It is widely acknowledged that increasing complexity is a key attribute of ecosystem genesis. This is particularly true for primary succession on homogeneous substrates. However, a mechanistic understanding of spatial colonisation and pattern formation during primary succession has not been achieved yet. Thus, we studied this topic for 7 years within an experimental catchment (6 ha) established in the post-mining landscape of eastern Germany. Equidistant permanent plots (120 plots à 25m²) allowed for autocorrelation analyses, and thus tracing the spatial development of species cover performance. For each species tested, the “cover balance” first increased due to colonization, while decreasing in the course of succession. Drawing a benefit from these temporal trends, we suggested cover balance levels revealed by autocorrelation analyses to best indicate well-defined phases in primary succession at spatial entities. Hence, with the help of this spatial approach, terrestrial succession can be understood now much better at the most general level of the hierarchy provided by Pickett et al. (1987). In accordance with these authors, at subordinated levels of the causal hierarchy differential species performance might get collectively explained by contributing processes or conditions, such as ecophysiological traits, life history strategies, competition and allelopathy of the occurring plant species. Further research is needed to understand their relative contributions to the pattern formation.
Netzwerk Nagetier-übertragene Pathogene: Monitoring von Hantavirus-Infektionen in Deutschland
(2009)
Competition and moral behavior: A meta-analysis of forty-five crowd-sourced experimental designs
(2023)
Does competition affect moral behavior? This fundamental question has been debated among leading scholars for centuries, and more recently, it has been tested in experimental studies yielding a body of rather inconclusive empirical evidence. A potential source of ambivalent empirical results on the same hypothesis is design heterogeneity—variation in true effect sizes across various reasonable experimental research protocols. To provide further evidence on whether competition affects moral behavior and to examine whether the generalizability of a single experimental study is jeopardized by design heterogeneity, we invited independent research teams to contribute experimental designs to a crowd-sourced project. In a large-scale online data collection, 18,123 experimental participants were randomly allocated to 45 randomly selected experimental designs out of 95 submitted designs. We find a small adverse effect of competition on moral behavior in a meta-analysis of the pooled data. The crowd-sourced design of our study allows for a clean identification and estimation of the variation in effect sizes above and beyond what could be expected due to sampling variance. We find substantial design heterogeneity—estimated to be about 1.6 times as large as the average standard error of effect size estimates of the 45 research designs—indicating that the informativeness and generalizability of results based on a single experimental design are limited. Drawing strong conclusions about the underlying hypotheses in the presence of substantive design heterogeneity requires moving toward much larger data collections on various experimental designs testing the same hypothesis.
Successional phases describe changes in ecological communities that proceed in steps rather than continuously. Despite their importance for the understanding of ecosystem development, there still exists no reliable definition of phases and no quantitative measure of phase transitions. In order to obtain these data, we investigated primary succession in an artificial catchment (6 ha) in eastern Germany over a period of 6 years. The data set consists of records of plant species and their cover values, and initial substrate properties, both from plots in a regular grid (20 m × 20 m) suitable for spatial data analysis. Community assembly was studied by analyses of species co-occurrence and nestedness. Additionally, we correlated lognormal and log series distributions of species abundance to each community. We here introduce a new general method for detection of successional phases based on the degree of transient spatial homogeneity in the study system. Spatially coherent vegetation patterns revealed non-overlapping partitions within this sequence of primary succession and were characterized as two distinct ecological phases. Patterns of species co-occurrence were increasingly less random, and hence the importance of demographic stochasticity and neutral community assembly decreased during the study period. Our findings highlight the spatial dimension of successional phases and quantify the degree of change between these steps. They are an element for advancing a more reliable terminology of ecological successions.
From biodiversity to health: Quantifying the impact of diverse ecosystems on human well-being
(2023)
During early plant succession, the phylogenetic structure of a community changes in response to important environmental filters and emerging species interactions. We traced the development of temperate-zone plant communities during the first 7 years of primary succession on catchment soils to explore patterns of initial species assembly. We found pronounced small-scale differences in the phylogenetic composition of neighbouring plant assemblages and a large-scale trend towards phylogenetic evenness. This small-scale variability appears to be mediated by soil properties,
particularly carbonate content. Therefore, abiotic environmental conditions might counteract or even supersede the effects of interspecific competition among closely related species, which are usually predicted to exhibit patterns of phylogenetic evenness. We conclude that theories
on phylogenetic community composition need to incorporate effects of small-scale variability of environmental factors.
Theory on plant succession predicts a temporal increase in the complexity of spatial community structure and of competitive interactions: initially random occurrences of early colonising species shift towards spatially and competitively structured plant associations in later successional stages. Here we use long-term data on early plant succession in a German post mining area to disentangle the importance of random colonisation, habitat filtering, and competition on the temporal and spatial development of plant community structure. We used species co-occurrence analysis and a recently developed method for assessing competitive strength and hierarchies (transitive versus intransitive competitive orders) in multispecies communities. We found that species turnover decreased through time within interaction neighbourhoods, but increased through time outside interaction neighbourhoods. Successional change did not lead to modular community structure. After accounting for species richness effects, the strength of competitive interactions and the proportion of transitive competitive hierarchies increased through time. Although effects of habitat filtering were weak, random colonization and subsequent competitive interactions had strong effects on community structure. Because competitive strength and transitivity were poorly correlated with soil characteristics, there was little evidence for context dependent competitive strength associated with intransitive competitive hierarchies.
The total space of traits covered by the members of plant communities is an important parameter of ecosystem functioning and complexity. We trace the variability of trait space during early plant succession and ask how trait space co-varies with phylogenetic community structure and soil conditions. Particularly, we are interested in the small-scale variability in trait space and the influence of biotic and abiotic filters. We use data on species richness and soil conditions from the first 7 years of initial succession of an artificial catchment in north-eastern Germany. Total functional attribute diversity serves as a proxy to total trait space.
Total trait space steadily increased during succession. We observed high small-scale variability in total trait space that was positively correlated with species richness and phylogenetic segregation and negatively correlated with total plant cover. Trait space increased with soil carbonate content, while pH and the fraction of sandy material behaved indifferently. Our results indicate that during early succession, habitat filtering processes gain importance leading to a lesser increase in trait space than expected from the increase in species richness alone.
Ecological multifunctionality quantifies the functional performance of various important plant traits and increases with growing structural habitat heterogeneity, number of plant functional traits, and species richness. However, the successional changes in multifunctionality have not been traced so far. We use quantitative plant samples of 1 m2 plots from the first 6 years of initial vegetation dynamics in a German created catchment to infer the temporal changes in plant functional trait space and multifunctionality. Multifunctionality at the plot level was in all study years lower than expected from a random sample of the local pool of potential colonizers and was lowest at intermediate states of succession. In each year species containing a specific set of traits occurred with limited but focused functionality. The observed average low degree of multifunctionality contrasts with recent models predicting a tendency towards maximum multifunctionality during plant community development. However, variability in multifunctionality among plots increased during succession and the respective multifunctionality distribution among plots was increasingly right skewed indicating an excess of plots with relatively high multifunctionality. This relative excess of plots with high multifunctionality might act as an important trigger of community development paving the way for new species and functions to become established.