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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Discovery of Sabellaria spinulosa reefs in an intensively fished area of the Dutch Continental Shelf, North Sea
Reijden, Karin J. Van Der; Koop, Leo ; O'flynn, Sarah ; Garcia, Silvia ; Bos, Oscar ; Sluis, Christiaan Van; Maaholm, David J. ; Herman, Peter M.J. ; Simons, Dick G. ; Olff, Han ; Ysebaert, Tom ; Snellen, Mirjam ; Govers, Laura L. ; Rijnsdorp, Adriaan D. ; Aguilar, Ricardo - \ 2019
Journal of Sea Research 144 (2019). - ISSN 1385-1101 - p. 85 - 94.
Biogenic Reef - Brown Bank - Ecosystem Engineer - Sabellaria spinulosa - North Sea
The tube-building polychaete Sabellaria spinulosa (Ross worm) can form conspicuous biogenic reefs that stabilize the seabed and increase biodiversity by providing a habitat for a multitude of other species. These reefs, however, are assumed to be vulnerable to human-induced physical disturbances of the seabed. In the Greater North Sea, S. spinulosa reefs are recognized to be under threat and worthy of protection. In August 2017, three S. spinulosa reefs with a minimum extent of 1016m2 were discovered in the Dutch Brown Bank area. This area comprises a large-scale sandbank and adjacent troughs. The reefs were found within the sandbank troughs, which have proven to be subject to high demersal fishing intensities (fished>5 times a year). Detailed bathymetry measurements showed that S. spinulosa reefs were mainly located within valleys of smaller-scaled sand waves, which have a perpendicular orientation compared to the large-scale sandbank structure of the Brown Bank. We hypothesize that the valleys in between sand waves offer suitable substrate for settlement and refuge from abrasion by fishing activities, enabling the S. spinulosa reefs to persist despite high fishing intensities. ROV footage of the reefs showed higher estimates of species abundances on the reefs compared with adjacent habitats, with some species present that are typical for hard substrate (rock gunnel, Pholis gunnellus; edible crab, Cancer pagurus; and velvet swimming crab, Necora puber). The information presented could be used for drafting management policies to protect these reefs, as Contracting Parties of the OSPAR Convention are committed to take measures and protect biodiversity.
Data from: Agricultural pastures challenge the attractiveness of natural saltmarsh for a migratory goose
Dokter, A.M. ; Fokkema, Wimke ; Ebbinge, B.S. ; Olff, H. ; Jeugd, Henk P. van der; Nolet, B.A. - \ 2018
NIOO-KNAW
pastures - saltmarsh - brent geese - human-goose conflict - accelerometer - GPS tracking - intertidal - habitat switching - migration - fuelling
Broad-scale land conversions and fertilizer use have dramatically altered the available staging area for herbivorous long-distance migrants. Instead of natural land, these birds rely increasingly on pastures for migratory fuelling and stopover, often conflicting with farming practices. To be able to predict and manage birds’ future habitat use, the relative advantages and disadvantages of natural (e.g. saltmarsh, intertidal) versus anthropogenic staging sites for foraging need to be understood. 2. We compared the migratory staging of brent geese on saltmarsh and pasture sites in spring. Food quality (nitrogen and fibre content), intra-specific antagonistic behaviour, and body weight were quantified at nearby sites in simultaneous seasons. Individuals were tracked with high-resolution GPS and accelerometers to compare timing of migration and time-budgets during fuelling. 3. On pastures, birds rested more and experienced higher ingestion rates, similar or superior food quality and reduced antagonistic interactions than on saltmarsh. 4. Brent geese using fertilized grasslands advanced their fuelling and migration schedules compared to those using saltmarsh. Pasture birds reached heavy weights earlier, departed sooner, and arrived in the Arctic earlier. 5. Intertidal mudflats were frequently visited by saltmarsh birds during the day, and available food there (algae, some seagrass) was of higher quality than terrestrial resources. Availability of intertidal resources was an important factor balancing the otherwise more favourable conditions on pastures relative to saltmarsh. 6. Policy implications: Disadvantages of longer foraging effort, more antagonistic interactions and delayed fuelling schedules on traditional saltmarshes may cause a trend of geese exchanging this traditional niche in favour of pastures, especially in a warming climate that requires advancement of migratory schedules. However, the high quality of intertidal forage allows it to complement terrestrial foraging, potentially removing the incentive for habitat switches to pastures. The relatively high quality of green algae and seagrass, and birds’ remarkable preference for these resources when available, provides a key for managers to create landscapes that can sustain this specialist’s intertidal lifestyle. To keep natural habitats attractive to staging geese with the purpose to prevent conflicts with farming practices, management actions should focus on conservation and restoration of saltmarsh and especially intertidal habitat.
Data from: Body stores persist as fitness correlate in a long-distance migrant released from food constraints
Dokter, Adriaan M. ; Fokkema, Wimke ; Bekker, Steven K. ; Bouten, Willem ; Ebbinge, B.S. ; Muskens, G.J.D.M. ; Olff, H. ; Jeugd, Henk P. van der; Nolet, B.A. - \ 2018
arctic waterfowl - cultivated grassland - recruitment - GPS tracking - migratory fueling - carry-over effects
Long-distance migratory birds rely on acquisition of body reserves to fuel their migration and reproduction. Breeding success depends on the amount of body reserve acquired prior to migration, which is thought to increase with access to food at the fuelling site. Here we studied how food abundance during fuelling affected time budgets and reproductive success. In a regime of plenty, we expected that (1) limitations on food harvesting would become lifted, allowing birds to frequently idle, and (2) that birds would reach sufficient fuel loads, such that departure weight would no longer affect reproductive success. Our study system comprised brent geese (Branta b. bernicla) staging on high-quality agricultural pastures. Fuelling conditions were assessed by a combination of high-resolution GPS-tracking, acceleration-based behavioural classification, thermoregulation modelling, and measurements of food digestibility and excretion rates. Mark-resighting analysis was used to test for correlations between departure weight and offspring recruitment. Our results confirm that birds loafed extensively, actively postponed fuelling in early spring, and took frequent digestion pauses, suggesting that traditional time constraints on harvest and fuelling rates are absent on modern-day fertilized grasslands. Nonetheless, departure weight remained correlated with recruitment success. The persistence of this correlation after a prolonged stopover with access to abundant high-quality food, suggests that between-individual differences in departure condition are not so much enforced by food quality and availability during stopover, but reflect individual quality and longer-lived life-history traits, such as health status and digestive capacity, which may be developed before the fuelling period.
North Sea demersal fisheries prefer specific benthic habitats
Reijden, Karin J. van der; Hintzen, Niels T. ; Govers, Laura L. ; Rijnsdorp, Adriaan D. ; Olff, Han - \ 2018
PLoS ONE 13 (2018)12. - ISSN 1932-6203

Introduction The future protection of marine biodiversity through good conservation planning requires both the identification of key habitats with unique ecological characteristics and detailed knowledge of their human utilization through fisheries. Demersal fisheries are important disturbers of benthic habitats. They often have a heterogeneous spatial distribution, pressurizing particular habitats with high abundances of target species. For the North Sea, we quantified the commonness/rarity of habitats in relation to the environmental determinants of so-called fishing hotspots, to support better-informed conservation planning of benthic habitats in this intensively used continental shelf. Methods We first distinguished 9 main seascapes in the study area based on seabed morphology. Secondly, we determined average fishing intensity and fishing hotspots using VMS-data for the three dominant Dutch fisheries from 2008 to 2015: beam-trawlers targeting sole Solea solea (Beam-Sole), beam-trawlers targeting plaice Pleuronectes platessa (Beam-Plaice), and otter-trawlers targeting Norway lobster Nephrops norvegicus and demersal fish (Otter-Mix). Within the seascapes subjected to >80% of the fishing activity, nineteen environmental factors (summarized by PCA) were used to ecologically characterize fishing hotspot locations using MaxEnt response modelling. Results We found that all three fisheries target highly specific, uncommon habitats. Beam-Sole fishers targeted warmer, shallow, dynamic, nearshore habitats, and within these specifically the depressions between sand ridges. Beam-Plaice fishers mainly targeted the exposed, non-muddy flanks of the Dogger Bank and similar large-scale elevations (50–75 km) where especially the ridges of smaller sand banks are used. Otter-Mix fisheries concentrated in areas with low bed shear stress, located in muddy, relatively deeper areas. Implications This study is the first to provide insight in benthic habitat types that are frequently targeted by fishers in the North Sea. We demonstrated unequal exploitation pressure between seabed habitats, with the majority of hotspots in the less common habitats. Our results hence contribute to a more effective, ecologically informed planning for the protection and monitoring of all seabed habitats and biodiversity of the North Sea.

Agricultural pastures challenge the attractiveness of natural saltmarsh for a migratory goose
Dokter, Adriaan M. ; Fokkema, Wimke ; Ebbinge, Barwolt S. ; Olff, Han ; Jeugd, Henk P. van der; Nolet, Bart A. - \ 2018
Journal of Applied Ecology 55 (2018)6. - ISSN 0021-8901 - p. 2707 - 2718.
accelerometer - brent geese - GPS tracking - habitat switching - human–goose conflict - migration - pastures - saltmarsh

Broad-scale land conversions and fertilizer use have dramatically altered the available staging area for herbivorous long-distance migrants. Instead of natural land, these birds rely increasingly on pastures for migratory fuelling and stopover, often conflicting with farming practices. To predict and manage birds’ future habitat use, the relative advantages and disadvantages of natural (e.g. saltmarsh, intertidal) versus anthropogenic staging sites for foraging need to be understood. We compared the migratory staging of brent geese on saltmarsh and pasture sites in spring. Food quality (nitrogen and fibre content), antagonistic behaviour, and body weight were quantified at nearby sites in simultaneous seasons. Individuals were tracked with high-resolution GPS and accelerometers to compare timing of migration and time budgets during fuelling. On pastures, birds rested more and experienced higher ingestion rates, similar or superior food quality and reduced antagonistic interactions than on saltmarsh. Brent geese using fertilized grasslands advanced their fuelling and migration schedules compared to those using saltmarsh. Pasture birds reached heavy weights earlier, departed sooner, and arrived in the Arctic earlier. Intertidal mudflats were frequently visited by saltmarsh birds during the day, and available food there (algae, some seagrass) was of higher quality than terrestrial resources. Availability of intertidal resources was an important factor balancing the otherwise more favourable conditions on pastures relative to saltmarsh. Synthesis and applications. Disadvantages of longer foraging effort, more antagonistic interactions and delayed fuelling schedules on traditional saltmarshes may cause geese to exchange this traditional niche in favour of pastures, especially in a warming climate that requires advancement of migratory schedules. However, due to its high quality, intertidal forage can complement terrestrial foraging, potentially removing the incentive for habitat switches to pastures. The relatively high quality of green algae and seagrass, and birds’ remarkable preference for these resources when available, provides a key for managers to create landscapes that can sustain this specialist’s intertidal lifestyle. To keep natural habitats attractive to staging geese with the purpose of preventing conflicts with farming practices, management actions should focus on conservation and restoration of saltmarsh and especially intertidal habitat.

Body stores persist as fitness correlate in a long-distance migrant released from food constraints
Dokter, Adriaan M. ; Fokkema, Wimke ; Bekker, Steven K. ; Bouten, Willem ; Ebbinge, Barwolt S. ; Müskens, Gerard ; Olff, Han ; Jeugd, Henk P. van der; Nolet, Bart A. - \ 2018
Behavioral Ecology 29 (2018)5. - ISSN 1045-2249 - p. 1157 - 1166.
arctic waterfowl - carry-over effects - cultivated grassland - GPS tracking - migratory fueling - recruitment

Long-distance migratory birds rely on the acquisition of body stores to fuel their migration and reproduction. Breeding success depends on the amount of body stores acquired prior to migration, which is thought to increase with access to food at the fueling site. Here, we studied how food abundance during fueling affected time budgets and reproductive success. In a regime of plenty, we expected that 1) limitations on food harvesting would become lifted, allowing birds to frequently idle, and 2) birds would reach sufficient fuel loads, such that departure weight would no longer affect reproductive success. Our study system comprised brent geese (Branta b. bernicla) staging on high-quality agricultural pastures. Fueling conditions were assessed by a combination of high-resolution GPS tracking, acceleration-based behavioral classification, thermoregulation modeling, and measurements of food digestibility and excretion rates. Mark-resighting analysis was used to test for correlations between departure weight and offspring recruitment. Our results confirm that birds loafed extensively, actively postponed fueling in early spring, and took frequent digestion pauses, suggesting that traditional time constraints on harvest and fueling rates are absent on modern-day fertilized grasslands. Nonetheless, departure weight remained correlated with recruitment success. The persistence of this correlation after a prolonged stopover with access to abundant high-quality food, suggests that between-individual differences in departure condition are not so much enforced by food quality and availability during stopover, but reflect individual quality and longer-lived life-history traits, such as health status and digestive capacity, which may be developed before the fueling period.

Biotic resistance affects growth and reproduction, but not survival of a high-impact woody invader in African savannas
Beest, Mariska te; Mpandza, Nokukhanya J. ; Olff, Han - \ 2018
Journal of Vegetation Science 29 (2018)3. - ISSN 1100-9233 - p. 532 - 540.
Chromolaena odorata - Colonization - Drought - Exotic species - Experiment - Grassland - Impact - Invasion - Moisture - Persistence - Water availability
Question: Biotic resistance is defined as the reduction in invasion success caused by the native community through competition, herbivory and/or pathogens. Biotic resistance has mostly been studied during the initial stages of invasion. However, to what extent biotic resistance hampers survival, or persistence, of invaders in the longer term is often not known. We studied how native grassland communities affected growth, reproduction and survival during the adult life stage of the high-impact woody invader Chromolaena odorata under different water availability treatments. Location: Hluhluwe-iMfolozi Park, South Africa. Methods: We performed a 2-years full-factorial field experiment in a savanna grassland where we manipulated water availability and neighbouring vegetation; in one-third of the plots vegetation was cleared and planted with C. odorata monocultures, in one-third C. odorata shrubs were planted in grasslands, and one-third were unplanted grassland controls. Results: Growth and reproduction of adult C. odorata were greatly reduced due to competition with native grasses, but not survival of C. odorata. Shrub survival was high and did not differ in plots with and without grass. Water availability did not affect growth, reproduction and competitive ability of C. odorata, but higher water availability did increase the competitive ability of the grasses. Soil moisture levels were lower in grasslands planted with C. odorata compared to unplanted controls, independent of the water treatment, suggesting higher water use of C. odorata compared to native grasses. Conclusions: Savanna grasslands have a strong competitive effect on invasion by the exotic woody shrub C. odorata, reducing growth and reproduction, but not survival of the shrub. We found no evidence that biotic resistance was stronger under more unfavourable abiotic conditions, as C. odorata was equally impacted in all water treatments. The high survival rates of C. odorata suggest that competitive interactions are not likely to prevent invader persistence in the landscape. Invader persistence is important in determining longer-term invasion success as well as invader impact, and the concept of persistence should not be overlooked in studies on invasive species.
Unexpected dietary preferences of Eurasian Spoonbills in the Dutch Wadden Sea: spoonbills mainly feed on small fish not shrimp
Jouta, Jeltje ; Goeij, Petra De; Lok, Tamar ; Velilla, Estefania ; Camphuysen, Cornelis J. ; Leopold, Mardik ; Veer, Henk W. Van Der; Olff, Han ; Overdijk, Otto ; Piersma, Theunis - \ 2018
Journal of Ornithology 159 (2018)3. - ISSN 2193-7192 - p. 839 - 849.
Platalea leucorodia leucorodia - Regurgitate analysis - Restoration - Stable isotope analysis in R - Intertidal - Bayesian mixing models
After an historical absence, over the last decades Eurasian Spoonbills Platalea leucorodia leucorodia have returned to breed on the barrier islands of the Wadden Sea. The area offers an abundance of predator-free nesting habitat, low degrees of disturbance, and an extensive intertidal feeding area with increasing stocks of brown shrimp Crangon crangon, the assumed main prey of P. leucorodia leucorodia. Nevertheless, newly established and expanding colonies of spoonbills have surprisingly quickly reached plateau levels. Here we tested the often stated assertion that spoonbills mainly rely on brown shrimp as food, by quantifying the diet of chicks on the basis of regurgitates and by analysis of blood isotopes using stable isotope Bayesian mixing models. Both methods showed that, rather than brown shrimp being the staple food of spoonbill chicks,
small flatfish (especially plaice Pleuronectes platessa) and gobies (Pomatoschistus spp.) were their main prey. Unlike shrimp, small flatfish have been reported to be rather scarce in the Wadden Sea in recent years, which may explain the rapid saturation of colony size due to food-related density-dependent recruitment declines of growing colonies. By way of their diet and colony growth characteristics, spoonbills may thus indicate the availability of small fish in the Wadden Sea. We predict that the recovery to former densities of young flatfish and other juvenile/small fish in the Wadden Sea will be tracked by changing diets (more fish) and an increase in the size of Eurasian Spoonbill colonies across the Wadden Sea.
Benthic primary producers are key to sustain the Wadden Sea food web : stable carbon isotope analysis at landscape scale
Christianen, M.J.A. ; Middelburg, J.J. ; Holthuijsen, S.J. ; Jouta, J. ; Compton, T.J. ; Heide, T. van der; Piersma, T. ; Sinninghe Damsté, J.S. ; Veer, H.W. van der; Schouten, S. ; Olff, H. - \ 2017
Ecology 98 (2017)6. - ISSN 0012-9658 - p. 1498 - 1512.
carbon subsidy - coastal food web - Dutch Wadden Sea - estuary - macrobenthos - stable carbon isotopes - tidal wetland ecosystem
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.
Biodiversity and food web indicators of community recovery in intertidal shellfish reefs
Christianen, M.J.A. ; Heide, T. van der; Holthuijsen, S.J. ; Reijden, K.J. van der; Borst, A.C.W. ; Olff, H. - \ 2017
Biological Conservation 213 (2017). - ISSN 0006-3207 - p. 317 - 324.
Biodiversity - Ecological networks - Facilitation - Foundation species - Habitat modification - Trophic interactions
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).
Data from: How habitat-modifying organisms structure the food web of two coastal ecosystems
Zee, Els M. van der; Angelini, Christine ; Govers, Laura L. ; Christianen, M.J.A. ; Altieri, Andrew H. ; Reijden, K.J. van der; Silliman, Brian R. ; Koppel, Johan van de; Geest, Matthijs van der; Gils, Jan A. van; Veer, Henk W. van der; Piersma, Theunis ; Ruiter, P.C. de; Olff, H. ; Heide, Tjisse van der - \ 2016
food web - non-trophic interactions - foundation species - ecological networks - ecosystem engineering - facilitation
The diversity and structure of ecosystems has been found to depend both on trophic interactions in food webs and on other species interactions such as habitat modification and mutualism that form non-trophic interaction networks. However, quantification of the dependencies between these two main interaction networks has remained elusive. In this study, we assessed how habitat-modifying organisms affect basic food web properties by conducting in-depth empirical investigations of two ecosystems: North American temperate fringing marshes and West African tropical seagrass meadows. Results reveal that habitat-modifying species, through non-trophic facilitation rather than their trophic role, enhance species richness across multiple trophic levels, increase the number of interactions per species (link density), but decrease the realized fraction of all possible links within the food web (connectance). Compared to the trophic role of the most highly connected species, we found this non-trophic effects to be more important for species richness and of more or similar importance for link density and connectance. Our findings demonstrate that food webs can be fundamentally shaped by interactions outside the trophic network, yet intrinsic to the species participating in it. Better integration of non-trophic interactions in food web analyses may therefore strongly contribute to their explanatory and predictive capacity.
How habitat-modifying organisms structure the food web of two coastal ecosystems
Zee, Els M. van der; Angelini, Christine ; Govers, Laura L. ; Christianen, Marjolijn J.A. ; Altieri, Andrew H. ; Reijden, Karin J. van der; Silliman, Brian R. ; Koppel, Johan van de; Geest, Matthijs van der; Gils, Jan A. van; Veer, Henk W. van der; Piersma, Theunis ; Ruiter, Peter C. de; Olff, Han ; Heide, Tjisse van der - \ 2016
Proceedings of the Royal Society. B: Biological Sciences 283 (2016)1826. - ISSN 0962-8452 - 9 p.
Consumer–resource interactions - Ecological networks - Ecosystem engineering - Facilitation - Foundation species - Non-trophic interactions
The diversity and structure of ecosystems has been found to depend both on trophic interactions in food webs and on other species interactions such as habitat modification and mutualism that form non-trophic interaction networks. However, quantification of the dependencies between these two main interaction networks has remained elusive. In this study, we assessed how habitat-modifying organisms affect basic food web properties by conducting in-depth empirical investigations of two ecosystems: North American temperate fringing marshes and West African tropical seagrass meadows. Results reveal that habitat-modifying species, through non-trophic facilitation rather than their trophic role, enhance species richness across multiple trophic levels, increase the number of interactions per species (link density), but decrease the realized fraction of all possible links within the food web (connectance). Compared to the trophic role of the most highly connected species, we found this non-trophic effects to be more important for species richness and of more or similar importance for link density and connectance. Our findings demonstrate that food webs can be fundamentally shaped by interactions outside the trophic network, yet intrinsic to the species participating in it. Better integration of non-trophic interactions in food web analyses may therefore strongly contribute to their explanatory and predictive capacity.
Drought, Mutualism Breakdown, and Landscape-Scale Degradation of Seagrass Beds
Fouw, Jimmy de; Govers, Laura L. ; Koppel, Johan van de; Belzen, Jim van; Dorigo, Wouter ; Sidi Cheikh, Mohammed A. ; Christianen, Marjolijn J.A. ; Reijden, Karin J. van der; Geest, Matthijs van der; Piersma, Theunis ; Smolders, Alfons J.P. ; Olff, Han ; Lamers, Leon P.M. ; Gils, Jan A. van; Heide, Tjisse van der - \ 2016
Current Biology 26 (2016)8. - ISSN 0960-9822 - p. 1051 - 1056.
In many marine ecosystems, biodiversity critically depends on foundation species such as corals and seagrasses that engage in mutualistic interactions [1-3]. Concerns grow that environmental disruption of marine mutualisms exacerbates ecosystem degradation, with breakdown of the obligate coral mutualism ("coral bleaching") being an iconic example [2, 4, 5]. However, as these mutualisms are mostly facultative rather than obligate, it remains unclear whether mutualism breakdown is a common risk in marine ecosystems, and thus a potential accelerator of ecosystem degradation. Here, we provide evidence that drought triggered landscape-scale seagrass degradation and show the consequent failure of a facultative mutualistic feedback between seagrass and sulfide-consuming lucinid bivalves that in turn appeared to exacerbate the observed collapse. Local climate and remote sensing analyses revealed seagrass collapse after a summer with intense low-tide drought stress. Potential analysis - a novel approach to detect feedback-mediated state shifts - revealed two attractors (healthy and degraded states) during the collapse, suggesting that the drought disrupted internal feedbacks to cause abrupt, patch-wise degradation. Field measurements comparing degraded patches that were healthy before the collapse with patches that remained healthy demonstrated that bivalves declined dramatically in degrading patches with associated high sediment sulfide concentrations, confirming the breakdown of the mutualistic seagrass-lucinid feedback. Our findings indicate that drought triggered mutualism breakdown, resulting in toxic sulfide concentrations that aggravated seagrass degradation. We conclude that external disturbances can cause sudden breakdown of facultative marine mutualistic feedbacks. As this may amplify ecosystem degradation, we suggest including mutualisms in marine conservation and restoration approaches.
Data from: Facultative grazing and bioturbation by macrodetritivores alter saltmarsh plant-plant interactions under stress
Howison, Ruth A. ; Olff, H. ; Puijenbroek, M.E.B. van; Smit, Christian - \ 2016
abiotic stress - bioturbation - facultative grazing - plant-plant interactions - salt marsh - stress gradient hypothesis - water logging - Elytrigia atherica - Festuca rubra - Orchestia gammarellus - holocene
The importance of positive plant-plant interactions is generally suggested to increase towards more stressful conditions, due to mutual stress amelioration between plants. Bioturbating macrodetritivores can also ameliorate stress through bioturbation, but can also become selective herbivores under food-limited conditions, making the outcome of plant-plant interactions under stress in the presence of macrodetritivores unclear. We studied how combining environmental stress (waterlogging) with the presence of the soil macrodetritivore Orchestia gammarellus affected the outcome of the interaction between two salt marsh plants: the tall, late successional Elytrigia atherica and the shorter, early successional Festuca rubra. In a replacement design competition experiment under controlled conditions, we found that soil redox potential was negatively affected by waterlogging and positively affected by the presence of O. gammarellus. The survival and shoot biomass of E. atherica was not significantly affected by waterlogging or by the presence of bioturbators. The survival and shoot biomass of F. rubra was especially decreased when waterlogging was combined with the presence of O. gammarellus, as this macrodetritivore turned into a selective grazer on F. rubra under these conditions. We found that E. atherica produced double shoot biomass and F. rubra produced much less shoot biomass in their mixed cultures than was expected from the monocultures of same waterlogging/Orchestia treatments. Hence, the presence of the bioturbator strongly promoted the competitive advantage of E. atherica over F. rubra due to the combination of stress amelioration for the first species and selective herbivory on the second species. Synthesis: This study shows that the inclusion of bioturbating macrodetritivores complicates the standard prediction that plant-plant interactions become more positive towards more stressful conditions. A novel insight is that macrodetritivores can affect the structure and diversity of plant communities through multiple mechanisms. Under benign conditions bioturbating macrodetritivores ameliorated soil conditions, permitting co-occurrence of competing plant species. At high environmental stress (waterlogging) macrodetritivores selectively graze higher quality plant species and emerging seedlings, thus promoting dominance of the lower quality species. Hence the facultative feeding behavior of macrodetritivores deserves further attention
Facultative grazing and bioturbation by macrodetritivores alter saltmarsh plant–plant interactions under stress
Howison, Ruth A. ; Olff, H. ; Puijenbroek, M.E.B. van; Smit, Christian - \ 2016
Journal of Ecology 104 (2016)4. - ISSN 0022-0477 - p. 1149 - 1157.
1.The importance of positive plant–plant interactions is generally suggested to increase towards more stressful conditions, due to mutual stress amelioration between plants. Bioturbating macrodetritivores can also ameliorate stress through bioturbation, but can also become selective herbivores under food-limited conditions, making the outcome of plant–plant interactions under stress in the presence of macrodetritivores unclear.
2.We studied how combining environmental stress (waterlogging) with the presence of the soil macrodetritivore Orchestia gammarellus affected the outcome of the interaction between two salt marsh plants: the tall, late successional Elytrigia atherica and the shorter, early successional Festuca rubra.
3.In a replacement design competition experiment under controlled conditions, we found that soil redox potential was negatively affected by waterlogging and positively affected by the presence of O. gammarellus. The survival and shoot biomass of E. atherica was not significantly affected by waterlogging or by the presence of bioturbators. The survival and shoot biomass of F. rubra was especially decreased when waterlogging was combined with the presence of O. gammarellus, as this macrodetritivore turned into a selective grazer on F. rubra under these conditions.
4.We found that E. atherica produced double shoot biomass and F. rubra produced much less shoot biomass in their mixed cultures than was expected from the monocultures of same waterlogging/Orchestia treatments. Hence, the presence of the bioturbator strongly promoted the competitive advantage of E. atherica over F. rubra due to the combination of stress amelioration for the first species and selective herbivory on the second species.
5.Synthesis. This study shows that the inclusion of bioturbating macrodetritivores complicates the standard prediction that plant–plant interactions become more positive towards more stressful conditions. A novel insight is that macrodetritivores can affect the structure and diversity of plant communities through multiple mechanisms. Under benign conditions bioturbating macrodetritivores ameliorated soil conditions, permitting co-occurrence of competing plant species. At high environmental stress (waterlogging) macrodetritivores selectively graze higher quality plant species and emerging seedlings, thus promoting dominance of the lower quality species. Hence, the facultative feeding behaviour of macrodetritivores deserves further attention.
Indirect interactions among tropical tree species through shared rodent seed predators: a novel mechanism of tree species coexistence
Garzon-Lopez, C.X. ; Ballesteros-Mejia, L. ; Ordonez, A. ; Bohlman, S.A. ; Olff, H. ; Jansen, P.A. - \ 2015
Ecology Letters 18 (2015)8. - ISSN 1461-023X - p. 752 - 760.
rain-forest tree - apparent competition - density-dependence - spatial autocorrelation - plant recruitment - dispersal - palm - herbivores - diversity - survival
The coexistence of numerous tree species in tropical forests is commonly explained by negative dependence of recruitment on the conspecific seed and tree density due to specialist natural enemies that attack seeds and seedlings (‘Janzen–Connell’ effects). Less known is whether guilds of shared seed predators can induce a negative dependence of recruitment on the density of different species of the same plant functional group. We studied 54 plots in tropical forest on Barro Colorado Island, Panama, with contrasting mature tree densities of three coexisting large seeded tree species with shared seed predators. Levels of seed predation were far better explained by incorporating seed densities of all three focal species than by conspecific seed density alone. Both positive and negative density dependencies were observed for different species combinations. Thus, indirect interactions via shared seed predators can either promote or reduce the coexistence of different plant functional groups in tropical forest.
Effects of large herbivores on grassland arthropod diversity
Klink, R. van; Plas, F. van der; Noordwijk, C.G.E. ; Wallis de Vries, M.F. ; Olff, H. - \ 2015
Biological Reviews 90 (2015)2. - ISSN 1464-7931 - p. 347 - 366.
ungrazed chalk grassland - ground beetle coleoptera - plant-species richness - grazing management - phytophagous insects - seminatural grasslands - community structure - tallgrass prairie - long-term - butterfly communities
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.
Pattern formation at multiple spatial scales drives the resilience of mussel bed ecosystems
Liu, Q. ; Herman, P.M.J. ; Mooij, W.M. ; Huisman, J. ; Scheffer, M. ; Olff, H. ; Koppel, J. van de - \ 2014
Nature Communications 5 (2014). - ISSN 2041-1723
self-organization - trade-offs - dynamics - systems - model
Self-organized complexity at multiple spatial scales is a distinctive characteristic of biological systems. Yet, little is known about how different self-organizing processes operating at different spatial scales interact to determine ecosystem functioning. Here we show that the interplay between self-organizing processes at individual and ecosystem level is a key determinant of the functioning and resilience of mussel beds. In mussel beds, self-organization generates spatial patterns at two characteristic spatial scales: small-scale net-shaped patterns due to behavioural aggregation of individuals, and large-scale banded patterns due to the interplay of between-mussel facilitation and resource depletion. Model analysis reveals that the interaction between these behavioural and ecosystem-level mechanisms increases mussel bed resilience, enables persistence under deteriorating conditions and makes them less prone to catastrophic collapse. Our analysis highlights that interactions between different forms of self-organization at multiple spatial scales may enhance the intrinsic ability of ecosystems to withstand both natural and human-induced disturbances.
Grazing-induced changes in plant–soil feedback alter plant biomass allocation
Veen, C.F. ; Vries, S. de; Bakker, E.S. ; Putten, W.H. van der; Olff, H. - \ 2014
Oikos 123 (2014)7. - ISSN 0030-1299 - p. 800 - 806.
tallgrass prairie - borne pathogens - invasive plant - grassland - herbivores - community - competition - coexistence - defoliation - diversity
Large vertebrate herbivores, as well as plant–soil feedback interactions are important drivers of plant performance, plant community composition and vegetation dynamics in terrestrial ecosystems. However, it is poorly understood whether and how large vertebrate herbivores and plant–soil feedback effects interact. Here, we study the response of grassland plant species to grazing-induced legacy effects in the soil and we explore whether these plant responses can help us to understand long-term vegetation dynamics in the field. In a greenhouse experiment we tested the response of four grassland plant species, Agrostis capillaris, Festuca rubra, Holcus lanatus and Rumex acetosa, to field-conditioned soils from grazed and ungrazed grassland. We relate these responses to long-term vegetation data from a grassland exclosure experiment in the field. In the greenhouse experiment, we found that total biomass production and biomass allocation to roots was higher in soils from grazed than from ungrazed plots. There were only few relationships between plant production in the greenhouse and the abundance of conspecifics in the field. Spatiotemporal patterns in plant community composition were more stable in grazed than ungrazed grassland plots, but were not related to plant–soil feedbacks effects and biomass allocation patterns. We conclude that grazing-induced soil legacy effects mainly influenced plant biomass allocation patterns, but could not explain altered vegetation dynamics in grazed grasslands. Consequently, the direct effects of grazing on plant community composition (e.g. through modifying light competition or differences in grazing tolerance) appear to overrule indirect effects through changes in plant–soil feedback.
Effects of sampling scale on patterns of habitat association in tropical trees
Garzon-Lopez, C.X. ; Jansen, P.A. ; Bohlman, S.A. ; Ordonez, A. ; Olff, H. - \ 2014
Journal of Vegetation Science 25 (2014)2. - ISSN 1100-9233 - p. 349 - 362.
rain-forest trees - spatial-patterns - environmental heterogeneity - recruitment limitation - mesoscale distribution - ecological community - neotropical forest - neutral theory - landscape - distributions
Questions: Niche differentiation is a central explanation for the co-existence and distribution patterns of numerous tree species in tropical forests, but functional equivalence leading to neutral dynamics has been proposed as an alternative explanation. This niche vs neutral debate is fuelled by the highly variable results yielded by studies of the association between tree species distributions and environmental factors, where some studies find strong associations but others do not. Here, we ask how differences in sampling scale between studies contribute to this variation. Location: Barro Colorado Island, Panama. Methods: Using distribution maps of canopy-statured individuals, we evaluated patterns of habitat association in five tropical tree species on Barro Colorado Island across a wide range of sampling scales (from 50 to 1600 ha). We investigated the scale-dependency of species clumping patterns (Ripley's K) and the association of species distributions with important environmental variables (forest age, topography and geological formation) using point pattern analyses. Results: Clump size and clump density had high variances within and among spatial scales. Significant habitat associations were found in all five species, with the number of habitat associations generally increasing with the sampling scale. Ignoring dispersal constraints inflated the number of significant habitat associations. Conclusions: We found that patterns of habitat association (and hence conclusions on the importance of niche vs neutral processes) are strongly affected by the choice of sampling scale and location. Explicit inclusion of the effect of spatial scale is critical for studies of habitat association and the main processes that structure communities of tropical trees.
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