Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Spatial heterogeneity of plant–soil feedback affects root interactions and interspecific competition
Hendriks, M. ; Ravenek, J. ; Smit-Tiekstra, A.E. ; Paauw, J.W.M. van der; Caluwe, H. de; Putten, W.H. van der; Kroon, H. de; Mommer, L. - \ 2015
New Phytologist 207 (2015)3. - ISSN 0028-646X - p. 830 - 840.
nutrient heterogeneity - species-diversity - population-dynamics - relative abundance - deciduous woodland - temporal variation - borne pathogens - grassland - community - coexistence
Plant-soil feedback is receiving increasing interest as a factor influencing plant competition and species coexistence in grasslands. However, we do not know how spatial distribution of plant-soil feedback affects plant below-ground interactions. We investigated the way in which spatial heterogeneity of soil biota affects competitive interactions in grassland plant species. We performed a pairwise competition experiment combined with heterogeneous distribution of soil biota using four grassland plant species and their soil biota. Patches were applied as quadrants of 'own' and 'foreign' soils from all plant species in all pairwise combinations. To evaluate interspecific root responses, species-specific root biomass was quantified using real-time PCR. All plant species suffered negative soil feedback, but strength was species-specific, reflected by a decrease in root growth in own compared with foreign soil. Reduction in root growth in own patches by the superior plant competitor provided opportunities for inferior competitors to increase root biomass in these patches. These patterns did not cascade into above-ground effects during our experiment. We show that root distributions can be determined by spatial heterogeneity of soil biota, affecting plant below-ground competitive interactions. Thus, spatial heterogeneity of soil biota may contribute to plant species coexistence in species-rich grasslands.
Structure and composition of the liana assemblage of a mixed rainforest in the Congo Basin
Ewango, C.E.N. ; Bongers, F. ; Makana, J.R. ; Poorter, L. ; Sosef, M.S.M. - \ 2015
Plant Ecology and Evolution 148 (2015)1. - ISSN 2032-3913 - p. 29 - 42.
barro-colorado island - tree alpha-diversity - tropical forest - silvicultural treatments - habitat associations - community structure - species-diversity - secondary forest - lowland forest - growth-rates
Background and aims – The Congo Basin lowland forest represents one of the largest tropical forest blocks in the world, but its liana assemblage has never been characterized. We evaluate liana floristics, diversity, and structure in the Ituri Forest, and determine the effects of forest structure and edaphic variation on liana species composition. Methods – Two permanent 10-ha plots (200 × 500 m), 500 m apart, were established in mixed forest. All liana individuals = 2 cm dbh were identified, measured, mapped, and marked. For 20 × 20 m subplots we distinguished terra firme and swamp, and we estimated canopy openness. Key results – The combined 20-ha area contains 15,008 lianas (dbh = 2 cm) representing 195 species, 83 genera, and 34 families. Per hectare, species number averaged 64, mean basal area was 0.71 m2 and mean Fisher's alpha, Shannon index, and Simpson diversity index values were 17.9, 3.1 and 11.4, respectively. Ten dominant plant families represented 69% of total species richness, 92% of liana abundance and 92% of basal area, while ten dominant species accounted for 63% of abundance and 59% of basal area. A single species, Manniophyton fulvum, dominated the liana community (22% of all individuals). Forty-one species (21%) had one individual only. Twiners, zoochorous, light-demanding, and meso- or microphyllous species dominated. Liana abundance increased with abundance of medium-sized and large trees but was, surprisingly, independent of small-tree abundance. Canopy openness, habitat type, and tree size were the most important factors influencing abundance and distribution of liana individuals. Conclusions – The Ituri liana assemblage stands out by showing an extreme one-species dominance. Species floristic composition is, however, generally similar to that in other tropical African forests.
Mycorrhizae support oaks growing in a phylogenetically distant neighbourhood
Yguel, B. ; Courty, P.E. ; Jactel, H. ; Pan, X. ; Butenschoen, O. ; Murray, P.J. ; Prinzing, A. - \ 2014
Soil Biology and Biochemistry 78 (2014). - ISSN 0038-0717 - p. 204 - 212.
ectomycorrhizal community - niche conservatism - microbial biomass - species-diversity - quercus-robur - rain-forest - soil - trees - plants - fungi
Host-plants may rarely leave their ancestral niche and in which case they tend to be surrounded by phylogenetically distant neighbours. Phylogenetically isolated host-plants might share few mutualists with their neighbours and might suffer from a decrease in mutualist support. In addition host plants leaving their ancestral niche might face a deterioration of their abiotic and biotic environment and might hence need to invest more into mutualist partners. We tested whether phylogenetic isolation of hosts from neighbours decreases or increases abundance and activity of their mutualists and whether mutualist activity may help to compensate deterioration of the environment. We study oak-hosts and their ectomycorrhizal fungi mutualists established in the litter layer formed by the phylogenetically closely or distantly related neighbourhood. We find that oaks surrounded by phylogenetically distant neighbours show increased abundance and enzymatic activity of ectomycorrhizal fungi in the litter. Moreover, oaks surrounded by phylogenetically distant neighbours also show delayed budburst but ectomycorrhizal fungi activity partly compensates this negative effect of phylogenetic isolation. This suggests decreased nutrient availability in a phylogenetically distant litter partly compensated by increased litter-degradation by ectomycorrhizal fungi activity. Most observed effects of phylogenetic isolation cannot be explained by a change in baseline soil fertility (as reflected by nutritional status of fresh oak litter, or soil microbial biomass and activity) nor by simple reduction of percentages of oak neighbours, nor by the presence of gymnosperms. Our results show that colonizing new niche represented by the presence of distantly related neighbours may delay plant phenology but may be supported by mycorrhizal mutualists. Studies on other host-plant species are required to generalize our findings. (C) 2014 Elsevier Ltd. All rights reserved.
Plant functional types define magnitude of drought response in peatland CO2 exchange
Kuiper, J.J. ; Mooij, W.M. ; Bragazza, L. ; Robroek, B.J.M. - \ 2014
Ecology 95 (2014)1. - ISSN 0012-9658 - p. 123 - 131.
sphagnum mosses - nitrogen availability - removal experiment - species-diversity - moisture controls - water-content - carbon - ecosystems - grassland - bog
Peatlands are important sinks for atmospheric carbon (C), yet the role of plant functional types (PFTs) for C sequestration under climatic perturbations is still unclear. A plant-removal experiment was used to study the importance of vascular PFTs for the net ecosystem CO2 exchange (NEE) during (i.e., resistance) and after (i.e., recovery) an experimental drought. The removal of PFTs caused a decrease of NEE, but the rate differed between microhabitats (i.e., hummocks and lawns) and the type of PFTs. Ericoid removal had a large effect on NEE in hummocks, while the graminoids played a major role in the lawns. The removal of PFTs did not affect the resistance or the recovery after the experimental drought. We argue that the response of Sphagnum mosses (the only PFT present in all treatments) to drought is dominant over that of coexisting PFTs. However, we observed that the moment in time when the system switched from C sink to C source during the drought was controlled by the vascular PFTs. In the light of climate change, the shifts in species composition or even the loss of certain PFTs are expected to strongly affect the future C dynamics in response to environmental stress.
Selection for niche differentiation in plant communities increases biodiversity effects
Zuppinger-Dingley, D. ; Schmid, B. ; Petermann, J.S. ; Yadav, V. ; Deyn, G.B. de; Flynn, D.F.B. - \ 2014
Nature 515 (2014). - ISSN 0028-0836 - p. 108 - 111.
diversity-productivity relationships - grassland experiment - species-diversity - evolution - genotypes - richness
In experimental plant communities, relationships between biodiversity and ecosystem functioning have been found to strengthen over time1, 2, a fact often attributed to increased resource complementarity between species in mixtures3 and negative plant–soil feedbacks in monocultures4. Here we show that selection for niche differentiation between species can drive this increasing biodiversity effect. Growing 12 grassland species in test monocultures and mixtures, we found character displacement between species and increased biodiversity effects when plants had been selected over 8 years in species mixtures rather than in monocultures. When grown in mixtures, relative differences in height and specific leaf area between plant species selected in mixtures (mixture types) were greater than between species selected in monocultures (monoculture types). Furthermore, net biodiversity and complementarity effects1, 2 were greater in mixtures of mixture types than in mixtures of monoculture types. Our study demonstrates a novel mechanism for the increase in biodiversity effects: selection for increased niche differentiation through character displacement. Selection in diverse mixtures may therefore increase species coexistence and ecosystem functioning in natural communities and may also allow increased mixture yields in agriculture or forestry. However, loss of biodiversity and prolonged selection of crops in monoculture may compromise this potential for selection in the longer term.
Disturbance–diversity relationships for soil fauna are explained by faunal community biomass in a salt marsh
Thakur, M.P. ; Berg, M.P. ; Eisenhauer, N. ; Langevelde, F. van - \ 2014
Soil Biology and Biochemistry 78 (2014). - ISSN 0038-0717 - p. 30 - 37.
species-diversity - intermediate disturbance - richness - productivity - coexistence - succession - patterns - competition - collembola - dynamics
Disturbance–diversity relationships have long been studied in ecology with a unimodal relationship as the key prediction. Although this relationship has been widely contested, it is rarely tested for soil invertebrate fauna, an important component of terrestrial biodiversity. We tested disturbance–diversity relationships for soil meso- and macrofauna in a salt marsh where periodic sea water inundation and cattle grazing occur as stressors. We hypothesized a unimodal inundation frequency–diversity relationship, whereas we expected grazing to overrule the effects of inundation frequency due to its large effects on the habitat of soil fauna. We found a negative relationship between inundation frequency and diversity at the ungrazed sites and no relationship at the grazed sites. Moreover, we found a negative relationship between community biomass and diversity for soil fauna that may have caused this negative disturbance–diversity relationship. Community biomass at the intermediate inundation frequency increased due to the dominance of Orchestia gammarellus (a macro-detritivore species), which could exploit low quality litters at the ungrazed sites. We highlight that the negative relationship between faunal community biomass and faunal diversity may influence disturbance–diversity relationships and illustrate that total biomass distribution of feeding guilds of soil fauna can improve our understanding of the soil fauna response to stressors in salt marshes.
Suitability of close-to-nature silviculture for adapting temperate European forests to climate change
Brang, P. ; Spathelf, P. ; Larsen, J.B. ; Bauhus, J. ; Boncina, A. ; Mohren, G.M.J. - \ 2014
Forestry 87 (2014). - ISSN 0015-752X - p. 492 - 503.
spruce picea-abies - fagus-sylvatica l. - norway spruce - ecological stability - species-diversity - stand structure - change impacts - mixed stands - management - drought
In many parts of Europe, close-to-nature silviculture (CNS) has been widely advocated as being the best approach for managing forests to cope with future climate change. In this review, we identify and evaluate six principles for enhancing the adaptive capacity of European temperate forests in a changing climate: (1) increase tree species richness, (2) increase structural diversity, (3) maintain and increase genetic variation within tree species, (4) increase resistance of individual trees to biotic and abiotic stress, (5) replace high-risk stands and (6) keep average growing stocks low. We use these principles to examine how three CNS systems (single-tree selection, group selection and shelterwood) serve adaptation strategies. Many attributes of CNS can increase the adaptive capacity of European temperate forests to a changing climate. CNS promotes structural diversity and tree resistance to stressors, and growing stocks can be kept at low levels. However, some deficiencies exist in relation to the adaptation principles of increasing tree species richness, maintaining and increasing genetic variation, and replacing high-risk stands. To address these shortcomings, CNS should make increased use of a range of regeneration methods, in order to promote light-demanding tree species, non-native species and non-local provenances.
Infectious disease agents mediate interaction in food webs and ecosystems
Selakovic, S. ; Ruiter, P.C. de; Heesterbeek, J.A.P. - \ 2014
Proceedings of the Royal Society. B: Biological Sciences 281 (2014)1777. - ISSN 0962-8452 - 11 p.
biological-control - population-dynamics - species-diversity - mustela-nigripes - canine-distemper - african lions - host behavior - coral-reef - parasites - communities
Infectious agents are part of food webs and ecosystems via the relationship with their host species that, in turn, interact with both hosts and non-hosts. Through these interactions, infectious agents influence food webs in terms of structure, functioning and stability. The present literature shows a broad range of impacts of infectious agents on food webs, and by cataloguing that range, we worked towards defining the various mechanisms and their specific effects. To explore the impact, a direct approach is to study changes in food-web properties with infectious agents as separate species in the web, acting as additional nodes, with links to their host species. An indirect approach concentrates not on adding new nodes and links, but on the ways that infectious agents affect the existing links across host and non-host nodes, by influencing the 'quality' of consumer-resource interaction as it depends on the epidemiological state host involved. Both approaches are natural from an ecological point of view, but the indirect approach may connect more straightforwardly to commonly used tools in infectious disease dynamics.
Diversity patterns of leaf-associated aquatic hyphomycetes along a broad latitudinal gradient
Jabiol, J. ; Bruder, A. ; Gessner, M.O. ; Makkonen, M. ; McKie, B.G. ; Peeters, E.T.H.M. ; Vos, V.C.A. ; Chauvet, E. - \ 2013
Fungal Ecology 6 (2013)5. - ISSN 1754-5048 - p. 439 - 448.
species-diversity - community structure - fungal communities - stream - litter - biodiversity - temperature - leaves - colonization - decomposition
Information about the global distribution of aquatic hyphomycetes is scarce, despite the primary importance of these fungi in stream ecosystem functioning. In particular, the relationship between their diversity and latitude remains unclear, due to a lack of coordinated surveys across broad latitudinal ranges. This study is a first report on latitudinal patterns of aquatic hyphomycete diversity associated with native leaf-litter species in five streams located along a gradient extending from the subarctic to the tropics. Exposure of leaf litter in mesh bags of three different mesh sizes facilitated assessing the effects of including or excluding different size-classes of litter-consuming invertebrates. Aquatic hyphomycete evenness was notably constant across all sites, whereas species richness and diversity, expressed as the Hill number, reached a maximum at mid-latitudes (Mediterranean and temperate streams). These latitudinal patterns were consistent across litter species, despite a notable influence of litter identity on fungal communities at the local scale. As a result, the bell-shaped distribution of species richness and Hill diversity deviated markedly from the latitudinal patterns of most other groups of organisms. Differences in the body-size distribution of invertebrate communities colonizing the leaves had no effect on aquatic hyphomycete species richness, Hill diversity or evenness, but invertebrates could still influence fungal communities by depleting litter, an effect that was not captured by the design of our experiment. (C) 2013 Elsevier Ltd and The British Mycological Society. All rights reserved.
Early root overproduction not triggered by nutrients decisive for competitive success belowground
Padilla, F.M. ; Mommer, L. ; Caluwe, H. de; Smit-Tiekstra, A.E. ; Wagemaker, C.A.M. ; Ouborg, N.J. ; Kroon, H. de - \ 2013
PLoS ONE 8 (2013)1. - ISSN 1932-6203 - 9 p.
interspecific competition - plant diversity - niche differentiation - negative feedback - species-diversity - seed yield - productivity - communities - maintenance - mechanisms
Background - Theory predicts that plant species win competition for a shared resource by more quickly preempting the resource in hotspots and by depleting resource levels to lower concentrations than its competitors. Competition in natural grasslands largely occurs belowground, but information regarding root interactions is limited, as molecular methods quantifying species abundance belowground have only recently become available. Principal Findings - In monoculture, the grass Festuca rubra had higher root densities and a faster rate of soil nitrate depletion than Plantago lanceolata, projecting the first as a better competitor for nutrients. However, Festuca lost in competition with Plantago. Plantago not only replaced the lower root mass of its competitor, but strongly overproduced roots: with only half of the plants in mixture than in monoculture, Plantago root densities in mixture were similar or higher than those in its monocultures. These responses occurred equally in a nutrient-rich and nutrient-poor soil layer, and commenced immediately at the start of the experiment when root densities were still low and soil nutrient concentrations high. Conclusions/Significance - Our results suggest that species may achieve competitive superiority for nutrients by root growth stimulation prior to nutrient depletion, induced by the presence of a competitor species, rather than by a better ability to compete for nutrients per se. The root overproduction by which interspecific neighbors are suppressed independent of nutrient acquisition is consistent with predictions from game theory. Our results emphasize that root competition may be driven by other mechanisms than is currently assumed. The long-term consequences of these mechanisms for community dynamics are discussed.
Repeated parallel evolution reveals limiting similarity in subterranean diving beetles
Vergnon, R.O.H. ; Leijs, P. ; Nes, E.H. van; Scheffer, M. - \ 2013
American Naturalist 182 (2013)1. - ISSN 0003-0147 - p. 67 - 75.
species-diversity - competition - dytiscidae - patterns - convergence - coexistence - coleoptera - divergence - morphology - community
The theory of limiting similarity predicts that co-occurring species must be sufficiently different to coexist. Although this idea is a staple of community ecology, convincing empirical evidence has been scarce. Here we examine 34 subterranean beetle communities in arid inland Australia that share the same habitat type but have evolved in complete isolation over the past 5 million years. Although these communities come from a range of phylogenetic origins, we find that they have almost invariably evolved to share a similar size structure. The relative positions of coexisting species on the body size axis were significantly more regular across communities than would be expected by chance, with a size ratio, on average, of 1.6 between coexisting species. By contrast, species' absolute body sizes varied substantially from one community to the next. This suggests that self-organized spacing according to limiting-similarity theory, as opposed to evolution toward preexisting fixed niches, shaped the communities. Using a model starting from random sets of founder species, we demonstrate that the patterns are indeed consistent with evolutionary self-organization. For less isolated habitats, the same model predicts the coexistence of multiple species in each regularly spaced functional group. Limiting similarity, therefore, may also be compatible with the coexistence of many redundant species. © 2013 by The University of Chicago.
Interpretation and predictions of the emergent neutrality model: A reply to Barabás et al
Vergnon, R.O.H. ; Nes, E.H. van; Scheffer, M. - \ 2013
Oikos 122 (2013)11. - ISSN 0030-1299 - p. 1573 - 1575.
species-diversity - biodiversity - maintenance - similarity - transients - evolution - niches
Formulated in 2006, Scheffer and van Nes' Emergent neutrality model predicts that competing species might self-organize into groups of species similar in their traits. Recently, Vergnon et al. showed that the model consistently generates multimodal species abundance distributions, in accordance with empirical data. Barabás et al. argue that Emergent neutrality model relies on unmodeled, 'hidden' species differences. They also suggest that an Emergent neutrality model explicitly integrating such differences may fail to generate multimodal species abundance distributions, while other models can robustly produce those patterns. Here we demonstrate that density dependence - the process deemed problematic by Barabás et al. - may permanently maintain groups of similar species without need for additional species differences. More broadly, we make it clear that density dependence is not the only likely mechanism that could allow the permanent coexistence of similar species in the Emergent neutrality framework. We welcome the finding that models other than Emergent neutrality can generate multimodal abundance distributions and we briefly discuss their novelty and relevance.
Testing the stress gradient hypothesis in herbivore communities: facilitation peaks at intermediate nutrient levels
Bakker, E.S. ; Dobrescu, I. ; Straile, D. ; Holmgren, M. - \ 2013
Ecology 94 (2013)8. - ISSN 0012-9658 - p. 1776 - 1784.
fresh-water ecosystems - positive interactions - acentria-ephemerella - biotic interactions - submersed macrophytes - plant interactions - species-diversity - abiotic stress - prairie dogs - competition
The role of positive interactions in structuring plant and animal communities is increasingly recognized, but the generality of current theoretical models has remained practically unexplored in animal communities. The stress gradient hypothesis predicts a linear increase in the intensity of facilitation as environmental conditions become increasingly stressful, whereas other theoretical models predict a maximum at intermediate environmental stress. We tested how competition and facilitation between herbivores change over a manipulated gradient of nutrient availability. We studied the effect of grazing by pond snails (Lymnaea stagnalis L.) as bulk grazers on aquatic caterpillars (Acentria ephemerella Denis and Schiffermüller) as small specialist grazers along an experimental gradient of environmental nutrient concentration. Higher nutrient levels increased overall total plant biomass but induced a shift toward dominance of filamentous algae at the expense of macrophytes. Facilitation of caterpillars by snail presence peaked at intermediate nutrient levels. Both caterpillar biomass and caterpillar grazing on macrophytes were highest at intermediate nutrient levels. Snails facilitated caterpillars possibly by removing filamentous algae and increasing access to the macrophyte resource, whereas they did not affect macrophyte biomass or C¿:¿nutrient ratios, a measure of food quality. We conclude that competition and facilitation in herbivore communities change along nutrient availability gradients that affect plant biomass and community composition. Understanding how interspecific interactions may change in strength and direction along environmental gradients is important to predict how the diversity and structure of communities may respond to the introduction or removal of herbivore species in ecosystems.
Leaf litter quality drives litter mixing effects through complementary resource use among detritivores
Vos, V.C.A. ; Ruijven, J. van; Berg, M.P. ; Peeters, E.T.H.M. ; Berendse, F. - \ 2013
Oecologia 173 (2013)1. - ISSN 0029-8549 - p. 269 - 280.
species-diversity - ecosystem function - soil processes - decomposition - biodiversity - mixtures - forest - respiration - millipedes - richness
To comprehend the potential consequences of biodiversity loss on the leaf litter decomposition process, a better understanding of its underlying mechanisms is necessary. Here, we hypothesize that positive litter mixture effects occur via complementary resource use, when litter species complement each other in terms of resource quality for detritivores. To investigate this, monocultures and mixtures of two leaf litter species varying in quality were allowed to decompose with and without a single macro-detritivore species (the terrestrial woodlice Oniscus asellus). Resource quality of the mixture was assessed by the mean concentration, the dissimilarity in absolute and relative concentrations, and the covariance between nitrogen (N), phosphorus (P) and calcium (Ca) supply. Our results clearly show that litter mixing effects were driven by differences in their resource quality for detritivores. In particular, complementary supply of N and P was a major driver of litter mixing effects. Interestingly, litter mixing effects caused by the addition of woodlice were predominantly driven by N dissimilarity, whereas in their absence, increased P concentration was the main driver of litter mixing effects. These results show that ultimately, litter diversity effects on decomposition may be driven by complementary resource use of the whole decomposer community (i.e., microbes and macro-detritivores).
Interactive effects of landscape context constrain the effectiveness of local agri-environmental management
Concepción, E.D. ; Díaz, M. ; Kleijn, D. ; Báldi, A. ; Batáry, P. ; Clough, Y. ; Gabriel, D. ; Herzog, F. ; Holzschuh, A. ; Knop, E. ; Marshall, J.P. ; Tscharntke, T. ; Verhulst, J. - \ 2012
Journal of Applied Ecology 49 (2012)5. - ISSN 0021-8901 - p. 695 - 705.
different spatial scales - farmland biodiversity - agricultural landscapes - species-diversity - field margins - schemes - corridors - europe - matrix - birds
summary 1. Ecological theory predicts that the effectiveness of local agri-environmental management to enhance species richness at field scales will be the highest at intermediate levels of landscape complexity because of nonlinear effects of landscape context on field-scale diversity. 2. We examined how landscape complexity determined effectiveness of local agri-environmental management in terms of effects on species richness of birds, plants, spiders and bees in 232 extensive and intensive paired fields (112 arable fields and 120 grasslands) from 18 regions located in six European countries. 3. As predicted, landscape complexity enhanced field-scale species richness in a mostly nonlinear (sigmoidal) way, with earlier species richness increases in extensive than in intensive fields along landscape complexity gradients. Length of semi-natural boundaries (for arable fields) and proportion of unfarmed habitat (for grasslands) were the landscape features influencing species richness. 4. The relationships between effectiveness of local management and landscape complexity for all taxa were best described with hump-shaped curves, indicating the highest effectiveness at intermediate landscape complexities. 5. Synthesis and applications. We used models to investigate how and why effects of local management intensity on species richness vary along wide gradients of landscape complexity. We conclude that landscape-scale management options should take priority over local extensification measures within agri-environmental programmes. These programmes should follow a hierarchical multi-scale approach directed to address landscape-scale constraints on local diversity.
Impact of grazing management on hibernating caterpillars of the butterfly Melitaea cinxia in calcareous grasslands
Noordwijk, C.G.E. ; Flierman, D.E. ; Remke, E. ; Wallis de Vries, M.F. ; Berg, M.P. - \ 2012
Journal of Insect Conservation 16 (2012)6. - ISSN 1366-638X - p. 909 - 920.
life-history strategies - restoration management - seminatural grasslands - intraguild predation - phytophagous insects - species-diversity - conservation - intensity - herbivores - vegetation
Semi-natural grasslands are increasingly grazed by large herbivores for nature conservation purposes. For many insects such grazing is essential for the conservation of their habitat, but at the same time, populations decrease at high grazing intensity. We hypothesised that grazing management may cause increased butterfly mortality, especially for life-stages with low mobility, such as hibernating caterpillars. To test this, we measured the effect of sheep grazing on overwinter larval survival. We used the Glanville fritillary (Melitaea cinxia), which has gregarious caterpillars hibernating in silk nests, as a model species. Caterpillar nests were monitored throughout the hibernating period in calcareous grassland reserves with low and high intensity sheep grazing and in an ungrazed control treatment. After grazing, 64 % of the nests at the high intensity grazing treatment were damaged or missing, compared to 8 and 12 % at the ungrazed and low intensity grazing treatment, respectively. Nest volume and caterpillar survival were 50 % lower at the high intensity grazing treatment compared to both ungrazed and low intensity grazing treatments. Nest damage and increased mortality were mainly caused by incidental ingestion of the caterpillars by the sheep. It is likely that grazing similarly affects other invertebrates, depending on their location within the vegetation and their ability to actively avoid herbivores. This implies that the impact of grazing strongly depends on the timing of this management in relation to the phenology of the species. A greater focus on immature and inactive life-stages in conservation policy in general and particularly in action plans for endangered species is required to effectively preserve invertebrate diversity.
Diversity and production of Ethiopian dry woodlands explained by climate- and soil- stress gradients
Eshete, A. ; Sterck, F.J. ; Bongers, F. - \ 2011
Forest Ecology and Management 261 (2011)9. - ISSN 0378-1127 - p. 1499 - 1509.
species-diversity - altitudinal gradients - boswellia-papyrifera - deciduous forest - african savanna - rain-forest - costa-rica - frankincense - regeneration - communities
Dry woodlands cover about 14% of the total African land surface and represent about 25% of the natural vegetation. They are characterized by a seasonal climate, with a dry season of 4–7 months. Large parts of these ecosystems are degrading due to grazing, fire or exploitation by people. We studied species richness and productivity patterns of dry woodlands in Ethiopia. For such ecosystems, classic productivity and diversity hypotheses predict that species richness and productivity increase as the wet season length increases, and decrease when soil conditions create water stress. We inventoried and measured trees in 18 2-ha plots distributed in two sites, one higher altitude site with a shorter wet season than the lower altitude site. We found that the stand volume per hectare was lower in the site with a shorter wet season. Across all 18 plots we observed that stand volume decreased with soil water stress (estimated from texture and depth). This was in line with the prediction. The species richness was lower in the short-wet-season woodlands, but was unaffected by variation in soil conditions. This suggests that climate driven constraints (wet season length) set the limits to species richness, and not soil conditions. As far as we know, this study is one of the first studies that evaluated these productivity and diversity hypotheses for dry African woodlands. --------------------------------------------------------------------------------
Spatiotemporal variation of plant diversity on ditch banks under different management regimes
Leng, X. ; Musters, C.J.M. ; Snoo, G.R. de - \ 2011
Basic and Applied Ecology 12 (2011)1. - ISSN 1439-1791 - p. 38 - 46.
species-diversity - beta-diversity - agricultural landscapes - dispersal limitation - spatial variation - alpha-diversity - richness - biodiversity - heterogeneity - conservation
Agricultural intensification has led to a loss of biological diversity at various spatial and temporal scales and understanding the mechanisms driving these changes would help target conservation efforts accordingly. In this study we used additive partitioning of diversity and the Jaccard index of similarity to estimate the spatial and temporal patterns of plant diversity on ditch banks under different management regimes (nature reserves and agricultural areas). We focused on a total of 118 species, including 18 indicator species of conservation interest, at 42 sites in three successive sampling periods. For all species taken together, beta diversity contributed most to total observed species diversity, but was less than expected under random distribution. Indicator species showed greater beta diversity on a spatial scale compared to all species, but much less so on a temporal scale. Importantly, the differences in indicator species composition on a spatial scale are probably due to environmental heterogeneity and dispersal limitation, indicating that management strategies should focus on both factors. Nature reserves showed higher alpha diversity within sites because of possible lower nutrient inputs and grazing intensity compared with agricultural areas, while both exhibited scale-dependent dispersal limitation.
Soil microbes contribute to the classic plant diversity-productivity pattern
Schnitzer, S.A. ; Klironomos, J.N. ; HilleRisLambers, J. ; Kinkel, L.L. ; Reich, P.B. ; Nes, E.H. van; Scheffer, M. - \ 2011
Ecology 92 (2011)2. - ISSN 0012-9658 - p. 296 - 303.
arbuscular mycorrhizae - nitrogen deposition - species-diversity - elevated co2 - biodiversity - feedback - disease - ecosystems - communities - pathogens
Ecosystem productivity commonly increases asymptotically with plant species diversity, and determining the mechanisms responsible for this well-known pattern is essential to predict potential changes in ecosystem productivity with ongoing species loss. Previous studies attributed the asymptotic diversity–productivity pattern to plant competition and differential resource use (e.g., niche complementarity). Using an analytical model and a series of experiments, we demonstrate theoretically and empirically that host-specific soil microbes can be major determinants of the diversity–productivity relationship in grasslands. In the presence of soil microbes, plant disease decreased with increasing diversity, and productivity increased nearly 500%, primarily because of the strong effect of density-dependent disease on productivity at low diversity. Correspondingly, disease was higher in plants grown in conspecific-trained soils than heterospecific-trained soils (demonstrating host-specificity), and productivity increased and host-specific disease decreased with increasing community diversity, suggesting that disease was the primary cause of reduced productivity in species-poor treatments. In sterilized, microbe-free soils, the increase in productivity with increasing plant species number was markedly lower than the increase measured in the presence of soil microbes, suggesting that niche complementarity was a weaker determinant of the diversity–productivity relationship. Our results demonstrate that soil microbes play an integral role as determinants of the diversity–productivity relationship
Biodiversity change after climate-induced ice-shelf collapse in the Antarctic
Gutt, J. ; Barratt, I. ; Domack, E. ; Scheidat, M. - \ 2011
Deep-Sea Research. Part II, tropical studies in oceanography 58 (2011)1-2. - ISSN 0967-0645 - p. 74 - 83.
western weddell sea - deep-sea - species-diversity - southern-ocean - 1st insights - ross sea - peninsula - impact - aggregations - biogeography
The marine ecosystem on the eastern shelf of the Antarctic Peninsula was surveyed 5 and 12 years after the climate-induced collapse of the Larsen A and B ice shelves. An impoverished benthic fauna was discovered, that included deep-sea species presumed to be remnants from ice-covered conditions. The current structure of various ecosystem components appears to result from extremely different response rates to the change from an oligotrophic sub-ice-shelf ecosystem to a productive shelf ecosystem. Meiobenthic communities remained impoverished only inside the embayments. On local scales, macro- and mega-epibenthic diversity was generally low, with pioneer species and typical Antarctic megabenthic shelf species interspersed. Antarctic Minke whales and seals utilised the Larsen A/B area to feed on presumably newly established krill and pelagic fish biomass. Ecosystem impacts also extended well beyond the zone of ice-shelf collapse, with areas of high benthic disturbance resulting from scour by icebergs discharged from the Larsen embayments
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