Werner Ulrich

Aquatic plants are well suited as subjects for studies on the distribution and abundance of co‐occurring species, especially due to the simple structure of their communities, well defined toposequences and relatively easily measurable environmental factors. Here we show that underwater plants occurring in semi‐natural lakes form stable communities, where species interactions dominate over dispersal dynamics to form a modular community structure with a high degree of zonation (turnover) and low within‐module species richness. In turn, human‐induced disturbance largely destroyed the modular structure. Our results indicate that (1) species abundance distributions (SADs) of underwater plant communities are well described by the lognormal model; (2) environmental characters did not significantly influence the SADs of underwater plant communities; (3) log‐series SADs do not indicate specific types of community organization; (4) in our lake communities only few satellites (tourists) occur; (5) the co‐occurrence of species is highly dependent on the turnover across lakes and water depth zones; and (6) species zonation is a function of lake properties.

Aim Species–body size distributions (SBDs) are plots of species richness across body size classes. They have been linked to energetic constraints, speciation–extinction dynamics and to evolutionary trends. However, little is known about the spatial variation of size distributions. Here we study SBDs of European springtails (Collembola) at a continental scale and test whether minimum, average and maximum body size and the shapes of size distributions change across latitudinal and longitudinal gradients and whether SBDs of islands and mainlands differ. We also test whether the island rule and the positive body size–range size relationship of vertebrates also holds for Collembola.Location Europe.Methods We use a unique data set on the spatial distributions of 2102 species of European springtails across 52 countries and larger islands together with associated data on body size, area, climate variables, longitude and latitude. Differences in the central moments of SBDs are inferred from simultaneous spatial autoregression models.Results The SBD of the European Collembola and its largest suborder Entomobryomorpha is unimodal and symmetrical. Average, minimum and maximum body weight and the skewness of the mainland/island SBDs peaked at intermediate latitudes. We could not find simple latitudinal gradients in minimum and maximum body weight. Average and maximum body size increased with country/island area in accordance with the island rule in vertebrates, while minimum body size did not significantly differ between islands and mainlands. Finally, we found a weak but statistically significant positive correlation of range size and body size.Main conclusions We provide evidence for differences in body size distributions between islands and mainlands that are in part in line with the island rule in invertebrates. We also find evidence for an interspecific body size–range size relationship similar to that of vertebrates although the vertebrate pattern is much stronger than the springtail pattern. Our results on latitudinal gradients of maximum and average body size imply the need to account for species richness and area effects in the study of latitudinal gradients in body size. We recommend implementing sample size and area effects in the study of body size distributions on islands and mainlands.

A statistical challenge in community ecology is to identify segregated and aggregated pairs of species from a binary presence–absence matrix, which often contains hundreds or thousands of such potential pairs. A similar challenge is found in genomics and proteomics, where the expression of thousands of genes in microarrays must be statistically analyzed. Here we adapt the empirical Bayes method to identify statistically significant species pairs in a binary presence–absence matrix. We evaluated the performance of a simple confidence interval, a sequential Bonferroni test, and two tests based on the mean and the confidence interval of an empirical Bayes method. Observed patterns were compared to patterns generated from null model randomizations that preserved matrix row and column totals. We evaluated these four methods with random matrices and also with random matrices that had been seeded with an additional segregated or aggregated species pair. The Bayes methods and Bonferroni corrections reduced the frequency of false-positive tests (type I error) in random matrices, but did not always correctly identify the non-random pair in a seeded matrix (type II error). All of the methods were vulnerable to identifying spurious secondary associations in the seeded matrices. When applied to a set of 272 published presence–absence matrices, even the most conservative tests indicated a fourfold increase in the frequency of perfectly segregated “checkerboard” species pairs compared to the null expectation, and a greater predominance of segregated versus aggregated species pairs. The tests did not reveal a large number of significant species pairs in the Vanuatu bird matrix, but in the much smaller Galapagos bird matrix they correctly identified a concentration of segregated species pairs in the genus Geospiza. The Bayesian methods provide for increased selectivity in identifying non-random species pairs, but the analyses will be most powerful if investigators can use a priori biological criteria to identify potential sets of interacting species.

We use data of bat species richness of 58 European countries and larger islands from Fauna Europaea augmented by recent faunal surveys of particular countries to evaluate the effects of area, latitude, annual temperature range, and mean winter length (days < 0°C), geographical heterogeneity, number of plant species, and distance from Turkey on bat species richness. Area, latitude, and temperature range explained more than 73% of the total variability in European bat species richness. Latitude and temperature corrected species-area relationships of vespertilionid bats were fitted by the power function model with mainland countries having a lower slope (z = 0.09) than islands (z = 0.15) consistent with current theory. The area corrected centre of vespertilionid species richness was at about 46°N with Croatia being most species rich (34 species). Non-vespertilionid bats peaked at 41°N and did not show a simple latitudinal gradient. The inclusion of plant species richness in the model for Vespertilio...

The question whether and to what degree urbanization causes a decrease in diversity of animal and plant species and changes in community structure is still a matter of debate. While many studies used ground beetles, vertebrates, and butterflies as assumed model taxa, little work has been done with other, particularly insect, taxa. Here we report on rural and urban diversities of communities of carcass visiting destruent and predatory beetles (Coleoptera). From 8 rural and 2 city sites, we sampled 15323 destruent beetles representing 58 species and 1871 predators from 43 species. We observed a reduced diversity and changes in community structure of both beetle guilds towards the city. However, these changes were guild specific and our study gives no evidence that there are simple rules that govern rural and urban patterns of diversity. Species abundance distributions did not significantly differ between the study sites. There is also no evidence that the intermediate disturbance hypothesis might apply. Lastly, we found only little support for a homogenizing effect of urban environments on carrion visiting beetles

Two opposing patterns of meta‐community organization are nestedness and negative species co‐occurrence. Both patterns can be quantified with metrics that are applied to presence‐absence matrices and tested with null model analysis. Previous meta‐analyses have given conflicting results, with the same set of matrices apparently showing high nestedness (Wright et al. 1998) and negative species co‐occurrence (Gotelli and McCabe 2002). We clarified the relationship between nestedness and co‐occurrence by creating random matrices, altering them systematically to increase or decrease the degree of nestedness or co‐occurrence, and then testing the resulting patterns with null models. Species co‐occurrence is related to the degree of nestedness, but the sign of the relationship depends on how the test matrices were created. Low‐fill matrices created by simple, uniform sampling generate negative correlations between nestedness and co‐occurrence: negative species co‐occurrence is associated with disordered matrices. However, high‐fill matrices created by passive sampling generate the opposite pattern: negative species co‐occurrence is associated with highly nested matrices. The patterns depend on which index of species co‐occurrence is used, and they are not symmetric: systematic changes in the co‐occurrence structure of a matrix are only weakly associated with changes in the pattern of nestedness. In all analyses, the fixed‐fixed null model that preserves matrix row and column totals has lower type I and type II error probabilities than an equiprobable null model that relaxes row and column totals. The latter model is part of the popular nestedness temperature calculator, which detects nestedness too frequently in random matrices (type I statistical error). When compared to a valid null model, a matrix with negative species co‐occurrence may be either highly nested or disordered, depending on the biological processes that determine row totals (number of species occurrences) and column totals (number of species per site).

Nestedness is a common biogeographic pattern in which small communities form proper subsets of large communities. However, the detection of nestedness in binary presence–absence matrices will be affected by both the metric used to quantify nestedness and the reference null distribution. In this study, we assessed the statistical performance of eight nestedness metrics and six null model algorithms. The metrics and algorithms were tested against a benchmark set of 200 random matrices and 200 nested matrices that were created by passive sampling. Many algorithms that have been used in nestedness studies are vulnerable to type I errors (falsely rejecting a true null hypothesis). The best‐performing algorithm maintains fixed row and fixed column totals, but it is conservative and may not always detect nestedness when it is present. Among the eight indices, the popular matrix temperature metric did not have good statistical properties. Instead, the Brualdi and Sanderson discrepancy index and Cutler's index of unexpected presences performed best. When used with the fixed‐fixed algorithm, these indices provide a conservative test for nestedness. Although previous studies have revealed a high frequency of nestedness, a reanalysis of 288 empirical matrices suggests that the true frequency of nested matrices is between 10% and 40%.

The question how animal body size changes along urban–rural gradients has received much attention from carabidologists, who noticed that cities harbour smaller species than natural sites. For Carabidae this pattern is frequently connected with increasing disturbance regimes towards cities, which favour smaller winged species of higher dispersal ability. However, whether changes in body size distributions can be generalised and whether common patterns exist are largely unknown. Here we report on body size distributions of carcass‐visiting beetles along an urban–rural gradient in northern Poland. Based on samplings of 58 necrophages and 43 predatory beetle species, mainly of the families Catopidae, Silphidae, and Staphylinidae, we found contrary patterns of necrophages and predatory beetles. Body sizes of necrophages decreased towards the city centre and those of predators remained unchanged. Small necrophages and large predators dominated in abundance in the city centre. Necrophage body sizes appeared to be more regularly spaced in the city centre than expected from a random null model and in comparison to the rural pattern, pointing to increased competition.

In order to study the influence of dispersal ability on community structure of ground beetles (carabidae), 15 lake islands and 2 mainland sites of the lake Mamry archipelago, northern Poland, were sampled by using pitfall traps. Of the 71 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 macropterous to brachypterous species towards a nested distribution across the sites and towards over‐dispersed (aggregated) species co‐occurrences. Canonical correspondence analysis pointed to site isolation and area as main factors influencing site abundance and spatial distribution. Our results imply that further studies on species co‐occurrences and community assembly have to consider dispersal ability as a key element influencing ecological distributions at the regional scale.

Species number–body weight distributions are generally thought to be skewed to the right. Hence it is assumed that the number of relatively small species is larger than the number of relatively large species. While this pattern is well documented in vertebrates, comparative studies on larger invertebrate taxa are still scarce. Here I show that the weight distributions of European Hymenoptera (based on 12 601 species body weight data compiled from major catalogues) do not exhibit a general trend towards right skewed species–body weight distributions. Skewness did not depend on the number of species per taxon. Species richness peaked at intermediate body weights irrespective of taxonomic level. Kernel density analysis revealed that hymenopteran taxa had between one and four peaks in their size distributions with larger taxa having fewer peaks. Within genus variability in body weight was allometrically related to mean body weight (σ ² =μ ^1.81 ) in line with a proportional rescaling pattern. These results call for a rethinking about the generality of current vertebrate centred models of body size evolution.