Top-down Pressure Research Articles

Predation and parasitism on herbivorous insects change in opposite directions in a latitudinal gradient crossing a boreal forest zone.

The latitudinal biotic interaction hypothesis (LBIH) predicts that the strength of various biotic interactions decreases from low to high latitudes. Inconsistency between studies testing this hypothesis may result from variations among different types of interactions and among study systems. Therefore, exploration of multiple interactions within one system would help to disentangle latitudinal patterns across individual interactions and to evaluate latitudinal changes in the overall impact of enemies on prey. We tested the prediction based on the LBIH that the pressure of natural enemies on herbivorous insects decreases with increase in latitude across the boreal forest zone. We also asked whether the impacts of major groups of these enemies exhibit similar latitudinal patterns and whether these patterns are consistent across study years. In 10 forest sites located from 60°N to 69°N in Northern Europe, each summer, from 2016 to 2019, we measured (a) mortality of three groups of leafmining insects caused by birds, ants, parasitoids and unknown factors, (b) bird attacks on caterpillar-shaped plasticine models and (c) birch foliar damage caused by defoliators and leafminers. Latitudinal patterns in both insect herbivory on birch and top-down pressure on herbivorous insects varied considerably and inconsistently among the four study years, so that only some of the year-specific correlations with latitude were statistically significant. Nevertheless, meta-analysis combining correlations across years, preys and enemies revealed general decreases in predation by birds (on both natural and model prey) and ants, but an increase in parasitism rates, from low to high latitudes. We found that the direction of latitudinal changes in the strength of biotic interactions was interaction-specific: predation and herbivory supported LBIH, whereas parasitism exhibited an opposite trend. Consequently, the overall impact of natural enemies on herbivorous insects did not change with latitude and was therefore an unlikely reason for the poleward decrease in herbivory observed in our gradient. Considerable among-year variation in the strength of the latitudinal patterns in all the studied interactions suggests that this variation is a widespread phenomenon.

Revenue Extraction Is Not Enough: The Ambiguous Effectiveness of the Rwandan Revenue Authority

The objective of this paper is to understand the RRA’s relatively high, and yet uneven, performance. While the organization is effective regarding overall revenue collection, and processes of tax filling and payment, it is much less so with regard to everyday bookkeeping, reporting and provision of inputs to policymaking. The paper argues that the dominant nature of the political settlement and the ruling elite’s paradigmatic ideas of national self-reliance supported the performance of the RRA in extracting revenues. On the other hand, the top-down pressure on the RRA to perform produced a range of perverse incentives in the organization, making everyday processes of bookkeeping and reporting secondary. In addition, vested interests regarding property tax and the tension between state-centered and marketed ideas about development led to a series of policy gaps that limited revenue mobilization. Furthermore, the vulnerability of the elite anchored in its minority status, and its origins in the diaspora, meant that the state in general, and the RRA in particular, while autonomous from social pressure, might not be much embedded in society. This led to an uneven performance. The organization performed well in the raw task of extracting revenue, which requires a high level of autonomy, but much less so when its tasks, such as providing advice to policy formulation, required some embeddedness with key segments of society.

Relationships between a common Caribbean corallivorous snail and protected area status, coral cover, and predator abundance

As coral populations decline across the Caribbean, it is becoming increasingly important to understand the forces that inhibit coral survivorship and recovery. Predation by corallivores, such as the short coral snail Coralliophila abbreviata, are one such threat to coral health and recovery worldwide, but current understanding of the factors controlling corallivore populations, and therefore predation pressure on corals, remains limited. To examine the extent to which bottom-up forces (i.e., coral prey), top-down forces (i.e., predators), and marine protection relate to C. abbreviata distributions, we surveyed C. abbreviata abundance, percent coral cover, and the abundance of potential snail predators across six protected and six unprotected reefs in the Florida Keys. We found that C. abbreviata abundance was lower in protected areas where predator assemblages were also more diverse, and that across all sites snail abundance generally increased with coral cover. C. abbreviata abundance had strong, negative relationships with two gastropod predators—the Caribbean spiny lobster (Panulirus argus) and the grunt black margate (Anisotremus surinamensis), which may be exerting top-down pressure on C. abbreviata populations. Further, we found the size of C. abbreviata was also related to reef protection status, with larger C. abbreviata on average in protected areas, suggesting that gape-limited predators such as P. argus and A. surinamensis may alter size distributions by targeting small snails. Combined, these results provide preliminary evidence that marine protection in the Florida Keys may preserve critical trophic interactions that indirectly promote coral success via control of local populations of the common corallivorous snail C. abbreviata.

Amplifying and nullifying the impact of democratic sanctions through aid to civil society

ABSTRACT Both foreign aid and sanctions are foreign policy tools to promote democracy. Yet, it is unclear how far incentives and coercion enhance democratization. Since sanctions and aid are often employed at the same time, the goal of this study is to determine their joint effect on democratization in target/recipient countries. We argue that sending democracy aid through civil society organizations enhances the effectiveness of sanctions as a democracy promotion tool because the civil society is empowered to introduce democratic changes. Thus, in addition to the top-down pressure on the target government created by sanctions, there is a bottom-up pressure exerted by the civil society. Our empirical results show that democratic sanctions by the European Union and the United States are more likely to have a positive effect when aid flows bypass the government. Conversely, aid channeled through the public sector mitigates the generally positive effect of sanctions on democracy. In order to estimate these joint effects, we employ a new comprehensive dataset on economic sanctions: the EUSANCT Dataset which integrates and updates existing databases on sanctions for the period between 1989 and 2015, merged with disaggregated OECD aid data and V-Dem democracy scores.

Bottom-up and top-down processes influence contemporary patterns of mammal species richness in Australia's monsoonal tropics

In recent decades severe mammal declines have occurred in the vast and uncleared tropical savannas of northern Australia. Mounting evidence suggests that feral cats (Felis catus), large feral herbivores and increased frequency of high-severity fires, are all contributing to declines; however, the respective influence of each threat remains unclear. There is an urgent need to quantify the relative impacts of both ‘bottom-up’ (i.e. the depletion of resources and habitat simplification from contemporary disturbance regimes) and ‘top-down’ (i.e. increased predation pressure) factors on small mammal populations to inform where, and how, remedial conservation efforts should be targeted in northern Australia. We conducted an extensive survey of mammals across ca. 370,000 km2 of monsoonal northern Australia using both camera-trapping and live-trapping methods. From multispecies occupancy models, we found that feral herbivore abundance, dingo abundance and feral cat occupancy were the best predictors of species richness of small (<5500 g) mammals, with species richness declining as the respective pressures increased. Our results highlight that underlying productivity has seemingly enhanced the capacity of native mammals to withstand pressures, as species that have severely declined are now more likely to occur in areas with greater productivity. We suggest that a disturbance-driven reduction in habitat complexity and productivity has significantly disrupted bottom-up processes in northern Australia, subsequently increasing top-down pressure from predation, causing severe declines across much of the native mammal assemblage. Without maintaining, enhancing or recovering habitat condition in this region, long-term conservation and recovery of mammal diversity is unlikely.

Application of neural networks to model changes in fish community biomass in relation to pressure indicators and comparison with a linear approach

Neural networks (NN) are considered well suited to modelling ecological data, especially nonlinear relationships, and were applied here to investigate which pressures best model changes in the fish community of the Grand Bank, Northwest Atlantic. Nine fishing and environmental pressures were used to simultaneously model the biomasses of six fish functional groups before and after the collapse of fish biomass in the region and over the full data series. The most influential pressures were identified, and the fit and predictive power were evaluated. The analysis was repeated with different types and lengths of time delay imposed on the pressures. Results were compared with a similar analysis using a multivariate linear regression (MLR) approach. MLR generally resulted in better fit, although the ecological implications of the approaches were typically similar. Findings show that both top-down and bottom-up pressures influenced the fish community over the past several decades, over short and long time scales. NN may have useful forecast potential, although future work is required to improve the forecasts shown here before they can directly inform management.

Mobilities of policy and mobile parents – creating a new dynamic in policy borrowing within state schooling

ABSTRACT In this article, we focus on the transformations imposed on schools by individual parents, arguing that schools as modern organisations change not only through top-down pressures orchestrated by an array of international organisations, for-profit companies and media as shown in previous research, but also through the agency of mobile parents, who seek to import reforms from elsewhere, based on their previous schooling experiences abroad. We focus on a specific group of middle class parents, who are continuously mobile, moving between global cities for employment. This paper brings into the discussion the role of individual parental strategies as they seek to promote education policy-borrowing. By applying the theoretical lens of stakeholder identification and salience, using a multi case study research design, we suggest that parents express high levels of power, legitimacy and a sense of urgency, thus being able to successfully advocate for change. We argue that while exploring organisational reform occurring due to the globalisation of education, we must view parents as central actors in this new space.

Top-down and bottom-up controls on an herbivore on a native and introduced plant in a tropical agricultural landscape.

The recent introduction in a tropical agricultural environment of a weedy open-habitat plant (Solanum myriacanthum) and subsequent host range expansion of a common forest-edge butterfly (Mechanitis menapis) onto that plant provides an opportunity to examine reconfiguration of tritrophic networks in human-impacted landscapes. The objectives of this study were (1) determine if the caterpillars on the exotic host are more or less limited by plant defenses (bottom-up forces) and if they experience enemy release (decrease of top-down pressure) and (2) define how anthropic open pasture habitat influences the herbivore’s tritrophic niche. Field and laboratory monitoring of larval survival and performance on a native (Solanum acerifolium) host plant and the exotic (S. myriacanthum) host plant were conducted in the Mindo Valley, Ecuador. Plant physical defenses were also measured. Results showed that larval mortality was mostly top-down on S. acerifolium, linked to parasitism, but mostly bottom-up on S. myriacanthum, possibly linked to observed increased plant defenses. Thus, in the absence of co-evolved relationships, herbivores on the exotic host experienced little top-down regulation, but stronger bottom-up pressures from plant defenses. These findings provide a rare empirical example of enemy-free space as a mechanism underlying host-range expansion. S. myriacanthum was less colonized in open pastures than in semi-shaded habitats (forest edges, thickets): fewer eggs were found, suggesting limited dispersal of adult butterflies into the harsh open environments, and the survival rate of first instar larvae was lower than on semi-shaded plants, likely linked to the stronger defenses of sun-grown leaves. These findings show how environmental conditions modulate the rewiring of trophic networks in heavily impacted landscapes, and limit a biocontrol by a native herbivore on an invasive plant in open habitats.

‘What works’ won't do

Too much top-down pressure to create early years policy that meets narrow, pre-determined outcomes must be adjusted with a wider focus. This is an international issue, discovers Sue Allingham.

Predator type influences the frequency of functional responses to prey in marine habitats.

The functional response of a consumer to a gradient of resource density is a widespread and consistent framework used to quantify the importance of consumption to population dynamics and stability. Within benthic marine ecosystems, both crustaceans and fishes can provide strong top-down pressure on prey populations. Taxon-specific differences in biomechanics or habitat use, among other factors, may lead to variable functional response forms or parameter values (attack rate, handling time). Based on a review of 189 individual functional response fits, we find that these predator guilds differ in their frequency distribution of functional response types, with crustaceans exhibiting nearly double the proportion of sigmoidal, density-dependent functional responses (Holling type III) as predatory fishes. The implications of this finding for prey population stability are significant because type III responses allow prey persistence while type II responses are de-stabilizing and can lead to extinction. Comparing per capita predation rates across diverse taxa can provide integrative insights into predatory effects and the ability of predation to drive community structure.

Using One Dying Regime to Save Another: The Influence of International Drug Conventions on United States’ Cannabis Research Policy

Cannabis reforms are proliferating. A handful of nations have already legalized the drug for recreational purposes, and several more may soon follow suit. These national cannabis reforms are generating bottom-up pressure to liberalize the transnational legal order (TLO) for cannabis prohibition, one that involves not only international law, but also domestic law and regulatory practice. Based on a trio of international conventions, this TLO currently requires member states to limit access to marijuana, especially for non-medical or non-scientific purposes. But even as it comes under attack from below, the existing cannabis prohibition TLO may be exerting its own downward pressure on national cannabis policies. This essay uses a timely case study involving the United States’ marijuana research policy to explore the two-way relationship between international law and national cannabis policies in the dynamics of transnational legal ordering. It highlights an overlooked way the international conventions are currently helping to stifle national cannabis reforms, and it discusses the possible ramifications of that top-down pressure for the future of the cannabis prohibition TLO.

Academics' perceptions of students' motivation for learning and their own motivation for teaching in a marketized higher education context.

The marketization of higher education (HE), which positions students as consumers and academics as service providers, may adversely affect students' motivation for learning and academics' motivation for teaching. According to self-determination theory (SDT), high-quality forms of motivation are achieved when individuals experience fulfilment of three psychological needs: competence, autonomy, and relatedness. This study applied SDT to examine academics' perceptions of whether the marketized HE contextin England, UK, supported or undermined these three psychological needs for their students and for themselves. It also examined their perceptions of the impact that this context had on their teaching. Participants were 10 academics teaching at five post-1992 HE institutions in England, UK. Semi-structured interviews were conducted and subsequentlyanalysed using thematic analysis. Academics observed that students identifying as consumers seemed to display lower levels of competence, autonomy, and relatedness. This contributed to an HE environment that diminished the academics' own psychological needs. Although some felt able to improve student motivation through their teaching, others felt demotivated and disempowered by top-down pressure from managers and bottom-up pressure from students. The marketized HE context may undermine high-quality motivation for students' learning and academics' teaching. Academics should be supported to teach in ways that facilitate competence, autonomy, and relatedness in their students and themselves.

Coarse- and fine-scale acoustic telemetry elucidates movement patterns and temporal variability in individual territories for a key coastal mesopredator

Great barracuda (Sphyraena barracuda) are a high trophic level predator that uses a wide variety of habitats globally throughout tropical and subtropical waters. Despite the important top-down pressure this species likely exerts on fish communities within its foraging territories, the specifics of spatial ecology remain relatively unknown. This study tracked 17 great barracuda throughout Buck Island Reef National Monument, a marine-protected area located in St. Croix, U.S. Virgin Islands (17.786944° N, − 64.620556° W) from July 2014 to May 2016. Broad- and fine-scale acoustic telemetry was used to examine individual variability and study population patterns in residency, site fidelity, territoriality, and complexity of spatial use within home ranges. Network analysis of broad-scale data revealed spatial and temporal differentiation among the population in location of core use areas and showed that these areas contained multiple unique receiver groups or communities, a product of spatial or temporal variation within core activity spaces. Results from the fine-scale positioning system reinforced spatial and temporal partitioning in core use areas between individuals, indicating territorial behaviors, and showed evidence for both resident and transient movements. Preliminary fine-scale analysis also suggested diel variation in location of activity spaces. Although ubiquitous throughout all shallow water habitats, detection patterns for the study population appear to be influenced by high residency, territoriality, spatial partitioning, and diel variation. Understanding the complexities of individual space use is fundamental to ecologically founded and effective area-based spatial management frameworks at community scales.

Top-down pressure by generalist and specialist natural enemies in relation to habitat heterogeneity and resource availability

Habitat heterogeneity might promote the abundance and richness of natural enemies potentially leading to higher top-down pressure on herbivorous insects. Heterogeneous habitats could provide natural enemies with more abundant and alternative resources and a greater variety of micro-habitats. Natural enemies with different searching behaviours, e.g. generalists and specialists, could be affected in different ways by habitat heterogeneity, thus affecting their pressure on herbivorous insects.To understand how top-down pressure on herbivorous insects is promoted by habitat heterogeneity, it is crucial to investigate which parameters contributing to habitat heterogeneity affect not only the abundance and richness but also the searching behaviour of different natural enemies. We investigated the relationship between heterogeneity in forest habitats and the top-down pressure exerted by generalist predators and specialist parasitoids on larvae of the European pine sawfly (Neodiprion sertifer).We used forest stands with endemic or epidemic densities of resident sawfly populations. Within each stand we selected experimental trees to create variation in tree species diversity and density in their surrounding area, i.e. habitat heterogeneity. We found that a higher tree density increased the predation by generalists on sawfly larvae in stands with endemic sawfly densities. Parasitoids were less successful in stands with endemic sawfly densities. Total mortality depended on stand character and the proportion of pine around experimental trees.The explained variation in the response variables by the models is relatively low, indicating that other measures of heterogeneity, like understory vegetation and presence of dead wood could contribute to the observed variation. Also, interference between generalist and specialist enemies could affect the realized mortality pressure. Thus, the effect of tree species diversity in combination with these other measures of heterogeneity needs to be recognized to promote the presence and the activity of natural enemies in managed habitats.

Biotic Interactions in Experimental Antarctic Soil Microcosms Vary with Abiotic Stress

Biotic interactions structure ecological communities but abiotic factors affect the strength of these relationships. These interactions are difficult to study in soils due to their vast biodiversity and the many environmental factors that affect soil species. The McMurdo Dry Valleys (MDV), Antarctica, are relatively simple soil ecosystems compared to temperate soils, making them an excellent study system for the trophic relationships of soil. Soil microbes and relatively few species of nematodes, rotifers, tardigrades, springtails, and mites are patchily distributed across the cold, dry landscape, which lacks vascular plants and terrestrial vertebrates. However, glacier and permafrost melt are expected to cause shifts in soil moisture and solutes across this ecosystem. To test how increased moisture and salinity affect soil invertebrates and their biotic interactions, we established a laboratory microcosm experiment (4 community × 2 moisture × 2 salinity treatments). Community treatments were: (1) Bacteria only (control), (2) Scottnema (S. lindsayae + bacteria), (3) Eudorylaimus (E. antarcticus + bacteria), and (4) Mixed (S. lindsayae + E. antarcticus + bacteria). Salinity and moisture treatments were control and high. High moisture reduced S. lindsayae adults, while high salinity reduced the total S. lindsayae population. We found that S. lindsayae exerted top-down control over soil bacteria populations, but this effect was dependent on salinity treatment. In the high salinity treatment, bacteria were released from top-down pressure as S. lindsayae declined. Ours was the first study to empirically demonstrate, although in lab microcosm conditions, top-down control in the MDV soil food web.

The Practice of Civic Tech: Tensions in the Adoption and Use of New Technologies in Community Based Organizations

This article reports on a qualitative study of community based organizations’ (CBOs) adoption of information communication technologies (ICT). As ICTs in the civic sector, otherwise known as civic tech, get adopted with greater regularity in large and small organizations, there is need to understand how these technologies shape and challenge the nature of civic work. Based on a nine-month ethnographic study of one organization in Boston and additional interviews with fourteen other organizations throughout the United States, the study addresses a guiding research question: how do CBOs reconcile the changing (increasingly mediated) nature of civic work as ICTs, and their effective adoption and use for civic purposes, increasingly represent forward-thinking, progress, and innovation in the civic sector?—of civic tech as a measure of “keeping up with the times.” From a sense of top-down pressures to innovate in a fast-moving civic sector, to changing bottom-up media practices among community constituents, our findings identify four tensions in the daily practice of civic tech, including: 1) function vs. representation, 2) amplification vs. transformation, 3) grassroots vs. grasstops, and 4) youth vs. adults. These four tensions, derived from a grounded theory approach, provide a conceptual picture of a civic tech landscape that is much more complicated than a suite of tools to help organizations become more efficient. The article concludes with recommendations for practitioners and researchers.

Internationalization, Mobility and Englishization in Higher Education Across OECD Countries

Although the European Union policies explicitly support the notion of multilingualism, the impact of increasing internationalization on the linguistic landscape of the European higher education system has been dramatic. In the post-Bologna period, the desire of higher education institutions to attract a more skilled and diverse body of students seems to turn English into the medium of instruction of a significant number of higher education institutions based in the continent. Particularly, competitiveness in the academic market that leads to bottom-up and top-down pressures within universities to become more international may have caused many higher education institutions to directly associate internationalization with Englishization. As this situation reinvigorates the status of English as the lingua franca, the present article investigates the links between internationalization, language policies, and Englishization through having a closer look at the OECD international student mobility data. The article also points to several practical and pedagogical considerations involved in implementing language policies in higher education.

Community Perspectives of a 3-Delays Model Intervention: A Qualitative Evaluation of Saving Mothers, Giving Life in Zambia.

Saving Mothers, Giving Life (SMGL), a health systems strengthening approach based on the 3-delays model, aimed to reduce maternal and perinatal mortality in 6 districts in Zambia between 2012 and 2017. By 2016, the maternal mortality ratio in SMGL-supported districts declined by 41% compared to its level at the beginning of SMGL-from 480 to 284 deaths per 100,000 live births. The 10.5% annual reduction between the baseline and 2016 was about 4.5 times higher than the annual reduction rate for sub-Saharan Africa and about 2.6 times higher than the annual reduction estimated for Zambia as a whole. While outcome measures demonstrate reductions in maternal and perinatal mortality, this qualitative endline evaluation assessed community perceptions of the SMGL intervention package, including (1) messaging about use of maternal health services, (2) access to maternal health services, and (3) quality improvement of maternal health services. We used purposive sampling to conduct semistructured in-depth interviews with women who delivered at home (n=20), women who delivered in health facilities (n=20), community leaders (n=8), clinicians (n=15), and public health stakeholders (n=15). We also conducted 12 focus group discussions with a total of 93 men and women from the community and Safe Motherhood Action Group members. Data were coded and analyzed using NVivo version 10. Delay 1: Participants were receptive to SMGL's messages related to early antenatal care, health facility-based deliveries, and involving male partners in pregnancy and childbirth. However, top-down pressure to increase health facility deliveries led to unintended consequences, such as community-imposed penalty fees for home deliveries. Delay 2: Community members perceived some improvements, such as refurbished maternity waiting homes and dedicated maternity ambulances, but many still had difficulty reaching the health facilities in time to deliver. Delay 3: SMGL's clinician trainings were considered a strength, but the increased demand for health facility deliveries led to human resource challenges, which affected perceived quality of care. While SMGL's health systems strengthening approach aimed to reduce challenges related to the 3 delays, participants still reported significant barriers accessing maternal and newborn health care. More research is needed to understand the necessary intervention package to affect system-wide change.

Perceptual inhibitors of instructional leadership in Israeli principals

ABSTRACTThe instructional leadership approach expects school leaders to give top priority to ongoing improvement of teaching quality and academic outcomes. Researchers have found that despite the top-down pressures to assume an instructional leadership role, school principals demonstrate limited direct involvement in such leadership. The current qualitative study, based on semi-structured interviews, aimed to expand inquiry into inhibitors of instructional leadership in Israeli principals. Data analysis uncovered that Israeli principals’ perceptions served as key inhibitors of instructional leadership, identifying three main perceptual inhibitors: (1) perceptions regarding principal-teacher relationships; (2) perceptions regarding the role of the principal; and (3) perceptions regarding the goal of schooling. These findings expands the available knowledge by illustrating how for Israeli principals, the inhibitors of instructional leadership did not only involve the constraints and capabilities of school principals but also deep disagreements with the conceptual framework that underpins instructional leadership. Implications and further research are discussed.

Contribution of different predator guilds to tritrophic interactions along ecological clines.

The strengths of interactions between plants, herbivores, and predators are predicted to relax with elevation. Despite the fundamental role predators play in tritrophic interactions, high-resolution experimental evidence describing predation across habitat gradients is still scarce in the literature and varies by predator. With this opinion paper, we look at how tritrophic strength of systems including different vertebrate and invertebrate predator guilds changes with elevation. Specifically, we focus on how birds, ants, parasitoids, and nematodes exert top-down pressure as predators and propose ways, in which each group could be better understood through elevational gradient studies. We hope to enrich future perspectives for disentangling the different biotic and abiotic factors underlying predator-mediated trophic interactions in a diversity of habitats.