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123 results for “bottom-up”
Disentangling the roles of bottom-up and top-down drivers in the trade-off between food acquisition and safety in prey with multiple predators
1. Prey face a trade-off between acquiring food and avoiding predation, but food availability, and therefore its effect, is rarely measured in field studies investigating non-lethal effects of predation. The main aim of this study is to investigate the role of the presence of predators in the functional adjustments of feeding parameters with patch quality in a medium-size herbivore. 2. In Hwange National Park (Zimbabwe), we set up an experiment by manipulating, over two years, patch quality for impala (Aepyceros melampus), a medium-sized herbivore. We assess predation risk by monitoring the presence of three GPS-equipped predators: African lions (Panthera leo), spotted hyaenas (Crocuta crocuta) and African wild dogs (Lycaon pictus). 3. In enriched, fertilised plots the impalas reduced step rates (i.e. the rates of change in feeding stations), and increased their number of bites per feeding station while bite rates were not affected. Thus, the main adjustment of their feeding was the step rate. The total time the impalas spent vigilant appeared to be a good predictor of the variation of their bite rate. Although vigilance caused a reduction in bite rate when at a feeding station, the impalas reduced the relative costs of vigilance by continuing chewing and processing their food when scanning for predators. 4. When predators were in the vicinity, the impalas increased their exclusive vigilance (high-cost vigilance) but not their vigilance while chewing (low-cost vigilance) and decreased their bite rate while their step rate and the number of bites per feeding station did not change significantly. The impalas were thus visually disconnected from their patch, and reduced their bite rate when actually foraging. Exclusive vigilance increased when both lions and hyaenas were in the vicinity, and when wild dogs were nearby. 5. Patterns of vigilance that altered bite rate were linked to the presence of predators during the previous 24h. Over the long term patch quality was the main determinant of the feeding parameters (step rate and bite rate). This study shows how predators, by affecting the time prey devote to predator detection, shape the functional adjustments of food acquisition by prey to local patch quality.
Data from: Context-dependency of top-down, bottom-up, and density-dependent influences on cheetah demography
1. Research on drivers of demographic rates has mostly focused on top predators and their prey, and comparatively less research has considered the drivers of mesopredator demography. Of those limited studies, most focused on top-down effects of apex predators on mesopredator population dynamics, whereas studies investigating alternative mechanisms are less common. 2. In this study, we tested hypotheses related to top-down, bottom-up, and density-dependent regulation of demographic rates in an imperiled mesopredator, the cheetah (Acinonyx jubatus). 3. We used a 25-year dataset of lion density, cheetah density, and prey density from the Mun-Ya-Wana Conservancy in South Africa and assessed the effects of top-down, bottom-up, and density-dependent drivers on cheetah survival and reproduction. 4. In contrast to the top-down and bottom-up predications, both adult and juvenile cheetahs experienced the lowest survival during months with high prey densities and low lion densities. We only observed support for a density-dependent response in juvenile cheetahs, where they had a higher probability of reaching independence during times with low cheetah density, and low prey density. We did not identify any strong drivers of litter size. 5. Collectively, our results indicate that high apex predator abundance might not always have negative effects on mesopredator populations, and suggest that context dependency in top-down, bottom-up, and density-dependent factors may regulate demographic rates of cheetahs and other mesopredators. Our results highlight the complexities of population-level drivers of cheetah demographic rates and the importance of considering multiple hypotheses of mesopredator population regulation.
Data from: Berry production drives bottom-up effects on body mass and reproductive success in an omnivore
Obligate herbivores dominate studies of the effects of climate change on mammals, however there is limited empirical evidence for how changes in the abundance or quality of plant food affect mammalian omnivores. Omnivores can exploit a range of different food resources over the course of a year, but they often rely on seasonally restricted highly nutritious fruiting bodies during critical life stages. Brown bears Ursus arctos in Sweden are dependent on berries for fattening before entering hibernation. We used a ten-year time series to evaluate the effect of temperature and snow on annual variation in berry abundance and how this variation affected bears. We found marked interannual variation in berry production of bilberry Vaccinium myrtillus and lingonberry V. vitis-idaea, that we could attribute in part to temperature during plant dormancy and flowering and precipitation during fruit ripening. Both, autumn weights of female bears and spring weights of yearling bears increased linearly with bilberry abundance. When bilberry abundance was low, lightweight female bears had a lower reproductive success than females in better condition. This effect vanished when food abundance was above average, indicating that lightweight females could compensate for their initial weight during good bilberry years. Our study highlights the importance of considering individuals' dynamic responses to variation in food availability, which leave some more vulnerable to food shortage than others. Individual life-history heterogeneity in response to resource variation likely affects long-term population recruitment. Our findings emphasize that Scandinavian bears can be dependent on a single food resource during a critical period of the year and are therefore less resilient to environmental change than expected for an omnivore. Future climate scenarios predict ambiguous trends for weather covariates that affected crucial stages of berry phenology, preventing a clear prognosis of how climate change may affect long-term bilberry production.
Data from: Combined bottom-up and top-down pressures drive catastrophic population declines of Arctic skuas in Scotland
1. Understanding drivers of population change is critical for effective species conservation. In the northeast Atlantic Ocean, recent changes amongst seabird communities are linked to human and climate change impacts on foodwebs. Many species have declined severely, with food shortages and increased predation reducing productivity. Arctic skua Stercorarius parasiticus, a kleptoparasite of other seabirds, is one such species. 2. The aim of the study was to determine relative effects of bottom-up and top-down pressures on Arctic skuas across multiple colonies in a rapidly declining national population. 3. Long-term monitoring data were used to quantify changes in population size and productivity of Arctic skuas, their hosts (black-legged kittiwake Rissa tridactyla, common guillemot Uria aalge, Atlantic puffin Fratercula arctica, Arctic tern Sterna paradisaea), and an apex predator (great skua Stercorarius skua) over 24 years (1992–2015) in Scotland. We used digital mapping and statistical models to determine relative effects of bottom-up (host productivity) and top-down (great skua density) pressures on Arctic skuas across 33 colonies, and assess variation between three colony types classified by host abundance. 4. Arctic skuas declined by 81% and their hosts by 42–92%, whereas at most colonies great skuas increased. Annual productivity declined in Arctic skuas and their hosts, and reduced Arctic skua breeding success was a driver of the species' population decline. Arctic skua productivity was positively associated with annual breeding success of hosts, and negatively with great skua density. Inter-colony variation suggested Arctic skua trends and productivity were most sensitive to top-down pressures at smaller colonies of host species where great skuas had increased most, whereas bottom-up pressures dominated at large colonies of host species. 5. Scotland's Arctic skua population is declining rapidly, with bottom-up and top-down pressures simultaneously reducing breeding success to unsustainably low levels. Marine food web alterations, strongly influenced by fisheries management and climate change, are driving the decline, and this study demonstrates severe vulnerability of seabirds to rapid change in human-modified ecosystems. Potential but untested conservation solutions for Arctic skuas include Marine Protected Areas, supplementary feeding within colonies, and management of great skuas.
Data from: Bottom-up effects of host-plant species diversity and top-down effects of ants interactively increase plant performance
While plant diversity is well known to increase primary productivity, whether these bottom-up effects are enhanced by reciprocal top-down effects from the third trophic level is unknown. We studied whether pine tree species diversity, aphid-tending ants and their interaction determined plant performance and arthropod community structure. Plant diversity had a positive effect on aphids, but only in the presence of mutualistic ants, leading to threefold greater number of both groups in the tri-specific cultures than in monocultures. Plant diversity increased ant abundance not only by increasing aphid number, but also by increasing ant recruitment per aphid. The positive effect of diversity on ants in turn cascaded down to increase plant performance; diversity increased plant growth (but not biomass), and this effect was stronger in the presence of ants. Consequently, bottom-up effects of diversity within the same genus and guild of plants and top-down effects from the third trophic level (predatory ants) interactively increased plant performance.
Data from: The changing contribution of top-down and bottom-up limitation of mesopredators during 220 years of land use and climate change
Apex predators may buffer bottom-up driven ecosystem change, as top-down suppression may dampen herbivore and mesopredator responses to increased resource availability. However, theory suggests that for this buffering capacity to be realized, the equilibrium abundance of apex predators must increase. This raises the question: will apex predators maintain herbivore/mesopredator limitation, if bottom-up change relaxes resource constraints? Here, we explore changes in mesopredator (red fox Vulpes vulpes) abundance over 220 years in response to eradication and recovery of an apex predator (Eurasian lynx Lynx lynx), and changes in land use and climate which are linked to resource availability. A three-step approach was used. First, recent data from Finland and Sweden were modelled to estimate linear effects of lynx density, land use and winter temperature on fox density. Second, lynx density, land use and winter temperature was estimated in a 22 650 km2 focal area in boreal and boreo-nemoral Sweden in the years 1830, 1920, 2010 and 2050. Third, the models and estimates were used to project historic and future fox densities in the focal area. Projected fox density was lowest in 1830 when lynx density was high, winters cold and the proportion of cropland low. Fox density peaked in 1920 due to lynx eradication, a mesopredator release boosted by favourable bottom-up changes - milder winters and cropland expansion. By 2010, lynx recolonization had reduced fox density, but it remained higher than in 1830, partly due to the bottom-up changes. Comparing 1830 to 2010, the contribution of top-down limitation decreased, while environment enrichment relaxed bottom-up limitation. Future scenarios indicated that by 2050, lynx density would have to increase by 79% to compensate for a projected climate driven increase in fox density. We highlight that although top-down limitation in theory can buffer bottom-up change, this requires compensatory changes in apex predator abundance. Hence apex predator recolonization/recovery to historical levels would not be sufficient to compensate for widespread changes in climate and land use, which have relaxed the resource constraints for many herbivores and mesopredators. Variation in bottom-up conditions may also contribute to context dependence in apex predator effects.
Data from: The fluctuating world of a tundra predator guild: bottom-up constraints overrule top-down species interactions in winter
Global warming is predicted to change ecosystem functioning and structure in Arctic ecosystems by strengthening top-down species interactions, i.e. predation pressure on small herbivores and interference between predators. Yet, previous research is biased towards the summer season. Due to greater abiotic constraints, Arctic ecosystem characteristics might be more pronounced in winter. Here we test the hypothesis that top-down species interactions prevail over bottom-up effects in Scandinavian mountain tundra (Northern Sweden) where effects of climate warming have been observed and top-down interactions are expected to strengthen. But we test this a-priori hypothesis in winter and throughout the 3-4 year rodent cycle, which imposes additional pulsed resource constraints. We used snowtracking data recorded in 12 winters (2004-2015) to analyse the spatial patterns of a tundra predator guild (arctic fox Vulpes lagopus, red fox Vulpes vulpes, wolverine Gulo gulo) and small prey (ptarmigan, Lagopus spp). The a-priori top-down hypothesis was then tested through structural equation modelling, for each phase of the rodent cycle. There was weak support for this hypothesis, with top-down effects only discerned on arctic fox (weakly, by wolverine) and ptarmigan (by arctic fox) at intermediate and high rodent availability respectively. Overall, bottom-up constraints appeared more influential on the winter community structure. Cold specialist predators (arctic fox and wolverine) showed variable landscape associations, while the boreal predator (red fox) appeared strongly dependent on productive habitats and ptarmigan abundance. Thus, we suggest that the unpredictability of food resources determines the winter ecology of the cold specialist predators, while the boreal predator relies on resource rich habitats. The constraints imposed by winters and temporary resource lows should therefore counteract productivity-driven ecosystem change and have a stabilizing effect on community structure. Hence, the interplay between summer and winter conditions should determine the rate of Arctic ecosystem change in the context of global warming.
COMPARING THE CO2 EMISSION INTENSITY OF THE STEEL INDUSTRIES IN THE EU AND CHINA RESULTING FROM TOP-DOWN AND BOTTOM-UP APPROACHES SUPPLEMENTARY
<p>The provided .xlsx file contains the following addtional data for the conference paper "Comparing CO<sub>2</sub> emission intensity of the steel industries in EU and China resulting from top-down and bottom-up approaches":</p> <ul> <li>The data used to plot Figure 1, 4, 5 and 6</li> <li>Scope adaption calculation</li> <li>EAF case study</li> </ul>
Top-down vs. bottom-up synthesis of Ga based supported catalytically active liquid metal solutions (SCALMS) for the dehydrogenation of isobutane
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Bottom-up identification of subsystems in Swiss water governance
Anonymized data and R scripts needed to replicate the identification of subsystems in Swiss water governance described in the study "Bottom-up identification of subsystems in complex governance systems". Study doi: tbd Study abstract: tbd
Dataset for "Constructing many-body dissipative particle dynamics models of fluids from bottom-up coarse-graining"
<ul> <li>The trajectory files used for processing time correlation functions, as reported in the original paper, are provided here.</li> <li>The analysis tools can be found in the following GitHub repository: <a href="https://github.com/jaehyeokjin/ManyBodyDPD/tree/main/Time-Correlation" target="_new" rel="noopener">ManyBodyDPD/Time-Correlation</a>. These tools are designed to work with the two trajectory files included in this repository.</li> </ul>
Datasets supplementing journal article "Scalable Bottom-up Synthesis of Co-Ni-Doped Graphene"
<p>Datasets supporting the journal article "Scalable Bottom-up Synthesis of Co-Ni-Doped Graphene".</p>
D2.3 Inventory of priority practices and innovations bottom-up M16
<p>Deliverable 2.3 presents the results of the second bottom-up survey analysis carried out by B-THENET, the first Thematic Network for European Beekeepers. The aim of the current analysis was to identify a list of good beekeeping practices that are considered a priority by EU beekeepers and advisors.<br>A total of 1,054 replies from 22 EU countries were received and a total of 28 priority practices were identified.</p>
D2.2_Inventory of priority practices and innovations bottom-up
<p>Deliverable 2.2 is the result of a bottom-up survey analysis carried out by B-THENET, the first Thematic Network for EU Beekeepers. The deliverable consists of two documents:<br> The present summary report, meant to support and contextualise the results of the survey included in the database;<br> The database (Excel document) containing the results of the survey concerning the priority practices, as ANNEX 2.<br>A specific survey was set-up to prioritize practices and was distributed to EU beekeepers. We received 2,094 answers from beekeepers of 22 EU countries. The most relevant practices according to beekeepers needs were related to:<br>1. For the Good Beekeeping Practices category:<br>- “Properly place hives in the apiary” (24 practices);<br>- “Proper comb storage” (13 practices).<br>2. For the Biosecurity Measures category:<br>- “Optimize the efficacy of anti-varroa treatments” (29 practices);<br>- “Produce nuclei and swarms with no clinical signs of varroa” (5 practices).</p>
Automatic Bottom-Up Taxonomy Construction: A Software Application Domain Study - Data
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Top-down and bottom-up controls limit woody encroachment into persistent temperate rainforest meadows
<p><span>These data describe soils, woody plant seedlings, and ungulate herbivory in and around temperate montane meadows in the Oregon Coast Range, USA. Meadows such as these are a global study system for the accelerating phenomenon of woody encroachment, but study this phenomenon into meadows in western Oregon has been conducted almost entirely in the western and High Cascades, with only two extant observational studies of grassy balds in the Coast Range. These data describe factors limiting woody encroachment into meadows in the Oregon Coast Range, including bottom-up control by soil properties, plant-plant interactions, and top-down control by large herbivores.<b> </b>I measured chemical and physical properties of soils (depth of organic layer; bulk density of top 3 cm of mineral soil; and mineral soil profiles: particle size distribution, pH, % total C, % total N) to a depth of 50 cm in meadow and forest. I recorded community, density, and proportion browsed for shrubs, conifers, and deciduous trees ≤2 m tall along transects from meadow into forest. I experimentally planted 20 <i>Pseudotsuga menziesii</i> (Douglas-fir) seedlings in each of five meadows (<em>n </em>= 100) and factorially manipulated aboveground neighboring plant presence and ungulate herbivore access. I found that m</span><span>eadow soils were lower in C and C:N; slightly lower in N, and similar in plant-available water (derived from particle size distribution) and pH relative to forest soils. Shrubs were most dense, but experienced the lowest browse pressure, near the meadow edge; while trees were sparse and varied by site—although at one site, browse pressure was heavier in meadow than forest. Seedling survival and growth varied by site, herbivory reduced growth, and total soil N best explained residual variation in seedling growth among sites.</span><span><b> </b>My findings indicate that ungulate herbivores exert top-down control on woody encroachment into temperate montane meadows, perhaps in concert with local N-limitation.</span></p>
Phenology under bottom-up control: when change in host quality induces diapause in parasitoids
<p>This is the dataset and the supplementary material for the article "Phenology under bottom-up control: when change in host quality induces diapause in parasitoids" published in the <em><strong>Peer Community Journal</strong></em></p> <p>When organisms coevolve, any change in one species can affect phenotypes and ecology of the other species. Upper trophic levels have to synchronize their life-cycle to both abiotic conditions and lower trophic level species’ phenotypic variations and phenology. The role such interactions play in ecosystems is central, but their mechanistic bases remain underexplored. We tested the effect of seasonal variation in host quality on parasitoid diapause induction by using viviparous and oviparous female morphs of the pea aphid <em>Acyrthosiphon pisum</em>. <em>Aphidius ervi</em> parasitoids from populations of contrasted climatic origin (harsh <em>vs.</em> mild winter areas) were allowed to parasitize each morph in a split-brood design and were next reared under either fall-like or summer-like temperature-photoperiod conditions. We found that oviparous morphs, present before winter, are cues <em>per se</em> for diapause induction; parasitoids entered diapause at higher levels when developing in oviparous hosts (19.4 ±3.0%) than in viviparous ones (3.6 ±1.3%), under summer-like conditions (i.e., when oviparous aphids appear in the fields). This pattern was only observed in parasitoids from the harsh winter area, suggesting local adaptations to variation in host quality as an overwintering cue. Analyses of the relative proportion of forty-seven metabolites and lipid reserves in both aphid morphs produced under the same conditions suggest parasitoids’ response to be mainly influenced by chemical cues derived from the host, with higher proportion of polyols and sugars, and more fat reserves being found in oviparous morphs. Host quality thus varies across the seasons and represents one of the multiple environmental parameters affecting parasitoid diapause. Our results underline coevolutionary processes between hosts and parasitoids in their area of origin, likely leading to phenological synchronization with the environment. There was no decrease in host suitability (in terms of quantity or quality), showing that parasitoids may rely on host phenotypic variation across the seasons as an information for upcoming detrimental conditions, affecting their overwintering strategies. We point out the importance of such bottom-up effects for ecosystem functioning and for the provision of ecosystem services such as biological control.</p>
Cognitive Remediation in Schizophrenia: Efficacy and Role of Neuroplasticity in "Top-down" and "Bottom-up" Mechanisms
ClinicalTrials.gov study NCT06482918. IPD Sharing: Not stated. Countries: 1. Publications: 18.
Rehabilitation For Acquired Visual Field Defects: Development Of A Bottom-Up Approach
ClinicalTrials.gov study NCT01730560. IPD Sharing: Not stated. Countries: 1. Publications: 1.
Data from: Search for top-down and bottom-up drivers of latitudinal trends in insect herbivory in oak trees in Europe
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