Oliver Purschke | German Centre for Integrative Biodiversity Research (iDiv) (original) (raw)

Papers by Oliver Purschke

New Phytologist, 2014

Biodiversity loss may alter ecosystem processes, such as herbivory, a key driver of ecological fu... more Biodiversity loss may alter ecosystem processes, such as herbivory, a key driver of ecological functions in species-rich (sub)tropical forests. However, the mechanisms underlying such biodiversity effects remain poorly explored, as mostly effects of species richnessa very basic biodiversity measurehave been studied. Here, we analyze to what extent the functional and phylogenetic diversity of woody plant communities affect herbivory along a diversity gradient in a subtropical forest.

Plant communities differ in their species composition, and, thus, also in their functional trait ... more Plant communities differ in their species composition, and, thus, also in their functional trait composition, at different stages in the succession from arable fields to grazed grassland. We examine whether aerial hyperspectral (414-2501 nm) remote sensing can be used to discriminate between grazed vegetation belonging to different grassland successional stages. Vascular plant species were recorded in 104.1 m 2 plots on the island of Öland (Sweden) and the functional properties of the plant species recorded in the plots were characterized in terms of the ground-cover of grasses, specific leaf area and Ellenberg indicator values. Plots were assigned to three different grassland age-classes, representing 5-15, 16-50 and >50 years of grazing management. Partial least squares discriminant analysis models were used to compare classifications based on aerial hyperspectral data with the age-class classification. The remote sensing data successfully classified the plots into age-classes: the overall classification accuracy was higher for OPEN ACCESS Remote Sens. 2014, 6 7733 a model based on a pre-selected set of wavebands (85%, Kappa statistic value = 0.77) than one using the full set of wavebands (77%, Kappa statistic value = 0.65). Our results show that nutrient availability and grass cover differences between grassland age-classes are detectable by spectral imaging. These techniques may potentially be used for mapping the spatial distribution of grassland habitats at different successional stages.

Remote Sensing, 2014

PLoS ONE, 2014

Future climates are likely to include extreme events, which in turn have great impacts on ecologi... more Future climates are likely to include extreme events, which in turn have great impacts on ecological systems. In this study, we investigated possible effects that could mitigate stem breakage caused by a rare and extreme ice storm in a Chinese subtropical forest across a gradient of forest diversity. We used Bayesian modeling to correct stem breakage for tree size and variance components analysis to quantify the influence of taxon, leaf and wood functional traits, and stand level properties on the probability of stem breakage. We show that the taxon explained four times more variance in individual stem breakage than did stand level properties; trees with higher specific leaf area (SLA) were less susceptible to breakage. However, a large part of the variation at the taxon scale remained unexplained, implying that unmeasured or undefined traits could be used to predict damage caused by ice storms. When aggregated at the plot level, functional diversity and wood density increased after the ice storm. We suggest that for the adaption of forest management to climate change, much can still be learned from looking at functional traits at the taxon level.

Oecologia, 2012

Dispersal limitation and long-term persistence are known to delay plant species' responses to hab... more Dispersal limitation and long-term persistence are known to delay plant species' responses to habitat fragmentation, but it is still unclear to what extent landscape history may explain the distribution of dispersal traits in present-day plant communities. We used quantitative data on long-distance seed dispersal potential by wind and grazing cattle (epi-and endozoochory), and on persistence (adult plant longevity and seed bank persistence) to quantify the linkages between dispersal and persistence traits in grassland plant communities and current and past landscape configurations. The long-distance dispersal potential of present-day communities was positively associated with the amounts of grassland in the historical (1835, 1938) landscape, and with a long continuity of grazing management-but was not associated with the properties of the current landscape. The study emphasises the role of history as a determinant of the dispersal potential of present-day grassland plant communities. The importance of long-distance dispersal processes has declined in the increasingly fragmented modern landscape, and long-term persistent species are expected to play a more dominant role in grassland communities in the future. However, even within highly fragmented landscapes, long-distance dispersed species may persist locally-delaying the repayment of the extinction debt.

Oecologia, 2014

plant species richness. Plant phylogenetic diversity had no consistent effect on spider FD. the r... more plant species richness. Plant phylogenetic diversity had no consistent effect on spider FD. the results contrast with the negative effect of diversity on spider species richness and suggest that functional redundancy among spiders decreased with increasing plant richness through nonrandom species loss. moreover, increasing functional dissimilarity within spider assemblages with increasing plant richness indicates that the abundance distribution of predators in functional trait space affects ecological functions independent of predator species richness or the available trait space. While plant diversity is generally hypothesized to positively affect predators, our results only support this hypothesis for FD-and here particularly for trait distributions within the overall functional trait space-and not for patterns in species richness. understanding the way predator assemblages affect ecosystem functions in such highly diverse, natural ecosystems thus requires explicit consideration of FD and its relationship with species richness.

Journal of Vegetation Science, 2012

To what extent is species richness in semi-natural grasslands related to local environmental fact... more To what extent is species richness in semi-natural grasslands related to local environmental factors and (present/past) surrounding landscape structure? Do responses of species richness depend on degree of habitat specialization (specialists vs generalists) and/or scale of the study?

Journal of Ecology, 2013

1. Theory predicts that the processes generating biodiversity after disturbance will change durin... more 1. Theory predicts that the processes generating biodiversity after disturbance will change during succession. Comparisons of phylogenetic and functional (alpha and beta) diversity with taxonomic diversity can provide insights into the extent to which community assembly is driven by deterministic or stochastic processes, but comparative approaches have yet to be applied to successional systems. 2. We characterized taxonomic, phylogenetic and functional plant (alpha and beta) diversity within and between four successional stages in a > 270-year-long arable-to-grassland chronosequence. Null models were used to test whether functional and phylogenetic turnover differed from random expectations, given the levels of species diversity. 3. The three facets of diversity showed different patterns of change during succession. Between early and early-mid succession, species richness increased but there was no increase in functional or phylogenetic diversity. Higher than predicted levels of functional similarity between species within the early and early-mid successional stages, indicate that abiotic filters have selected for sets of functionally similar species within sites. Between late-mid and late succession, there was no further increase in species richness, but a significant increase in functional alpha diversity, suggesting that functionally redundant species were replaced by functionally more dissimilar species. Functional turnover between stages was higher than predicted, and higher than within-stage turnover, indicating that different assembly processes act at different successional stages. 4. Synthesis. Analysis of spatial and temporal turnover in different facets of diversity suggests that deterministic processes generate biodiversity during post-disturbance ecosystem development and that the relative importance of assembly processes has changed over time. Trait-mediated abiotic filtering appears to play an important role in community assembly during the early and early-mid stages of arable-to-grassland succession, whereas the relative importance of competitive exclusion appears to have increased towards the later successional stages. Phylogenetic diversity provided a poor reflection of functional diversity and did not contribute to inferences about underlying assembly processes. Functionally deterministic assembly suggests that it may be possible to predict future post-disturbance changes in biodiversity, and associated ecosystem attributes, on the basis of species' functional traits but not phylogeny.

Journal of Ecology, 2014

1. Plant communities and their ecosystem functions are expected to be more resilient to future ha... more 1. Plant communities and their ecosystem functions are expected to be more resilient to future habitat fragmentation and deterioration if the species comprising the communities have a wide range of dispersal and persistence strategies. However, the extent to which the diversity of dispersal and persistence traits in plant communities is determined by the current and historical characteristics of sites and their surrounding landscape has yet to be explored. 2. Using quantitative information on long-distance seed dispersal potential by wind and animals (dispersal in space) and on species' persistence/longevity (dispersal in time), we (i) compared levels of dispersal and persistence trait diversity (functional richness, FRic, and functional divergence, FDiv) in seminatural grassland plant communities with those expected by chance, and (ii) quantified the extent to which trait diversity was explained by current and historical landscape structure and local management historytaking into account spatial and phylogenetic autocorrelation. 3. Null model analysis revealed that more grassland communities than expected had a level of trait diversity that was lower or higher than predicted, given the level of species richness. Both the range (FRic) and divergence (FDiv) of dispersal and persistence trait values increased with grassland age. FDiv was mainly explained by the interaction between current grazing intensity and the amount of grassland habitat in the surrounding landscape in 1938. 4. Synthesis. The study suggests that the variability of dispersal and persistence traits in grassland plant communities is driven by deterministic assembly processes, with both history and current management (and their interactions), playing a major role as determinants of trait diversity. While a long continuity of grazing management is likely to have promoted the diversity of dispersal and persistence traits in present-day grasslands, communities in sites that are well grazed at the present day, and were also surrounded by large amounts of grassland in the past, showed the highest diversity of dispersal and persistence strategies. Our results indicate that the historical context of a site within a landscape will influence the extent to which current grazing management is able to maintain a diversity of dispersal and persistence strategies and buffer communities (and their associated functions) against continuing habitat fragmentation.

Fungal Diversity, 2014

Foliar fungal pathogens affect forest ecosystem processes by exerting highly species-specific imp... more Foliar fungal pathogens affect forest ecosystem processes by exerting highly species-specific impacts on growth and survival of trees. As many ecosystem processes in forests depend on functional diversity of specific tree species, a close relationship is expected between this and foliar fungal pathogen infestation. Testing for such a relationship in the German tree diversity experiment BIOTREE (Bechstedt), we hypothesized that pathogen richness and pathogen load decline with increasing functional diversity of tree communities. Using macro-and microscopic analyses, we assessed pathogen richness and load on 16 tree species in plots that, although differing in functional diversity, had the same tree species richness. We found no effects of functional diversity on pathogen richness or load. However, we encountered strong species identity effects in plot species composition, as susceptible tree species contributed positively to each community's pathogen richness and load. Furthermore, testing for effects of particular leaf traits and geographical range size of host species revealed a significant effect of total leaf phenolics, which was unexpected as pathogen richness increased with increasing content in polyphenolics. Our study showed that at the community level, host species' identity was more important for foliar fungal pathogen richness and load than the functional diversity of host trees. The positive relationship between pathogen richness and phenolics in leaves, along with the finding that pathogen richness is very much conserved in tree species, point to an evolutionary arms race between hosts and fungi resulting from fungi increasing their capacity to infect tree leaves and trees boosting their defences.

Ecology, 2008

Sophisticated statistical analyses are common in ecological research, particularly in species dis... more Sophisticated statistical analyses are common in ecological research, particularly in species distribution modeling. The effects of sometimes arbitrary decisions during the modeling procedure on the final outcome are difficult to assess, and to date are largely unexplored. We conducted an analysis quantifying the contribution of uncertainty in each step during the model-building sequence to variation in model validity and climate change projection uncertainty. Our study system was the distribution of the Great Grey Shrike in the German federal state of Saxony. For each of four steps (data quality, collinearity method, model type, and variable selection), we ran three different options in a factorial experiment, leading to 81 different model approaches. Each was subjected to a fivefold cross-validation, measuring area under curve (AUC) to assess model quality. Next, we used three climate change scenarios times three precipitation realizations to project future distributions from each model, yielding 729 projections. Again, we analyzed which step introduced most variability (the four model-building steps plus the two scenario steps) into predicted species prevalences by the year 2050. Predicted prevalences ranged from a factor of 0.2 to a factor of 10 of present prevalence, with the majority of predictions between 1.1 and 4.2 (inter-quartile range). We found that model type and data quality dominated this analysis. In particular, artificial neural networks yielded low cross-validation robustness and gave very conservative climate change predictions. Generalized linear and additive models were very similar in quality and predictions, and superior to neural networks. Variations in scenarios and realizations had very little effect, due to the small spatial extent of the study region and its relatively small range of climatic conditions. We conclude that, for climate projections, model type and data quality were the most influential factors. Since comparison of model types has received good coverage in the ecological literature, effects of data quality should now come under more scrutiny.