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27 results for “bottom-up effects”
Bottom-up effects of apple cultivars on parasitoids via aphid hosts
<p>Variability of intraspecific host plant quality for phytophagous insects may have consequences on the structure and functioning of associated food webs. The quality of host plants can affect aphids fitness, influencing their life history traits and altering the nutritional resources available to higher trophic levels, potentially affecting the development of solitary parasitoids. Here, we assessed the potential bottom-up effects of intraspecific variability amongst three cultivars (Gala, Ariane and Greensleeves) of the domesticated apple tree (<em>Malus domestica</em>) with putative resistance towards the rosy apple aphid (<em>Dysaphis plantaginea</em>) on the aphid’s performance, and its cascading effects on the parasitoid <em>Ephedrus cerasicola</em>. We measured aphid pre-reproductive period, lipid and water contents, and recorded their feeding behavior using the electropenetrography technique. Parasitoid developmental duration, sex ratio, hind tibia size and female egg load were measured and used to evaluate <em>E. cerasicola</em> performance according to the cultivar on which their aphid hosts had been reared. Only the development time of parasitoids was found to be longer on Ariane and Green Sleeves cultivars than on the Gala cultivar. Aphid feeding behavior variables related to phloem consumption were negatively impacted on apple tree cultivars on which the development time of parasitoids had been reduced. We discuss in what way cultivar quality can be an important component of tritrophic interactions: the resistant Ariane and Green Sleeves cultivars negatively impacted the aphids but appeared to have limited bottom-up effects on the parasitoids. </p>
Variation in the relative effects of top-down and bottom-up forces on herbivores and herbivory along an elevational gradient in the southern Appalachian mountains in 2001
It is a well established fact that top-down (predation), bottom-up (resource availability) and lateral (interference) interactions are the dominant biotic forces in terrestrial ecosystems in addition to a host of other interactions like mutualism and symbiosis. The primary emphasis has always been to look for a singular mechanistic explanation in determining community dynamics. The ecological literature is replete with controversy on the subject of whether top-down or bottom-up forces predominate in ecosystems and their role in dynamics of ecological communities. The emerging consensus is that both top-down and bottom-up forces act in concert and the impetus is shifting towards the elucidation of the context, biotic and abiotic, under which these forces come into play. There are very few studies that have addressed this question and looked at the simultaneous interaction of these forces. I propose to study the effects of spatial heterogeneity in biotic and abiotic factors along an elevation gradient on the relative impacts of top-down and bottom-up forces and the result of their interactive effects on folivory. Specifically, I shall address the effects of spatial variation in plant quality and predation pressure and their interactive impacts on insect herbivore biomass and consumption. I shall also address the effects of complexity within/among trophic levels on the impact of these forces. The study aims to bring about a greater understanding of the role played by abiotic factors and complexity in community dynamics.
Legacy effect of grazing intensity mediates the bottom-up controls of resource addition on soil food webs
<p>1. Large-scale studies have demonstrated that nitrogen (N) and water (W) availability greatly affect terrestrial ecosystems worldwide, and this is especially true for the resource-poor semi-arid grasslands. Yet, experimental evidence is lacking for how N and W availability affect soil food webs across historical grazing intensity-altered environments at a local scale.</p> <p>2. Here, we included N- and W-addition treatments in an 8-year grazing experiment (with four grazing intensities) to determine how the legacy effects of grazing intensity mediate the responses of key components of soil food webs (plants, microorganisms, and nematodes) to resource addition in a semi-arid grassland.</p> <p>3. After 4 years of N- and W-addition treatments (with no grazing during that 4-year period), we found that a legacy of grazing, even light grazing, had significant negative effects on the components of plant community and soil food webs. Both N and W addition increased above- and below-ground plant biomass, especially under moderate and heavy grazing. N addition had negative effects on the biomass of bacteria under no grazing, while W addition increased the biomass of actinomycetes under light grazing. N addition decreased the abundance of omnivorous + carnivorous nematodes under light and heavy grazing, while W addition increased their abundance under heavy grazing. Overall, the effects of resource addition on soil food webs progressively decreased from the lowest trophic level (primary producers, i.e., plants), to intermediate tropic levels (microorganisms and root-feeding nematodes), to higher trophic levels (microbial-feeding nematodes and omnivorous + carnivorous nematodes).</p> <p>4. Synthesis and applications. Our results, which are the first data concerning the effects of resource addition on key components of soil food webs across a historical grazing-induced environmental gradient, show that the strong bottom-up controls of resource addition on soil food webs are mediated by the legacy of grazing intensity. These finding should be useful for predicting the responses of grassland ecosystems to future climate change and suggest that the recovery of degraded grasslands will require more than restoration measure of resource inputs alone.</p>
Bottom-up effect of host protective symbionts on parasitoid diversity: Limited evidence from two field experiments
<p>1. Protective symbionts can provide effective and specific protection to their hosts. This protection can differ between different symbiont strains with each strain providing protection against certain components of the parasite and pathogen community their host faces. Protective symbionts are especially well known from aphids where, among other functions, they provide protection against different parasitoid wasps. However, most of the evidence for this protection comes from laboratory experiments.</p> <p>2. Our aim was to understand how consistent protection is across different symbiont strains under natural field conditions and whether symbiont diversity enhanced the species diversity of colonizing parasitoids, as could be expected from the specificity of their protection.</p> <p>3. We used experimental colonies of the black bean aphid, Aphis fabae, to investigate symbiont conferred protection under natural field conditions over two seasons. Colonies differed only in their symbiont composition, carrying either no symbionts, a single strain of the protective symbiont Hamiltonella defensa, or a mixture of three H. defensa strains. These aphid colonies were exposed to natural parasitoid communities in the field. Subsequently, we determined the parasitoids hatched from each aphid colony.</p> <p>4. The evidence for a protective effect of H. defensa was limited and inconsistent between years, and aphid colonies harboring multiple symbiont strains did not support a more diverse parasitoid community. Instead, parasitoid diversity tended to be highest in the absence of H. defensa.</p> <p>5. Symbiont conferred protection, although a strong and repeatable effect under laboratory conditions, may not always cause the predicted bottom-up effects under natural conditions in the field.</p>
Data related to: Bottom-up effects of fungicides on tadpoles of the European common frog (Rana temporaria)
<p>We have uploaded a range of files informding about ergosterol and bacteria levels on leaf litter (LeafMicrobes.xlsx); the feces production, leaf consumption and legnth development of tadpoles during the study and among the two experimental phases as detailed in the mansucript (FecesFeedingLength.xlxs); composition of fatty acids in tadpoles and leaf litter (NFLA.xlxs); metamophoses event (Metamorphosis.xlsx)</p> <p> </p> <p>Paper abstract as submitted:</p> <p><span><span><span><span><span><span><span><span><span><span><span>Biodiversity is under pressure world-wide, with amphibians being particularly threatened. Stressors related to human activity, such as chemicals, are contributing to this decline. It remains, however, unclear whether chemicals exhibiting a fungicidal activity could indirectly affect tadpoles, that depend on microbially conditioned leaf litter as food source. The indirect effect of fungicides (sum concentration of a fungicide mixture composed of azoxystrobin, carbendazim, crybrodinil, quinoxifen and tebuconcazole: 100 µg/L) on tadpoles was assessed relative to leaf litter colonised by microbes in absence of fungicides (control) and a worst case scenario, that is leached leaf litter without microbial colonisation. The quality of leaf litter as food for tadpoles of the European common frog (<i>Rana temporaria</i>) was characterised through neutral lipid fatty acid profiles and microbial sum parameters and verified by sublethal responses in tadpoles (i.e. feeding rate, feces production, growth and fatty acid composition). Fungicides changed the nutritious quality of leaf litter likely through alterations in leaves' neutral lipid fatty acid profiles (i.e., changes in some physiologically important highly unsaturated fatty acids reached more than 200%) in combination with a potential adsorption onto leaves during conditioning. These changes were reflected by differences in the development of tadpoles ultimately resulting in an earlier start of metamorphosis. Our data provide a first indication that fungicides potentially affect tadpole development indirectly through bottom-up effects. This pathway is so far not addressed in fungicide environmental risk assessment and merits further attention.</span></span></span></span></span></span></span></span></span></span></span></p>
Bottom-up effects of plant quantity and quality on arthropod diversity across multiple trophic levels in a semi-arid grassland
<p><span>1. </span><span>Plant quantity and quality can independently affect the diversity of the entire arthropod communities and multiple arthropod taxa in grassland ecosystems. However, it remains unclear how these effects on arthropod taxa at one trophic level propagate through food web to influence the diversity of higher trophic levels.</span></p> <p><span>2. </span><span>We performed a monoculture experiment with 15 herbaceous species in the Inner Mongolian grassland to investigate how natural variations in plant productivity and host leaf traits affect herbivore taxon richness, which in turn affects predator taxon richness.</span></p> <p><span>3. </span><span>For herbivores, plant productivity indirectly promoted herbivore taxon richness by increasing herbivore biomass, which was attributed to the increases in the richness of dominant sucking herbivores and endophytes</span> <span>with high food requirements. However, the high plant quality indicator (e.g. high leaf protein, phosphorus and water contents, and high leaf protein to carbohydrate ratio) directly increased, whereas the low plant quality indicator (e.g. high leaf lignin content) directly decreased herbivore taxon richness. Taxon richness of chewing and sucking herbivores with specific feeding modes (tearing or sucking mouthparts) showed strong positive responses to increas</span><span>ing</span><span> plant quality.</span></p> <p><span>4. </span><span>For predators, herbivore taxon richness, rather than herbivore biomass, mainly mediated the positive effects of plant productivity and the high plant quality indicator, but the negative effect of the low plant quality indicator, on predator taxon richness. At the feeding guild level, the taxon richness of parasitoids, other predators and spiders exhibited positive responses to different herbivores, which was attributed to their different diet preferences. Predator diversity could be promoted by prey partitioning among predator guilds facilitating species coexistence. At the family level, the taxon richness of most predator families was positively correlated with that of more than one herbivore family, suggesting that high predator diversity may </span><span>be caused by balanced diets owing to high prey diversity.</span></p> <p><span>5. Synthesis</span><span>.</span><span> Natural variations in plant quantity and quality can substantially affect the diversity of herbivores and cascade up the food web to affect predators. Specificity and mechanisms of feeding have a large impact on the responses of arthropod guilds at each trophic level.</span></p>
Bottom-up effect of host protective symbionts on parasitoid diversity: Limited evidence from two field experiments
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Data related to: Bottom-up effects of fungicides on tadpoles of the European common frog (Rana temporaria)
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Legacy effect of grazing intensity mediates the bottom-up controls of resource addition on soil food webs
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Data from: Plant functional traits affect invertebrate predator diversity via bottom-up effects in a deadwood-based food web
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Bottom-up effects of plant quantity and quality on arthropod diversity across multiple trophic levels in a semi-arid grassland
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Data from: Bottom-up trait-mediated indirect effects decrease pathogen transmission in a tritrophic system
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Bottom-up and top-down drivers influence urbanization effects on insect herbivory in oaks
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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: 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: Berry production drives bottom-up effects on body mass and reproductive success in an omnivore
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Data from: Bottom-up effects of host-plant species diversity and top-down effects of ants interactively increase plant performance
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Integrating top-down and bottom-up effects of local density across scales and a complex life cycle
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Data from: Bottom-up effects of a no-take zone on endangered penguin demographics
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Data from: Artificial light at night causes top-down and bottom-up trophic effects on invertebrate populations
1. Globally, many ecosystems are exposed to artificial light at night. Nighttime lighting has direct biological impacts on species at all trophic levels. However, the effects of artificial light on biotic interactions largely remain to be determined. 2. We exposed experimental mesocosms containing combinations of grassland plants and invertebrate herbivores and predators to illumination at night over a three-year period to simulate conditions under different common forms of street lighting. 3. We demonstrate both top-down (predation controlled) and bottom-up (resource controlled) impacts of artificial light at night in grassland communities. The impacts on invertebrate herbivore abundance were wavelength dependent and mediated via other trophic levels. 4. White LED lighting decreased the abundance of a generalist herbivore mollusc by 55% in the presence of a visual predator, but not in its absence, while monochromatic amber light (with a peak wavelength similar to low pressure sodium lighting) decreased abundance of a specialist herbivore aphid (by 17%) by reducing the cover and flower abundance of its main food plant in the system. Artificial white light also significantly increased the food plant's foliar carbon to nitrogen ratio. 5. We conclude that exposure to artificial light at night can trigger ecological effects spanning trophic levels, and that the nature of such impacts depends on the wavelengths emitted by the lighting technology employed. 6. Policy implications Our results confirm that artificial light at night, at illuminance levels similar to roadside vegetation, can have population effects mediated by both top-down and bottom-up effects on ecosystems. Given the increasing ubiquity of light pollution at night, these impacts may be widespread in the environment. These results underlines the importance of minimising disruption of natural ecosystems by reducing light pollution into natural and semi-natural ecosystems.26-Jun-2018
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