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

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.

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.

Dispersal failure contributes to plant losses in NW Europe.

The ongoing decline of many plant species in Northwest Europe indicates that traditional conservation measures to improve the habitat quality, although useful, are not enough to halt diversity losses. Using recent databases, we show for the first time that differences between species in adaptations to various dispersal vectors, in combination with changes in the availability of these vectors, contribute significantly to explaining losses in plant diversity in Northwest Europe in the 20th century. Species with water- or fur-assisted dispersal are over-represented among declining species, while others (wind- or bird-assisted dispersal) are under-represented. Our analysis indicates that the 'colonization deficit' due to a degraded dispersal infrastructure is no less important in explaining plant diversity losses than the more commonly accepted effect of eutrophication and associated niche-based processes. Our findings call for measures that aim to restore the dispersal infrastructure across entire regions and that go beyond current conservation practices.

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.

SaudiVeg ecoinformatics: Aims, current status and perspectives.

During the last decade many electronic databases of vegetation plots were established in many countries around the world. These databases contain valuable phytosociological information assisting both governmental and NGO (Non-governmental organizations) agencies to formulate strategies and on-ground plans to manage and protect nature resources. This paper provides an account on aims, current status and perspectives of building of a vegetation database for the Central Region (Najd) of Saudi Arabia - the founding element of the Saudi Vegetation Database (SVD). The data stored by the database are sample plots (vegetation relevés) collected according to the field techniques of the Braun-Blanquet approach (lists of taxa accompanied by semi-quantitative cover assessment), and are accompanied by general vegetation characteristics such as vegetation layering and cover, information on life-form of the recorded species, geographical coordinates, altitude, soil typology, topography and many more. More than 2900 vegetation-plot records (relevés) have so far been collected in the Najd region; of these more than 2000 have already been stored using the Turboveg database platform. These field records cover many habitats such as depressions, wadis (dry river beds), agricultural lands, sand dunes, sabkhas, and ruderal habitats. The ecological information collected in the database is currently the largest set of vegetation data collated into a database in the Middle East. These data are of great importance for biodiversity studies in Saudi Arabia, since the region is recording a loss of biodiversity at a fast rate due to environmental problems such as global warming and land-use changes. We envisage that this database would catalyze further data collection on vegetation of the entire Arabian Peninsula, and shall serve as one of the most important datasets for classification and mapping of the vegetation of the Kingdom of Saudi Arabia.

Local dominance of exotic plants declines with residence time: a role for plant-soil feedback?

Recent studies have shown that introduced exotic plant species may be released from their native soil-borne pathogens, but that they become exposed to increased soil pathogen activity in the new range when time since introduction increases. Other studies have shown that introduced exotic plant species become less dominant when time since introduction increases, and that plant abundance may be controlled by soil-borne pathogens; however, no study yet has tested whether these soil effects might explain the decline in dominance of exotic plant species following their initial invasiveness. Here we determine plant-soil feedback of 20 plant species that have been introduced into The Netherlands. We tested the hypotheses that (i) exotic plant species with a longer residence time have a more negative soil feedback and (ii) greater local dominance of the introduced exotic plant species correlates with less negative, or more positive, plant-soil feedback. Although the local dominance of exotic plant species decreased with time since introduction, there was no relationship of local dominance with plant-soil feedback. Plant-soil feedback also did not become more negative with increasing time since introduction. We discuss why our results may deviate from some earlier published studies and why plant-soil feedback may not in all cases, or not in all comparisons, explain patterns of local dominance of introduced exotic plant species.