Bottom-up Effects Research Articles

Soil nutrient limitation controls trophic cascade effects of micro-food web-derived ecological functions in degraded agroecosystems.

Soil nutrient supply drives the ecological functions of soil micro-food webs through bottom-up and top-down mechanisms in degraded agroecosystems. Nutrient limitation responds sensitively to variations in degraded agroecosystems through restoration practices, such as legume intercropping. This study examined the effects of legume intercropping on trophic cascade dynamics through resource supply in degraded purple soil ecosystems. A field experiment was conducted with three plantation types: Camellia oleifera monoculture (CK), C. oleifera-Arachis hypogaea (peanut) intercropping (CP), and C. oleifera-Senna tora intercropping (CS). Using soil nutrient limitation as a premise, modified by legume intercropping, we assessed the biodiversity of soil biotic taxa, analysed their community composition, and applied partial least squares path modelling (PLS-PM) to link trophic cascade with ecological functions. Legume intercropping altered the abundance of biotic taxa, leading to changes in biotic diversity and microbial life strategies. The PLS-PM results indicated that legume intercropping enhanced bacterial diversity by aggravating soil P limitation, which subsequently increased protist consumer diversity and omnivore-predator nematode abundance through a bottom-up effect. Omnivore-predator nematodes and protist consumers indirectly influenced soil P metabolism, down-regulated through bacteria in the top-down effect. We observed high consistency between the untargeted metabolomic analysis and soil nutrient limitations. These findings indicate that soil micro-food web structure and function responded sensitively to legume intercropping in degraded ecosystems. The results highlight the role of soil nutrient limitation in shaping micro-food webs and suggest that soil P limitation controls the down-regulation of soil P-related ecological functions through bottom-up and top-down effects.

Are three zebras more than three frogs: examining conceptual and physical congruency in numerosity judgements of familiar objects.

Researchers in numerical cognition have extensively studied the number sense-the innate human ability to extract numerical information from the environment quickly and effortlessly. Much of this research, however, uses abstract stimuli (e.g., dot configurations) that are also strictly controlled for their low-level visual confounds, such as size. Nonetheless, individuals rarely extract numerical information from abstract stimuli in everyday life. Yet, numerical judgments of familiar objects remain poorly understood and understudied. In the current study, we examined the cognitive mechanisms underlying the numerical decisions of familiar objects. In two experiments, we asked adult participants (Experiment 1) and two groups of children (aged 7-9years and 11-12years, Experiment 2) to perform an animal numerosity task (i.e., "Which animal is more numerous?"), while the conceptual congruency (i.e., the congruency between an object's real-life size and its numerosity) and physical congruency (the congruency between the number of items and the total space they occupy on the screen) were manipulated. Results showed that the conceptual congruency effect (i.e., better performance when the animal with a larger size in real life is more numerous) and a physical congruency effect (i.e., better performance when the physically larger animal is more numerous) were present in adults and children. However, the effects differed across the age groups and were also a subject of developmental change. To our knowledge, this study is the first one to demonstrate that conceptual knowledge can interfere with numerosity judgements in a top-down manner. This interference effect is distinct from the bottom-up interference effect, which comes from the physical properties of the set. Our results imply that the number sense is not a standalone core system for numbers but is embedded in a more extensive network where both low-level and higher-order influences are possible. We encourage numerical cognition researchers to consider employing not only abstract but also familiar objects when examining numerosity judgements across the lifespan.

Corrigendum: Modelling the bottom-up effects of climate change on primary production in the Gulf of St. Lawrence and eastern Scotian Shelf

Corrigendum: Modelling the bottom-up effects of climate change on primary production in the Gulf of St. Lawrence and eastern Scotian Shelf

Bottom-Up Effects of Various Plant Growth Promoting Treatments on Fitness Parameters of Hippodamia variegata.

Plant growth-promoting activities using biological, chemical, and organic fertilizers are well-documented for pest insects, their impacts on predators are less commonly studied. This research investigates whether bell pepper plants treated with plant growth-promoting rhizobacteria (PGPRs), arbuscular mycorrhizal fungi (AMF), vermicompost (30%), and zinc sulfate either separately or in selected combinations affect the nutrient indices and population growth traits of the ladybug predator, Hippodamia variegata (Goeze), when fed on aphids, Myzus persicae (Sulzer). Bell pepper plants were individually treated with two PGPRs (Bacillus subtilis and Pseudomonas fluorescens), one AMF (Glomus intraradices), soil amended with 30% vermicompost (v/v), and foliar application of zinc sulfate under greenhouse conditions. Combined treatments of AMF × B. subtilis and AMF × P. fluorescens were also tested. Nutritional indices and population growth parameters of predator were reared on the treated plants infested with aphids. Results showed that the efficiency of conversion of ingested food (ECI) in predator larvae was highest on B. subtilis-treated aphids and lowest on vermicompost-treated aphids. The relative growth rate (RGR) of predator was the highest on zinc sulfate-treated aphids and lowest on vermicompost-treated aphids. Predators fed on vermicompost-treated aphids had the lowest net reproductive rate (R₀) and intrinsic rate of increase (r), while R₀ was highest for predators fed on B. subtilis-treated aphids and r was highest on P. fluorescens- and B. subtilis-treated aphids. These findings suggest that zinc sulfate and biological fertilizers involving PGPRs can enhance the ecological fitness of predators and could be effective in biocontrol-based integrated pest management of aphids.

Top-down and bottom-up effects on visual perception during data-based scientific reasoning in the context of population dynamics

ABSTRACT This study investigates the role of visual perception in data-based scientific reasoning within population dynamics. Visual perception involves representational characteristics of stimuli and context-based conceptions, influenced by top-down (contextual assumptions) and bottom-up (data representation) effects. In population dynamics, top-down effects relate to assumptions like natural equilibrium, while bottom-up effects concern how data are represented, typically through line graphs. We assessed pre-service biology teachers’ (N = 20) initial conceptions on population dynamics, categorizing them as either the Balance of Nature (BoN) or Flux of Nature (FoN) metaphors. Participants viewed line graphs depicting population dynamics while eye-tracking technology recorded their visual focus and think-aloud protocols provided verbal data. ANOVA results showed significant differences in eye-tracking metrics between AOI groups of BoN and FoN graphs, but no significant effects between initial conceptions and eye-tracking measures. Heat map analyses revealed that participants focused on visually prominent graph features, especially when interpretation required conceptual knowledge and pattern identification.

Temporal and spatial variations of soil nematode assemblages across distinct forest ecosystems

The bottom-up effects of vegetation are widely recognized as important factors influencing the structure and functioning of soil food webs in forests. However, the influence of forest type on the composition and stability of soil nematode communities remains underexplored. In this study, we investigated the abundance, composition, diversity, and various aspects of soil nematode communities across three distinct forest types - Sub-tropical Pine Forests (STPF), Himalayan Moist Temperate Forests (HMTF), and Himalayan Dry Temperate Forests (HDTF) - during two seasons (summer and autumn). In both summer and autumn, total nematode abundance and the abundance of bacterivores were significantly higher in STPF compared to the other two forest types. Taxonomic diversity, as indicated by the Simpson index, was also greater in STPF during both seasons. The higher maturity index and sigma maturity index values observed in STPF suggest a more stable nematode community in the summer season. The soil nematode faunal profile indicated an enriched and structured food web in STPF across both seasons. Additionally, the metabolic footprint of the entire nematode community was considerably higher in STPF during the summer. Overall, soil nematode communities were most stable in STPF and least stable in HDTF. Our findings suggest that the Sub-tropical Pine Forests in the Pir-Panjal mountain range, across two contrasting seasons, support a higher level of soil food web structure and more complex soil biological communities than the other forest types. This study provides a foundation for understanding soil food web structure, function, and seasonal stability, which has important implications for sustainable forest management.

Nutrition Rather Than Phytohormone-Dependent Defense of Host Plant Mediates the Different Response of Red- and Green-Morph Pea Aphids to Nitrogen Fertilization

Nitrogen fertilization is widely known to affect plant metabolism, which subsequently influences phytophagous insects through a bottom-up effect. The interplay between plants and insects is often overlooked in studies examining the effects of nitrogen fertilization on insect performance. Here, we assessed the performance of green and red morphs of pea aphid Acyrthosiphon pisum feeding on alfalfa Medicago truncatula with and without nitrogen fertilization and examined how nitrogen fertilization and aphid infestation affect plant amino acid composition and phytohormone-dependent defenses. The results showed that nitrogen fertilization significantly enhanced the growth rate and fecundity of the green-morph aphid but only slightly increased the growth rate of the red morph. The feeding behaviors of the two morphs of aphid were similarly inhibited by nitrogen fertilization, manifested as prolonged stylet pathway duration and shortened phloem ingestion duration. With nitrogen fertilization, the green-morph-aphid-infested plant accumulated more free amino acids, particularly essential amino acids, when compared with the red-morph aphid. Furthermore, the infestation of both morphs of aphid repressed the expression of genes involved in salicylic acid-dependent defense while enhancing those involved in jasmonic acid/ethylene signaling under nitrogen fertilization. These results suggest that nitrogen fertilization and aphid infestation interact in manipulating plant metabolism, with nutritional changes playing a vital role in the aphid morph-specific growth and fecundity response to nitrogen fertilization.

Unlocking agro-ecosystem sustainability: exploring the bottom-up effects of microbes, plants, and insect herbivores.

Agricultural ecosystem formation and evolution depend on interactions and communication between multiple organisms. Within this context, communication occurs between microbes, plants, and insects, often involving the release and perception of a wide range of chemical cues. Unraveling how this information is coded and interpreted is critical to expanding our understanding of how agricultural ecosystems function in terms of competition and cooperation. Investigations examining dual interactions (e.g. plant-microbe, insect-microbe, and insect-plant) have resolved some basic components of this communication. However, there is a need for systematically examining multitrophic interactions that occur simultaneously between microorganisms, insects, and plants. A more thorough understanding of these multitrophic interactions has been made possible by recent advancements in the study of such ecological interactions, which are based on a variety of contemporary technologies such as artificial intelligence sensors, multi-omics, metabarcoding, and others. Frequently, these developments have led to the discovery of startling examples of each member manipulating the other. Here, we review recent advances in the understanding of bottom-up chemical communication between microorganisms, plants, and insects, and their consequences. We discuss the components of these "chemo-languages" and how they modify outcomes of multi-species interactions across trophic levels. Further, we suggest prospects for translating the current basic understanding of multitrophic interactions into strategies that could be applied in agricultural ecosystems to increase food safety and security.

Bottom-up effects of nutrient solutions on grape-grape phylloxera (Daktulosphaira vitifoliae) interaction.

Fertilizers generally influence the nutritional quality or defense ability of the plants, which can indirectly cause an increase in populations of herbivorous insect pests such as grape phylloxera, Daktulosphaira vitifoliae (Homoptera: Phylloxeridae, Fitch). The effects of nutrient solutions on grape-grape phylloxera interactions were analyzed using five concentrations (nitrogen content: 15, 30, 60, 120, and 180mg/L) of Hoagland's nutrient solution to irrigate Vitis vinifera L. × Vitis labrusca L. (Kyoho). Life table variables and life history variables showed a hump-shaped or an inverted hump-shaped curve as nutrient input level increased. Sixty microgram per liter treatment resulted in the greatest longevity and egg incubation, shortened the nymph duration and significantly increased the adult lifespan. Overall, both excessive and insufficient nutrient inputs curbed growth and multiplication of D. vitifoliae. These results provide a theoretical basis for vineyards for amending fertilizer inputs to prioritize the prevention and control of this pest.

Transfer and biological effects of cadmium along a tomato – thrip – predatory bug food chain

The heavy metal, cadmium (Cd) is an increasingly serious issue in agricultural ecosystems, mediating bottom-up effects on plants, herbivores and natural enemies. We measured how Cd modifies interactions between tomato Solanum lycopersicum, western flower thrips Frankliniella occidentalis, and the predatory bug Orius sauteri by examining Cd effects on the growth of tomato, the fitness of western flower thrips, and the survival and behavior of predators. The photosynthetic parameters of Pn (net photosynthetic rate), Gs (stomatal conductance), Ci (intercellular CO2 concentration), and Tr (transpiration rate) of tomato plants significantly decreased with the increase of Cd concentration. The total survival number of western flower thrips fed on tomato plants treated with different concentrations of Cd was significantly lower than that of the control, and sex ratios (female/male) gradually increased with the increase of Cd concentration. The numbers of thrips predated by O. sauteri on tomato plants treated with high concentrations of Cd (2.0 or 4.0 mg/L) were significantly reduced by the second day. Cadmium was accumulated and bioconcentrated in the roots, stems, leaves of tomato plants, and transferred to F. occidentalis, and O. sauteri. Cadmium translocated in significant quantities from roots to the stems and leaves of tomato plants, and from the tomato leaf to F. occidentalis. However, there was minimal (non-significant) transfer of Cd from F. occidentalis to O. sauteri. The presence of Cd significantly reduced the growth of tomato plants, the fitness of F. occidentalis, and the predation efficiency of O. sauteri. Collectively, Cd can mediate bottom-up effects on tomato, thrip, and predatory bug along food chain, potentially interrupting pest biological control in tomato in heavy metal-contaminated ecosystems.

Analysis of the top-down and bottom-up effects on zooplankton biomass in eutrophic Lake Yeniçağa

Several aquatic ecological studies have focused on the contrasting effects of top-down and bottom-up interactions on zooplankton communities. It is essential to comprehend the relative strength of these interactions to evaluate the trophic interactions of pelagic food webs, an area that is still extensively researched due to its complexity. Therefore, we examined the biomass of zooplankton over a one-year period in a freshwater lake that is subject to multiple stressors such as anthropogenic activities, eutrophication. Top-down effects, namely fish biomass, and bottom-up effects, including total phosphorus, total nitrogen, and chlorophyll a concentrations were considered. Structural equation modelling (SEM) was employed to evaluate the relative impact of top-down and bottom-up effects on zooplankton. The SEM analysis revealed that zooplankton is influenced by both top-down and bottom-up effects in Lake Yeniçağa. The biomass of cladocerans was found to have a negative correlation with increasing chlorophyll a, while the Calanoida group was negatively affected by both fish biomass and chlorophyll a from top-down and bottom-up controls. The fish biomass had a positive effect on both Cyclopoida and Rotifera, but only Rotifera showed a negative interaction with chlorophyll a. Direct bottom-up effects of total phosphorus and total nitrogen on chlorophyll a were found, with total nitrogen having a stronger interaction than total phosphorus.

Dryland state transitions alter trophic interactions in a predator-prey system.

Environmental change is expected to alter trophic interactions and food web dynamics with consequences for ecosystem structure, function and stability. However, the mechanisms by which environmental change influences top-down and bottom-up processes are poorly documented. Here, we examined how environmental change caused by shrub encroachment affects trophic interactions in a dryland. The predator-prey system included an apex canid predator (coyote; Canis latrans), an intermediate canid predator (kit fox; Vulpes macrotis), and two herbivorous lagomorph prey (black-tailed jackrabbit, Lepus californicus; and desert cottontail, Sylvilagus audubonii) in the Chihuahuan Desert of New Mexico, USA. We evaluated alternative hypotheses for how shrub encroachment could affect habitat use and trophic interactions, including (i) modifying bottom-up processes by reducing herbaceous forage, (ii) modifying top-down processes by changing canid space use or the landscape of fear experienced by lagomorph prey and (iii) altering intraguild interactions between the dominant coyote and the intermediate kit fox. We used 7 years of camera trap data collected across grassland-to-shrubland gradients under variable precipitation to test our a priori hypotheses within a structural equation modelling framework. Lagomorph prey responded strongly to bottom-up pulses during years of high summer precipitation, but only at sites with moderate to high shrub cover. This outcome is inconsistent with the hypothesis that bottom-up effects should be strongest in grasslands because of greater herbaceous food resources. Instead, this interaction likely reflects changes in the landscape of fear because perceived predation risk in lagomorphs is reduced in shrub-dominated habitats. Shrub encroachment did not directly affect predation pressure on lagomorphs by changing canid site use intensity. However, site use intensity of both canid species was positively associated with jackrabbits, indicating additional bottom-up effects. Finally, we detected interactions between predators in which coyotes restricted space use of kit foxes, but these intraguild interactions also depended on shrub encroachment. Our findings demonstrate how environmental change can affect trophic interactions beyond traditional top-down and bottom-up processes by altering perceived predation risk in prey. These results have implications for understanding spatial patterns of herbivory and the feedbacks that reinforce shrubland states in drylands worldwide.

The dance of power and responsibility: understanding the multilevel government influence on CSR practices in Chinese state-owned enterprises

ABSTRACT This study investigates how multilevel government influences the corporate social responsibility (CSR) practices of state-owned enterprises (SOEs). Using the control rights theory, we illustrate how the supervisor (the provincial government) utilizes residual control rights allocated by the principal (the central government) to exert both top-down binding and bottom-up buffering effects on the CSR practices of their agents (local governments and SOEs). Our findings reveal a U-shaped relationship between government control levels and SOEs’ CSR practices, with administrative intervention reinforcing this trend and fiscal decentralization leading to an inverted U-shaped relationship. These insights highlight complex inter-governmental dynamics influencing SOEs’ CSR practices.

Impacts of microplastic ingestion on fish communities in Haizhou Bay, China

Microplastics are pervasive throughout aquatic ecological communities. While their negative impacts on the life history traits of aquatic species are well studied, the effects on community dynamics remain elusive. Consequently, community-level assessments of microplastic effects on marine food webs are largely lacking, creating significant knowledge gaps regarding marine ecosystem structure and dynamics in the context of microplastic contamination. Here we expand a multispecies size-spectrum model by incorporating microplastic impacts on individual life-history traits, ultimately allowing us to study microplastic-mediated structural and functional changes in fish communities. As expected, microplastic ingestion may drive species extinction, but the microplastic-to-food ratio threshold for extinction is species-specific, and not necessarily correlated with species’ asymptotic weights. Interestingly, species responses to microplastics also propagate through the community as ingestion triggers both bottom-up and top-down effects on community dynamics. Which specific type of cascading effect is dominating depends on which species is ingesting microplastics as well as its trophic role in the community. Generally, low-trophic-level species ingesting microplastics can exert large detrimental effects on community biomass. Thus, this study highlights the necessity for a comprehensive risk assessment of species-specific responses to microplastic contamination as well as an understanding of individual species’ role in their communities.

Atlantis end-to-end modeling to explore ecosystem dynamics in the Strait of Sicily, Central Mediterranean Sea

This paper describes the first application of the end-to-end model Atlantis in the Strait of Sicily (SoS). The model is designed to simulate ecosystem dynamics under the influence of fishing activities. Model performance was evaluated by comparing predicted biomass and catch of target species against observed data, utilizing multiple quantitative metrics. It reproduces accurately trophic dynamics, and biomass and catch of main target species in the SoS. Sensitivity analysis of the key model parameters identified nutrient loading and fishing pressure as the major processes influencing the ecosystem trophic spectrum and generating bottom-up and top-down effects. The results also emphasized the importance of incorporating uncertainty estimation in model predictions and robust selection of key parameters. The SoS Atlantis represents a strategic tool for the application of Ecosystem Approach to Fisheries Management (EAFM) in the Strait of Sicily and for assessing the effect of alternative management scenarios under a holistic framework.

Quantifying the importance of ontogeny and prey type in modeling top-down and bottom-up effects of an ectothermic predator

Dietary decisions by predators can affect prey abundance and overall food web dynamics. Many predators do not forage on the same prey at the same frequency throughout their lives. Ontogenetic shifts in prey preference are not, however, often accounted for when modeling food web relationships, despite growing literature that suggests that stage specific dietary relationships may be an important consideration when modeling trophic interactions. We investigated the importance of considering size-structure of a predator population with ontogenetic diet shifts in evaluating relationships with prey response using a manipulative experiment with the brown treesnake (Boiga irregularis) in Guam. After removing ~ 40% of the snake population via toxic mammal carrion, we measured the strength of the relationship between snake density and the response of two types of prey (lizards and mammals). We evaluated these relationships based on total population size or division of the population into stage specific size categories based on diet preference predictions. We hypothesized that the density of juvenile snakes would correlate more strongly with lizard detections, while adult snakes would better correlate to rodent detections. We also measured reproductive output following changes in rates of prey detection. As expected by known ontogenetic shifts in dietary preference, explicit stage-based models better predicted shifts in rates of observed prey items than did total predator density for both lizards and mammals. Additionally, rodent detections were predictive of one reproductive pulse from snakes, while lizard detections were not predictive or correlated. Our findings support that consideration of predatory species stage-based dietary preference can be meaningful for understanding food web dynamics, particularly when a predator has a broad diet or one that changes through time.

Flow velocity determines detritus availability and microbial food web patterns in a river confluence

Detritus is the vital support for the microbial food web, which would further affect river ecological conditions. Determining the effects of detritus availability on microbial food webs in rivers is critical for protecting river ecological functions. However, the detritus availability was difficult to estimate directly, since the detritus transformation processes (i.e. detritus availability) and flow-induced transport processes are interdependent in rivers. Therefore, this study quantified the detritus transformation processes in a natural river and further identified the impacts of detritus availability on microbial food web patterns. Results revealed that the flow velocity was the main physical driver determining the detritus availability. The decreased velocity would promote detritus availability. Moreover, the increased detritus availability significantly promoted the diversity of bacteria, protozoan and metazoan (p < 0.05). The responses of low trophic levels to detritus availability were significantly greater than those of higher trophic levels, emphasizing the bottom-up cascading effect of detritus availability on microbial food web composition (p < 0.05). From microbial food web perspectives, the detritus availability was amplified with flow velocity decreased, promoting trophic transfer efficiency between different trophic levels. Results and findings revealed the ecological effect of detritus transformation processes on multi-trophic levels in rivers and provided advantageous information for river management.

Nutritional Quality of Basal Resource in Stream Food Webs Increased with Light Reduction—Implications for Riparian Revegetation

Biofilms are considered a basal resource with high nutritional quality in stream food webs, as periphytic algae are abundant of polyunsaturated fatty acids (PUFAs). PUFAs are essential for growth and reproduction of consumers who cannot or have very limited capacity to biosynthesize. Yet, how the nutritional quality based on PUFA of basal food sources changes with light intensity remains unclear. We conducted a manipulative experiment in mesocosms to explore the response and mechanisms of nutritional quality to shading, simulating riparian restoration. We found a significant increase in PUFA% (including arachidonic acid, ARA) under shading conditions. The increased PUFA is caused by the algal community succession from Cyanobacteria and Chlorophyta to Bacillariophyta which is abundant of PUFA (especially eicosapentaenoic acid, EPA; docosahexaenoic acid, DHA). On the other hand, shading increased PUFA via upregulating enzymes such as Δ12 desaturase (FAD2, EC:1.14.19.6) and 3-ketoacyl-CoA synthase (KCS, EC:2.3.1.199) in the biosynthesis of unsaturated fatty acid elongation pathways. Our findings imply that riparian reforestation by decreasing light intensity increases the nutritional quality of basal resources in streams, which may enhance transfer of good quality carbon to consumers in higher trophic levels through bottom-up effects.

Bottom-up effects of reduced fertilization on natural enemies and biocontrol efficacy

Bottom-up effects of reduced fertilization on natural enemies and biocontrol efficacy

Bottom-up effects of bamboo-charcoal soil amendment on the tomato insect pest Bemisia tabaci

Bottom-up effects of bamboo-charcoal soil amendment on the tomato insect pest Bemisia tabaci