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.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Elucidating the interaction between light competition and herbivore feeding patterns using functional-structural plant modelling
Vries, Jorad De; Poelman, Erik H. ; Anten, Niels ; Evers, Jochem B. - \ 2018
Annals of Botany 121 (2018)5. - ISSN 0305-7364 - p. 1019 - 1031.
Brassica - competition - functional-structural plant modelling - growth-defence trade-off - herbivore specialization - herbivory - nigra - plant-herbivore interactions - red far-red ratio
Background and Aims Plants usually compete with neighbouring plants for resources such as light as well as defend themselves against herbivorous insects. This requires investment of limiting resources, resulting in optimal resource distribution patterns and trade-offs between growth- and defence-related traits. A plant's competitive success is determined by the spatial distribution of its resources in the canopy. The spatial distribution of herbivory in the canopy in turn differs between herbivore species as the level of herbivore specialization determines their response to the distribution of resources and defences in the canopy. Here, we investigated to what extent competition for light affects plant susceptibility to herbivores with different feeding preferences. Methods To quantify interactions between herbivory and competition, we developed and evaluated a 3-D spatially explicit functional-structural plant model for Brassica nigra that mechanistically simulates competition in a dynamic light environment, and also explicitly models leaf area removal by herbivores with different feeding preferences. With this novel approach, we can quantitatively explore the extent to which herbivore feeding location and light competition interact in their effect on plant performance. Key Results Our results indicate that there is indeed a strong interaction between levels of plant-plant competition and herbivore feeding preference. When plants did not compete, herbivory had relatively small effects irrespective of feeding preference. Conversely, when plants competed, herbivores with a preference for young leaves had a strong negative effect on the competitiveness and subsequent performance of the plant, whereas herbivores with a preference for old leaves did not. Conclusions Our study predicts how plant susceptibility to herbivory depends on the composition of the herbivore community and the level of plant competition, and highlights the importance of considering the full range of dynamics in plant-plant-herbivore interactions.
Plant community evenness responds to spatial plant–soil feedback heterogeneity primarily through the diversity of soil conditioning
Wubs, E.R.J. ; Bezemer, T.M. - \ 2018
Functional Ecology 32 (2018)2. - ISSN 0269-8463 - p. 509 - 521.
competition - plant diversity - plant–soil interactions - spatial heterogeneity
Functional Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society. Plant–soil feedback (PSF) has been identified as a key driver of local plant diversity and evenness in competitive communities. However, while it has been shown that spatial PSF heterogeneity can alter plant performance and competitive interactions, there is no proof of principle that spatial PSF heterogeneity enhances community diversity. Using a grassland model system, we separated two aspects of spatial heterogeneity: the number of species conditioning the soil and spatial distribution of the PSFs. Our data show that PSFs promoted a higher plant evenness when the soil was conditioned by multiple species (mixed-conditioned) than when the soil was conditioned by a single species (mono-conditioned). On mono-conditioned soils, heterospecifics typically outperformed the focal species. In addition, there was a trend for increasing community evenness from uniform, via fine-grained to coarse-grained mixed-conditioned soils, but this was not significant. On mixed-conditioned soils, performance of all competing species was intermediate to the best and the worst mono-conditioned soils, leading to higher community evenness. Our data demonstrate that PSFs play a role in promoting plant evenness. Across mono-conditioned soils, PSF led to altered competitive hierarchies. However, on soils conditioned by multiple species, competitive ability among species was more similar and this led to higher plant evenness. The spatial distribution of the heterogeneity, on the other hand, did not significantly affect plant evenness. Our data therefore show that community evenness was more strongly related to the number of plant species that conditioned the soil than the spatial distribution of the PSF heterogeneity. Future studies need to investigate the importance of PSFs in the field across plant life stages and multiple generations. A plain language summary is available for this article.
Functional trait dissimilarity drives both species complementarity and competitive disparity
Wagg, Cameron ; Ebeling, Anne ; Roscher, Christiane ; Ravenek, Janneke ; Bachmann, Dörte ; Eisenhauer, Nico ; Mommer, Liesje ; Buchmann, Nina ; Hillebrand, Helmut ; Schmid, Bernhard ; Weisser, Wolfgang W. - \ 2017
Functional Ecology 31 (2017)12. - ISSN 0269-8463 - p. 2320 - 2329.
biodiversity - community ecology - competition - Jena experiment - trait-based experiment (TBE)
Niche complementarity and competitive disparity are driving mechanisms behind plant community assembly and productivity. Consequently, there is great interest in predicting species complementarity and their competitive differences from their functional traits as dissimilar species may compete less and result in more complete use of resources. Here we assessed the role of trait dissimilarities for species complementarity and competitive disparities within an experimental gradient of plant species richness and functional trait dissimilarity. Communities were assembled using three pools of grass and forb species based on a priori knowledge of traits related to (1) above- and below-ground spatial differences in resource acquisition, (2) phenological differences or (3) both. Complementarity and competitive disparities were assessed by partitioning the overyielding in mixed species communities into species complementarity and dominance effects. Community overyielding and the underlying complementarity and competitive dominance varied strongly among the three plant species pools. Overyielding and complementarity were greatest among species that were assembled based on their variation in both spatial and phenological traits. Competitive dominance was greatest when species were assembled based on spatial resource acquisition traits alone. In communities that were assembled based on species variation in only spatial or phenological traits, greater competitive dominance was predicted by greater differences in SLA and flowering initiation respectively, while greater complementarity was predicted by greater dissimilarity in leaf area and flowering senescence respectively. Greater differences in leaf area could also be linked to greater species complementarity in communities assembled based on variation in both phenological and spatial traits, but trait dissimilarity was unrelated to competitive dominance in these communities. Our results indicate that complementarity and competitive disparity among species are both driven by trait dissimilarities. However, the identity of the traits that drives the complementarity and competitive disparity depends on the trait variation among species that comprise the community. Moreover, we demonstrate that communities assembled with the greater variation in both spatial and phenological traits show the greatest complementarity among species. A plain language summary is available for this article.
Call for projects 'Nieuwe Energie voor het Landschap I+II' (Event)
Stremke, Sven - \ 2017
Energy - landscape - design - competition
Stimulieringsfonds Creative Industrie: Jury membership
Above- and below-ground responses of four tundra plant functional types to deep soil heating and surface soil fertilization
Wang, Peng ; Limpens, Juul ; Mommer, Liesje ; Ruijven, Jasper van; Nauta, Ake L. ; Berendse, Frank ; Schaepman-Strub, Gabriela ; Blok, Daan ; Maximov, Trofim C. ; Heijmans, Monique M.P.D. - \ 2017
Journal of Ecology 105 (2017)4. - ISSN 0022-0477 - p. 947 - 957.
accelerated thawing - active layer thickness - Arctic tundra - climate warming - competition - nutrient availability - plant functional types - root biomass - vegetation composition - vertical root distribution

Climate warming is faster in the Arctic than the global average. Nutrient availability in the tundra soil is expected to increase by climate warming through (i) accelerated nutrient mobilization in the surface soil layers, and (ii) increased thawing depths during the growing season which increases accessibility of nutrients in the deeper soil layers. Both processes may initiate shifts in tundra vegetation composition. It is important to understand the effects of these two processes on tundra plant functional types. We manipulated soil thawing depth and nutrient availability at a Northeast-Siberian tundra site to investigate their effects on above- and below-ground responses of four plant functional types (grasses, sedges, deciduous shrubs and evergreen shrubs). Seasonal thawing was accelerated with heating cables at c. 15 cm depth without warming the surface soil, whereas nutrient availability was increased in the surface soil by adding slow-release NPK fertilizer at c. 5 cm depth. A combination of these two treatments was also included. This is the first field experiment specifically investigating the effects of accelerated thawing in tundra ecosystems. Deep soil heating increased the above-ground biomass of sedges, the deepest rooted plant functional type in our study, but did not affect biomass of the other plant functional types. In contrast, fertilization increased above-ground biomass of the two dwarf shrub functional types, both of which had very shallow root systems. Grasses showed the strongest response to fertilization, both above- and below-ground. Grasses were deep-rooted, and they showed the highest plasticity in terms of vertical root distribution, as grass root distribution shifted to deep and surface soil in response to deep soil heating and surface soil fertilization respectively. Synthesis. Our results indicate that increased thawing depth can only benefit deep-rooted sedges, while the shallow-rooted dwarf shrubs, as well as flexible-rooted grasses, take advantage of increased nutrient availability in the upper soil layers. Our results suggest that grasses have the highest root plasticity, which enables them to be more competitive in rapidly changing environments. We conclude that root vertical distribution strategies are important for vegetation responses to climate-induced increases in soil nutrient availability in Arctic tundra, and that future shifts in vegetation composition will depend on the balance between changes in thawing depth and nutrient availability in the surface soil.

Benefits from living together? Clades whose species use similar habitats may persist as a result of eco-evolutionary feedbacks
Prinzing, Andreas ; Ozinga, Wim A. ; Brändle, Martin ; Courty, Pierre Emmanuel ; Hennion, Françoise ; Labandeira, Conrad ; Parisod, Christian ; Pihain, Mickael ; Bartish, Igor V. - \ 2017
New Phytologist 213 (2017)1. - ISSN 0028-646X - p. 66 - 82.
assembly of present and fossil communities - competition - conservation biology - enemy pressure and mutualism of coexisting species - evolution and conservatism - hybridization - niche breadth

(Table presented.). Summary: 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 co-occurrence 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. We tentatively 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.

Data from: Individual variation in winter supplementary food consumption and its consequences for reproduction in wild birds.
Crates, R.A. ; Firth, J.A. ; Farine, D.R. ; Garroway, C.J. ; Kidd, Lindall R. ; Aplin, L.M. ; Radersma, Reinder ; Milligan, Nicole D. ; Voelkl, Bernhard ; Culina, Antica ; Verhelst, B.L. ; Hinde, C.A. ; Sheldon, B.C. - \ 2016
competition - foraging - Passive Integrated Transponder - Parus major - Cyanistes caeruleus
The provision of wild birds with supplementary food has increased substantially over recent decades. While it is assumed that provisioning birds is beneficial, supplementary feeding can have detrimental ‘carry-over’ effects on reproductive traits. Due to difficulties in monitoring individual feeding behaviour, assessing how individuals within a population vary in their exploitation of supplementary food resources has been limited. Quantifying individual consumption of supplementary food is necessary to understand the operation of carry-over effects at the individual level. We used Radio Frequency Identification (RFID) technology and automated feeders to estimate individual consumption of supplementary winter food in a large wild population of great tits Parus major and blue tits Cyanistes caeruleus. Using these data, we identified demographic factors that explained individual variation in levels of supplementary food consumption. We also tested for carry-over effects of supplementary food consumption on recruitment, reproductive success and a measure of survival. Individual variation in consumption of supplementary food was explained by differences between species, ages, sexes and years. Individuals were consistent across time in their usage of supplementary resources. We found no strong evidence that the extent of supplementary food consumption directly influenced subsequent fitness parameters. Such effects may instead result from supplementary food influencing population demographics by enhancing the survival and subsequent breeding of less competitive individuals, which reduce average breeding parameters and increase density-dependent competition. Carry-over effects of supplementary feeding are not universal and may depend upon the temporal availability of the food provided. Our study demonstrates how RFID systems can be used to examine individual-level behaviour with minimal effects on fitness.
Plant-plant interactions mediate the plastic and genotypic response of Plantago asiatica to CO2 : An experiment with plant populations from naturally high CO2 areas
Loon, Marloes P. Van; Rietkerk, Max ; Dekker, Stefan C. ; Hikosaka, Kouki ; Ueda, Miki U. ; Anten, Niels P.R. - \ 2016
Annals of Botany 117 (2016)7. - ISSN 0305-7364 - p. 1197 - 1207.
Canopy functioning - climate change - competition - elevated CO - evolutionary response - game theory - genotypic response - naturally high CO - plant-plant interactions - Plantago asiatica L. - plastic response - selection pressure

Background and Aims The rising atmospheric CO2 concentration ([CO2]) is a ubiquitous selective force that may strongly impact species distribution and vegetation functioning. Plant-plant interactions could mediate the trajectory of vegetation responses to elevated [CO2], because some plants may benefit more from [CO2] elevation than others. The relative contribution of plastic (within the plant's lifetime) and genotypic (over several generations) responses to elevated [CO2] on plant performance was investigated and how these patterns are modified by plant-plant interactions was analysed. Methods Plantago asiatica seeds originating from natural CO2 springs and from ambient [CO2] sites were grown in mono stands of each one of the two origins as well as mixtures of both origins. In total, 1944 plants were grown in [CO2]-controlled walk-in climate rooms, under a [CO2] of 270, 450 and 750 ppm. A model was used for upscaling from leaf to whole-plant photosynthesis and for quantifying the influence of plastic and genotypic responses. Key Results It was shown that changes in canopy photosynthesis, specific leaf area (SLA) and stomatal conductance in response to changes in growth [CO2] were mainly determined by plastic and not by genotypic responses. We further found that plants originating from high [CO2] habitats performed better in terms of whole-plant photosynthesis, biomass and leaf area, than those from ambient [CO2] habitats at elevated [CO2] only when both genotypes competed. Similarly, plants from ambient [CO2] habitats performed better at low [CO2], also only when both genotypes competed. No difference in performance was found in mono stands. Conclusion The results indicate that natural selection under increasing [CO2] will be mainly driven by competitive interactions. This supports the notion that plant-plant interactions have an important influence on future vegetation functioning and species distribution. Furthermore, plant performance was mainly driven by plastic and not by genotypic responses to changes in atmospheric [CO2].

Data from: Positive shrub-tree interactions facilitate woody encroachment in boreal peatlands
Holmgren, M. ; Lin, C.Y. ; Murillo, J.E. ; Nieuwenhuis, A. ; Penninkhof, J.M. ; Sanders, N. ; Bart, T. van; Veen, H. van; Vasander, H. ; Vollebregt, M.E. ; Limpens, J. - \ 2015
boreal forests - climate change - competition - critical transition - ecosystem shift - peatbog - positive interactions - resilience - tree seedling establishment
Boreal ecosystems are warming roughly twice as fast as the global average, resulting in woody expansion that could further speed up the climate warming. Boreal peatbogs are waterlogged systems that store more than 30% of the global soil carbon. Facilitative effects of shrubs and trees on the establishment of new individuals could increase tree cover with profound consequences for the structure and functioning of boreal peatbogs, carbon sequestration and climate. We conducted two field experiments in boreal peatbogs to assess the mechanisms that explain tree seedling recruitment and to estimate the strength of positive feedbacks between shrubs and trees. We planted seeds and seedlings of Pinus sylvestris in microsites with contrasting water-tables and woody cover and manipulated both shrub canopy and root competition. We monitored seedling emergence, growth and survival for up to four growing seasons and assessed how seedling responses related to abiotic and biotic conditions. We found that tree recruitment is more successful in drier topographical microsites with deeper water-tables. On these hummocks, shrubs have both positive and negative effects on tree seedling establishment. Shrub cover improved tree seedling condition, growth and survival during the warmest growing season. In turn, higher tree basal area correlates positively with soil nutrient availability, shrub biomass and abundance of tree juveniles. Synthesis. Our results suggest that shrubs facilitate tree colonization of peatbogs which further increases shrub growth. These facilitative effects seem to be stronger under warmer conditions suggesting that a higher frequency of warmer and dry summers may lead to stronger positive interactions between shrubs and trees that could eventually facilitate a shift from moss to tree-dominated systems.
Experimental evidence shows the importance of behavioural plasticity and body size under competition in waterfowl
Zhang, Y. ; Prins, H.H.T. ; Versluijs, Martijn ; Wessels, R. ; Cao, L. ; Boer, W.F. de - \ 2015
competition - waterbirds - behavioral - niche
Modelling population effects of juvenile offshore fish displacement towards adult habitat
Wolfshaar, K.E. van de; Tulp, I.Y.M. ; Wennhage, H. ; Støttrup, J.G. - \ 2015
Marine Ecology Progress Series 540 (2015). - ISSN 0171-8630 - p. 193 - 201.
complex life-cycles - nursery grounds - spatial distribution - competition
Recent studies of fish distribution patterns highlight shifts in the spatial distributions of particular life-stages. Focus has thus far been on changes in habitat use and possible drivers for these changes. Yet, small-scale shifts in habitat use of certain life stages may have profound consequences on population dynamics through changes in resource use and competition. To explore this, a conceptual stage-structured model was developed with 3 stages and 2 resources and allowing a move of large juveniles from the shallow to the deep habitat. Large juveniles compete with small juveniles in shallow waters and with adults in deeper waters. Alternative stable states occur, with one state dominated by small juvenile biomass and the other dominated by adult biomass.
The model results show for both states that while large juvenile biomass responds to a change in time spent in the deep habitat, the biomass of small juveniles and adults is barely affected. Between the 2 states there is a profoundly different population response to increased fishing mortality. In the adult biomass dominated state, adult biomass is hardly affected while juvenile
biomass increases until population collapse, with increased fishing. In the small juvenile dominated state, adult and small juvenile biomass decrease, and large juvenile biomass increases. This state persists at much higher fishing mortality than the adult biomass dominated state. This study highlights that safeguarding nursery functions in a changing environment requires monitoring of juvenile life-stages in a range of habitats and a spatially adaptive management strategy
Strain diversity and phage resistance in complex dairy starter cultures
Spus, M. ; Alexeeva, S.V. ; Wolkers-Rooijackers, J.C.M. ; Zwietering, M.H. ; Abee, T. ; Smid, E.J. - \ 2015
Journal of Dairy Science 98 (2015)8. - ISSN 0022-0302 - p. 5173 - 5182.
streptococcus-cremoris - lactic streptococci - lactococcus-lactis - food fermentations - bacteriophages - competition - products - genomics - bacteria - plasmid
The compositional stability of the complex Gouda cheese starter culture Ur is thought to be influenced by diversity in phage resistance of highly related strains that co-exist together with bacteriophages. To analyze the role of bacteriophages in maintaining culture diversity at the level of genetic lineages, simple blends of Lactococcus lactis strains were made and subsequently propagated for 152 generations in the absence and presence of selected bacteriophages. We first screened 102 single-colony isolates (strains) from the complex cheese starter for resistance to bacteriophages isolated from this starter. The collection of isolates represents all lactococcal genetic lineages present in the culture. Large differences were found in bacteriophage resistance among strains belonging to the same genetic lineage and among strains from different lineages. The blends of strains were designed such that 3 genetic lineages were represented by strains with different levels of phage resistance. The relative abundance of the lineages in blends with phages was not stable throughout propagation, leading to continuous changes in composition up to 152 generations. The individual resistance of strains to phage predation was confirmed as one of the factors influencing starter culture diversity. Furthermore, loss of proteolytic activity of initially proteolytic strains was found. Reconstituted blends with only 4 strains with a variable degree of phage resistance showed complex behavior during prolonged propagation. Key words: starter culture; bacteriophage; diversity; proteolytic activity
Economic performance and sustainability of a novel intercropping system on the north China plain
Huang, C. ; Liu, Q. ; Heerink, N.B.M. ; Stomph, T.J. ; Li, B. ; Liu, R. ; Zhang, H. ; Wang, C. ; Li, X. ; Zhang, C. ; Werf, W. van der; Zhang, F. - \ 2015
PLoS One 10 (2015)8. - ISSN 1932-6203 - 16 p.
reducing environmental risk - nutrient-use efficiency - food security - crop productivity - n management - resource use - agriculture - competition - fertilizer - diversity
Double cropping of wheat and maize is common on the North China Plain, but it provides limited income to rural households due to the small farm sizes in the region. Local farmers in Quzhou County have therefore innovated their production system by integration of watermelon as a companion cash crop into the system. We examine the economic performance and sustainability of this novel intercropping system using crop yield data from 2010 to 2012 and farm household survey data collected in 2012. Our results show that the gross margin of the intercropping system exceeded that of the double cropping system by more than 50% in 2012. Labor use in the intercropping system was more than three times that in double cropping. The lower returns per labor hour in intercropping, however, exceeded the average off-farm wage in the region by a significant margin. Nutrient surpluses and irrigation water use are significant larger under the intercropping system. We conclude that the novel wheat-maize/watermelon intercropping system contributes to rural poverty alleviation and household-level food security, by raising farm incomes and generating more employment, but needs further improvement to enhance its sustainability.
Effects of salinity on growth of plant species from terrestrializing fens
Stofberg, S.F. ; Klimkovska, A. ; Paulissen, M.P.C.P. ; Witte, J.Ph.M. ; Zee, S.E.A.T.M. van der - \ 2015
Aquatic Botany 121 (2015). - ISSN 0304-3770 - p. 83 - 90.
climate-change - water - tolerance - salt - nutrient - netherlands - macrophytes - competition - vegetation - diversity
Terrestrializing lowland fens may be temporarily exposed to elevated surface water salinity, which may have serious consequences for nature conservation. We investigated the response of five fresh water fen plant species to elevated salinity. In a controlled greenhouse experiment, these species were exposed to salt concentrations up to 3000 mg Cl- l-1. Total biomass of the five species together was significantly reduced for salinity levels from 200 mg Cl- l-1. Four individual species showed leaf death and relative growth rate reduction, with effects at 1000 mg Cl- l-1 for Succisa pratensis, Thelypteris palustris and Viola palustris, and 3000 mg Cl- l-1 for Myosotis scorpioides. Comarum palustre showed no significant (.05 level) sensitivity. Biomass distribution was investigated as well. Root-shoot ratio of four species was affected by salinity, which in at least two cases seemed to be related to leaf death. Differences in specific leaf area as a result of salinity were only observed for C. palustre. Dry matter content increased in four species as a result of salinity. Salinity tolerance did not correspond to the environmental distributions of the species, nor could species traits be related to tolerance. Surface water salinity may affect vegetation development in terrestrializing fens at low concentrations. A reduction of plant growth would cause reduced fitness of some species and may lead to reduced root mat growth. Exposure to higher concentrations could eventually lead to a decrease of species richness.
Can we infer plant facilitation from remote sensing? A test across global drylands
Xu, C. ; Holmgren, M. ; Nes, E.H. van; Maestre, F.T. ; Soliveres, S. ; Berdugo, M. ; Kefi, S. ; Marquet, P.A. ; Abades, S. ; Scheffer, M. - \ 2015
Ecological Applications 25 (2015)6. - ISSN 1051-0761 - p. 1456 - 1462.
positive interactions - vegetation patterns - spatial-patterns - ecosystems - desertification - distributions - environments - competition - dynamics - ecology
Facilitation is a major force shaping the structure and diversity of plant communities in terrestrial ecosystems. Detecting positive plant-plant interactions relies on the combination of field experimentation and the demonstration of spatial association between neighboring plants. This has often restricted the study of facilitation to particular sites, limiting the development of systematic assessments of facilitation over regional and global scales. Here we explore whether the frequency of plant spatial associations detected from high-resolution remotely-sensed images can be used to infer plant facilitation at the community level in drylands around the globe. We correlated the information from remotely-sensed images freely available through Google EarthTM with detailed field assessments, and used a simple individual-based model to generate patch-size distributions using different assumptions about the type and strength of plant-plant interactions. Most of the patterns found from the remotely-sensed images were more right-skewed than the patterns from the null model simulating a random distribution. This suggests that the plants in the studied drylands show stronger spatial clustering than expected by chance. We found that positive plant co-occurrence, as measured in the field, was significantly related to the skewness of vegetation patch-size distribution measured using Google EarthTM images. Our findings suggest that the relative frequency of facilitation may be inferred from spatial pattern signals measured from remotely-sensed images, since facilitation often determines positive co-occurrence among neighboring plants. They pave the road for a systematic global assessment of the role of facilitation in terrestrial ecosystems.
Elephant-mediated habitat modifications and changes in herbivore species assemblages in Sabi Sand, South Africa
Boer, W.F. de; Oort, J.W.A. van; Grover, M. ; Peel, M.J.S. - \ 2015
European Journal of Wildlife Research 61 (2015)4. - ISSN 1612-4642 - p. 491 - 503.
kruger-national-park - colophospermum-mopane - savanna vegetation - woodland structure - woody vegetation - competition - population - season - management - dynamics
Elephant Loxodonta africana conservation might indirectly influence the wider herbivore community structure, as elephants have the ability to significantly modify the savanna habitat. Uncertainty remains as to the consequences of these effects, as elephants might either compete with other species or facilitate foraging especially for grazers and smaller browsing species by increasing the amount of grass or the amount of browse at lower feeding heights. We studied these potential cascading effects of elephants by using 16 years of data (1992–2011) from the Sabi Sand Wildtuin, South Africa, which showed a steady increase in elephant densities from 0.12 to 2.03 elephants/km2 over this period. We demonstrate that tree densities, and browse availability at feeding heights below 2 m, decreased with increasing elephant densities, and that there was no positive effect of elephants on browse availability. The changes in elephant densities were good predictors (R 2 adj¿>¿0.50) in explaining population fluctuations of other herbivore species. The total body mass of grazers increased more than that of the browsers, shifting the community toward a grazer and megaherbivore-dominated community. An increasing density of elephants changes the composition of the herbivore community, as mesobrowsers are unable to benefit from the impact of elephants on trees, but megagrazers show strong positive responses. Hence, changes in elephant densities as a result of poaching or conservation may trigger cascading community effects. These are neglected but important consequences of (negative or positive) human impacts on elephant numbers, especially in restricted areas such as reserves and national parks.
The contribution of phenotypic plasticity to complementary light capture in plant mixtures
Zhu, J. ; Werf, W. van der; Anten, N.P.R. ; Vos, J. ; Evers, J.B. - \ 2015
New Phytologist 207 (2015)4. - ISSN 0028-646X - p. 1213 - 1222.
functional diversity - current knowledge - biodiversity - productivity - photosynthesis - competition - model - communities - variability - environment
Interspecific differences in functional traits are a key factor for explaining the positive diversity– productivity relationship in plant communities. However, the role of intraspecific variation attributable to phenotypic plasticity in diversity–productivity relationships has largely been overlooked. By taking a wheat (Triticum aestivum)–maize (Zea mays) intercrop as an elementary example of mixed vegetation, we show that plasticity in plant traits is an important factor contributing to complementary light capture in species mixtures. We conceptually separated net biodiversity effect into the effect attributable to interspecific trait differences and species distribution (community structure effect), and the effect attributable to phenotypic plasticity. Using a novel plant architectural modelling approach, whole vegetation light capture was simulated for scenarios with and without plasticity based on empirical plant trait data. Light capture was 23% higher in the intercrop with plasticity than the expected value from monocultures, of which 36% was attributable to community structure and 64% was attributable to plasticity. For wheat, plasticity in tillering was the main reason for increased light capture, whereas for intercropped maize, plasticity induced a major reduction in light capture. The results illustrate the potential of plasticity for enhancing resource acquisition in mixed stands, and indicate the importance of plasticity in the performance of species-diverse plant communities.
Combining a weed traits database with a population dynamics model predicts shifts in weed communities
Storkey, J. ; Holst, N. ; Bøjer, Q. ; Bigongiali, F. ; Bocci, G. ; Colbach, N. ; Dorner, Z. ; Riemens, M.M. ; Sartorato, I. ; Sønderskov, M. ; Verschwele, A. - \ 2015
Weed Research 55 (2015)2. - ISSN 0043-1737 - p. 206 - 218.
agricultural intensification - invertebrate abundance - functional diversity - assembly theory - climate-change - winter-wheat - plant - flora - management - competition
A functional approach to predicting shifts in weed floras in response to management or environmental change requires the combination of data on weed traits with analytical frameworks that capture the filtering effect of selection pressures on traits. A weed traits database (WTDB) was designed, populated and analysed, initially using data for 19 common European weeds, to begin to consolidate trait data in a single repository. The initial choice of traits was driven by the requirements of empirical models of weed population dynamics to identify correlations between traits and model parameters. These relationships were used to build a generic model, operating at the level of functional traits, to simulate the impact of increasing herbicide and fertiliser use on virtual weeds along gradients of seed weight and maximum height. The model generated ‘fitness contours’ (defined as population growth rates) within this trait space in different scenarios, onto which two sets of weed species, defined as common or declining in the UK, were mapped. The effect of increasing inputs on the weed flora was successfully simulated; 77% of common species were predicted to have stable or increasing populations under high fertiliser and herbicide use, in contrast with only 29% of the species that have declined. Future development of the WTDB will aim to increase the number of species covered, incorporate a wider range of traits and analyse intraspecific variability under contrasting management and environments.
Food Insecurity and Food Access in U.S. Metro Areas
Bonanno, A. ; Li, J. - \ 2015
Applied Economics Perspectives and Policy 37 (2015)2. - ISSN 2040-5790 - p. 177 - 204.
stamp program - wal-mart - neighborhood characteristics - united-states - competition - variables - models - participation - supercenters - endogeneity
Household food insecurity in the United States has reached its highest levels to date. As public and private initiatives have emerged to help improve diets by fostering access to food, the availability of more food stores may result in lower levels of food insecurity. In this article, we assess the relationship between adult food insecurity and food store density in metropolitan areas of the United States. We find that while small grocery/convenience stores show a mitigating effect on adult food insecurity across different samples of households, the effects of large supermarkets/grocery stores and supercenters vary. We also find that Supplemental Nutrition Assistance Program participation and food access can have a simultaneously beneficial effect in reducing adult food insecurity. Implications for policies aiming to improve food security by fostering access to food stores are discussed.
Disentangling above- and belowground neighbor effects on the growth, chemistry and arthropod community on a focal plant
Kos, M. ; Bukovinszky, T. ; Mulder, P.P.J. ; Bezemer, T.M. - \ 2015
Ecology 96 (2015)1. - ISSN 0012-9658 - p. 164 - 175.
soil feedback - associational susceptibility - vegetational diversity - competition - herbivores - root - resistance - responses - fertilization - density
Neighboring plants can influence arthropods on a focal plant and this can result in associational resistance or associational susceptibility. These effects can be mediated by above- and belowground interactions between the neighbor and focal plant, but determining the relative contribution of the above- and belowground effects remains an open challenge. We performed a common garden experiment with a design that enabled us to disentangle the above- and belowground effects of five different plant species on the growth and chemistry of the focal plant ragwort (Jacobaea vulgaris), and the arthropod community associated to this plant. Aboveground effects of different neighboring plant species were more important for the growth and quality of J. vulgaris and for the arthropod abundance on this plant than belowground effects of neighbors. This remained true when only indirect neighbor effects (via affecting the biomass or quality of the focal plant) were considered. The aboveground neighbor effects on arthropod abundance on the focal plant were strongly negative. However, the magnitude of the effect depended on the identity of the neighboring species, and herbivore abundance on the focal plant was higher when surrounded by conspecific than by heterospecific plants. We also observed interactions between above- and belowground neighbor effects, indicating that these effects may be non-additive. We conclude that above- and belowground associational effects are not equally strong, and that neighbor effects on plant-arthropod interactions occur predominantly aboveground.
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