH HARING Tab. 2. Dispersion of species. Mean, variance and dispersion index DI over the 20 baits were calculated per day, daytime, species and sex; weighted mean values of these three statistics are shown in the table. Accumulations are expressed by a DI > 1. All species but S. pallida show an aggregated distribution. Species Flies Mean m Mean var Mean DI D. helvetica 94 0.84 1.81 2.1 D. immigrans 79 0.51 0.64 1.2 D. kuntzei 1,601 10.16 155.92 12.9 D.

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