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Identifying drivers of species diversity is a major challenge in understanding and predicting the dynamics of species-rich semi-natural grasslands. In particular in temperate grasslands changes in land use and its consequences, i.e. increasing fragmentation, the on-going loss of habitat and the declining importance of regional processes such as seed dispersal by livestock, are considered key drivers of the diversity loss witnessed within the last decades.
Are gastropods, rather than ants, important dispersers of seeds of myrmecochorous forest herbs?
(2012)
Seed dispersal by ants (myrmecochory) is widespread, and seed adaptations to myrmecochory are common, especially in the form of fatty appendices (elaiosomes). In a recent study, slugs were identified as seed dispersers of myrmecochores in a central European beech forest. Here we used 105 beech forest sites to test whether myrmecochore presence and abundance is related to ant or gastropod abundance and whether experimentally exposed seeds are removed by gastropods. Myrmecochorous plant cover was positively related to gastropod abundance but was negatively related to ant abundance. Gastropods were responsible for most seed removal and elaiosome damage, whereas insects (and rodents) played minor roles. These gastropod effects on seeds were independent of region or forest management. We suggest that terrestrial gastropods can generally act as seed dispersers of myrmecochorous plants and even substitute myrmecochory, especially where ants are absent or uncommon.
Intransitive competition is widespread in plant communities and maintains their species richness
(2015)
Intransitive competition networks, those in which there is no single best competitor, may ensure species coexistence. However, their frequency and importance in maintaining diversity in real-world ecosystems remain unclear. We used two large data sets from drylands and agricultural grasslands to assess: (1) the generality of intransitive competition, (2) intransitivity-richness relationships and (3) effects of two major drivers of biodiversity loss (aridity and land-use intensification) on intransitivity and species richness. Intransitive competition occurred in >65% of sites and was associated with higher species richness. Intransitivity increased with aridity, partly buffering its negative effects on diversity, but was decreased by intensive land use, enhancing its negative effects on diversity. These contrasting responses likely arise because intransitivity is promoted by temporal heterogeneity, which is enhanced by aridity but may decline with land-use intensity. We show that intransitivity is widespread in nature and increases diversity, but it can be lost with environmental homogenisation.
Recent declines in biodiversity have given new urgency to questions about the relationship between land-use change, biodiversity and ecosystem processes. Despite the existence of a large body of research on the effects of land use on species richness, it is unclear whether the effects of land use on species richness are principally direct or indirect, mediated by concomitant changes in ecosystem processes. Therefore, we compared the direct effects of land use (fertilization, mowing and grazing) on species richness with indirect ones (mediated via grassland productivity) for grasslands in central Europe. We measured the richness and above-ground biomass in 150 grassland plots in 3 regions of Germany (the so-called Biodiversity Exploratories). We used univariate and structural equation models to examine direct and indirect land-use effects. The direct effects of mowing (-0.37, effect size) and grazing (0.04) intensity on species richness were stronger compared with the indirect effects of mowing (-0.04) and grazing (-0.01). However, the strong negative effect of fertilization (-0.23) on species richness was mainly indirect, mediated by increased productivity compared with the weak direct negative effect (-0.07). Differences between regions in land-use effects showed five times weaker negative effects of mowing (-0.13) in the region with organic soils (Schorfheide-Chorin), strong overall negative effects of grazing (-0.29) for the region with organic soils opposed to a similar strong positive effect (0.30) in the Hainich-Dun region, whereas the Schwabische Alb region displayed a five times weaker positive effect (0.06) only. Further, fertilization effects on species richness were positive (0.03) for the region with organic soils compared to up to 25 times stronger negative effects in the other two regions. Synthesis. Our results clearly show the importance of studying both direct and indirect effects of land-use intensity. They demonstrate the indirect nature, via productivity, of the negative effect of fertilization intensity on plant species richness in the real-world context of management-induced gradients of intensity of fertilization, mowing and grazing. Finally, they highlight that careful consideration of regional environments is necessary before attempting to generalize land-use effects on species diversity.
The relationship of different types of grassland use with plant species richness and composition ( functional groups of herbs, legumes, and grasses) has so far been studied at small regional scales or comprising only few components of land use. We comprehensively studied the relationship between abandonment, fertilization, mowing intensity, and grazing by different livestock types on plant diversity and composition of 1514 grassland sites in three regions in North-East, Central and South-West Germany. We further considered environmental site conditions including soil type and topographical situation. Fertilized grasslands showed clearly reduced plant species diversity (-15% plant species richness, -0.1 Shannon diversity on fertilized grasslands plots of 16m(2)) and changed composition (-3% proportion of herb species), grazing had the second largest effects and mowing the smallest ones. Among the grazed sites, the ones grazed by sheep had higher than average species richness (+27%), and the cattle grazed ones lower (-42%). Further, these general results were strongly modulated by interactions between the different components of land use and by regional context: land-use effects differed largely in size and sometimes even in direction between regions. This highlights the importance of comparing different regions and to involve a large number of plots
Intensive land use is a major cause of biodiversity loss, but most studies comparing the response of multiple taxa rely on simple diversity measures while analyses of other community attributes are only recently gaining attention. Species-abundance distributions (SADs) are a community attribute that can be used to study changes in the overall abundance structure of species groups, and whether these changes are driven by abundant or rare species. We evaluated the effect of grassland management intensity for three land-use modes (fertilization, mowing, grazing) and their combination on species richness and SADs for three belowground (arbuscular mycorrhizal fungi, prokaryotes and insect larvae) and seven aboveground groups (vascular plants, bryophytes and lichens; arthropod herbivores; arthropod pollinators; bats and birds). Three descriptors of SADs were evaluated: general shape (abundance decay rate), proportion of rare species (rarity) and proportional abundance of the commonest species (dominance). Across groups, taxonomic richness was largely unaffected by land-use intensity and only decreased with increasing mowing intensity. Of the three SAD descriptors, abundance decay rate became steeper with increasing combined land-use intensity across groups. This reflected a decrease in rarity among plants, herbivores and vertebrates. Effects of fertilization on the three descriptors were similar to the combined land-use intensity effects. Mowing intensity only affected the SAD descriptors of insect larvae and vertebrates, while grazing intensity produced a range of effects on different descriptors in distinct groups. Overall, belowground groups had more even abundance distribtitions than aboveground groups. Strong differences among aboveground groups and between above- and belowground groups indicate that no single taxonomic group can serve as an indicator for effects in other groups. In the past, the use of SADs has been hampered by concerns over theoretical models underlying specific forms of SADs. Our study shows that SAD descriptors that are not connected to a particular model are suitable to assess the effect of land use on community structure.
We studied the effect of three major forest management types (unmanaged beech, selection beech, and age class forests) and stand variables (SMId, soil pH, proportion of conifers, litter cover, deadwood cover, rock cover and cumulative cover of woody trees and shrubs) on bryophyte species richness in 1050 forest plots in three regions in Germany. In addition, we analysed the species richness of four ecological guilds of bryophytes according to their colonized substrates (deadwood, rock, soil, bark) and the number of woodland indicator bryophyte species. Beech selection forests turned out to be the most species rich management type, whereas unmanaged beech forests revealed even lower species numbers than age-class forests. Increasing conifer proportion increased bryophyte species richness but not the number of woodland indicator bryophyte species. The richness of the four ecological guilds mainly responded to the abundance of their respective substrate. We conclude that the permanent availability of suitable substrates is most important for bryophyte species richness in forests, which is not stringently linked to management type. Therefore, managed age-class forests and selection forests may even exceed unmanaged forests in bryophyte species richness due to higher substrate supply and therefore represent important habitats for bryophytes. Typical woodland indicator bryophytes and their species richness were negatively affected by SMId (management intensity) and therefore better indicate forest integrity than the species richness of all bryophytes. Nature conservation efforts should focus on the reduction of management intensity. Moreover, maintaining and increasing a variability of substrates and habitats, such as coarse woody debris, increasing structural heterogeneity by retaining patches with groups of old, mature to over-mature trees in managed forests, maintaining forest climate conditions by silvicultural methods that assure stand continuity, e.g. by selection cutting rather than clear cutting and shelterwood logging might promote bryophyte diversity and in particular the one of woodland indicator bryophytes.
Land-use intensification is a key driver of biodiversity change. However, little is known about how it alters relationships between the diversities of different taxonomic groups, which are often correlated due to shared environmental drivers and trophic interactions. Using data from 150 grassland sites, we examined how land-use intensification (increased fertilization, higher livestock densities, and increased mowing frequency) altered correlations between the species richness of 15 plant, invertebrate, and vertebrate taxa. We found that 54% of pairwise correlations between taxonomic groups were significant and positive among all grasslands, while only one was negative. Higher land-use intensity substantially weakened these correlations(35% decrease in rand 43% fewer significant pairwise correlations at high intensity), a pattern which may emerge as a result of biodiversity declines and the breakdown of specialized relationships in these conditions. Nevertheless, some groups (Coleoptera, Heteroptera, Hymenoptera and Orthoptera) were consistently correlated with multidiversity, an aggregate measure of total biodiversity comprised of the standardized diversities of multiple taxa, at both high and lowland-use intensity. The form of intensification was also important; increased fertilization and mowing frequency typically weakened plant-plant and plant-primary consumer correlations, whereas grazing intensification did not. This may reflect decreased habitat heterogeneity under mowing and fertilization and increased habitat heterogeneity under grazing. While these results urge caution in using certain taxonomic groups to monitor impacts of agricultural management on biodiversity, they also suggest that the diversities of some groups are reasonably robust indicators of total biodiversity across a range of conditions.
Forest management is known to influence species diversity of various taxa but inconsistent or even contrasting effects are reported for arthropods. Regional differences in management as well as differences in regional species pools might be responsible for these inconsistencies, but, inter-regional replicated studies that account for regional variability are rare. We investigated the effect of forest type on the abundance, diversity, community structure and composition of two important ground-dwelling beetle families, Carabidae and Staphylinidae, in 149 forest stands distributed over three regions in Germany. In particular we focused on recent forestry history, stand age and dominant tree species, in addition to a number of environmental descriptors. Overall management effects on beetle communities were small and mainly mediated by structural habitat parameters such as the cover of forest canopy or the plant diversity on forest stands. The general response of both beetle taxa to forest management was similar in all regions: abundance and species richness of beetles was higher in older than in younger stands and species richness was lower in unmanaged than in managed stands. The abundance ratio of forest species-to-open habitat species differed between regions, but generally increased from young to old stands, from coniferous to deciduous stands and from managed to unmanaged stands. The response of both beetle families to dominant tree species was variable among regions and staphylinid richness varied in the response to recent forestry history. Our results suggest that current forest management practices change the composition of ground-dwelling beetle communities mainly by favoring generalists and open habitat species. To protect important forest beetle communities and thus the ecosystem functions and services provided by them, we suggest to shelter remaining ancient forests and to develop near-to-nature management strategies by prolonging rotation periods and increasing structural diversity of managed forests. Possible geographic variations in the response of beetle communities need to be considered in conservation-orientated forest management strategies. (C) 2014 Elsevier B.V. All rights reserved.