W.A. Ozinga

Less lineages - more trait variation: phylogenetically clustered plant communities are functionally more diverse

Functional diversity within communities may influence ecosystem functioning, but which factors drive functional diversity? We hypothesize that communities assembled from many phylogenetic lineages show large functional diversity if assembly is random, but low functional diversity if assembly is controlled by interactions between species within lineages. We combined > 9000 descriptions of Dutch plant communities, a species-level phylogeny, and information on 16 functional traits (including eight dispersal traits). We found that all traits were conserved within lineages, but nevertheless communities assembled from many lineages showed a smaller variation in trait-states of most traits (including dispersal traits) than communities assembled from few lineages. Hence, within lineages, species are not randomly assembled into communities, contradicting Neutral Theory. In fact, we find evidence for evolutionary divergence in trait-states as well as present-day mutual exclusion among related, similar species, suggesting that functional diversity of communities increased due to past and present interactions between species within lineages.

Museum specimens reveal loss of pollen host plants as key factor driving wild bee decline in The Netherlands

Significance Growing concern about bee declines and associated loss of pollination services has increased the urgency to identify the underlying causes. So far, the identification of the key drivers of decline of bee populations has largely been based on speculation. We assessed the relative importance of a range of proposed factors responsible for wild bee decline and show that loss of preferred host plant species is one of the main factors associated with the decline of bee populations in The Netherlands. Interestingly, species foraging on crop plant families have stable or increasing populations. These results indicate that mitigation strategies for loss of wild bees will only be effective if they target the specific host plants of declining bee species. Evidence for declining populations of both wild and managed bees has raised concern about a potential global pollination crisis. Strategies to mitigate bee loss generally aim to enhance floral resources. However, we do not really know whether loss of preferred floral resources is the key driver of bee decline because accurate assessment of host plant preferences is difficult, particularly for species that have become rare. Here we examine whether population trends of wild bees in The Netherlands can be explained by trends in host plants, and how this relates to other factors such as climate change. We determined host plant preference of bee species using pollen loads on specimens in entomological collections that were collected before the onset of their decline, and used atlas data to quantify population trends of bee species and their host plants. We show that decline of preferred host plant species was one of two main factors associated with bee decline. Bee body size, the other main factor, was negatively related to population trend, which, because larger bee species have larger pollen requirements than smaller species, may also point toward food limitation as a key factor driving wild bee loss. Diet breadth and other potential factors such as length of flight period or climate change sensitivity were not important in explaining twentieth century bee population trends. These results highlight the species-specific nature of wild bee decline and indicate that mitigation strategies will only be effective if they target the specific host plants of declining species.

Is biofuel policy harming biodiversity in Europe

We assessed the potential impacts of land‐use changes resulting from a change in the current biofuel policy on biodiversity in Europe. We evaluated the possible impact of both arable and woody biofuel crops on changes in distribution of 313 species pertaining to different taxonomic groups. Using species‐specific information on habitat suitability as well as land use simulations for three different biofuel policy options, we downscaled available species distribution data from the original resolution of 50 to 1 km. The downscaled maps were then applied to analyse potential changes in habitat size and species composition at different spatial levels. Our results indicate that more species might suffer from habitat losses rather than benefit from a doubled biofuel target, while abolishing the biofuel target would mainly have positive effects. However, the possible impacts vary spatially and depend on the biofuel crop choice, with woody crops being less detrimental than arable crops. Our results give an indication for policy and decision makers of what might happen to biodiversity under a changed biofuel policy in the European Union. The presented approach is considered to be innovative as to date no comparable policy impact assessment has been applied to such a large set of key species at the European scale.

Spatial distribution of Laccaria bicolor genets reflected by sporocarps after removal of litter and humus layers in a Pinus sylvestris forest

The spatial distribution of the genets of the ectomycorrhizal fungus Laccaria bicolor was studied by somatic incompatibility, two years after removal of the litter and humus layers in two plots of 225 m2 in a 17-years-old Scots pine (Pinus sylvestris) stand in The Netherlands. Pairings of isolates revealed the presence of three and four genets on the two sites. Genets were up to 12·5 m in size, indicating that mycelia are perennial and are of importance for mycelial spread. Age of the genets was estimated at 13 to 26 and 16 to 31 years, for the two sites. The smallest genet was represented by two sporocarps suggesting recent colonization by spores.

Do plant traits retrieved from a database accurately predict on-site measurements?

1. Trait-based approaches are increasingly used to obtain an insight into the functional aspects of plant communities. Since measuring traits can be time-consuming, large international databases of plant traits are being compiled to share the effort. From these databases, average trait values are often extracted per species by averaging trait values of individuals over multiple populations and habitats. However, the accuracy of such aggregated information from regional databases as a surrogate for on-site measurements has seldom been tested. 2. For the local species pool (aggregated at the habitat-level) and the plant communities on the plots (aggregated at the community-level), we quantified how accurately trait values for each species measured at the plot (plot scale) and those averaged per species and site (site scale) can be estimated from those retrieved from a North-west-European trait database. We analysed three widely used plant traits, canopy height (CH), leaf dry matter content (LDMC) and specific leaf area (SLA), of species occurring in a wet meadow and a salt marsh. 3. Database values more accurately predicted traits aggregated at the habitat-level than those aggregated at the community-level. In addition, traits with lower plasticity, such as LDMC, were more accurately predicted by database values. The performance of database values also depended upon the habitat studied, for example, habitat-level SLA values were accurately predicted by database values in the wet meadow but inaccurately predicted in the salt marsh. 4. Synthesis. This study reveals that the accuracy of traits retrieved from a database depends on the level of aggregation (lower at community-level), the trait (lower in plastic traits) and the habitat type (lower in extreme habitats). For studies focussing on processes mainly acting at the site scale (e.g. trait–environment relationships), traits retrieved from a regional database and filtered according to habitat will probably lead to good results. Whereas studying processes acting at the plot scale (e.g. niche partitioning), requires the additional effort of measuring traits on-site.

Phylogenetically Poor Plant Communities Receive More Alien Species, Which More Easily Coexist with Natives

Alien species can be a major threat to ecological communities, but we do not know why some community types allow the entry of many more alien species than do others. Here, for the first time, we suggest that evolutionary diversity inherent to the constituent species of a community may determine its present receptiveness to alien species. Using recent large databases from observational studies, we find robust evidence that assemblage of plant community types from few phylogenetic lineages (in plots without aliens) corresponds to higher receptiveness to aliens. Establishment of aliens in phylogenetically poor communities corresponds to increased phylogenetic dispersion of recipient communities and to coexistence with rather than replacement of natives. This coexistence between natives and distantly related aliens in recipient communities of low phylogenetic dispersion may reflect patterns of trait assembly. In communities without aliens, low phylogenetic dispersion corresponds to increased dispersion of most traits, and establishment of aliens corresponds to increased trait concentration. We conclude that if quantified across the tree of life, high biodiversity correlates with decreasing receptiveness to aliens. Low phylogenetic biodiversity, in contrast, facilitates coexistence between natives and aliens even if they share similar trait states.

Assessing the relative importance of dispersal in plant communities using an ecoinformatics approach

Increased insight into the factors that determine the importance of dispersal limitation on species richness and species composition is of paramount importance for conservation and restoration ecology. One way to explore the importance of dispersal limitation is to use seed-sowing experiments, but these do not enable the screening of large sets of species and habitats. In the present paper we present a complementary approach based on comparing small plots with larger regions with regard to species composition and distribution of functional traits. We developed a GIS tool based on ecological and geographical criteria to quantify species pools at various spatial scales. In this GIS tool, containing floristic, large databases, phytosociological and functional information are exploited. Our premise is that differences in the nature of the species in local and regional species pools with regard to functional traits can give important clues to the processes at work in the assembly of communities.We illustrate the approach with a case study for mesotrophic hay meadows (Calthion palustris). We tested the effects of differences in frequency in the local Habitat Species Pool and differences in dispersal and persistence traits of species on local species composition. Our results show that both species pool effects and functional traits affect the probability of occurrence in small plots. Species with a high propagule weight have, given the frequency in the Local Habitat Species Pool, a lower probability of occurrence in small plots. The probability of local occurrence, however, is increased by the ability to form a persistent soil seed bank and by adult longevity. This provides support for the view that the degree of dispersal limitation is dependent on the degree of spatial isolation of the focal site relative to source populations and moreover that species inherently differ in the degree to which dispersal limitation is a limiting factor for local occurrence.

Stimulatory and inhibitory effects of needle litter and grass extracts on the growth of some ectomycorrhizal fungi

Abstract Aqueous extracts of Scots pine needles, shoots and roots of the grass Deschampsia flexuosa were investigated for their effects on the growth of isolates of ectomycorrhizal fungi. The growth rates of Laccaria proxima and Rhizopogon luteolus were negatively affected by the needle extracts. Only the high concentrations of the needle extracts had significant inhibitory effects on the growth rates of Paxillus involutus and Xerocomus badius. The growth rate of Laccaria bicolor was significantly enhanced by the needle extracts. Extracts of the shoots of D. flexuosa had inhibitory effects on the growth rates of L. proxima, P. involutus and R. luteolus and a significant enhancing effect on the growth rate of L. bicolor. The shoot extracts contained about 3–5 times more high molecular weight components, aliphatic acids and phenolics than the root extracts.

Large vegetation databases and information systems: New instruments for ecological research, nature conservation, and policy making

Abstract Almost a century ago, Josias Braun-Blanquet developed his phytosociological approach for vegetation field study. At that time, nobody could foresee what the impact of this methodology would be for vegetation science as well as for its application in nature conservation. Hundreds of thousands of so-called relevés (vegetation plot records) have been made, collected in field books, and many of them have been published afterward. Some 20 years ago, the software package Turboveg was developed for the input, storage, and handling of vegetation data. Since then, many national and regional vegetation databases have been compiled, providing the basis for national and international classification overviews and other scientific studies. It is estimated that currently there have been more than 4.2 million relevés made throughout Europe, including 1.8 million relevés already available in electronic dabatases and about 45% of these available in Turboveg format. The computerized vegetation data have been shown to offer new possibilities for ecological research (a new branch of study, called eco-informatics), of which a number of examples will be discussed. Furthermore, the electronic data form a fundament for the compilation of ecological information systems. As an example of these, the information system SynBioSys will be discussed as a new tool for nature conservation and policy making, including Natura 2000.

The analysis of long-term changes in plant communities: case studies from the Netherlands

The nature of the plant community has been a long-standing point of discussion in vegetation science. Already in the early decades of the last century, debate focused on whether plant communities existed as discrete, intra-dependent entities or merelyas loose assemblages of species each responding individualistically to local environmental conditions. Despite the fundamental nature of this question, the issue is generally ignored in many studies. For example, within the study of succession, a major topic in vegetation science, the question of stability within vegetation types is rarely addressed. Generally, succession research investigates vegetation development in terms of communities passing through a series of vegetation types, without considering the nature of these types; they are implicitly regarded to be constant. To some extent, this idea is a misconception, as can be concluded from studies within the framework of the national vegetation classification of the Netherlands. During this programme, a large data set has been built up, comprising more than 350 000 vegetation releves, made in the period 1929-2001. Comparison of sets of releves from different decades revealed that in most ecosystems the floristic composition of the vegetation types involved has changed, although the appearance of the vegetation and the presence and abundance of (most of) the diagnostic species have remained the same. In the present study, three examples were elucidated: an aquatic vegetation type dominated by Stratiotes aloides (Stratiotetum), a species-rich grassland type on river dunes (Medicagini falcatae-Avenetum pubescentis), and a forest community (Betulo-Quercetum roboris).