Ecol Res (2008) 23: 241–248 DOI 10.1007/s11284-007-0369-9 ORIGINAL ARTICLE Werner Ulrich Æ Karol Komosin´ski Æ Marcin Zalewski Body size and biomass distributions of carrion visiting beetles: do cities host smaller species? Received: 15 November 2006 / Accepted: 14 February 2007 / Published online: 28 March 2007 Ó The Ecological Society of Japan 2007 Abstract The question how animal body size changes Introduction along urban–rural gradients has received much attention from carabidologists, who noticed that cities harbour Animal and plant body size is correlated with many smaller species than natural sites. For Carabidae this aspects of life history traits and species interactions pattern is frequently connected with increasing distur- (dispersal, reproduction, energy intake, competition; bance regimes towards cities, which favour smaller Brown et al. 2004; Brose et al. 2006). Therefore, species winged species of higher dispersal ability. However, body size distributions (here understood as the fre- whether changes in body size distributions can be gen- quency distribution of log body size classes, SSDs) are eralised and whether common patterns exist are largely often used to infer patterns of species assembly and unknown. Here we report on body size distributions of energy use (Peters 1983; Calder 1984; Holling 1992; carcass-visiting beetles along an urban–rural gradient in Gotelli and Graves 1996; Etienne and Olff 2004; Ulrich northern Poland. Based on samplings of 58 necrophages 2005a, 2006). and 43 predatory beetle species, mainly of the families Many of the studies on local SSDs focused on the Catopidae, Silphidae, and Staphylinidae, we found number of modes and the shape. Unimodal distributions contrary patterns of necrophages and predatory beetles. appeared to prevail (Loder 1997; Gaston and Blackburn Body sizes of necrophages decreased towards the city 2000; Ulrich 2006) and can be considered as the null centre and those of predators remained unchanged. expectation (May 1986) from which any deviation de- Small necrophages and large predators dominated in serves explanation. Vertebrate SSDs were frequently abundance in the city centre. Necrophage body sizes found to be right-skewed with an excess of smaller appeared to be more regularly spaced in the city centre species (Gaston and Blackburn 2000; Koz owski and than expected from a random null model and in com- ł Gawelczyk 2002; Smith et al. 2004). Arthropod com- parison to the rural pattern, pointing to increased munities tend to approach symmetrical distributions at competition. regional and local scales (Chislenko 1981; Espadaler and Gomez 2002; Ulrich 2005a, 2006; but see Gaston et al. Keywords Body size Æ Coleoptera Æ 2001), although there is a need for a critical meta-ana- Rural–urban gradient Æ Disturbance Æ Carrion lytical study to infer whether phylum-specific differences exist. W. Ulrich (&) Szyszko (1983) and later Gray (1989) and Blake et al. Department of Animal Ecology, Nicolaus Copernicus (1994) hypothesized that human-induced increased lev- University in Torun´, Gagarina 9, 87-100 Torun´, Poland els of disturbance should alter the distribution of body Tel.: +48-56-6114469 E-mail: [email protected] sizes towards a prevalence of small-sized species in URL: www.umk.pl/~ulrichw highly disturbed habitats. Such a decreasing body size pattern has subsequently been reported for several K. Komosin´ski ground beetle assemblages (Alaruikka et al. 2002; Nie- Department of Zoology, University of Warmia and Mazury, ul. Oczapowskiego 2, 10-719 Olsztyn, Poland mela¨ et al. 2000, 2002; Braun et al. 2004; Gaublomme et al. 2005; Magura et al. 2004, 2006; but see Lo¨ vei and M. Zalewski Magura 2004), although in a few cases it was only Polish Academy of Sciences, Centre for Ecological Studies, marginal (Niemela¨ et al. 2000, 2002). M. Konopnickiej 1, Dziekano´w Les´ny, 05-092 Łomianki, Poland The causes of this pattern are still not well under- E-mail: [email protected] stood. Lo¨ vei and Sunderland (1996) speculated that less 242 mobile larvae are more affected by changing conditions thropods rejected a regular spacing (Gotelli and Graves in disturbed habitats, whereas Thorbek and Bilde (2004) 1996; Ulrich 2006) or found only weak evidence for argued that lower total abundances under unfavourable nonrandom distributions (Weller and Ganzhorn 2004; conditions result in increased extinction rates of larger Ulrich 2005a). However, a detailed meta-analytical and therefore often less abundant species. In ground study is still missing. beetles, smaller species are frequently macropterous While the diversity patterns of arthropods, particu- whereas larger species are often wingless and therefore larly ground beetles, along disturbance gradients are potentially less dispersive (Thiele 1977). Thus, smaller now well known (Niemela¨ et al. 2002, Weller and species should be more abundant in fragmented or tem- Ganzhorn 2004; Angold et al. 2006; Magura et al. 2006), porary habitats. Lastly, disturbed habitats should par- there are astonishingly few detailed studies on the ticularly attract small-bodied r-strategists, thus shifting respective arthropod size distributions (Braun et al. the body size distribution towards lower weight classes 2004; Weller and Ganzhorn 2004; Magura et al. 2004, (Kotze and O’Hara 2003). 2006; Sadler et al. 2006;Lo¨ vei and Magura 2004; Ulrich Shifts in mean body size along a disturbance gradient 2006). The present study uses size distributions of beetle might also influence the general shape of the SSD. If the species (necrophages and their predators) that were mode of the SSD remains constant, any shift in body trapped from decaying dead fish exposed along an ur- size towards smaller species should be visible as a change ban–rural gradient in Northern Poland. Carrion-visiting in the skew towards more negative values (if measured species seem to be well suited to study size distributions by the third moment). Alternatively, the whole SSD because they form well-defined communities that depend might shift to the left, leaving the shape of the distri- on the same type of resource. bution unchanged (Fig. 1). The ecological interpretation The present paper intends to answer the following of the first case is an accumulation of smaller species at questions: the disturbed sites (assuming similar species richness) 1. Can the decreasing body size pattern be generalized? due to a reduced proportion of medium-sized species, 2. Are size distributions habitat-type-specific? while larger species still persist in the community. The 3. Do beetle body size distributions differ between tro- second case in turn implies the local extinction of larger phic groups? species at disturbed sites. Both processes, of course, can 4. Do SSD shapes differ with respect to disturbance? work together, as has been reported by Sadler et al. 5. Are body sizes in disturbed habitats more regularly (2006) for carabid assemblages. spaced than in undisturbed sites? Changes in body size distributions might also cause changes in the respective competitive regimes. Under the We will show that there are marked differences in the assumption that species of similar size also have similar size distributions of necrophagous beetles along the resource requirements, interspecific competition should gradient, while these differences are less pronounced in cause a more regular spacing of body sizes along the size the predators. axis than expected from a random draw (Strong et al. 1979; Gotelli and Graves 1996). Most studies on ar- Materials and methods Eighty traps (four at each of 20 sites) were placed along A two 120 km transects (west–east, north–south, Fig. 2) Undisturbed crossing in the centre of the city of Olsztyn (Mazurian lake district of northern Poland, 53°47¢N; 20°30¢E). Additionally we placed ten identical traps at two sites on Frequency Disturbed the periphery of the city and in the city centre (Ale- ksandrowicz and Komosin´ski 2005). The sampling sites log body size covered two major habitat types, a forested (mixed coniferous forests) and an open (grassland) type. Mean B Disturbed Undisturbed trap distance was ca. 1 km. The traps operated during August and September 1997. Material was collected at the end of the trapping period. Traps were made of glass jars (diameter 9 cm) dug into soil and covered with Frequency wooden roofs. To avoid the capture of too many acci- dental species, the upper edges were 3–4 cm above log body size ground level. Each trap had a layer of 2–3 cm of glycol. One hundred grams of rotten fish (placed above the Fig. 1A–B Two ways in which a shift towards smaller species could glycol layer) served to attract beetle species. Four traps change a SSD. A The skew of the distribution changes and the were lost. The voucher specimens are kept at the proportion of medium-sized species is reduced. B The whole distribution shifts to the left and the large species become extinct. Department of Zoology of the University of Warmia Both mechanisms can occur in combination and Mazury (Aleksandrowicz and Komosin´ski 2005). 243 N from 1,000 random draws. Computations were made with the software Structure (Ulrich 2005b). WE DOBRE MIASTO An often used graphical representation that links S body size distributions to abundance data is the Lorenz MR GOWO curve (Lorenz 1905), where the cumulative percentage of BISKUPIEC MOR G individuals is plotted against cumulative percentage of body size (Damgaard and Weiner 2000; Magura et al. BARCZEWO 2006). If all individuals are of the same body size, the OSTRÓDA curve follows the isocline of equality. Increasing differ- OLSZTYN ences in body size force the curve below this line. While the Lorenz curve allows for the identification of size OLSZTYNEK inequalities, the fact that it is always a concave function LUBAWA often makes it difficult to compare different communities SZCZYTNO (Dixon et al. 1987; Damgaard and Weiner 2000; Magura et al. 2006). Therefore, in the present study we use a slightly different approach and plot cumulative per- Fig.