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Light-demanding trees and thorny shrubs in temperate plant communities may reflect adaptations to now-extinct large grazers, such as aurochs and tarpans, rendering these adaptations ecological anachronisms. We explored the ecological functions of plant traits of Quercus robur and Prunus spinosa in areas grazed by cattle and horses, the domesticated descendants of aurochs and tarpans. Specifically, we tested the hypothesis that grazing induces a shifting mosaic of grassland, shrub thickets and woodlands through the key process of associational resistance: the protection of palatable young trees by thorny shrubs. An exclosure experiment with transplanted Q. robur seedlings revealed that Q. robur grew best in grassland exclosures and on the edge of thorny shrub thickets, which may be viewed as an optimal balance between sufficient protection from large herbivores and sufficient light availability. A cross-site comparison of four floodplain woodlands in north-western Europe showed that Q. robur can regenerate in the presence of large herbivores through spatial association with P. spinosa. However, we found that expansion of P. spinosa shrubs and Q. robur coincided with periods of low rabbit abundance and not with livestock density. From this, it appears that the process of associational resistance does not work with rabbits. With extensive grazing by large (domesticated) grazers in temperate floodplains, a shifting mosaic of grassland, shrubs and trees may develop that has high conservation value. Palatable, light-demanding Q. robur seedlings can successfully regenerate in spiny P. spinosa shrubs through associational resistance. This process does not offer protection from abundant small herbivores, such as rabbits, that can inhibit the recruitment of shrubs and trees in this mosaic vegetation. In floodplain meadows frequent flooding may be an efficient way to reduce rabbit populations, with dry conditions in summer and wet in winter. When floodplain meadows are combined with adjacent higher grounds, large herbivores can escape the floods through migration. [ABSTRACT FROM AUTHOR]

Herbivores are reported to slow down as well as enhance nutrient cycling in grasslands. These conflicting results may be explained by differences in herbivore type. In this study we focus on herbivore body size as a factor that causes differences in herbivore effects on N cycling. We used an exclosure set-up in a floodplain grassland grazed by cattle, rabbits and common voles, where we subsequently excluded cattle and rabbits. Exclusion of cattle lead to an increase in vole numbers and a 1.5-fold increase in net annual N mineralization at similar herbivore densities (corrected to metabolic weight). Timing and height of the mineralization peak in spring was the same in all treatments, but mineralization in the vole-grazed treatment showed a peak in autumn, when mineralization had already declined under cattle grazing. This mineralization peak in autumn coincides with a peak in vole density and high levels of N input through vole faeces at a fine-scale distribution, whereas under cattle grazing only a few patches receive all N and most experience net nutrient removal. The other parameters that we measured, which include potential N mineralization rates measured under standardized laboratory conditions and soil parameters, plant biomass and plant nutrient content measured in the field, were the same for all three grazing treatments and could therefore not cause the observed difference. When cows were excluded, more litter accumulated in the vegetation. The formation of this litter layer may have added to the higher mineralization rates under vole grazing, through enhanced nutrient return through litter or through modification of microclimate. We conclude that different-sized herbivores have different effects on N cycling within the same habitat. Exclusion of large herbivores resulted in increased N annual mineralization under small herbivore grazing. [ABSTRACT FROM AUTHOR]

Grasslands are often characterised by small-scale mosaics in plant community composition that contribute to their diversity. Although above- and belowground biota can both cause such mosaics, few studies have addressed their interacting effects. We studied multi-trophic interactions between aboveground vertebrate grazers, subterranean ants, plant-pathogenic soil biota (especially nematodes) and the vegetation in a temperate grassland. We found that when rabbits and cattle locally omit vegetation patches, yellow ants (Lasius flavus ) respond to the taller vegetation by digging up more sand from deeper soil layers (hence making taller nest mounds), probably to maintain sufficiently high soil temperatures. We found that this ant digging affects other soil biota, as the mounds contain fewer plant-parasitic and fungivore nematodes. Also, the mounds have lower moisture content and soil bulk densities, and higher pH and available nutrient content than the directly surrounding soil. The clonal sedge Carex arenaria grows vigorously on the mounds, producing more shoots and shorter rhizome internode lengths than in surrounding vegetation. Other plant species, such as the grass Festuca rubra , dominate the surrounding vegetation. A greenhouse bioassay experiment revealed that harmful soil organisms (as plant-parasitic nematodes and pathogenic fungi) outweighed the effect of beneficial organisms (e.g., mycorrhizae) in this system. Rhizome biomass and shoot production of C. arenaria were indeed inhibited less by biota in soil from ant mounds than by biota in soil from the surrounding vegetation. However, the total biomass production of C. arenaria was inhibited as strongly in both soil types. F. rubra was inhibited more strongly by biota in the surrounding soil. We suggest that various direct and indirect interactions between above- and belowground biota can contribute to community mosaics and hence diversity in grasslands. [ABSTRACT FROM AUTHOR]

Evaluates an experiment where fertilizer application to mown grassland was stopped in an attempt to restore former species-rich vegetation. Crop and species composition of different fields after cessation of fertilizer application; Dynamics of species replacement under a Gaussian response model; Discusses of results with regard to diversity-productivity relationships, nutrient cycling and adaptation of species to nutrient-poor conditions.

The results of a restoration experiment carried out on a permanent grassland on peaty, heavy clay in the Netherlands are described. The experiment started in 1985, 7 years after fertilizer application had ceased, and was designed to provide insight into ecologically significant processes accompanying restoration. An analysis was made of the effect of management regime and of raising the water table on nutrient availability, dry matter production, tissue nutrient concentration, dynamics of species numbers and plant species replacement. Three management practices were compared: cutting and removal (RR), cutting and mulching (MM), sod removal in 1985, and thereafter cutting and removal of the hay (RS). Data are presented on changes during a 5-year period. No trend was discernible in soil pH, total C, N and P in the RR treatment; extractable P and K decreased sharply in the field with the raised groundwater level. Nine years after fertilizer application ceased, dry matter production had fallen from 10–11 to 6–7 t ha&sup-1; years&up-1;. In the subsequent 5 years of the experiment it declined to 5–5 t ha&sup-1; year&sup-1; when all cut biomass was removed, and to about 4 t ha&sup-1; year&sup-1; after sod removal. Mulching caused an increase to 11 t ha&sup-1; year&sup-1;. No effect was seen of the raised water level. The dry matter yield of the first June cut in the RR treatment decreased. The tissue K concentration also decreased, but no increase of the tissue P concentration was detected. It was concluded that the availability of K and to some extent of P was more important than N availability in explaining the decrease in dry matter production. The tissue nutrient concentrations were not influenced by the water table. Sod removal to a depth of 5 cm resulted in the lowest productivity and the lowest tissue concentrations of P, while tissue concentrations of N and K were not affected. Raising the water level resulted in a more rapid establishment of species indicative of wet conditions, some of which invaded from nearby ditches. The: trends of dominant species are described with a set of response models. The species were ranked from disappearing to colonizing species. The relationship between rank order of replacement and indicator values of species was investigated. Raising: the water table resulted in species indicative of wet conditions becoming dominant, independently of vegetation management. The removal of nutrients resulted in the appearance of species with a lower maximal height, indicative of lower P and K availability. [ABSTRACT FROM AUTHOR]

Presents a study which looks at the interactions between soil changes, vegetation and herbivory, since different stages of salt marsh. Detailed information on the methodology used to conduct the study; Discussion based on the results of the study.

Analyzes the germination of 91 herbaceous species in response to a temperature gradient and to alternating temperature and stratification. Principal components analysis of the species; Changes in canopy structure; Relation of changes in species composition of species present at different stages to changes in germination attributes.

Studies the species dynamics and nutrient accumulation during early primary succession in coastal sand dunes on the Dutch island of Schiermonnikoog. Determinants of variance in species composition; Influence of nitrogen in limiting above aground biomass production; Comparison of nitrogen content in the soil organic layer in the plains versus sand dunes.

In situ persistence of salt marshes in the face of sea-level rise relies on their ability to maintain substrate elevation through sufficient vertical accretion of sediment. However, sedimentation rates in salt marshes vary spatially and temporally, which complicates the assessment of their ability to keep up with sea-level rise. Here, we explore the spatial and temporal variation in sediment accumulation in a single back-barrier salt marsh site. Using one-time in situ measurements at the landscape scale, we obtained synoptic information of elevation and sediment thickness over the entire salt marsh in a chronosequence over centuries. Repeated measurements along short elevation transects (0.3–0.9 m +MHT) revealed decadal changes, complementing the broader marsh data with detailed information on elevation, thickness of the marsh deposits and accumulation rates. Thickness of the deposits was largely related to the elevation gradient: the sediment layer was thinner at the higher marsh (near the dunes and far away from the intertidal flats), and thicker at the lower marsh (near the intertidal flats). Moreover, the thickness of the layer increased with salt marsh age along the chronosequence, and age accounted for 72 % of variability in sediment accumulation. The rate of sediment accumulation was higher than the local rate of sea-level rise in the younger marsh, whereas it was equal to the rate of sea-level rise in the older marsh. In the older salt marsh, sediment accumulation was lower, possibly due to autocompaction in the thicker, older layers. Both at the landscape scale and along short elevation transects within individual drainage basins, sediment accumulation decreased with distance to sediment supply routes. However, their relative importance depended on the scale of observation. Distance to creeks accounted for 17 % of the variability in sediment accumulation at the landscape scale, compared to 4 % at the smaller scale. Similarly, the influence of distance to intertidal flats varied from 1 % at the landscape scale to 13 % at the smaller scale. Our main findings indicate that lower-elevation older marshes and higher-elevation younger marshes far away from sediment sources are at risk of not keeping pace with the local rate of sea-level rise and are potentially vulnerable to increased flooding. • Spatial and temporal scales are combined to understand salt-marsh sedimentation. • Marsh age is an important factor for sedimentation rates; other factors depend on spatial scale. • Low-elevation old marshes and high-elevation young marshes more at risk with sea-level rise. [ABSTRACT FROM AUTHOR]

Abstract: In the last decades, the invasive Pacific oyster (Crassostrea gigas) increased dramatically in the Wadden Sea. One of the driving mechanisms for the success of the Pacific oyster could be a relatively low predation pressure by epibenthic predators and shore birds on oyster spat. Nevertheless, observations and experiments on predation rates on early life-stages of the Pacific oyster are rare. Therefore, we examined predation rates of brown shrimps on Pacific oyster spat in a number of laboratory experiments. Our results demonstrate that spat of Pacific oysters are most susceptible to predation by brown shrimps (Crangon crangon) in the first days after settlement, when attachment to the substrate (unglazed tiles in our study) is still absent or weak. At this stage the shell length of oyster spat is around ~300μm, and around 50% of the individuals in the experiment were consumed in the two hour trials. Predation rates decreased rapidly as the spat grew larger and reached zero within 10days after settlement of the spat (shell length>700μm). Additional experiments revealed that the attachment of oysters is probably limiting predation by brown shrimps rather than the size of the spat. This indicates that Pacific oyster spat may limit predation loss faster compared to native bivalves, which commonly depend on size to reduce predation rates. Overall, our results suggest that the invasive success of Pacific oysters may in part be explained by relatively low predation rates throughout their life stages. [Copyright &y& Elsevier]

Trait-based community assembly theory suggests that trait variation among co-occurring species is shaped by two main processes: abiotic filtering, important in stressful environments and promoting similarity, and competition, more important in productive environments and promoting dissimilarity. Previous studies have indeed found trait similarity to decline along productivity gradients. However, these studies have always been done on single trophic levels. Here, we investigated how interactions between trophic levels affect trait similarity patterns along environmental gradients. We propose three hypotheses for the main drivers of trait similarity patterns of plants and herbivores along environmental gradients: (1) environmental control of both, (2) bottom-up control of herbivore trait variation, and (3) top-down control of grass trait variation. To test this, we collected data on the community composition and trait variation of grasses (41 species) and grasshoppers (53 species) in 50 plots in a South African savanna. Structural equation models were used to investigate how the range and spacing of within-community functional trait values of both grasses and their insect herbivores (grasshoppers; Acrididae) respond to (1) rainfall and fire frequency gradients and (2) the trait similarity patterns of the other trophic level. The analyses revealed that traits of co-occurring grasses became more similar toward lower rainfall and higher fire frequency (environmental control), while showing little evidence for top-down control. Grasshopper trait range patterns, on the other hand, were mostly directly driven by vegetation structure and grass trait range patterns (bottom-up control), while environmental factors had mostly indirect effects via plant traits. Our study shows the potential to expand trait-based community assembly theory to include trophic interactions. [ABSTRACT FROM AUTHOR]

The relative importance of predation risk and food quality on spatial grazing pressure and activity patterns was tested in a central-place foraging herbivore: the European rabbit. Rabbits grazed less with increasing distance from their burrows into adjacent grassland, thereby creating a gradient of increasing vegetation height and plant biomass and decreasing plant nutrient concentration. When nitrogen concentration was experimentally increased by 150% through fertilizing and mowing, rabbits visited these plots four times more frequently than the untreated control plots. Addition of predator scent (mink pellets) did not result in different patch use by rabbits. The combined addition of fertilizer and mink pellets had the same effect as addition of fertilizer alone. However, the mink pellets changed the temporal activity pattern of rabbits as measured with infrared detectors. Rabbits were predominantly nocturnal but shifted their activities to the day when mink pellets were added, resulting in equal activities during night and day. We conclude that rabbits are sensitive to perceived predation risk, but that this does not influence their spatial grazing pressure. A selection for the highest food quality on the other hand can explain the observed natural rabbit grazing gradient. Food quality was highest close to the burrows, therefore rabbits selecting for high quality food should forage most intensely close to the burrows and only move further away for higher quality items or when the vegetation close to their burrows is depleted. Through intensive grazing close to the burrows rabbits facilitated for themselves either through stimulating fresh protein rich re-growth or the return of nutrients through faeces or both. This is in contrast with central-place foraging theory where intense feeding close to the burrow is assumed to lead to reduced food resources. [ABSTRACT FROM AUTHOR]

The coexistence of different species of large herbivores (ungulates) in grasslands and savannas has fascinated ecologists for decades. However, changes in climate, land‐use and trophic structure of ecosystems increasingly jeopardise the persistence of such diverse assemblages. Body size has been used successfully to explain ungulate niche differentiation with regard to food requirements and predation sensitivity. But this single trait axis insufficiently captures interspecific differences in water requirements and thermoregulatory capacity and thus sensitivity to climate change. Here, we develop a two‐dimensional trait space of body size and minimum dung moisture content that characterises the combined food and water requirements of large herbivores. From this, we predict that increased spatial homogeneity in water availability in drylands reduces the number of ungulate species that will coexist. But we also predict that extreme droughts will cause the larger, water‐dependent grazers as wildebeest, zebra and buffalo–dominant species in savanna ecosystems – to be replaced by smaller, less water‐dependent species. Subsequently, we explore how other constraints such as predation risk and thermoregulation are connected to this two‐dimensional framework. Our novel framework integrates multiple simultaneous stressors for herbivores and yields an extensive set of testable hypotheses about the expected changes in large herbivore community composition following climate change. [ABSTRACT FROM AUTHOR]

In conservation strategies of marine ecosystems, priority is given to habitat-structuring foundation species (e.g. seagrasses, mangroves and reef-building corals, shellfish) with the implicit goal to protect or restore associated communities and their interactions. However, the number and accuracy of community level metrics to measure the success of these strategies are limited. Using intertidal shellfish reefs as a model, we tested to what extent foundation species alter community and food web structure, and explored whether basic metrics of food web structure are useful indicators of ecosystem complexity compared to other often-used indices. We found that shellfish reefs strongly modified community and food web structure by modifying habitat conditions (e.g. hydrodynamics, sediment grain size). Stable isotope-based food web reconstruction captured important differences between communities from bare mudflat and shellfish reefs that did not emerge from classic abundance or diversity measures. On shellfish reefs, link density and the number of top predators were consistently higher, while both connectance and the richness of intermediate species was lower. Species richness (+ 42%), species density (+ 79%) and total biomass of benthos, fish and birds (+ 41%) was also higher on shellfish reefs, but this did not affect the Shannon diversity or Evenness. Hence, our results showed that basic food web metrics such as link density and number of top consumers and intermediate species combined with traditional measures of species richness can provide a robust tool to measure conservation and restoration success. We therefore suggest that these metrics are included as Essential Biodiversity Variables (EBV), and implemented as ecosystem health indicators in legislative frameworks such as the Marine Strategy Framework Directive (MSFD). [ABSTRACT FROM AUTHOR]

Coastal food webs can be supported by local benthic or pelagic primary producers and by the import of organic matter. Distinguishing between these energy sources is essential for our understanding of ecosystem functioning. However, the relative contribution of these components to the food web at the landscape scale is often unclear, as many studies lack good taxonomic and spatial resolution across large areas. Here, using stable carbon isotopes, we report on the primary carbon sources for consumers and their spatial variability across one of the world's largest intertidal ecosystems (Dutch Wadden Sea; 1460 km2 intertidal surface area), at an exceptionally high taxonomic (178 species) and spatial resolution (9,165 samples from 839 locations). The absence of overlap in δ13C values between consumers and terrestrial organic matter suggests that benthic and pelagic producers dominate carbon input into this food web. In combination with the consistent enrichment of benthic primary producers (δ13C −16.3‰) relative to pelagic primary producers (δ13C −18.8) across the landscape, this allowed the use of a two-food-source isotope-mixing model. This spatially resolved modelling revealed that benthic primary producers (microphytobenthos) are the most important energy source for the majority of consumers at higher trophic levels (worms, molluscs, crustaceans, fish, and birds), and thus to the whole food web. In addition, we found large spatial heterogeneity in the δ13C values of benthic primary producers (δ13C −19.2 to −11.5‰) and primary consumers (δ13C −25.5 to −9.9‰), emphasizing the need for spatially explicit sampling of benthic and pelagic primary producers in coastal ecosystems. Our findings have important implications for our understanding of the functioning of ecological networks and for the management of coastal ecosystems. [ABSTRACT FROM AUTHOR]

ABSTRACT Both arthropods and large grazing herbivores are important components and drivers of biodiversity in grassland ecosystems, but a synthesis of how arthropod diversity is affected by large herbivores has been largely missing. To fill this gap, we conducted a literature search, which yielded 141 studies on this topic of which 24 simultaneously investigated plant and arthropod diversity. Using the data from these 24 studies, we compared the responses of plant and arthropod diversity to an increase in grazing intensity. This quantitative assessment showed no overall significant effect of increasing grazing intensity on plant diversity, while arthropod diversity was generally negatively affected. To understand these negative effects, we explored the mechanisms by which large herbivores affect arthropod communities: direct effects, changes in vegetation structure, changes in plant community composition, changes in soil conditions, and cascading effects within the arthropod interaction web. We identify three main factors determining the effects of large herbivores on arthropod diversity: ( i) unintentional predation and increased disturbance, ( ii) decreases in total resource abundance for arthropods (biomass) and ( iii) changes in plant diversity, vegetation structure and abiotic conditions. In general, heterogeneity in vegetation structure and abiotic conditions increases at intermediate grazing intensity, but declines at both low and high grazing intensity. We conclude that large herbivores can only increase arthropod diversity if they cause an increase in (a)biotic heterogeneity, and then only if this increase is large enough to compensate for the loss of total resource abundance and the increased mortality rate. This is expected to occur only at low herbivore densities or with spatio-temporal variation in herbivore densities. As we demonstrate that arthropod diversity is often more negatively affected by grazing than plant diversity, we strongly recommend considering the specific requirements of arthropods when applying grazing management and to include arthropods in monitoring schemes. Conservation strategies aiming at maximizing heterogeneity, including regulation of herbivore densities (through human interventions or top-down control), maintenance of different types of management in close proximity and rotational grazing regimes, are the most promising options to conserve arthropod diversity. [ABSTRACT FROM AUTHOR]

Questions In African savannas, Macrotermes termites contribute to small-scale heterogeneity by constructing large mounds. Operating as islands of high nutrient and water availability and low fire frequency, these mounds support distinct, diverse communities of trees that have been shown to be highly attractive to browsers. However, the distinct traits of tree species on termite mounds have hardly been studied, even though this may help to understand processes determining (1) their characteristic community structure and (2) attractiveness for browsers. Here, we compare functional trait and browser preference values between tree species on and off termite mounds. Location Hluhluwe-i Mfolozi Park, Kwazulu- Natal, South Africa. Methods We recorded tree community compositions for 16 large Macrotermes natalensis mounds and 16 control plots of 100 m2 each in a paired design. For each observed tree species we measured 22 traits, related to water and nutrient use, fire tolerance, light competition and anti-herbivore defence, and compared average trait values between mound and control communities. Furthermore, we investigated the feeding preferences of ungulate browsers for the most common tree species and how this was linked to their associated traits. Results Termite mounds supported tree communities that were distinct from the surrounding savanna vegetation. Mounds hosted more evergreen and less leguminous tree species than control communities, and the dominant species were less mechanically defended, less nutritious, had larger leaves and lower wood density than the species dominating control plots. Browsers preferred leguminous tree species with high leaf N and P content, which were relatively rare on termite mounds. Conclusions Overall, we conclude that termite mounds in this savanna form small refuges for tree species that seem less adapted to fire (more evergreens), have low nutrient availability (less nitrogen fixers) and suffer from water stress (larger leaf sizes) than typical savanna trees. Surprisingly, despite their reputation as browsing hotspots, the tree species dominating mounds are less nutritious and less preferred by browsers than tree species of the surrounding savanna, which may be explained by the relatively nutrient-rich nature of this savanna or intraspecific trait differences. [ABSTRACT FROM AUTHOR]

Herbivores may influence the nitrogen (N) recycling rates and consequently increase or decrease the productivity of grasslands. Plant N concentration emerged as a critical parameter to explain herbivore effects from several conceptual models, which predict that herbivores decrease soil N availability when plant N concentration is low whereas they increase it when plant N concentration is high ( Hobbs 1996 , Ritchie et al. 1998 , Pastor et al. 2006 ). However, a broader cross-site comparison among published studies to test these predictions is hampered by the different methodologies used to measure soil N availability or a proxy thereof, and a lack of measurements of plant N concentration. Therefore it remains unclear whether these model predictions are generally valid across a range of grasslands. We tested whether there is a relationship between plant N concentration and herbivore impact on soil N availability (measured with resin bags) with a study of replicate 6–8 year old exclosures (with an unfenced control) of vertebrate herbivores (>1 kg) established at each of seven grassland sites in North America and Europe. Contrary to model predictions, we found a negative relationship between the effect of herbivores on resin bag soil N availability and plant N concentration. Our study confirms the importance of plant N concentration as a predictor of herbivore effect on soil N availability across grasslands, but contradicts the models. A possible explanation may be that the results represent a transient situation as the exclosures were relatively young whereas the models may refer to an equilibrium state. Simultaneous measurements of both plant N concentration and herbivore effect on soil N availability from more grassland sites, preferably with contrasting plant N concentrations and including exclosures of different ages, should resolve the contrast between model predictions and our field measurements. [ABSTRACT FROM AUTHOR]

The sandy seabed of shallow coastal shelf seas displays morphological patterns of various dimensions. The seabed also harbors a rich ecosystem. Increasing pressure from human‐induced disturbances necessitates further study on drivers of benthic community distributions over morphological patterns. Moreover, a greater understanding of the sand ripple distribution over tidal sand waves may improve morphological model predictions. Here we analyzed the biotic abundance and ripple morphology in sand wave troughs and crests using video transects. We found that both the epibenthos and endobenthos are significantly more abundant in sand wave troughs, where ripples are less abundant and more irregularly shaped. Finally, we show that camera systems are relatively quick and effective tools to study biotic spatial patterns in relation to seabed morphology. Plain Language Summary: Coastal seabeds are important areas for human activities and constructions and are also inhabited by many organisms, collectively referred to as benthos. The interaction of tides, wind, sand and biology leads to the growth of large, rhythmic seabed patterns. They can grow up to several meters high, hundreds of meters long, and shift a few meters per year. Computer models can predict this behavior, but they lack understanding of biological processes and variations in sand ripple patterns. To increase the understanding of these effects, we present findings from two video transects, for which we lowered a video camera to the seabed and recorded both organisms and sand ripples for ~200 m. We show that, relative to crests, troughs have more benthic organisms, and sand ripples are often absent or less regularly shaped. Finally, we show that a camera is a quick and effective tool to study benthic spatial patterns. Key Points: Video transects over tidal sand waves yielded detailed spatial information of both benthic organisms and small‐scale seabed morphologyBoth epibenthos and endobenthos are more abundant in sand wave troughs compared to the crestsSand ripples are less abundant and more often irregularly shaped in the troughs, suggesting variations in seabed roughness over sand waves [ABSTRACT FROM AUTHOR]