Dénes Schmera

A comparative analysis reveals weak relationships between ecological factors and beta diversity of stream insect metacommunities at two spatial levels

The hypotheses that beta diversity should increase with decreasing latitude and increase with spatial extent of a region have rarely been tested based on a comparative analysis of multiple datasets, and no such study has focused on stream insects. We first assessed how well variability in beta diversity of stream insect metacommunities is predicted by insect group, latitude, spatial extent, altitudinal range, and dataset properties across multiple drainage basins throughout the world. Second, we assessed the relative roles of environmental and spatial factors in driving variation in assemblage composition within each drainage basin. Our analyses were based on a dataset of 95 stream insect metacommunities from 31 drainage basins distributed around the world. We used dissimilarity-based indices to quantify beta diversity for each metacommunity and, subsequently, regressed beta diversity on insect group, latitude, spatial extent, altitudinal range, and dataset properties (e.g., number of sites and percentage of presences). Within each metacommunity, we used a combination of spatial eigenfunction analyses and partial redundancy analysis to partition variation in assemblage structure into environmental, shared, spatial, and unexplained fractions. We found that dataset properties were more important predictors of beta diversity than ecological and geographical factors across multiple drainage basins. In the within-basin analyses, environmental and spatial variables were generally poor predictors of variation in assemblage composition. Our results revealed deviation from general biodiversity patterns because beta diversity did not show the expected decreasing trend with latitude. Our results also call for reconsideration of just how predictable stream assemblages are along ecological gradients, with implications for environmental assessment and conservation decisions. Our findings may also be applicable to other dynamic systems where predictability is low.

Characterizing connectivity relationships in freshwaters using patch-based graphs

Spatial graphs in landscape ecology and conservation have emerged recently as a powerful methodology to model patterns in the topology and connectivity of habitat patches (structural connectivity) and the movement of genes, individuals or populations among these patches (potential functional connectivity). Most spatial graph’s applications to date have been in the terrestrial realm, whereas the use of spatially explicit graph-based methods in the freshwater sciences has lagged far behind. Although at first patch-based spatial graphs were not considered suitable for representing the branching network of riverine landscapes, here we argue that the application of graphs can be a useful tool for quantifying habitat connectivity of freshwater ecosystems. In this review we provide an overview of the potential of patch-based spatial graphs in freshwater ecology and conservation, and present a conceptual framework for the topological analysis of stream networks (i.e., riverscape graphs) from a hierarchical patch-based context. By highlighting the potential application of graph theory in freshwater sciences we hope to illustrate the generality of spatial network analyses in landscape ecology and conservation.

A measure for assessing functional diversity in ecological communities

Functional diversity is regarded as a key in understanding the link between ecosystem function and biodiversity, but its measurement is rather problematic. The two widely used continuous measures are the dendrogram-based measure (DBM) and the functional attribute diversity (FAD). In contrast to DBM, FAD does not require the knowledge of the entire species pool before the analysis, and hence FAD is a more ideal tool for measuring functional diversity. However, the original form of FAD and its variants have several undesirable properties. Here, we suggest a modified FAD (denoted by MFAD), which—as illustrated by artificial and actual data sets—allows calculating functional diversity without violating the twinning and monotonicity criteria such that the number of species collected is compensated for. These requirements are met by replacing the original species by so-called functional species and then by dividing FAD by the number of functional units. Accordingly, MFAD measures the dispersion of species in the functional traits space so that MFAD values for different communities can directly be compared if the same set of functional traits is used. Finally, using data of two freshwater communities (caddisfly and riverine fish), we evaluate the change of species richness and functional diversity in relation to sampling effort (sample unit size). We found that functional diversity is a better and more reliable community descriptor than species richness in a sense that it converges to the maximum faster in the function of sampling effort.

A proposed unified terminology of species traits in stream ecology

Traits-based community analyses are receiving increasing attention. However, consistent interpretation of empirical results and ecological understanding in stream ecology are limited by ambiguous terminology. Furthermore, the measurement scales used to analyze trait data, especially ordinal-scale data, are often inappropriately applied. We identify and discuss these shortcomings and offer a solution for an operative and algebraically correct treatment of traits and a unified nomenclature that facilitates direct comparison among traits-based studies. A unified terminology allows for logical translation among existing, alternative trait nomenclatures and should facilitate communication of research findings among stream ecologists and more directly connect stream traits-based research with general ecology.

Quantifying temporal variability in the metacommunity structure of stream fishes: the influence of non-native species and environmental drivers

Most studies characterize metacommunities based on a single snapshot of the spatial structure, which may be inadequate for taxa with high migratory behavior (e.g., fish). Here, we applied elements of metacommunity structure to examine variations in the spatial distributions of stream fishes over time and to explore possible structuring mechanisms. Although the major environmental gradients influencing species distributions remained largely the same in time, the best-fit pattern of metacommunity structure varied according to sampling occasion and whether or not we included non-native species in the analyses. Quasi-Clementsian and Clementsian structures were the predominant best-fit structures, indicating the importance of species turnover among sites and the existence of more or less discrete community boundaries. The environmental gradient most correlated with metacommunity structure was defined by altitude, area of artificial ponds in the catchment, and dissolved oxygen content. Our results suggest that the best-fit metacommunity structure of the native species can change in time in this catchment due to seasonal changes in distribution patterns. However, the distribution of non-native species throughout the landscape homogenizes the temporal variability in metacommunity structure of native species. Further studies are necessary from other regions to examine best-fit metacommunity structures of stream fishes within relatively short environmental gradients.

Optimization of a chemical attractant for Epicometis (Tropinota) hirta Poda

In field trapping tests in Hungary cinnamyl alcohol (3-phenyl-2-propen-1-ol) and transanethole [(1-methoxy-4-(1-propenyl)benzene)] attracted significantly more adult Epicometis (Tropinota) hirta (Coleoptera, Scarabaeidae, Cetoniinae) when presented together in the same bait compared to the single compounds. Best attraction was recorded by a 1:1 mixture. Addition of other common floral scent compounds, i.e. 3-methyl eugenol, 4-methoxy-cinnamaldehyde, anisylacetone, β-ionone, cinnamyl acetate, cinnamic aldehyde, eugenol, indole, 2-phenylethanol or phenylacetaldehyde did not influence catches. The binary cinnamyl alcohol/ trans-anethole bait described in this study is recommended for use in traps of E. hirta for agricultural purposes.

Functional diversity: a review of methodology and current knowledge in freshwater macroinvertebrate research

Although several studies have examined the functional diversity of freshwater macroinvertebrates, the variety of methodologies combined with the absence of a synthetic review make our understanding of this field incomplete. Therefore, we reviewed the current methodology for assessing functional diversity in freshwater macroinvertebrate research. Our review showed that most papers quantified functional diversity using biological traits, among which feeding habits were the most common traits probably due to the assumed links between feeding and ecosystem functions. A large number of diversity measures have been applied for quantifying functional diversity of freshwater macroinvertebrate assemblages, among which Rao’s quadratic entropy looks like the most frequent. In most papers, functional diversity was positively related to taxon richness, and functional redundancy was a key concept in explaining this correlation. Most studies detected strong influence of the environmental factors as well as human impact on functional diversity. Finally, our review revealed that functional diversity research is biased towards European running waters and is hindered by yet insufficient information on the autecology of macroinvertebrates.

Does functional redundancy of communities provide insurance against human disturbances? An analysis using regional-scale stream invertebrate data

Human-induced reductions in species richness might alter the quality of ecosystem services when the remaining species are not able to substitute the functions provided by extirpated species. We examined how human disturbances (nutrient enrichment, land use intensification, instream habitat degradation and the presence of alien species) influence the species richness of stream invertebrates. Stream invertebrates (425 native species) were collected by kick and sweep sampling technique at 274 stream sites covering the entire area of Hungary. We measured the species richness, functional richness (i.e. number of unique functional roles provided by community members) and functional redundancy (i.e. the functional insurance of the community) using information on the feeding habits of each species. To remove the effect of natural variability, we tested the effect of stressors on the residuals of models relating species richness, functional richness and functional redundancy with natural environmental gradients. Our results showed that species richness was negatively influenced by instream habitat degradation and nutrient enrichment. Independent of the way of quantifying functional richness and functional redundancy, we found that functional richness is more sensitive to human impact than functional redundancy of stream invertebrates. The finding that a reduction of species richness is associated with a loss of unique functional roles (functional richness) is important for conservation issues, because the number of unique functional roles is usually regarded as driver of ecosystem functioning.

Linking scale and diversity partitioning in comparing species diversity of caddisflies in riffle and pool habitats

Assessing and interpreting biodiversity is a key issue of current ecology and sampling is the first and most critical step in biodiversity assessment. We focused on how sampling scale influences the mesohabitat level species diversity components (i.e. alpha, beta, gamma) of caddisflies in a natural submontain stream. We interpreted scale as the relationship between observation unit size (grain), sample size (number of replicates) and total sampled area (sampling effort), and examined in three simulated experiments, how the individual and joint effects of these scale components influence the difference of caddisfly diversity between riffle and pool habitats. Additive partitioning of diversity into within observation unit (a), among observation unit (β) and total diversity components (y) in a scale-dependent manner showed that scale had a fundamental role in (1) quantifying values of diversity components and (2) in detecting differences between assemblages. Although sites showed considerable variability, the study clearly demonstrated that sample size and total sampled area are the most important and critical scale components of sampling, while the size of the observation unit might be indifferent. The analytical method applied here can be used for any aquatic assemblage collected with a sampling device of well defined area (or volume) and at any levels of the habitat hierarchy. The study reveals the importance of the among observation unit component (i.e. small scale beta diversity) in shaping total diversity and calls attention to the careful consideration of scale in environmental assessment and monitoring.

Native and alien macroinvertebrate richness in a remnant of the former river Rhine: a source for recolonisation of restored habitats?

Rivers are among the most endangered ecosystems of the world with dramatically decreasing biodiversity. Rehabilitation programmes aiming at restoration of riverine ecosystems rely on the recolonisation of native macroinvertebrates from refuges. We examined whether a relatively natural remnant of the former river Rhine (Altrhein) harbours a higher richness of benthic macroinvertebrates than two sites of the modified Rhine with artificial and semi-natural embankments near Basel. All three sites were bimonthly sampled between May 2007 and May 2008 using three techniques: Kick and Sweep, drifting animals collected from pieces of stone turned by hand, and animals collected from stone surfaces. Taxa richness was higher in the Altrhein than in the two sampling sites in the river Rhine, but it was mainly a result of the large number of individuals sampled at this site. Despite 17% of taxa recorded were alien, the three sampling sites differed neither in the number of alien taxa nor in their abundances. However, lower percentages of both alien taxa and individuals were recorded in the Altrhein than at the other two sites in the Rhine. Indicator value analysis showed that the macroinvertebrate community of the Altrhein maintains several native and specific taxa. Multivariate analyses supported the separation of the communities collected at different sampling sites and also the uniqueness of the community in the Altrhein. The observed patterns, however, strongly depended on the sampling method applied, thereby calling the attention to the application of standard sampling methods and also to the restriction of result comparisons on projects using identical sampling methodology. Our study shows that the remnant of the former river Rhine serves as a refuge for macroinvertebrates which may facilitate future restoration of the river embankment.