Search

Most terrestrial large mammals went extinct on different continents at the end of the Pleistocene, between 50,000 and 10,000 years ago. Besides the loss in species diversity and the truncation of body mass distributions, those extinctions were even more impactful to interaction diversity. Along with each extinction, dozens of ecological interactions were lost, reorganizing species interaction networks, which attained species-poor configurations with low functional redundancy. Extinctions of most large herbivores impacted energy flow and the rates of nutrient cycling, reconfiguring ecosystem-level networks. Because large mammals have high mobility, their loss also shortened seed-dispersal distance and reduced nutrient diffusivity, disrupting spatial networks. This review examines the recent advances in understanding how different types of ecological networks have been restructured by megafaunal extinctions and how this reorganization affected ecosystem functions. Megafaunal extinctions resulted in the loss of multiple ecological interactions in terrestrial systems. Interaction loss reshaped different types of ecological networks including food webs and spatial networks. The reorganization of ecological networks changed how terrestrial ecosystems are structured and function. [ABSTRACT FROM AUTHOR]

Investigating species responses to trophic interactions and abiotic factors is crucial to better understanding their ecology and creating effective management strategies. In carnivore communities, smaller species are often regulated by larger ones via top‐down interference competition. Smaller subordinate carnivores can also be regulated by bottom‐up and abiotic factors, such as the availability of important prey, habitat features, and climatic conditions. However, substantial ambiguity remains regarding the relative roles these complex factors play in shaping subordinate carnivore populations, especially during winter. To investigate this issue, we conducted a large‐scale camera‐trapping study (n = 197 sites distributed across a ~60,000 km2 landscape) using a balanced study design that sampled a gradient of forest disturbance and climatic conditions. We used dynamic occupancy modeling to examine the influences of top‐down (interference competition), bottom‐up (prey and habitat), and abiotic (climate) factors on a widespread, generalist subordinate carnivore, the red fox (Vulpes vulpes), in Maine, USA. Across three winters, we collected 107 red fox and 185 coyote (Canis latrans) daily detections, and 3875 snowshoe hare (Lepus americanus) detections. We found evidence for the top‐down effects of coyotes on red fox detection probability and site colonization. However, contrary to theoretical expectations, the association between coyotes and red foxes was positive rather than negative. Snowshoe hares had a positive association with local extinction by red foxes, which also contrasts with prevailing theory given that snowshoe hares are an important winter prey of red foxes in this ecosystem. The intensity of forest disturbance and the proportion of conifer forest had negative effects on red fox occurrence and detection probability, while snow depth had a strong negative effect on site colonization. Together, these results suggest red foxes are limited more by abiotic and bottom‐up factors related to habitat than by the top‐down interference competition or primary prey availability in winter. Our study supports recent findings that bottom‐up factors may shape carnivore distributions during less productive times of year. Our work also highlights how caution is needed when extrapolating previous results from summer studies to winter, as the role of top‐down and bottom‐up factors may change seasonally. [ABSTRACT FROM AUTHOR]

Soil nematodes play pivotal roles in the soil food web. However, the trophic regulation on nematodes in the soil micro‐food web and its temporal dynamics are less explored. Here, we investigated the seasonal dynamics of soil nematode community in an alpine grassland on the Qinghai–Tibet Plateau at non‐degraded (ND), moderately degraded (MD) and severely degraded (SD) stages, either under open‐top chamber warming (W) or not (NW). Nematode richness was higher in SD than in MD and ND that did not differ, accompanied by a clear shift from the bottom‐up regulation via belowground productivity in ND to the top‐down regulation via omnivore and predator nematodes in SD. The intensified top‐down regulation in SD was explained by increased proportions of predator and omnivore nematodes, likely induced by the expanded soil pore size in SD. As a result, accelerated temporal turnover of nematode community was observed under grassland degradation, which were 0.006 (slope, p = 0.78), 0.045 (p = 0.07), and 0.077 (p = 0.001) in ND, MD, and SD, respectively. Moreover, grassland degradation strengthened the association between nematode density and ecosystem respiration, whose slope was higher in SD (0.0025, p < 0.05) than in MD (0.0008, p < 0.01) or ND (insignificant). In contrast, warming did not affect the temporal turnover of the nematode community, richness, nor its role in ecosystem respiration. Overall, we revealed the accelerated temporal turnover of nematode community and its strengthened role in determining ecosystem respiration under alpine grassland degradation, suggesting that trophic cascade changes under ecosystem degradation may alter the ecosystem functioning. [ABSTRACT FROM AUTHOR]

There is mounting evidence that top‐down control by natural enemies helps maintain plant diversity in natural ecosystems. Previous work has concentrated on either forest trees or grassland herbs. Our knowledge of how natural enemies affect herb diversity in forests is limited.We used fungicides and insecticide to experimentally examine the effects of fungi and insects on herb abundance and diversity at the community‐wide scale and within groups of species with certain traits. We also assessed how the effects of fungi and insects on herb assemblages were modified by neighbouring tree diversity and composition in an old‐growth temperate forest.We found that fungicides increased overall herb abundance by 7% while decreasing herb diversity by 5%. This effect of fungicides on both herb abundance and diversity weakened with the increase of neighbouring tree diversity. Insecticide did not affect either herb abundance or diversity noticeably, except in areas dominated by deciduous trees where insecticide application reduced herb diversity.Fungicides and insecticide decreased the diversity of relatively less defended species (i.e. thin‐leaved and non‐clonal) but had no effect on the diversity of herbs with stronger defensive traits (i.e. thick‐leaved and clonal). Fungicides increased the abundance of non‐mycorrhizal (NM) species but not arbuscular‐mycorrhizal (AM) species, although the effect of fungicides on herb diversity was unrelated to species' mycorrhizal association. Insecticide had stronger effects on the abundance and diversity of NM species than AM species.Synthesis. We conclude that fungi and insect herbivores are critical to regulating herb abundance and diversity in this temperate forest, with their effects dependent on species' traits and neighbouring tree diversity and composition. Our results highlight the importance of top‐down control of understory herb communities by natural enemies in temperate forests, advancing our understanding of the processes shaping plant diversity in natural ecosystems. [ABSTRACT FROM AUTHOR]

Pain, a sign of warning and danger, is difficult to conciliate with sleep onset. Phasic pain only disrupts sleep in 30% of cases in a transitory way, without leaving any memory on morning awaking. The factors that favour the interruption of sleep seem to involve the transient reappearance of an effective cerebral connectivity and a high-level cerebral processing. In chronic pain, top-down mechanisms allow 25% of patients to sleep properly, while vulnerability factors prevent these mechanisms in the others. [ABSTRACT FROM AUTHOR]

Climate change will lead to extreme droughts, but it is difficult to predict how this will affect crop pests. In particular, it is unclear how interactions between natural enemies and pests will be influenced. In the field, bird cherry‐oat aphids (Rhopalosiphum padi (L.)) have been observed to reside close to, or below the ground surface during dry conditions. We hypothesized that this will increase the niche overlap between R. padi and ground‐dwelling predators such as carabid beetles and wolf spiders and that aphid numbers will therefore decline during dry conditions. A fully factorial mesocosm experiment was conducted testing the combined effects of drought and predator presence on aphid position and abundance on barley (Hordeum vulgare) plants. In support of our hypothesis, we found that (a) aphids moved below ground during dry conditions, (b) predators reduced aphid numbers, but only during dry conditions, and (c) predators reduced the proportion of aphids below ground in dry conditions. This increased predation effect during dry conditions was, however, compensated for by a corresponding increase in aphid performance on the plants and so the net effect of drought on aphid numbers ended up being neutral. Thus, pests can be affected by drought in complex ways via a combination top‐down and bottom‐up mechanisms. Predicting how pest populations will be affected by droughts in the future is thus a formidable research challenge. [ABSTRACT FROM AUTHOR]

This paper focuses on the ethical and regulatory issues raised by gene editing. In the introduction of this paper, authors provide the background where the ethical and regulatory issues by gene editing have been raised including the scientific dimension of gene‐editing techniques. In the second part of the paper, the authors focus on ethical issues in human gene editing with the start of Huang Junjiu case and He Jiankui case. Here, the authors discuss the criteria for evaluating action, general ethical issues in gene editing, and try to answer two crucial questions: is it ethically justifiable to use human embryo in ex vivo genome editing study and is it ethically justifiable to perform heritable human genome editing? In answering the second question, the authors discuss the arguments against and for heritable human genome editing, methodological problem, and the building of an ethical framework for heritable human genome editing. In the third part of the paper, the authors focus on regulatory issues in gene editing including proactionary approach versus ethically thinking ahead approach, self‐regulation versus top‐down regulation, transparency versus confidentiality, and education versus punishment. [ABSTRACT FROM AUTHOR]

Objectives The study aims were 1) to investigate the direction of mutual inhibitory pathways on itch intensity by utilizing conditioned pain modulation paradigms for pain and itch attenuation and 2) to explore whether itch severity is affected by the individual pain sensitivity profile, as well as pain scores reported during the tests and the past week. Design Cross-sectional. Setting Testing was conducted at the Department of Dermatology, Rambam Health Care Campus. Subjects Forty patients suffering from chronic skin disorders associated with itch and treated in the Dermatology Clinic at Rambam Health Care Campus participated in the study. Methods Efficacy of descending inhibition was evaluated by two conditioned pain modulation (CPM) paradigms: by pruriception (CPMItch) induced by cold and heat as counterstimuli to inhibit itch intensity and by nociception (CPMPain). Severity and interference of clinical pain were assessed using the Brief Pain Inventory (BPI). Results Robust CPMItch responses were obtained following the various noxious stimulations. No associations were observed between CPMPain and CPMItch, itch severity, skin disease severity, and clinical pain symptoms. According to the linear regression model, itch severity was independently associated with less efficient CPMItch (B = –0.750, P  < 0.001) and more efficient CPMPain (B = 0.031, P  = 0.016), which affects itch in opposing manners. Conclusions Findings indicate that the intrinsic capacity to inhibit pain and itch by exposure to exogenous noxious stimuli autonomously affects itch intensity in an opposing manner. These findings may shed new light on the mutual mechanistic similarity and dissimilarity between pain and itch and their hierarchy. [ABSTRACT FROM AUTHOR]

This article discusses the various manifestations of free will. Making it an adequately defined subject for neuroscientific study requires basic phenomenological analysis. The inadequacy of denying free will on the basis of Libet's and Soon's experiments is demonstrated. The manifestations of free will are the phenomena of subjective reality. The question is how they are connected with cerebral processes. An information-based approach is proposed to answer this difficult question. Mental causality is regarded as informational causality and is linked with the concept of "top-down emergent causality" [Sperry, 1994], which provides an explanation of free will as an expression of the process of self-organization or self-determination at the level of the Ego system of the brain. The strategic importance of neuroscientific investigations of the problem of the "I" and the activity of consciousness as the ability to express will are emphasized. [ABSTRACT FROM AUTHOR]

Natural enemies, that is, species that inflict harm on others while feeding on them, are fundamental drivers of biodiversity dynamics and represent a substantial portion of biodiversity as well. Along the life history of the Earth, natural enemies have been involved in probably some of the most productive mechanisms of biodiversity genesis; that is, adaptive radiation mediated by enemy-victim coevolutionary processes. At ecological timescales, natural enemies are a fundamental piece of food webs and can contribute to biodiversity preservation by promoting stability and coexistence at lower trophic levels through top-down regulation mechanisms. However, natural enemies often produce dramatic losses of biodiversity, especially when humans are involved.

Historic hunting has led to severe reductions of many marine mammal species across the globe. After hunting ceased, some populations have recovered to pre-exploitation levels and may have regained their prominent position as top predator in marine ecosystems. Also, the harbor seal population in the international Wadden Sea grew at an exponential rate following a ban on seal hunting in 1960s, and the current number ~38,000 is close to the historic population size. Here we estimate the impact of the harbor seal predation on the fish community in the Wadden Sea and nearby coastal waters. Fish remains in fecal samples and published estimates on the seal's daily energy requirement were used to estimate prey selection and the magnitude of seal consumption. Estimates on prey abundance were derived from demersal fish surveys, and fish growth was estimated using a Dynamic Energy Budget model. GPS tracking provided information on where seals most likely caught their prey. Harbor seals hauling-out in the Dutch Wadden Sea fed predominantly on demersal fish, for example, flatfish species (flounder, sole, plaice, dab), but also on sandeel, cod, and whiting. Although harbor seals acquire the majority of prey further offshore in the adjacent North Sea, and only spend 14% of their diving time in the Wadden Sea, seal predation was still estimated to cause an average annual mortality of 43% of the remaining fish in the Wadden Sea and 60% in the nearby shallow coastal waters (<20 m). There were however large sources of uncertainty in the estimated impact of seals on fish, including the migration of fish between the North Sea and Wadden Sea, and catchability estimates of the fish survey sampling gear, particularly for sandeel and other pelagic fish species. Our estimate suggested a considerable top-down pressure by harbor seals on demersal fish. However, predation by seals may also alleviate density-dependent competition between the remaining fish, allowing for increased fish growth, and partly compensating for the reduction in fish numbers. This study shows that recovering coastal marine mammal populations could become an important component in the functioning of shallow coastal ecosystems. [ABSTRACT FROM AUTHOR]

Highlights • We studied brain activity in different stages of a high-demanding working memory task. • Results show constant activation in the dorsal anterior cingulate cortex and anterior insular. • These areas form the neural basis of a core control network of CES. • Dynamic configuration of multiple downstream systems indicates the regulation mechanism of CES. Abstract The central executive system (CES) may be the most fundamental yet least understood component of working memory. There is an ongoing debate about which brain regions underlie the top-down regulation of CES during working memory tasks. The neural substrates and regulatory mechanisms of CES remain controversial partly because few previous studies have been focused on comprehensive activation and deactivation joint analysis on all systems involved in all working memory stages, which have shown increasing importance in depicting the neural configuration of working memory. To address these questions, we conducted a functional magnetic resonance imaging study using a comprehensive activation-deactivation-behavior joint analysis to examine the dynamics of a set of cortical systems in healthy subjects performing a modified Sternberg working memory task which was designed to push the subjects to their limit in working memory and to introduce strong demands for regulation by CES. We assessed brain activity during various working memory stages using general linear model and single trial-stage estimation, and examined the relationship between the single trial-stage activity and behavioral performance. We identified constant activation in the dorsal anterior cingulate cortex and anterior insula in all working memory stages and its relationship with performance, which indicate the CES's neural basis. We also identified dynamic configuration of multiple downstream systems in different working memory stages, which indicates the regulation mechanism of CES. [ABSTRACT FROM AUTHOR]

The precise regulation of fluid and energy homeostasis is essential for survival. It is well appreciated that ingestive behaviors are tightly regulated by both peripheral sensory inputs and central appetite signals. With recent neurogenetic technologies, considerable progress has been made in our understanding of basic taste qualities, the molecular and/or cellular basis of taste sensing, and the central circuits for thirst and hunger. In this review, we first highlight the functional similarities and differences between mammalian and invertebrate taste processing. We then discuss how central thirst and hunger signals interact with peripheral sensory signals to regulate ingestive behaviors. We finally indicate some of the directions for future research. [ABSTRACT FROM AUTHOR]

We hypothesize that the hexokinases of trypanosomes of the subgenus Trypanozoon match the blood glucose levels of hosts. We studied the kinetic properties of purified hexokinase in T . equiperdum (specific activity = 302 U/mg), and compare with other members of Trypanozoon . With ATP ( K m = 104.7 μM) as phosphate donor, hexokinase catalyzes the phosphorylation of glucose ( K m = 24.9 μM) and mannose ( K m = 8.8 μM). With respect to glucose, mannose and inorganic pyrophosphate respectively are a competitive, and a mixed inhibitor of hexokinase. With respect to ATP, both are mixed inhibitors of this enzyme. In T . equiperdum , hexokinase shows a high affinity for glucose. Pleomorphism—transformation of trypanosomes from a multiplicative to a non-multiplicative form—results in a self-limited growth stabilizing glucose consumption. It delays the death of the host, thus prolonging its exposure to tsetse flies. When glucose levels descend, top-down regulation allows trypanosomes to survive through the expression of alternative metabolic pathways. It accelerates the death of the host, but helps trypanosome density to increase enough to ensure transmission without tsetse flies. Pleomorphism, and a hexokinase with a high affinity for glucose, are two main adaptive traits of T . b . brucei . The latter trait, and a strong top-down regulation, are two main adaptive traits of T . equiperdum . For trypanosomes living in glucose-rich blood, a hexokinase with a high affinity for glucose would unnecessarily harm hosts. This may explain why the human parasites, T . b . gambiense and T . b . rhodesiense , possess hexokinases with a low affinity for glucose. [ABSTRACT FROM AUTHOR]

Decades of grazing studies have identified a number of key plant and soil processes affected by large herbivores and how those grazer effects vary among different grassland types. However, there remains little mechanistic understanding about how the effects of grazers on plants and soils may be biogeochemically linked in regulating grassland processes., Here we measured monthly plant and soil variables, including soil moisture, soil nitrogen (N) availability, plant biomass, shoot N concentration and plant production, in grazed and ungrazed (fenced) grasslands during the 2012-2014 growing seasons. Measurements were used to assess direct and indirect biogeochemical pathways by which grazers influenced net above-ground plant production ( NAP) in dry and mesic grasslands in Yellowstone National Park ( YNP)., Herbivores only had direct effects on plant variables at the dry grassland compared to direct and indirect effects on both plant and soil variables at the mesic grassland. By enhancing leaf N content at both grasslands, grazers shifted the resource controlling NAP from N in ungrazed grassland to moisture, and potentially phosphorus and/or other soil nutrients, in grazed grassland., Synthesis. These results indicate the mechanistic linkage between top-down (herbivore) and bottom-up (soil resource) control of grassland production. Changing the resources that limit net above-ground plant production ( NAP) likely has a profound impact on how grazed vs. ungrazed Yellowstone National Park ( YNP) grasslands respond to environmental (e.g., climate, atmospheric N deposition) variability. Because grazing enhances leaf N among many types of grasslands, increasing the sensitivity of plant production to the availability of moisture and nutrients other than N may be a general response of grasslands to grazing. [ABSTRACT FROM AUTHOR]

In response to the increased competition for water, the Chinese government has determined to promote water-saving irrigation (WSI) followed by a range of institutional arrangements and policy goals. Three management mechanisms are analyzed in this study in terms of effectiveness, including the top-down regulation mechanism using direct control or economic instruments, the design-bid funding mechanism mobilizing local governments by competitive grants program, and the bottom-up participation mechanism transferring more irrigation management responsibilities to end-users. Although the WSI management has achieved notable improvements by the combination of different mechanisms, conflicts among different policy goals, uneven distribution of financial resources, and insufficient participation from water users caused the difficulty in aligning stakeholders' incentives. Approaches are needed to enable sustainable management by coordinating incentives from different stakeholders in the management, as well as incorporating end water users to assist decision-making. [ABSTRACT FROM AUTHOR]

Most demonstrated trophic cascades originate with predators, but infectious agents can also cause top-down indirect effects in ecosystems. Here we synthesize the literature on trophic cascades initiated by infectious agents including parasitoids, pathogens, parasitic castrators, macroparasites, and trophically transmitted parasites. Like predators, infectious agents can cause density-mediated and trait-mediated indirect effects through their direct consumptive and nonconsumptive effects respectively. Unlike most predators, however, infectious agents are not fully and immediately lethal to their victims, so their consumptive effects can also trigger trait-mediated indirect effects. We find that the frequency of trophic cascades reported for different consumer types scales with consumer lethality. Furthermore, we emphasize the value of uniting predator–prey and parasite–host theory under a general consumer–resource framework. [ABSTRACT FROM AUTHOR]

In Greenland waters, Atlantic cod ( Gadus morhua) is showing signs of recovery following a collapse in the early 1990s, and quantitative diet studies are needed to address predation on highly commercial species such as northern shrimp ( Pandalus borealis). We analyzed 2483 Atlantic cod stomachs from Greenland offshore waters and the correlation between Atlantic cod and northern shrimp abundance. Fish and crustacean prey accounted for 96% of the prey by weight, with the relative importance shifting from crustaceans to fish with increasing cod size. Spatial differences were distinct and northern shrimp dominated the diet in Northwest Greenland (>50% by weight), but declined in importance in Southwest Greenland and was absent from the diet in East Greenland. Instead, other crustacean preys such as krill were important in Southwest Greenland while fish prey was most important in East Greenland. Southwest Greenland was sampled in both summer and autumn, and there was a significant seasonal effect on most prey groups, but most pronounced for Atlantic cod and krill both of which increased in importance. Extensive cannibalism was limited to the largest cod (]70-100 cm]) and mainly in Southwest Greenland. In Southwest Greenland, Atlantic cod and northern shrimp biomass were significantly negatively correlated, while no significant trends were found in Northwest or East Greenland. [ABSTRACT FROM AUTHOR]

Food web studies provide a useful tool to assess the organization and complexity of natural communities. Nevertheless, the seasonal dynamics of food web properties, their environmental correlates, and potential association with community diversity and stability remain poorly studied. Here, we condensed an incomplete 6-year community dataset of a subtropical coastal lake to examine how monthly variation in diversity impacts food web structure over an idealized time series for an averaged year. Phytoplankton, zooplankton, macroinvertebrates, and fish were mostly resolved to species level ( n = 120 trophospecies). Our results showed that the seasonal organization of the food web could be aggregated into two clusters of months grouped here as 'summer' and 'winter'. During 'winter', the food web decreases in size and complexity, with the number of trophospecies dropping from 106 to 82 (a 22.6% decrease in the number of nodes) and the trophic interactions from 1,049 to 637 between month extremes (a 39.3% drop in the number of links). The observed simplification in food web structure during 'winter' suggests that community stability is more vulnerable to the impact of any change during this period. [ABSTRACT FROM AUTHOR]

Forest insect pests are becoming increasingly common in Europe. A recent paper published in this journal dealt with a particular case of pest spreading in Portuguese coniferous forests.The authors discussed the effect that mass trapping and clear‐cut belts had on slowing down the invasion and suggested that likely causes of pest spreading are stress due to global warming and the introduction of exotic species. Inspired by that paper, we defend here the point that forest communities are not only regulated by bottom‐up mechanisms, such as water stress, but also by top‐down mechanisms, such as predation.We provide information from European metadata showing that forest biomass grew by 38% (1991–2015) whereas forest insectivorous passerine trends were stable (1980–2016).Synthesis and applications. We suggest that rebounding European forests are too young to support large communities of insectivorous birds and that an effective way to solve pest problems could be to promote the use of nest boxes for them (and for other insect predators), as it was done in the past in large reforestations implemented in Spain. Additionally, the presence of large mammalian herbivores is needed to reduce the density of trees in forests. Priority should be given to this ecological management in comparison with massive trapping and clear‐cut belt construction or at least it should be used together with those engineering practices. [ABSTRACT FROM AUTHOR]

A fundamental question in ecology is the role of predators in limiting their prey populations. This question can be approached for shallow marine fish communities by comparison of abundance of species inside and outside marine protected areas (MPAs), where fishing restrictions may enforce large abundance differences in large (top) predators. The first step in demonstrating differences in these populations is the development and testing of methods capable of estimating abundance of fast-swimming and alert species which generally are difficult to quantify with traditional net-based sampling or visual census. That the method of experimental fishing with hook and line is capable of sampling predatory fish of a wide range of sizes, from 15 to 125 cm, inside and outside an MPA in the central Adriatic Sea, Kornati National Park, Croatia, was demonstrated in this preliminary study. Evidence of significantly more abundant top predators inside the MPA and a significantly higher mean size of fish overall was found. A total of 11 species of fish were sampled across several benthic habitats, of which six were found only in the MPA. It is concluded that the MPA represents a natural experiment with greater abundance of larger predators than outside, and that experimental fishing can take advantage of these differences to test the hypothesis of top-down regulation of fish communities.

[Display omitted] • Impervious surface cover around street trees can increase tree canopy temperature. • Fitness of soft scale insects is increased more by impervious surface in hot than cool sites. • Absence of a positive numerical response of parasitoids in hot sites suggests scale outbreaks are driven by bottom up factors. • Presence of a positive numerical response of parasitoids to low host densities suggest potential for biological control. • Elevated temperatures may increase pest abundances in ways that are not mitigated by natural enemies. Urban habitats can alter tree physiology in ways that make trees more susceptible to insect pests. We examined how urban conditions (e.g., impervious surfaces and warming) affected the soft scale insect, European fruit lecanium, Parthenolecanium corni Bouché (Hemiptera: Coccidae) and the health of thornless honeylocust trees (Gleditsia tricanthos L. var. inermis) in Indianapolis, Indiana, USA. Hot and cool study sites were selected based on surface air temperatures obtained from thermal LANDSAT-8 images overlaid against a map of honeylocust tree locations. Based on temperature probe data, study trees located in hot sites had mean average daily temperatures up to 1.56 °C and 1.79 °C warmer than cool sites in 2019 and 2020, respectively. We hypothesized that abundance and fecundity of scale insects would be higher on trees in hot sites and those surrounded by more impervious surface cover within a 20 m radius. Although our data supported these hypotheses, impervious surface cover predicted more of the variation in abundance and fecundity of scale insects in hot sites compared to cool sites. Rates of parasitism were not affected by impervious surface cover or whether the site was from a hot or cool location. However, we found strong density dependence in parasitism of scale insects in both hot and cool sites when scale densities were at or below the levels present in cool sites. This suggests that lower densities of scale insects were associated with a positive numerical response of parasitoids, a necessary prerequisite for population regulation by top-down effects. In contrast, this numerical response was lacking at the higher densities of scales found on trees located in hot sites where, presumably bottom-up factors like water-stress increased the fecundity of scale insects. These findings add to a growing body of evidence linking rising global temperatures with increased pest abundance in ways that cannot be mitigated by local populations of natural enemies. [ABSTRACT FROM AUTHOR]

Vertebrate scavenging assemblages include two major functional groups: obligate scavengers (i.e., vultures), which depend totally on carrion and are undergoing severe declines around the globe, and facultative scavengers, which exploit carrion opportunistically and are generally ubiquitous. Our goal was to investigate the hypothesis that vultures can indirectly regulate the abundance of mesopredators (i.e., facultative scavengers) through modulating their access to carrion resources. We studied scavenging efficiency and red fox ( Vulpes vulpes ) abundance in two neighbouring areas of South-eastern Spain where vultures (mainly griffon vultures Gyps fulvus ) are present (Cazorla) and absent (Espuña). To do so, we monitored ungulate carcasses consumption during winter and summer, and counted red fox scats along walking transects as a proxy of fox density. Our results confirmed that scavenging efficiency was higher in Cazorla and in carcasses visited by vultures. This resulted in increasing scavenging opportunities for facultative scavengers where vultures were absent. Accordingly, mean red fox abundance was higher in Espuña. These results suggest the existence of a vulture-mediated mesopredator release (i.e., an increase of mesopredator numbers following vulture loss), which could trigger important indirect ecological effects. Also, our study demonstrates that facultative scavengers are hardly able to functionally replace vultures, mainly because the former exploit carrion on a slower time scale. [ABSTRACT FROM AUTHOR]

Trophic cascade theory predicts that apex predators structure ecosystems by regulating mesopredator and herbivore abundance and behaviour. Studies on trophic cascades have typically focused on short linear chains of species interactions. A framework that integrates more realistic and complex interactions is needed to make broader predictions on ecosystem structuring., Network analysis is used to study food webs and other types of species interaction networks. These often comprise large numbers of species but rarely account for multiple interaction types and strengths. Here, we develop an intermediate complexity theoretical framework that allows specification of multiple interaction types and strengths for the study of trophic cascades. This ecological network is designed to suit data typically derived from field-based studies. The trophic cascade network contains fewer nodes than food webs, but provides semi-weighted directional links that enable different types of interactions to be included in a single model., We use this trophic cascade network model to explore how an apex predator shapes ecosystem structure in an Australian arid ecosystem. We compared two networks that contrasted in the dominance of an apex predator, the dingo ( Canis dingo), using published results ranking the direction and strength of key interactions. Nodes and links interacted dynamically to shape these networks. We examined how changes to an apex predator population affect ecosystem structure through their direct and indirect influences on different components of this ecological community., Under strong apex predator influence, the network structure was denser and more complex, even and top-down driven; and dingo predation and soil commensalism formed denser interactive modules. Under weak apex predator influence (e.g. reflecting predator control), the resulting network structure was frayed, with mesopredator predation and grazing forming modules., Our study demonstrates that networks of intermediate complexity can provide a powerful tool for elucidating potential ecosystem-wide effects of apex predators and predicting the consequences of management interventions such as predator control. Integrating trophic cascades, with their array of complex interactions, with the three-dimensional structure of ecological networks, has the potential to reveal 'ecological architecture' that neither captures on its own. [ABSTRACT FROM AUTHOR]

Herbivore effects on diversity and succession were often studied in plants, but not in cryptogams. Besides direct herbivore effects on cryptogams, we expected indirect effects by changes in competitive interactions among cryptogams. Therefore, we conducted a long-term gastropod exclusion experiment testing for grazing effects on epiphytic cryptogam communities. We estimated the grazing damage, cover and diversity of cryptogams before gastropods were excluded and three and six years thereafter. Gastropod herbivory pronouncedly affected cryptogams, except for bryophytes, strongly depending on host tree species and duration of gastropod exclusion. On control trees, gastropod grazing regulated the growth of algae and non-lichenized fungi and thereby maintained a high lichen diversity and cover. On European beech, the release from gastropod grazing temporarily increased lichen vitality, cover, and species richness, but later caused rapid succession where algae and fungi overgrew lichens and thereby reduced their cover and diversity compared with the control. On Norway spruce, without gastropods lichen richness decreased and lichen cover increased compared with the control. Our findings highlight the importance of long-term exclusion experiments to disentangle short-term, direct effects from longer-term, indirect effects via changes in competitive relationships between taxa. We further demonstrated that gastropod feeding maintains the diversity of cryptogam communities. [ABSTRACT FROM AUTHOR]

Phosphorus fertilization is employed in some reservoirs to increase fish production. To clarify whether silver carp regulate phosphorus (P) concentration or if fertilizing leads to phytoplankton blooms, a 6-week experiment was conducted with 18 enclosures in Nanwan Reservoir, central China. Treatments were three levels of P concentration (low: 45 μg/L; medium: 90 μg/L; high: 180 μg/L) with or without silver carp stocking (10 g/m3). The effect of silver carp stocking on phytoplankton community changed with P fertilization in the water column. No significant fish effect was observed on total phytoplankton biomass at the low P level, while the chlorophyllaconcentration, total phytoplankton biomass, and biomass of phytoplankton > 30 μm were enhanced significantly by silver carp at the medium P level. In addition, at the medium P level, the biomass of Bacillariophyta was significantly greater, whereas the biomass of Chlorophyta was significantly lower in the enclosures with silver carp stocking. Potentially, silver carp enhanced the total phytoplankton biomass by nutrient recycling. Zooplankton had a weak grazing efficiency and had limited effects on control of phytoplankton biomass at the three P levels. The 6-week experiment confirmed that P fertilization could consistently cause greater fish productivity with phytoplankton biomass increasing at the same time. We therefore propose a mechanism for the observed relationship between silver carp stocking and phytoplankton. Under the condition of ambient fish density (10 g/m3), silver carp could not control phytoplankton biomass with phosphorus fertilization; instead, the fish may have promoted phytoplankton growth via nutrient recycling. Silver carp seem to have only a weak effect on the phytoplankton community without P fertilization. Therefore, from the viewpoint of phytoplankton regulation, P fertilization should be considered as a cautious operation for water protection and reasonable fish enhancement. [ABSTRACT FROM AUTHOR]

Little attention has been paid to the potential top-down effects of population ecology on metabolism. Because it is capable of a fast growth that dramatically modifies its blood environment, the parasitic protozoan, Trypanosoma evansi , is a promising model for the study of density-dependent metabolic processes. We assess the in vivo growth rate, doubling time, biomass yield, glycolytic flux, and enzyme expression of T. evansi . Then, we explore the metabolic changes likely occurring during its growth. At low T. evansi densities, most host glucose is used to produce energy, which results in the release of pyruvate. Part of glucose is used for NADPH production through the pentose phosphate pathway. At high T. evansi densities, fructose, mannose, and glycerol become additional energy sources. Part of host glucose is used for biosynthesis and for NADPH production through alternative metabolic pathways, which results in the release of succinate, alanine, and acetate. The ability of organisms to adjust to resource changes is crucial to their survival. Irrespective if the triggering mechanism is direct (nutrient limitation) or indirect (a pheromone-like factor), nutrient availability is necessarily the main evolutionary factor responsible for the density-dependent metabolic properties of trypanosome populations. [ABSTRACT FROM AUTHOR]

Community structure and interspecific interactions are particularly vulnerable to rapidly changing climatic regimes. Recent changes in both climate and vertebrate community assemblages have created a unique opportunity to examine the impacts of two dynamic forces on population regulation. We examined the effects of warming winter conditions and the reestablishment of a previously extirpated predator, the fisher (Martes pennanti), on regulatory mechanisms in a northern-adapted mammal, the porcupine (Erethizon dorsatum), along their southern range boundary. Using a long-term (17-year) capture-recapture data set, we (1) quantified the impacts of climate change and increased fisher predation on the survival of adult porcupines at their regional southern terminus, (2) assessed recruitment (via both adult fecundity and juvenile survival) of porcupines, and (3) modeled the relative importance of predation and winter conditions on the demography and population growth rate (λ). Severe winters and abundant predators interacted synergistically to reduce adult survivorship by as much as 44%, while expanding predator populations led to near reproductive failure among porcupines. Increasing predatory pressure, disruptions in this community module, and more frequent extreme winter weather events led to predicted extirpation within 50 years, whereas in the absence of predators, the population was viable. Our results provide a mechanistic understanding behind distributional shifts resulting from climate change and may be broadly relevant for predicting future distributional shifts in other northern-adapted mammalian species. [ABSTRACT FROM AUTHOR]

• Urban tree isolation affects the abundance of pests and their enemies. • Urban tree isolation affects the top-down regulation of pests by their enemies. • Monospecific Eucalyptus patches had more herbivore insects than isolated trees. • Pest parasitism rate was 30-fold greater in urban forest patches than isolated trees. • Pest-predator-parasitoid abundance interdependence differed by tree arrangement. The proximity to transportation hubs and the large movement of goods and people in cities make trees especially prone to invasive insect pests. Urban tree arrangements, in isolated tree sites or in forest patches, may alter their susceptibility to insect herbivory. Surprisingly little is known about how urban tree spatial arrangements influence pest abundance and top-down regulation by natural enemies. We sampled the abundance of an invasive pest of Eucalyptus , the psyllid Glycaspis brimblecombei, and of two of its natural enemies, the specialist exotic parasitoid Psyllaephagus bliteus and the generalist native predator Anthocoris nemoralis over two years. We measured insect abundances in isolated trees versus monospecific planted forest patches in 17 pairs of sites, each within a Portuguese city. The abundance of the exotic pest was three-fold higher in forest patches than in isolated trees. The parasitism rate was ∼ 30 times higher in forest patches (11.5 %) than in isolated trees (0.4 %). The interdependence among insect species abundances also differed between spatial arrangements. In isolated trees, predator and parasitoid abundances depended markedly on prey abundance. In forest patches, we found a marked dependence of the predator on the composition of the surrounding landscape. Our study adds empirical data indicating that urban tree isolation matters for pest abundance and regulation by its enemies. In similar systems, avoiding dense monospecific patches of exotic trees and increasing the compositional heterogeneity of the landscape are promising paths to maintain the sustainability of urban trees and their environmental and societal benefits. [ABSTRACT FROM AUTHOR]

Novel assemblages of native and introduced species characterize a growing proportion of ecosystems worldwide. Some introduced species have contributed to extinctions, even extinction waves, spurring widespread efforts to eradicate or control them. We propose that trophic cascade theory offers insights into why introduced species sometimes become harmful, but in other cases stably coexist with natives and offer net benefits. Large predators commonly limit populations of potentially irruptive prey and mesopredators, both native and introduced. This top-down force influences a wide range of ecosystem processes that often enhance biodiversity. We argue that many species, regardless of their origin or priors, are allies for the retention and restoration of biodiversity in top-down regulated ecosystems. [ABSTRACT FROM AUTHOR]

Lytic bacteriophages and protozoan predators are the major causes of bacterial mortality in natural microbial communities, which also makes them potential candidates for biological control of bacterial pathogens. However, little is known about the relative impact of bacteriophages and protozoa on the dynamics of bacterial biomass in aqueous and biofilm phases. Here, we studied the temporal and spatial dynamics of bacterial biomass in a microcosm experiment where opportunistic pathogenic bacteria Serratia marcescens was exposed to particle-feeding ciliates, surface-feeding amoebas, and lytic bacteriophages for 8 weeks, ca. 1300 generations. We found that ciliates were the most efficient enemy type in reducing bacterial biomass in the open water, but least efficient in reducing the biofilm biomass. Biofilm was rather resistant against bacterivores, but amoebae had a significant long-term negative effect on bacterial biomass both in the open-water phase and biofilm. Bacteriophages had only a minor long-term effect on bacterial biomass in open-water and biofilm phases. However, separate short-term experiments with the ancestral bacteriophages and bacteria revealed that bacteriophages crash the bacterial biomass dramatically in the open-water phase within the first 24 h. Thereafter, the bacteria evolve phage-resistance that largely prevents top-down effects. The combination of all three enemy types was most effective in reducing biofilm biomass, whereas in the open-water phase the ciliates dominated the trophic effects. Our results highlight the importance of enemy feeding mode on determining the spatial distribution and abundance of bacterial biomass. Moreover, the enemy type can be crucially important predictor of whether the rapid defense evolution can significantly affect top-down regulation of bacteria. [ABSTRACT FROM AUTHOR]

Ecosystem-level models that trace flows of mass and energy to quantify species interactions are important tools in whole ecosystem-based approaches to managing marine resources. A critical input parameter for such models is an estimate of the consumption rates and biomasses of prey consumed by fish populations. Here we estimate the annual prey consumption of an abundant coastal piscivore, Arripis trutta, which may exert substantial top-down control on its prey over its broad latitudinal range (28-43°S) in the coastal waters off south-eastern (SE) Australia. Three independent techniques were used to estimate annual prey consumption at two environmentally-relevant temperatures, 15 and 20°C: experimental gastric evacuation experiments (coupled with stomach content analyses); bioenergetics modelling, and; empirical regression modelling. Each technique yielded a similar range of estimates with annual food consumed/biomass (Q/B) ranging from 3.20 to 4.02 at 15°C and 4.23 to 5.25 at 20°C. Using an estimated A. trutta stock biomass in SE Australia of 10,000t, total mean annual prey consumption was estimated to be 42,200t, consisting primarily (93%) of small zooplanktivorous teleosts, particularly Australian sardines Sardinops sagax (35%) and scads Trachurus spp. (30%). These results indicate that A. trutta do possess a top-down influence on the pelagic ecosystem of coastal SE Australia via consumption of considerable biomasses of small pelagic fish. However, despite the use of a maximum regional estimate of A. trutta abundance and the presence of at least two other ecologically similar predatory fish species with higher annual prey consumption rates in SE Australian coastal waters, A. trutta may remove only a small proportion (~15%) of the estimated spawning biomasses of its major prey species in this region annually. The multiple-technique approach used in this study has for the first time quantified the diet of A. trutta in SE Australia and provided broad and repeatable estimates of its annual prey consumption for use in ecosystem models designed to manage coastal fisheries resources in this region. [ABSTRACT FROM AUTHOR]

Top-down population regulation can influence the success of biological control agents when they are released into the field. Entomopathogenic nematodes ( EPNs) are used commonly in biological control programmes, but their efficacy suffers from poor persistence. Although abiotic soil conditions have been shown to reduce EPN persistence, consumption of infected insects by scavengers and of infective juvenile ( IJ) nematodes by predators may also regulate these populations. In the present study, the effects of different soil arthropods on EPNs in laboratory conditions were measured. It was hypothesised that arthropods commonly found in soil communities where EPNs are applied would consume cadavers of insects parasitised by the nematodes and the IJs themselves., Some species of scavengers consume EPN-infected insects. Crickets ( Gryllus bimaculatus De Geer), American cockroaches [ Periplaneta Americana (Linnaeus)], ants [ Tetramorium chefketi Forel and Pheidole pallidula (Nylander)], earwigs ( Labidura riparia Pallas), mites ( Sancassania polyphyllae Zachvatkin), and springtails ( Sinella curviseta Brook and Folsomia candida Willem) have different responses to nematode-killed insects. Results suggested that ants ( T. chefketi), cockroaches, mites, and earwigs fed on Steinernema-killed insects whereas neither crickets nor springtails consumed them., In the second part of the study, experiments were conducted to determine whether mites and springtails consumed IJ EPNs. Results showed that S. polyphyllae mites do not consume infective juveniles in soil, whereas both springtail species consumed significant numbers of the IJs., Top-down regulatory processes can be a limiting factor for EPN populations under laboratory conditions. Both host cadavers and IJs are consumed (albeit by different arthropods), so these results may help explain the difficulties associated with the persistence of EPN application to soil. [ABSTRACT FROM AUTHOR]

The medial prefrontal cortex (MFC) is critical for our ability to learn from previous mistakes. Here we provide evidence that neurophysiological oscillatory long-range synchrony is a mechanism of post-error adaptation that occurs even without conscious awareness of the error. During a visually signaled Go/No-Go task in which half of the No-Go cues were masked and thus not consciously perceived, response errors enhanced tonic (i.e., over 1-2 seconds) oscillatory synchrony between MFC and occipital cortex leading up to and during the subsequent trial. Spectral Granger causality analyses demonstrated that MFC > occipital cortex directional synchrony was enhanced during trials following both conscious and unconscious errors, whereas transient stimulus-induced occipital > MFC directional synchrony was independent of errors in the previous trial. Further, the strength of pre-trial MFC-occipital synchrony predicted individual differences in task performance. Together, these findings suggest that synchronous neurophysiological oscillations are a plausible mechanism of MFC-driven cognitive control that is independent of conscious awareness.

Selective predation by planktivore fish appears to be an important regulatory factor of zooplankton communities, potentially causing large changes in species composition and size distributions within populations. In this study, prey preferences and size-selective predation on zooplankton by Arctic charr were examined in six subarctic lakes with Arctic charr as the dominant pelagic fish species. Most of the lakes had a zooplankton community dominated by copepods ( Cyclops scutifer and Eudiaptomus graciloides), but the pelagic charr evidently selected cladoceran species ( Bythotrephes longimanus, Daphnia sp. and Bosmina sp.), likely because the copepods have a higher mobility and evasiveness than the cladocerans. Furthermore, a strong size selection was also revealed for both Bosmina sp. and Daphnia sp., as individual prey from Arctic charr stomachs were exclusively larger than individuals sampled in the environment. Additionally, visibility due to size, morphology and pigmentation (egg-carrying females) was also a major factor for the selection of zooplankton prey. In conclusion, Arctic charr was found to be highly selective on zooplankton both in respect to species composition and individual size of Bosmina sp. and Daphnia sp. [ABSTRACT FROM AUTHOR]

Studies demonstrating trophic cascades through the loss of top-down regulatory processes in productive and biologically diverse terrestrial ecosystems are limited., Elk Island National Park, Alberta and surrounding protected areas have a wide range of ungulate density due to the functional loss of top predators, management for high ungulate numbers and variable hunting pressure. This provides an ideal setting for studying the effects of hyper-abundant ungulates on vegetation and shrub-dependent bird and butterfly species., To examine the cascading effects of high ungulate density, we quantified vegetation characteristics and abundances of yellow warbler Dendroica petechia and Canadian tiger swallowtail Papilio canadensis under different ungulate density in and around Elk Island National Park., Using Structural Equation Models we found that ungulate density was inversely related to shrub cover, whereas shrub cover was positively related to yellow warbler abundance. In addition, chokecherry Prunus virginiana abundance was inversely related to browse impact but positively related to P. canadensis abundance., These results demonstrate a cascade resulting from hyper-abundant ungulates on yellow warblers and Canadian tiger swallowtails through reductions in shrub cover and larval host plant density. The combined effect of the functional loss of top predators and management strategies that maintain high ungulate numbers can decouple top-down regulation of productive temperate ecosystems. [ABSTRACT FROM AUTHOR]

Highlights: [•] Species with unique ecological roles may be used as surrogates of intact ecosystem functioning. [•] We used jaguar, tapir, white-lipped peccary and muriqui as surrogates of intact ecosystem functioning in the remaining Atlantic Forest. [•] We found that 88% of the remaining Atlantic Forest is depleted of all four species and 96% is depleted of at least one of them. [•] We also found that only 16% is still environmentally suitable for all four species and 55% is unsuitable to all of them. [•] Our results suggest that ecosystems with long history of human impact may be suffering from ecological degradation not seen at first glance. [ABSTRACT FROM AUTHOR]

Reproductive success and population growth of an herbivorous mite are limited by activities of phytoseiid predators. However, occurrences on upper versus lower leaf surfaces are sometimes mismatched between these prey and predators. The mismatch potentially mitigates predation risk for the prey species. We assessed factors that affect mite distributions on leaf surfaces, testing whether the presence of the phytoseiid mite Phytoseius nipponicus alters the leaf-surface distribution and reproductive success of the herbivorous false spider mite Brevipalpus obovatus. The host plant was Viburnum erosum var. punctatum (Adoxaceae). Leaves were set in natural (TRUE) and reversed (upside down; INVERTED) orientations using experimental devices. Both surfaces were accessible to mites. We detected lower and abaxial leaf-surface preferences in P. nipponicus. In contrast, upper and adaxial surfaces were preferred by B. obovatus. Thus, prey and predatory mites accumulated on different sides of leaves. Presence of the predator also indirectly decreased egg production in B. obovatus. Brevipalpus obovatus females actively avoided leaf surfaces with elevated predator numbers; these females shifted their distributions and changed oviposition sites to leaf surfaces with fewer predators. In consequence, B. obovatus eggs on the upper sides of leaves were less frequently preyed upon than were those on lower sides. We suggest that upper leaf-surface exploitation in this particular herbivorous mite species mitigates predation risk from phytoseiid mites, which prefer lower leaf surfaces. [ABSTRACT FROM AUTHOR]

It has generally been assumed that high-level cognitive and emotional processes are based on amodal conceptual information. In contrast, however, 'embodied simulation' theory states that the perception of an emotional signal can trigger a simulation of the related state in the motor, somatosensory, and affective systems. To study the effect of social context on the mimicry effect predicted by the 'embodied simulation' theory, we recorded the electromyographic (EMG) activity of participants when looking at emotional facial expressions. We observed an increase in embodied responses when the participants were exposed to a context involving social valence before seeing the emotional facial expressions. An examination of the dynamic EMG activity induced by two socially relevant emotional expressions (namely joy and anger) revealed enhanced EMG responses of the facial muscles associated with the related social prime (either positive or negative). These results are discussed within the general framework of embodiment theory. [ABSTRACT FROM AUTHOR]

Invasive species represent a significant threat to global biodiversity and a substantial economic burden. Burmese pythons, giant constricting snakes native to Asia, now are found throughout much of southern Florida, including all of Everglades National Park (ENP). Pythons have increased dramatically in both abundance and geographic range since 2000 and consume a wide variety of mammals and birds. Here we report severe apparent declines in mammal populations that coincide temporally and spatially with the proliferation of pythons in ENP. Before 2000, mammals were encountered frequently during nocturnal road surveys within ENP. In contrast, road surveys totaling 56,971 km from 2003-2011 documented a 99.3% decrease in the frequency of raccoon observations, decreases of 98.9% and 87.5% for opossum and bobcat observations, respectively, and failed to detect rabbits. Road surveys also revealed that these species are more common in areas where pythons have been discovered only recently and are most abundant outside the python's current introduced range. These findings suggest that predation by pythons has resulted in dramatic declines in mammals within ENP and that introduced apex predators, such as giant constrictors, can exert significant top-down pressure on prey populations. Severe declines in easily observed and/or common mammals, such as raccoons and bobcats, bode poorly for species of conservation concern, which often are more difficult to sample and occur at lower densities. [ABSTRACT FROM AUTHOR]

This paper presents a possible context-sensitive mechanism in a neural network and at single neuron levels based on the experiments of hippocampal CA1 and their theoretical models. First, the spatiotemporal learning rule (STLR, non-Hebbian) and the Hebbian rule (HEBB) are experimentally shown to coexist in dendrite-soma interactions in single hippocampal pyramidal cells of CA1. Second, the functional differences between STLR and HEBB are theoretically shown in pattern separation and pattern completion. Third, the interaction between STLR and HEBB in neural levels is proposed to play an important role in forming a selective context determined by value information, which is related to expected reward and behavioral estimation. [ABSTRACT FROM AUTHOR]

Three newly isolated strains of flavobacteria from coastal aquifer sediments have been found to be predatory, lysing a range of live and pasteurized microbial prey. The three strains have been classified on the basis of 16S rRNA gene phylogeny as belonging to the recently described Olleya (strains VCSA23 and VCSM12) and Tenacibaculum (strain VCSA14A) genera. Two of the closest cultured relatives to the strain VCSA14A, Tenacibaculum discolor and Tenacibaculum gallaicum, were also found to be bacteriolytic. These five predatory strains exhibit gliding motility and have been observed to lyse prey cells after surrounding them with social swarms, similar to known predatory bacteria such as myxobacteria and members of the genus Lysobacter. Flavobacteria are often numerically significant in a wide variety of freshwater and marine environments, particularly in association with particles, and are thought to be involved in the degradation of biopolymeric substances. If predatory capability is widespread among flavobacteria, they may be a previously unrecognized source of ‘top-down’ bacterial mortality with an influence on the composition and activity of surrounding microbial communities. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the effect of benthic and pelagic predators on intertidal mussel population in the marine protected area in South Africa. The study uses various treatments including caged treatment, roof treatment, and fence treatment as well as factorial analysis of variance (ANOVA) to determine the effects of different types of predators on the juvenile mussel samples which were collected from Plettenberg Bay in July 2009. The results show that mussels which were exposed to all predators have 50% survival rate, and benthic and pelagic predators were well balanced on juvenile mussels predation. Moreover, the result of ANOVA reveals that mortality was lower in the full cage treatment and equal in treatments with fences, roofs, or no protection.

The central thesis is that professionals and state regulators have incompatible perspectives, both on their professional practice and on the role of (self-) regulation. Regulators have a top-down perspective (with the state at the top) and focus on the product of the professions. Quantitative measurable output is what counts primarily, and regulation is an instrument to improve that output. Professionals have a centreperiphery perspective (with the profession at the centre) and focus on the professional practice. The quality of professional work is what we should focus on primarily and the standards implicit in the profession are what should guide us here. External regulation is usually a nuisance or a burden. These perspectives clash, which may explain the current dissatisfaction among professionals. I discuss two partly successful strategies to mitigate this conflict. The first is to construct a buffer or transformer between the two perspectives, consisting of an interstitial managerial layer. The second is to try to reframe the opposition. [ABSTRACT FROM AUTHOR]

Herbivory can lead to shifts in ecosystem state or changes in ecosystem functioning, and recovery from herbivory is particularly slow in disturbance-sensitive ecosystems such as arctic tundra. Herbivore impacts on ecosystems are variable in space and time due to population fluctuations and selective utilization of habitats; thus there is a need to accurately predict herbivore impacts at the landscape scale. The habitat utilization and extent of disturbance caused by increasing populations of pink-footed geese ( Anser brachyrhynchus) foraging in the high arctic tundra of Svalbard were assessed using a predictive model of the population’s habitat use. Pink-footed geese arrive in Svalbard in early spring when they forage for belowground plant parts; this foraging (called grubbing) can cause vegetation loss and soil disturbance. Surveys of the extent and intensity of grubbing were carried out to develop predictive models that were subsequently tested against data collected during the following year from different areas. Both habitat type at a particular point and the amount of preferred fen habitat in the surrounding area were powerful predictors of grubbing likelihood and the developed model correctly classified over 69% of validation observations with an AUC of 0.75. Pink-footed geese showed a strong preference for wetter habitats within low-lying landscapes. Extrapolation of the predictive model across the archipelago showed that a maximum potential area of 2300 km2 (3.8% of the archipelago) could be disturbed by grubbing. Thus, increasing populations of geese may cause large-scale vegetation loss and soil disturbance in arctic ecosystems. [ABSTRACT FROM AUTHOR]

Sensory representations depend strongly on the descending regulation of perceptual processing. Generalization among similar stimuli is a fundamental cognitive process that defines the extent of the variance in physical stimulus properties that becomes categorized together and associated with a common contingency, thereby establishing units of meaning. The olfactory system provides an experimentally tractable model system in which to study the interactions of these physical and psychological factors within the framework of their underlying neurophysiological mechanisms. The authors here show that olfactory associative learning systematically regulates gradients of odor generalization. Specifically, increasing odor-reward pairings, odor concentration, or reward quality-each a determinant of associative learning-significantly transformed olfactory generalization gradients, each narrowing the range of variance in odor quality perceived as likely to share the learned contingency of a conditioned odor stimulus. However, differences in the qualitative features of these three transformations suggest that these different determinants of learning are not necessarily theoretically interchangeable. These results demonstrate that odor representations are substantially shaped by experience and descending influences. [ABSTRACT FROM AUTHOR]

Top predators have been described as highly interactive keystone species. Their decline has been linked to secondary extinctions and their increase has been linked to ecological restoration. Several authors have recently argued that the dingo Canis lupus dingo is another example of a top predator that maintains mesopredators and generalist herbivores at low and stable numbers, thereby increasing biodiversity and productivity. Due to the sensitivity of many Australian species to introduced mesopredators and herbivores, the top predator hypothesis predicts that threatened species will not survive where dingoes are rare or absent. However, several threatened species have survived inside the Dingo Barrier Fence (DBF). We present a new view on the survival of the yellow-footed rock-wallaby Petrogale xanthopus xanthopus and the malleefowl Leipoa ocellata inside the DBF where the dingo is considered very rare, or in areas where the dingo is believed to have been eradicated several decades ago. We found that dingoes co-occurred with both threatened species. Dingoes were present at all wallaby colonies surveyed and occurred throughout their range. The most common predator detected in areas inhabited by the wallabies was in fact the dingo, and we found no significant difference between dingo abundance inside compared to outside the DBF. Malleefowl nests were found to be scent marked by dingoes at the three sites that we surveyed, despite these sites being close to human settlement and sheep farms, and in small and fragmented patches of wilderness. These findings provide further evidence for an association between the presence of dingoes and the survival of threatened species, which is in agreement with the top predator hypothesis. The results of this study challenges the current assumption that the presence and ecological consequence of dingoes in sheep country are negligible and we suggest that wildlife managers verify whether dingoes are present before predator control... [Copyright &y& Elsevier]

1. The significance of top-down regulation by carnivores is receiving increasing global recognition. As a consequence, key objectives in many programmes that seek to maintain ecosystem function now include conserving carnivores and understanding their interactions. This study examined overlap in resource use (space and diet) of introduced eutherian carnivores and an endangered marsupial carnivore, the spotted-tailed quoll Dasyurus maculatus, in eastern Australia. We also investigated mechanisms of niche partitioning and evidence for interspecific aggression. 2. Dietary overlap between quolls, red foxes Vulpes vulpes and wild dogs Canis lupus ssp. was assessed by analysis of scats. Trapping, radio-tracking and direct observations were used to quantify spatial overlap between quolls, foxes, wild dogs and feral cats Felis catus. 3. Dietary overlap among the carnivores was extensive. Medium-sized mammals were the most important prey for all three predators, indicating potential for exploitative interactions. However, hunting of different size classes of secondary prey and consumption by quolls of more arboreal prey than their counterparts may assist coexistence. Remains of quoll were found in two dog scats, and cat hair in another, possibly indicating intraguild predation. 4. We observed extensive spatial overlap between quolls and eutherian carnivores. However, we inferred from dietary data that quolls foraged primarily in forested habitat, while canids foraged mainly in cleared habitat. 5. Synthesis and applications. Our results indicate strong potential for competition between spotted-tailed quolls and eutherian carnivores, and thus a situation where control of introduced predators may be desirable, not only for the conservation of prey species but also for the protection of native carnivores. Concern over potential non-target mortality of quolls has hindered efforts to control foxes in eastern Australia using poison baits. We contend that, rather than harming quoll populations, baiting for foxes should aid the conservation of quolls and should be implemented in areas of sympatry where fox numbers are high. [ABSTRACT FROM AUTHOR]