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.
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.
Aim: Despite several recent efforts to map plant traits and to identify their climatic drivers, there are still major gaps. Global trait patterns for major functional groups, in particular, the ...differences between woody and herbaceous plants, have yet to be identified. Here, we take advantage of big data efforts to compile plant species occurrence and trait data to analyse the spatial patterns of assemblage means and variances of key plant traits. We tested whether these patterns and their climatic drivers are similar for woody and herbaceous plants. Location: New World (North and South America). Methods: Using the largest currently available database of plant occurrences, we provide maps of 200 × 200 km grid-cell trait means and variances for both woody and herbaceous species and identify environmental drivers related to these patterns. We focus on six plant traits: maximum plant height, specific leaf area, seed mass, wood density, leaf nitrogen concentration and leaf phosphorus concentration. Results: For woody assemblages, we found a strong climate signal for both means and variances of most of the studied traits, consistent with strong environmental filtering. In contrast, for herbaceous assemblages, spatial patterns of trait means and variances were more variable, the climate signal on trait means was often different and weaker. Main conclusion: Trait variations for woody versus herbaceous assemblages appear to reflect alternative strategies and differing environmental constraints. Given that most large-scale trait studies are based on woody species, the strikingly different biogeographic patterns of herbaceous traits suggest that a more synthetic framework is needed that addresses how suites of traits within and across broad functional groups respond to climate.
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.
1. Mycorrhizal symbiosis is a widespread association between plant roots and mycorrhizal fungi, which is thought to contribute to plant niche differentiation and expansion. However, this has so far ...not been explicitly tested. 2. To address the effect of mycorrhizal symbiosis on plants' realized niches, we addressed how mycorrhizal status (i.e. the frequency of occurrence of mycorrhizal symbiosis), flexibility (i.e. the ability to grow both with and without mycorrhizal symbiosis) and type of a plant species affect the realized niche optima, widths and volumes. For this, we used co-occurrence data from the flora of the Netherlands along soil fertility, moisture, pH, salinity, light and temperature gradients. Phylogenetic dependency of the species was taken into account using phylogenetic generalized least squares models. 3. We show that facultatively and flexibly mycorrhizal plants have the widest niches compared to non-mycorrhizal and obligately mycorrhizal, and inflexible plants respectively. Among obligate plant symbionts, ecto- and ericoid mycorrhizal plants exhibited the widest niches compared to plants with other mycorrhizal types. Also, plants with different mycorrhizal statuses and types differed in their realized niche optima. 4. Synthesis. Our results indicate that mycorrhizal symbiosis mediates plant niche differentiation and expansion, facilitating the understanding of current distribution patterns of plant species, as well as predicting shifts in plant distribution and dominance due to environmental changes.
Previous studies of Eurasian grasslands have suggested that nutrient ratios, rather than absolute nutrient availabilities and associated productivity, may be driving plant species richness patterns. ...However, the underlying assumption that species occupy distinct niches along nutrient ratio gradients remains to be tested. We analysed plant community composition and nutrient status of 644 Eurasian wet grassland plots. The importance of nutrient ratios driving variation in species composition was analysed using ordination methods (DCA and CCA). Subsequently, we assessed the niche position and width along the most important nutrient ratio gradient N:P for each species. We found that the N:P ratio explained part of the variation in species composition independent from conventional explanatory variables. The N:P ratio explained less variation than soil moisture or pH, but more than productivity or the availability of N and P separately, highlighting its importance for grassland species composition. Species occupied distinct niches along the N:P gradient, and species’niche widths decreased toward extreme nutrient limitation. After correcting for niche position, there was no overall difference in niche width between endangered and non-endangered species. Surprisingly, endangered species with niche optima at the extreme P-limited end of the gradient had broader niches than their non-endangered counterparts. As species occupied distinct niches along a nutrient ratio gradient, future grassland conservation efforts may benefit from targeting changes in nutrient ratios, i. e. the balance between N and P, rather than only focussing on a general reduction in nutrient availability. However, what management interventions can be used for this purpose remains unclear.
QUESTION: Quantification of the effect of species traits on the assembly of communities is challenging from a statistical point of view. A key question is how species occurrence and abundance can be ...explained by the trait values of the species and the environmental values at the sites. METHODS: Using a sites × species abundance table, a site × environment data table and a species × trait data table, we address the above question using a novel generalized linear mixed model (GLMM) approach. The GLMM overcomes problems of pseudo‐replication and heteroscedastic variance by including sites and species as random factors. The method is equally applicable to presence–absence data as to count and multinomial data. We present a tiered forward selection approach for obtaining a parsimonious model and compare the results with alternative methods (the fourth corner method and RLQ ordination). RESULTS: We illustrate the approach on a presence–absence version on two data sets. In the Dune Meadow data, species presence is parsimoniously explained by moisture and manure on the meadows in combination with seed mass and specific leaf area (SLA). In the Grazed Grassland data, species presence is parsimoniously explained by the grazing intensity and soil phosphorus in combination with the C:N ratio and flowering mode. CONCLUSIONS: Our GLMM approach can be used to identify which species traits and environmental variables best explain the species distribution, and which traits are significantly correlated with environmental variables. We argue that the method is better suited for providing an interpretable and predictive model than the fourth corner method and RLQ.
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.
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.
1. Large-scale destruction of ecosystems caused by surface mining provides an opportunity for the study of colonization processes starting with primary succession. Surprisingly, over several decades ...and without any restoration measures, most of these sites spontaneously developed into valuable biotope mosaics with many endangered plant species. 2. Investigations were carried out in 10 open-cast mined sites. Data from extensive floristic mapping of mined sites and their surroundings were combined with functional traits. 3. Using binary logistic regression, we showed that eight variables have a significant influence on the probability of the occurrence of particular plant species in mined sites. The regional species pool explained the highest proportion of variance. Further significant variables were distance of source populations, abundance in the habitat species pool, capacity for long-distance dispersal by wind and birds, terminal velocity of seeds and requirements for light and nitrogen. 4. In the 10 study mine sites, 143 establishing events of Red List species have been recorded. For 40% of these establishing events, the nearest recorded seed source is 3-10 km away, while for 19%, the distance to the nearest seed source exceeds 10 km. 5. This study showed for the first time that the abundance of species up to a distance of at least 17 km plays an important role in colonization processes following large-scale destruction of ecosystems. In large-scale, nutrient-deficient, open sites, an accumulation of plant species, including rare species, can be expected in time frames amenable to planning (several decades), because the sites acted as huge seed traps in the landscape. 6. Synthesis and applications. The floristic colonization probability of restoration sites is higher if large-scale, open and nutrient-poor habitats are available. In regions where such habitats have become highly fragmented, restoration planning of derelict land (e.g. surface mines, quarries, landfills) that supports the creation of such conditions can contribute to the regional survival of rare pioneer species. In future restoration planning, a new protocol must be established that combines the utilization of site potential with spontaneous colonization processes.
Benefits from living together? Prinzing, Andreas; Ozinga, Wim A.; Brändle, Martin ...
The New phytologist,
01/2017, Letnik:
213, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Recent decades have seen declines of entire plant clades while other clades persist despite changing environments. We suggest that one reason why some clades persist is that species within these ...clades use similar habitats, because such similarity may increase the degree of cooccurrence of species within clades. Traditionally, co-occurrence among clade members has been suggested to be disadvantageous because of increased competition and enemy pressure. Here, we hypothesize that increased co-occurrence among clade members promotes mutualist exchange, niche expansion or hybridization, thereby helping species avoid population decline from environmental change. We review the literature and analyse published data for hundreds of plant clades (genera) within a well-studied region and find major differences in the degree to which species within clades occupy similar habitats.Wetentatively show that, in clades for which species occupy similar habitats, species tend to exhibit increased co-occurrence, mutualism, niche expansion, and hybridization – and rarely decline. Consistently, throughout the geological past, clades whose species occupied similar habitats often persisted through long time-spans. Overall, for many plant species, the occupation of similar habitats among fellow clade members apparently reduced their vulnerability to environmental change. Future research should identify when and how this previously unrecognized eco-evolutionary feedback operates.
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