The Experts below are selected from a list of 447882 Experts worldwide ranked by ideXlab platform
Brian R Silliman - One of the best experts on this subject based on the ideXlab platform.
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Top-Down Control of foundation species recovery during coastal wetland restoration.
The Science of the total environment, 2021Co-Authors: Wanqing Qian, Jianshe Chen, Qun Zhang, Brian R SillimanAbstract:Abstract Restoration has been increasingly adopted to halt trends in coastal wetland loss globally. Existing restoration often assumes that once abiotic stress is relieved, disturbances are prevented, and invasive species are eradicated, coastal wetlands will recover if propagules of native species are supplied either through natural dispersal or planting. Whether other factors including consumers can help explain the often suboptimal performance of existing restoration remains poorly understood. In a series of field experiments in the Yangtze estuary, we examined the relative importance of abiotic stress and crab grazing in regulating the recovery of the native foundation plant species Scirpus mariqueter in salt marsh areas where exotic cordgrass was successfully eradicated. We found that grazing by herbivorous crabs, rather than abiotic stress, was the primary obstacle restricting the recovery of planted Scirpus. This negative effect of crab grazing varied predictably across elevation and was strongest at low elevations where abiotic conditions were positive for Scirpus. These findings highlight that i) measures to Control crab grazing are needed to enhance the success of Scirpus restoration, even in areas where abiotic conditions are set to be optimal, and ii) restoration measures purely focused on reducing abiotic stress could be ineffective or suboptimal in field conditions, likely jeopardizing restoration investment and success. Since Top-Down Control of foundation plant species is common in many coastal wetlands and can be especially important in degraded systems where herbivores are abundant, we urge that future coastal wetland restoration assesses for the impacts of grazers and, when present, apply intervention measures.
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top down Control of spartina alterniflora production by periwinkle grazing in a virginia salt marsh
Ecology, 2001Co-Authors: Brian R Silliman, Jay C ZiemanAbstract:Top-Down forces, such as grazing and predation, have long been thought to be unimportant in Controlling plant growth in salt marshes. Instead, bottom-up forces, such as porewater ammonium and oxygen availability, are thought to be the primary regulating factors. In the field, we observed the periwinkle, Littoraria irrorata, grazing on live saltmarsh cordgrass, Spartina alterniflora. To examine the relative importance of periwinkle grazing and nutrient availability in Controlling marsh grass growth, we manipulated snail and nitrogen levels in a season-long field experiment in a Virginia salt marsh. Snails differentially affected plant growth at varying nitrogen levels. In unfertilized plots, snail removal increased S. alterniflora aboveground production by 38%, whereas in nitrogen addition plots, snail removal increased cordgrass growth by 78%. Snail addition decreased aboveground production by 51% in unfertilized stands, while in fertilized stands, snail addition led to even greater reductions (66%). By comparison, nitrogen addition increased S. alterniflora production by 443% in snail removal treatments, while in Controls and snail addition treatments, fertilization effects were dampened significantly, as nitrogen enrichment increased marsh grass growth by 322% and 189%, respectively. Feeding assays examining the rate at which snails ingested live S. alterniflora revealed that snail consumption alone could not be responsible for these large biomass reductions. Experimental results suggest that grazer-induced defoliation and grazer Control of plant demand for nitrogen fertilizer were the likely mechanisms involved. A survey of salt marshes from Maryland to Georgia showed that periwinkle grazing on live S. alterniflora is widespread. Our results show that L. irrorata can exert strong Top-Down Control of S. alterniflora production, and that this effect increases with increasing nitrogen avaliability. Together, these findings question the widely accepted notion that grazers play a relatively unimportant role in the salt marsh community.
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top down Control of spartina alterniflora production by periwinkle grazing in a virginia salt marsh
Ecology, 2001Co-Authors: Brian R Silliman, Jay C ZiemanAbstract:Top-Down forces, such as grazing and predation, have long been thought to be unimportant in Controlling plant growth in salt marshes. Instead, bottom-up forces, such as porewater ammonium and oxygen availability, are thought to be the primary regulating factors. In the field, we observed the periwinkle, Littoraria irrorata, grazing on live saltmarsh cordgrass, Spartina alterniflora. To examine the relative importance of periwinkle grazing and nutrient availability in Controlling marsh grass growth, we manipulated snail and nitrogen levels in a season-long field experiment in a Virginia salt marsh. Snails differentially affected plant growth at varying nitrogen levels. In unfertilized plots, snail removal increased S. alterniflora aboveground production by 38%, whereas in nitrogen addition plots, snail removal increased cordgrass growth by 78%. Snail addition decreased aboveground production by 51% in unfertilized stands, while in fertilized stands, snail addition led to even greater reductions (66%). By comparison, nitrogen addition increased S. alterniflora production by 443% in snail removal treatments, while in Controls and snail addition treatments, fertilization effects were dampened significantly, as nitrogen enrichment increased marsh grass growth by 322% and 189%, respectively. Feeding assays examining the rate at which snails ingested live S. alterniflora revealed that snail consumption alone could not be responsible for these large biomass reductions. Experimental results suggest that grazer-induced defoliation and grazer Control of plant demand for nitrogen fertilizer were the likely mechanisms involved. A survey of salt marshes from Maryland to Georgia showed that periwinkle grazing on live S. alterniflora is widespread. Our results show that L. irrorata can exert strong Top-Down Control of S. alterniflora production, and that this effect increases with increasing nitrogen avaliability. Together, these findings question the widely accepted notion that grazers play a relatively unimportant role in the salt marsh community.
W.h. Van Der Putten - One of the best experts on this subject based on the ideXlab platform.
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Interspecific differences in nematode Control between range-expanding plant species and their congeneric natives
Soil Biology and Biochemistry, 2016Co-Authors: Rutger A. Wilschut, Stefan Geisen, F.c. Ten Hooven, W.h. Van Der PuttenAbstract:Climate change enables range expansions of plants, animals and microbes to higher altitudes and latitudes. Plants may benefit from range expansion when they escape from natural enemies. However, range expansion becomes a disadvantage when plants become disconnected from organisms that Control enemies in the new range. Here, we examined nematode Control in the root zone of range-expanding plant species and congeneric natives. In a greenhouse, we determined bottom-up (by the plants) and Top-Down (by natural enemies of the nematodes) Control of two root-feeding nematode species (Helicotylenchus pseudorobustus and Meloidogyne hapla) in the rhizospheres of two range-expanding plant species, Centaurea stoebe and Geranium pyrenaicum, and two congeneric natives, Centaurea jacea and Geranium molle. Pots with plants growing in sterilized soil were inoculated with either a microbial soil community from the newly colonized natural habitat, a mixture of native microbial nematode antagonists, or a combination of these two communities. We tested the hypotheses that bottom-up Control of root-feeding nematodes would be strongest in the root zone of range expanders and that Top-Down Control would be strongest in the root zone of native plant species. We observed profound intra- and interspecific differences in bottom-up and Top-Down Control among all four plant species. Bottom-up Control by the range-expanding plant species was either strong or weak. Top-Down Control by microbes was strongest in native Centaurea. The addition of a mixture of both microbial communities reduced Control of M. hapla in the root zones of the native plant species, and enhanced its Control in the root zones of range-expanding plant species. We conclude that there was species-specific bottom-up and Top-Down Control of root-feeding nematodes among the four plant species tested. Range-expanding plant species influenced their microbial rhizosphere community differently compared to native plant species, but Top-Down Control in the root zone of natives was not systematically superior to that of range-shifting plant species.
Andreas Oschlies - One of the best experts on this subject based on the ideXlab platform.
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Data_Sheet_1_Can Top-Down Controls Expand the Ecological Niche of Marine N2 Fixers?.pdf
'Frontiers Media SA', 2021Co-Authors: Angela Landolfi, A Friederike E Prowe, Markus Pahlow, Christopher J. Somes, Chia-te Chien, Markus Schartau, Wolfgang Koeve, Andreas OschliesAbstract:The ability of marine diazotrophs to fix dinitrogen gas (N2) is one of the most influential yet enigmatic processes in the ocean. With their activity diazotrophs support biological production by fixing about 100–200 Tg N/year and turning otherwise unavailable dinitrogen into bioavailable nitrogen (N), an essential limiting nutrient. Despite their important role, the factors that Control the distribution of diazotrophs and their ability to fix N2 are not fully elucidated. We discuss insights that can be gained from the emerging picture of a wide geographical distribution of marine diazotrophs and provide a critical assessment of environmental (bottom-up) versus trophic (Top-Down) Controls. We expand a simplified theoretical framework to understand how Top-Down Control affects competition for resources that determine ecological niches. Selective mortality, mediated by grazing or viral-lysis, on non-fixing phytoplankton is identified as a critical process that can broaden the ability of diazotrophs to compete for resources in Top-Down Controlled systems and explain an expanded ecological niche for diazotrophs. Our simplified analysis predicts a larger importance of Top-Down Control on competition patterns as resource levels increase. As grazing Controls the faster growing phytoplankton, coexistence of the slower growing diazotrophs can be established. However, these predictions require corroboration by experimental and field data, together with the identification of specific traits of organisms and associated trade-offs related to selective Top-Down Control. Elucidation of these factors could greatly improve our predictive capability for patterns and rates of marine N2 fixation. The susceptibility of this key biogeochemical process to future changes may not only be determined by changes in environmental conditions but also via changes in the ecological interactions.
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top down Control of marine phytoplankton diversity in a global ecosystem model
Progress in Oceanography, 2012Co-Authors: A Friederike E Prowe, Markus Pahlow, Stephanie Dutkiewicz, Michael J Follows, Andreas OschliesAbstract:The potential of marine ecosystems to adapt to ongoing environmental change is largely unknown, making prediction of consequences for nutrient and carbon cycles particularly challenging. Realizing that biodiversity might influence the adaptation potential, recent model approaches have identified bottom-up Controls on patterns of phytoplankton diversity regulated by nutrient availability and seasonality. Top-Down Control of biodiversity, however, has not been considered in depth in such models. Here we demonstrate how zooplankton predation with prey-ratio based food preferences can enhance phytoplankton diversity in a ecosystem-circulation model with self-assembling community structure. Simulated diversity increases more than threefold under preferential grazing relative to standard density-dependent predation, and yields better agreement with observed distributions of phytoplankton diversity. The variable grazing pressure creates refuges for less competitive phytoplankton types, which reduces exclusion and improves the representation of seasonal phytoplankton succession during blooms. The type of grazing parameterization also has a significant impact on primary and net community production. Our results demonstrate how a simple parameterization of a zooplankton community response affects simulated phytoplankton community structure, diversity and dynamics, and motivates development of more detailed representations of Top-Down processes essential for investigating the role of diversity in marine ecosystems.
Rutger A. Wilschut - One of the best experts on this subject based on the ideXlab platform.
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Interspecific differences in nematode Control between range-expanding plant species and their congeneric natives
Soil Biology and Biochemistry, 2016Co-Authors: Rutger A. Wilschut, Stefan Geisen, F.c. Ten Hooven, W.h. Van Der PuttenAbstract:Climate change enables range expansions of plants, animals and microbes to higher altitudes and latitudes. Plants may benefit from range expansion when they escape from natural enemies. However, range expansion becomes a disadvantage when plants become disconnected from organisms that Control enemies in the new range. Here, we examined nematode Control in the root zone of range-expanding plant species and congeneric natives. In a greenhouse, we determined bottom-up (by the plants) and Top-Down (by natural enemies of the nematodes) Control of two root-feeding nematode species (Helicotylenchus pseudorobustus and Meloidogyne hapla) in the rhizospheres of two range-expanding plant species, Centaurea stoebe and Geranium pyrenaicum, and two congeneric natives, Centaurea jacea and Geranium molle. Pots with plants growing in sterilized soil were inoculated with either a microbial soil community from the newly colonized natural habitat, a mixture of native microbial nematode antagonists, or a combination of these two communities. We tested the hypotheses that bottom-up Control of root-feeding nematodes would be strongest in the root zone of range expanders and that Top-Down Control would be strongest in the root zone of native plant species. We observed profound intra- and interspecific differences in bottom-up and Top-Down Control among all four plant species. Bottom-up Control by the range-expanding plant species was either strong or weak. Top-Down Control by microbes was strongest in native Centaurea. The addition of a mixture of both microbial communities reduced Control of M. hapla in the root zones of the native plant species, and enhanced its Control in the root zones of range-expanding plant species. We conclude that there was species-specific bottom-up and Top-Down Control of root-feeding nematodes among the four plant species tested. Range-expanding plant species influenced their microbial rhizosphere community differently compared to native plant species, but Top-Down Control in the root zone of natives was not systematically superior to that of range-shifting plant species.
Albert Compte - One of the best experts on this subject based on the ideXlab platform.
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mechanism for top down Control of working memory capacity
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Fredrik Edin, Torkel Klingberg, Par Johansson, Fiona Mcnab, Jesper Tegner, Albert CompteAbstract:Working memory capacity, the maximum number of items that we can transiently store in working memory, is a good predictor of our general cognitive abilities. Neural activity in both dorsolateral prefrontal cortex and posterior parietal cortex has been associated with memory retention during visuospatial working memory tasks. The parietal cortex is thought to store the memories. However, the role of the dorsolateral prefrontal cortex, a Top-Down Control area, during pure information retention is debated, and the mechanisms regulating capacity are unknown. Here, we propose that a major role of the dorsolateral prefrontal cortex in working memory is to boost parietal memory capacity. Furthermore, we formulate the boosting mechanism computationally in a biophysical cortical microcircuit model and derive a simple, explicit mathematical formula relating memory capacity to prefrontal and parietal model parameters. For physiologically realistic parameter values, lateral inhibition in the parietal cortex limits mnemonic capacity to a maximum of 2-7 items. However, at high loads inhibition can be counteracted by excitatory prefrontal input, thus boosting parietal capacity. Predictions from the model were confirmed in an fMRI study. Our results show that although memories are stored in the parietal cortex, interindividual differences in memory capacity are partly determined by the strength of prefrontal Top-Down Control. The model provides a mechanistic framework for understanding Top-Down Control of working memory and specifies two different contributions of prefrontal and parietal cortex to working memory capacity.
