Diversity and Distributions, (Diversity Distrib.) (2006) 12, 767–775 Blackwell Publishing Ltd BIODIVERSITY Dispersal as a key element of community RESEARCH structure: the case of ground beetles on lake islands Marcin Zalewski1 and Werner Ulrich2* 1Centre for Ecological Studies, Polish Academy of ABSTRACT Sciences, M. Konopnickiej 1, Dziekanów Le1ny, In order to study the influence of dispersal ability on community structure of 05-092 0omianki, Poland, 2Nicolaus Copernicus University in Toru˜, ground beetles (carabidae), 15 lake islands and 2 mainland sites of the lake Mamry Department of Animal Ecology, Gagarina 9, archipelago, northern Poland, were sampled by using pitfall traps. Of the 71 87-100 Toru˜; Poland ground beetle species detected, 47 were macropterous, 16 wing-dimorphic and 8 brachypterous. Macropterous species had lower site abundances and occupied fewer sites than dimorphic and brachypterous species. There were trends from macropter- ous to brachypterous species towards a nested distribution across the sites and towards over-dispersed (aggregated) species co-occurrences. Canonical correspond- ence analysis pointed to site isolation and area as main factors influencing site abun- dance and spatial distribution. Our results imply that further studies on species co-occurrences and community assembly have to consider dispersal ability as a *Correspondence: Werner Ulrich, Nicolaus Copernicus University in Torun, Department of key element influencing ecological distributions at the regional scale. n Animal Ecology, Gagarina 9, 87-100 Toru ; Keywords Poland. Tel.: 0048-56-611 4469; E-mail: [email protected], Carabidae, wing polymorphism, abundance, species–area relationship, co- Internet: www.uni.torun.pl/~ulrichw occurrences, nestedness. ARR for weak dispersers, which might be a more widespread INTRODUCTION phenomenon (Lesica et al., 2006). Many studies have revealed correlations between local population A second major ecological distribution that is influenced by density and regional distribution (the abundance–range size dispersal is the well-known species–area relationship (SAR). relationship, ARR, cf. Gaston, 1996; Gaston & Blackburn, 2000). Island biogeography (MacArthur & Wilson, 1967) and meta- One factor generally believed to influence range sizes is dispersal population (Levins, 1969; Hanski, 1999) theory predict local extinc- ability (Hanski et al., 1993). The question of how dispersal ability tion and colonization to be major drivers of species numbers. shapes the structure of animal communities has been widely Species numbers per site should be correlated with dispersal discussed and is one of the major themes of macroecology ability and local survival rates and the relationships cause SAR (Brown, 1995; Blackburn & Gaston, 2003), metapopulation slopes (when using the power function model) to be steeper in ecology (Hanski, 1999) and the discussion around neutral less dispersive species (Rosenzweig, 1995; Hovestadt et al., 2005). models (Hubbell, 2001, 2005; Chave, 2004; Ulrich, 2004a). Third, dispersal ability should influence patterns of co- Dispersal ability has been linked to local and regional occurrences. A lower than randomly expected number of co- abundance, particularly to rarity (understood as low abundance) occurrences of species (underdispersion) has been linked to sites (Gaston, 1994; Kunin & Gaston, 1997). However, critical assess- with higher colonization rates (Badano et al., 2005). On the con- ments about the influence of dispersal ability on regional and trary, high rates of colonization with respect to local persistence local community structure are surprisingly scarce. Morse et al. should randomize the faunal composition and cause random (1988) argued for higher frequencies of rarity in species with patterns of species co-occurrences. However, direct tests of high mobility, because they might be able to mate and reproduce whether and how dispersal ability influences patterns of species at comparably low abundance. For butterflies, Cowley et al. co-occurrences are largely missing. Azeria (2004) reported (2001) showed that more dispersive species had lower mean higher numbers of co-occurrences of species (over-dispersion) at abundances and were less aggregated because of their migration medium rates of colonization and local extinction. The study into less suitable habitats. Such a pattern has been predicted suggests therefore a trade-off between colonization rates and by the aggregation hypothesis of Hartley (1998), developed local persistence to influence species co-occurrence. to explain the positive ARR relationship (Gaston, 1996). In line Ground beetles are particularly suited for studying the influence with this theory, Cowley et al. (2001) did not find a significant of dispersal on local community structure because they can be © 2006 The Authors DOI: 10.1111/j.1366-9516.2006.00283.x Journal compilation © 2006 Blackwell Publishing Ltd www.blackwellpublishing.com/ddi 767 M. Zalewski and W. Ulrich divided into groups of winged and wingless species, which differ ground beetles available (Madison et al., 1999) and subfamily from each other with respect to dispersal ability (Niemelä, and tribe relationships are not well resolved. Hence, we were 1988; Den Boer, 1990). Furthermore, most communities contain unable to compute phylogenetic contrasts at the genus level wing-dimorphic (hereafter dimorphic) species, in which only a (Felsenstein, 2004). To account at least in part for this possible part of the population is fully winged. These species exhibit an source of errors, we computed bivariate comparisons and intermediate dispersal strategy. Flight, and therefore dispersal, ARRs twice, once using species values and once using genus ability depends also on other factors, like the development of means. Because of the low number of data points for brach- thoracic muscles (Nelemans, 1987; Den Boer, 1990), although ypterous species, we were unable to use genus means for these wing size seems to be the best predictor when comparing the species. dispersal abilities of different carabid species (Den Boer et al., We used the canonical correspondence analysis (CCA) to refer 1980; Gutiérrez & Menéndez, 1997; Gutiérrez et al., 2004; beetle occurrences to the previously mentioned site characteris- Zalewski, 2004). tics. To account for possible inhomogeneities in the data struc- The present paper aims at studying whether and how dispersal ture, we used ranked values for all parameters and abundances. ability influences patterns of regional distribution, SARs and Ordination scores were scaled via the optimize species option species co-occurrence. We use data from a 2-year survey of implemented in - version 4.2 (McCune & Mefford, 1999). ground beetles on small lake islands in northern Poland (Ulrich Significances were inferred by Monte Carlo simulation, assuming & Zalewski, 2006) and show that macropterous, dimorphic and no structure in the main matrix. For CCA, assuming unimodal brachypterous species differ in patterns of spatial distribution response curves, we first checked for appropriateness by and co-occurrences. performing a detrended correspondence analysis that provides estimates of axis lengths. The length of our first axis (1.89) was above the minimum length of 1.5 recommended by ter Braak & METHODS Prentice (1988) for applying CCA. Fifteen island and two forested mainland sites (variants of Tilio We used C-scores (Stone & Roberts, 1990) and species carpinetum and Carici elongatae-alnetum associations) from the combination scores (Pielou & Pielou, 1968) to study species co- largest archipelago of islands in Poland — the Mazurian Lake occurrence patterns of presence–absence matrices. The C-score Mamry (21°30′–21°52′ E, 54°00′–54°10′ N) were sampled using measures mean matrix-wide underdispersion (segregation) pitfall traps (0.5-L plastic mug, mouth diameter 120 mm, between sites (checkerboard patterns), the species combination wooden roof). Between 3 (on the smallest site only two) and 21 score by contrast screens for unique species combinations traps were used per site, depending on its habitat diversity and (Gotelli & McCabe, 2002). Both scores therefore measure different size making up a total of 107 traps. Habitat diversity was assessed aspects of co-occurrence (Gotelli & McCabe, 2002). Standardized according to existing maps and from a survey of soil types. As scores are Z-transformed and should have a mean of 0 and a recommended by Krebs (1989) and Digweed et al. (1995), a standard deviation of 1. Significant species under-dispersion single main line crossing all habitats of an island was chosen. or over-dispersion, on the other hand, should result in Z- From this line, perpendicular trap lines were placed (trap transformed scores above 1.96 or below −1.96 (at the 5% error distance 25 m). Traps operated from June to September 1997 and level). Random matrices for generating standardized scores and 1998 and were emptied monthly and refilled with fresh glycol significance levels were computed with 7.72 (Gotelli & (Zalewski, 2000; Ulrich & Zalewski, 2006). Entsminger, 2005). We used fixed sum row and column con- All carabid species except the genus Europhilus were identified straints and the sequential swap algorithm for randomization as to species level using the keys of Hürka (1996) and Lindroth advocated by Gotelli (2000) for the study of island data. (1985) (Table 1). Nomenclature follows Hürka (1996). Life To account for possible sampling errors and bias introduced history and morphological characteristics