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Biological sex affects the morphology, physiology, behaviour, and distribution of organisms and populations. Integrating intraspecific variation of biological traits into community dynamics has improved our understanding of food web and ecosystem dynamics and stability. However, biological sex is rarely considered. The inclusion of sex-specific variation in theoretical models has highlighted that sex-based differences can significantly influence community dynamics, but empirical tests are limited. Methodological and logistical challenges often prevent the consideration of organisms' sex in the field, limiting our understanding of the role of sex in community functioning. Where these limitations have been overcome, field studies highlighted sex-based species interactions and their cascading ecological outcomes in marine, freshwater, and terrestrial ecosystems. Understanding how natural communities and ecosystems are structured and respond to anthropogenic pressures in a rapidly changing world is key to successful management and conservation. A fundamental but often overlooked biological characteristic of organisms is sex. Sex-based responses are often considered when conducting studies at organismal and population levels, but are rarely investigated in community ecology. Focusing on kelp forests as a model system, and through a review of other marine and terrestrial ecosystems, we found evidence of widespread sex-based variation in species interactions. Sex-based variation in species interactions is expected to affect ecosystem structure and functioning via multiple trophic and nontrophic pathways. Understanding the drivers and consequences of sex-based variation in species interactions can inform more effective management and restoration. [ABSTRACT FROM AUTHOR]

Human activities have triggered profound changes in natural landscapes, resulting in species loss and disruption of pivotal ecological interactions such as insect herbivory. This antagonistic interaction is affected by complex pathways (e.g., abundance of herbivores and predators, plant chemical defenses, and resource availability), but the knowledge regarding how forest loss and fragmentation affect insect herbivory in human‐modified tropical landscapes still remains poorly understood. In this context, we assessed multi‐pathways by which changes in landscape structure likely influence insect herbivory in 20 Atlantic forest fragments in Brazil. Using path analysis, we estimated the direct effects of forest cover and forest edge density, and the indirect effect via canopy openness, number of understory plants and phenolic compounds, on leaf damage in understory plants located in the edge and interior of forest fragments. In particular, plants located in forest edges experienced greater leaf damage than interior ones. We observed that landscape edge density exerted a positive and direct effect on leaf damage in plants sampled at the edge of forest fragments. Our findings also indicated that forest loss and increase of edge density led to an increase in the canopy opening in the forest interior, which causes a reduction in the number of understory plants and, consequently, an increase in leaf damage. In addition, we detected that phenolic compounds negatively influence leaf damage in forest interior plants. Given the increasing forest loss in tropical regions, in which forest fragments become stranded in highly deforested, edge‐dominated and degraded landscapes, our study highlights the pervasive enhancement in insect herbivory in remaining forest fragments—especially along forest edges and canopy gaps in the forest interior. As a result, increased herbivory is likely to affect forest regeneration and accelerate the ecological meltdown processes in these highly deforested and disturbed anthropogenic landscapes. [ABSTRACT FROM AUTHOR]

The South American insect Tuta absoluta is a significant leaf-mining pest for tomato plants (Solanum lycopersicum). In the last fifteen years, it has invaded and rapidly expanded across most European and African countries. This poses increasing threats to key tomato-growing regions worldwide. Despite the global significance of crop damages caused by T. absoluta, existing models have primarily focused on the developmental growth at the individual level, with limited consideration for population and community-level interactions, especially the plant-pest relationship. Here we introduce and discuss an ecological, process-based, mathematical model that accounts for the interdependent dynamics between a population of the herbivorous insect and the tomato plants it feeds on. The model explicitly integrates the impacts of water and nutrients availability, as well as temperature, on the growth of both insect and plant populations. After calibrating the model using empirical data, we find that its simulations can replicate different observed patterns. Leveraging the mechanistic nature of our approach, we analyze the combined effects of various temperature, fertilization/irrigation (fertigation) and biocontrol scenarios on (i) crop growth and (ii) the overall health of the production system. This enables us to identify knowledge gaps and to discuss the effectiveness and trade-offs associated with different management policies. [ABSTRACT FROM AUTHOR]

Heliozoans are ambush protists that inhabit most limnetic systems. However, ecological information about planktonic heliozoans is still limited. In this study, we investigated seasonal changes in planktonic heliozoan abundance in the deep northern and shallow southern basins of Lake Biwa at pelagic stations between August 2020 and December 2021. We compared planktonic heliozoan abundance levels between the two basins and examined the relationship between heliozoan abundance and environmental variables. In both basins, high levels of planktonic heliozoan abundance were detected in autumn, winter and spring. In the south basin, there was a significant positive correlation between planktonic heliozoan abundance and chlorophyll a concentration as well as the abundance of the diatoms Aulacoseira granulata and Aulacoseira ambigua. These results suggest that planktonic heliozoans directly or indirectly consume diatoms and that heliozoan abundance is subjected to bottom-up control. Furthermore, planktonic heliozoan abundance in the south basin was higher than that in the north basin, possibly due to the presence of waterweeds, which can serve as habitat for heliozoans, and the redistribution of planktonic heliozoans through resuspension from lake bottom sediments. [ABSTRACT FROM AUTHOR]

Community structure is driven by the interaction of physical processes and biological interactions that can vary across environmental gradients and the strength of top‐down control is expected to vary along gradients of primary productivity. In coastal marine systems, upwelling drives regional resource availability through the bottom‐up effect of nutrient subsidies. This alters rates of primary production and is expected to alter algae–herbivore interactions in rocky intertidal habitats. Despite the potential for upwelling to alter these interactions, the interaction of upwelling and grazing pressure is poorly understood, particularly for warm‐temperate systems. Using in situ herbivore exclusion experiments replicated across multiple upwelling regimes, we investigated the effects of both grazing pressure, upwelling, and their interactions on the sessile invertebrate community and biomass of macroalgal communities in a warm‐temperate system. The sessile invertebrate cover showed indirect effects of grazing, being consistently low where algal biomass was high at upwelling sites and at nonupwelling sites when grazers were excluded. The macroalgal cover was greater at upwelling sites when grazers were excluded and there was a strong effect of succession throughout the experimental period. Grazing effects were greater at upwelling sites, particularly during winter months. There was a nonsignificant trend toward greater grazing pressure on early than later successional stages. Our results show that the positive bottom‐up effects of nutrient supply on algal production do not overwhelm top‐down control in this warm‐temperate system but do have knock‐on consequences for invertebrates that compete with macroalgae for space. We speculate that global increases in air and sea surface temperatures in warm‐temperate systems will promote top‐down effects in upwelling regions by increasing herbivore metabolic and growth rates. [ABSTRACT FROM AUTHOR]

Research on economic, ecological and relative benefits from organic and conventional farming systems has gained significant importance. Organic farming increases species diversity, enhances biological control services, and thus complements sustainable pest management. However, published literature is scarce on cotton crops grown organically with respect to the abundance and diversity of biological control agents and their effects on herbivore populations, typically from developing nations. To address the question, the non‐transgenic cotton variety CIM‐573 was cultivated under two fertility management systems, that is, organic and conventional in 2019 and 2021, and subsequently, differences in the abundance and diversity of arthropod communities were carried out. We applied cattle manure in organic fields 1 month before planting; however, synthetic fertilizers were used in conventional fields. We sampled arthropods weekly after 7 weeks of sowing from the middle rows of treatments for both types of fields. We recorded 10 herbivores as well as eight natural enemy species. Herbivores were more abundant in conventional cotton. However, natural enemies were higher in organic cotton fields. Principal component analysis of herbivores assemblages depicted that Shannon diversity and abundance were positively correlated in the conventional cotton while Menhinick richness and Simpson dominance index were higher in organic cotton. Likewise, natural enemies' abundance, Shannon diversity, Menhinick richness and Simpson dominance were typically more concentrated in organic cultivated cotton. Regression analysis confirmed that the abundance and diversity of natural enemies played a significant role in lowering herbivores populations. Seed cotton yield was significantly higher in conventional cotton and the yield difference between organic and conventional cotton was 27.98%. Our study clearly demonstrates that organic cotton provides more functional and complementary niches to natural enemies and plays a crucial role in pest suppression. Implications of our results for future pest management with respect to ecosystem services in organically grown cotton crops are also discussed. [ABSTRACT FROM AUTHOR]

In the long‐term absence of disturbance, ecosystems often enter a decline or retrogressive phase which leads to reductions in primary productivity, plant biomass, nutrient cycling and foliar quality. However, the consequences of ecosystem retrogression for higher trophic levels such as herbivores and predators, are less clear. Using a post‐fire forested island‐chronosequence across which retrogression occurs, we provide evidence that nutrient availability strongly controls invertebrate herbivore biomass when predators are few, but that there is a switch from bottom‐up to top‐down control when predators are common. This trophic flip in herbivore control probably arises because invertebrate predators respond to alternative energy channels from the adjacent aquatic matrix, which were independent of terrestrial plant biomass. Our results suggest that effects of nutrient limitation resulting from ecosystem retrogression on trophic cascades are modified by nutrient‐independent variation in predator abundance, and this calls for a more holistic approach to trophic ecology to better understand herbivore effects on plant communities. [ABSTRACT FROM AUTHOR]

Legume intercropping by biological nitrogen (N) fixation is supposed as a more sustainable way than chemical N addition to enhance soil N availability in agronomy, however, the effects of the two types of N input on soil food web are scarcely determined. To fill the knowledge gap, we conducted a field experiment with randomized block design in an oil‐tea (Camellia oleifera) plantation, which included five N manipulation treatment: legume intercropping (Arachis hypogaea and Cassia tora), chemical N fertilizer application (84 and 168 kg N ha−1 yr−1), and the control (no N addition). The soil nematode communities and physicochemical properties were monitored in the seedling, heading, and mature stages of the legumes respectively. The results showed that the legume intercropping significantly increased the abundances of bacterivores and omnivore‐predators compared with the N fertilizations. Weighted nematode fauna analysis showed that N fertilization treatments were mainly located in the degraded plot (quadrat IV), and legume treatments were located in the structure plot (quadrat III). Structural equation model revealed that the legume intercropping positively correlated with the abundance of bacterivores and omnivore‐predators while N fertilization rate negatively correlated with the abundance of bacterivores and fungivores. Our results suggest that the legume biological N fixation was more conducive to providing N sources to soil organisms than the chemical N fertilizer, which resulted in an enhanced and a degraded soil food web respectively. Thus, legume intercropping is a more sustainable N management practice for the cultivation of C. oleifera plantations. [ABSTRACT FROM AUTHOR]

Resources and temperature play major roles in determining biological production in lake ecosystems. Lakes have been warming and 'browning' over recent decades due to climate change and increased loading of terrestrial organic matter. Conflicting hypotheses and evidence have been presented about whether these changes will increase or decrease fish growth within lakes. Most studies have been conducted in low-elevation lakes where terrestrially derived carbon tends to dominate over carbon produced within lakes. Understanding how fish in high-elevation mountain lakes will respond to warming and browning is particularly needed as warming effects are magnified for mountain lakes and treeline is advancing to higher elevations. We sampled 21 trout populations in the Sierra Nevada Mountains of California to examine how body condition and individual growth rates, measured by otolith analysis, varied across independent elevational gradients in temperature and dissolved organic carbon (DOC). We found that fish grew faster at warmer temperatures and higher nitrogen (TN), but slower in high DOC lakes. Additionally, fish showed better body condition in lakes with higher TN, higher elevation and when they exhibited a more terrestrial δ13C isotopic signature. The future warming and browning of lakes will likely have antagonistic impacts on fish growth, reducing the predicted independent impact of warming and browning alone.

Dinitrogen (N2) fixed by a group of prokaryotes (diazotrophs) is the dominant process adding bioavailable nitrogen into the ocean. Although it has been intensively studied how N2 fixation is controlled by resources (bottom-up factors), it is unclear whether the grazing (top-down control) effectively impacts growth and distribution of different diazotroph groups. In this study, we evaluate this question by conducting log-log regression of diazotroph biomass onto corresponding N2 fixation rates in the global ocean. The slope of the regression for Trichodesmium is ∼0.8, indicating that a small portion of the increase in N2 fixation does not accumulate as its biomass. This leads to a conclusion that Trichodesmium is under a substantial top-down control, although bottom-up control still dominates. We also analyze the residuals of the regression in the North Atlantic, concluding that free trichomes of Trichodesmium are subject to stronger top-down control than its colonies. The weak correlation between the biomass and N2 fixation of unicellular cyanobacterial diazotrophs indicates that the degree of top-down control on this type of diazotrophs varies greatly. The analyses obtain unrealistic results for diatom-diazotroph assemblages due to complicated nitrogen sources of these symbioses. Our study reveals the variability of top-down control among different diazotroph groups across time and space, suggesting its importance in improving our understandings of ecology of diazotrophs and predictions of N2 fixation in biogeochemical models. Measurements of size-specific N2 fixation rates and growth rates of different diazotroph groups can be useful to more reliably analyze the top-down control on these key organisms in the global ocean. [ABSTRACT FROM AUTHOR]

Abstract The historical ecological paradigm of wetland ecosystems emphasized the role of physical or “bottom‐up” factors in maintaining functions and services. However, recent studies have shown that the loss of predators in coastal salt marshes can lead to a significant reduction in wetland extent due to overgrazing of vegetation by herbivores. Such studies indicate that consumers or “top‐down” factors may play a much larger role in the maintenance of wetland ecosystems than was previously thought. The objective of this study was to evaluate whether altering top‐down control by manipulating the presence of predators can lead to measurable changes in salt marsh ecosystem properties. Between May and August of 2015 and 2016, we established exclosure and enclosure cages within three New England coastal wetland areas and manipulated the presence of green crab predators to assess how they and their fiddler and purple marsh crab prey affect changes in ecosystem properties. Predator presence was associated with changes in soil nitrogen and aboveground biomass at two of the three field sites, though the magnitude and direction of these effects varied from site to site. Further, path analysis results indicate that across field sites, a combination of bottom‐up and top‐down factors influenced changes in measured variables. These results challenge the growing consensus that consumers have strong effects, indicating instead that predator impacts may be highly context‐dependent.

Natural systems show heterogeneous patchy distributions of vegetation over large landscapes. Reaction–diffusion systems can demonstrate such heterogeneity of species distributions. Here, we analyse a reaction–diffusion model of plant–herbivore interactions in two-dimensional space to illustrate non-homogeneous distributions of plants and herbivores. The non-spatial system shows bottom-up control, where herbivore density is low under low and high primary productivity but increased at intermediate productivity. In addition, the non-spatial system provides bistability between a dense vegetation state devoid of herbivores and a coexisting state of plants and herbivores. In the spatiotemporal model, we give analytical conditions of occurring diffusion-driven (Turing) instability, where a novel point in our model is the relative dispersal of herbivores, which represents the movement of herbivores from a higher to a lower vegetation state in addition to the self-diffusion of both species. It is shown that heterogeneity in the population distribution does not occur if the relative dispersal of herbivores is low, but it appears in the opposite case. Due to bistability in the underlying non-spatial system, the spatiotemporal model produces initial value-dependent patterns. The two initial values make different patterns despite having the same primary productivity and relative dispersal rate. As productivity increases with a given relative herbivore dispersal, pattern transition occurs from a blend of stripes and spots of low vegetation state to a predominantly low-density vegetation state with smaller patches of densely vegetated states with one initial value. On the contrary, a discernible change in vegetation patterns from cold spots in the dense vegetation to hot stripes in the primarily low-vegetated state is noticed under the other initial population value. Furthermore, the population distributions of plants and herbivores in the entire domain after a long period are heterogeneous for both initial values, provided the relative herbivore dispersal is substantial. We estimated mean population densities to observe species fitness in the whole domain under variable productivity. When productivity is high, the mean population density of plants may go up or down, depending on the herbivore's relative dispersal rate. In contrast to the bottom-up control dynamics of the non-spatial system, the system exhibits a top-down control under high relative dispersal, where the herbivore regulates vegetation growth under high productivity. On the other hand, herbivores are extinct under high productivity if the relative dispersal is low. [ABSTRACT FROM AUTHOR]

Many continental saline lakes are under the effects of salinity increase and anthropogenic eutrophication exacerbated by global change. The response of the food web to these drivers of change is not straightforward. To understand the consequences of salinity and eutrophication interactive effects on the food web, we studied the seasonal dynamics of zooplankton and phytoplankton and water quality parameters in 20 lakes of different salinity (from freshwater to hypersaline) and nutrient status (from oligotrophic to eutrophic) located in southern Siberia. We observed a pronounced bottom-up effect of nutrients, which induced an increase in the biomass of phytoplankton and zooplankton and a decline in water quality. A significant decrease in the species abundance of zooplankton was observed at a threshold salinity of 3 g L−1 and the disappearance of fish at 10 g L−1. The top-down effect induced by salinity manifested itself in an increase in the biomass of zooplankton with the disappearance of fish, and in the change of the size distribution of phytoplankton particles with an increase in the proportion of cladocerans in the zooplankton. Even though we observed that with the salinity increase the food web in saline lakes transformed from three-trophic to two-trophic without fish, we conclude that in the salinity range from 10 to 20–30 g L−1 this transition in most cases will not increase the ability of zooplankton to control phytoplankton. Interactive effects of salinity and eutrophication strongly depend on the size and depth of the lake, as deep stratified lakes tend to have a better water quality with lower biomasses of both phyto- and zooplankton. Thus, the salinity per se is not the driver of the decline in water clarity or the uncontrolled development of phytoplankton. Moreover, for deep lakes, salinity may be a factor affecting the stability of stratification, which mitigates the consequences of eutrophication. Thus, small shallow lakes will be the most vulnerable to the joint effect of salinity increase and eutrophication with the degradation of ecosystem functioning and water quality at moderate salinities of 3–20 g L−1. [ABSTRACT FROM AUTHOR]

Autotrophs, mixotrophs and bacteria exhibit complex interrelationships containing multiple ecological mechanisms. A mathematical model based on ecological stoichiometry is proposed to describe the interactions among them. Some dynamic analysis and numerical simulations of this model are presented. The roles of autotrophs and mixotrophs in controlling bacterioplankton are explored to examine the experiments and hypotheses of Medina–Sánchez, Villar–Argaiz and Carrillo for La Caldera Lake. Our results show that the dual control (bottom-up control and top-down control) of bacteria by mixotrophs is a key reason for the ratio of bacterial and phytoplankton biomass in La Caldera Lake to deviate from the general tendency. The numerical bifurcation diagrams suggest that the competition between phytoplankton and bacteria for nutrients can also be an important factor for the decrease of the bacterial biomass in an oligotrophic lake. [ABSTRACT FROM AUTHOR]

In order to understand how global warming effects on ecosystem primary production may change depending on nutrient enrichment, a new classification is proposed to disentangle and recognize the combination of interactions among several factors, based on the effect direction (positive, negative, or neutral) and its changes induced in it by the other factor (synergizing, antagonizing, inducing no change, or changing it in some other way). Marine macroalgae were chosen (as primary producers for which there is the most experimental information available) to review the relevant studies on which this new classification can be tested. It was observed the positive effects of elevated temperature and nutrient enrichment often synergized each other within the temperature range between relatively low and optimal growth levels. However, the negative effect of further temperature elevation from optimal to higher levels was antagonized by nutrient enrichment in some studies but was synergized in others, depending on the range of temperature elevation. The positive effect of nutrient enrichment was antagonized (but still positive) by temperature increase above the optimum in many cases, although the effect sometimes switched to a negative effect depending on the magnitude of nutrient enrichment. These results predict that global warming will enhance bottom-up effects on primary production in cold seasons and areas, and there will be a negative warming effect on production in hot seasons and areas, but it may be possible to mitigate this effect by appropriate levels of nutrient enrichment.

The ability of marine diazotrophs to fix dinitrogen gas (N2) is one of the most influential yet enigmatic processes in the ocean. With their activity diazotrophs support biological production by fixing about 100–200 Tg N/year and turning otherwise unavailable dinitrogen into bioavailable nitrogen (N), an essential limiting nutrient. Despite their important role, the factors that control the distribution of diazotrophs and their ability to fix N2 are not fully elucidated. We discuss insights that can be gained from the emerging picture of a wide geographical distribution of marine diazotrophs and provide a critical assessment of environmental (bottom-up) versus trophic (top-down) controls. We expand a simplified theoretical framework to understand how top-down control affects competition for resources that determine ecological niches. Selective mortality, mediated by grazing or viral-lysis, on non-fixing phytoplankton is identified as a critical process that can broaden the ability of diazotrophs to compete for resources in top-down controlled systems and explain an expanded ecological niche for diazotrophs. Our simplified analysis predicts a larger importance of top-down control on competition patterns as resource levels increase. As grazing controls the faster growing phytoplankton, coexistence of the slower growing diazotrophs can be established. However, these predictions require corroboration by experimental and field data, together with the identification of specific traits of organisms and associated trade-offs related to selective top-down control. Elucidation of these factors could greatly improve our predictive capability for patterns and rates of marine N2 fixation. The susceptibility of this key biogeochemical process to future changes may not only be determined by changes in environmental conditions but also via changes in the ecological interactions.

The ability of marine diazotrophs to fix dinitrogen gas (N2) is one of the most influential yet enigmatic processes in the ocean. With their activity diazotrophs support biological production by fixing about 100–200 Tg N/year and turning otherwise unavailable dinitrogen into bioavailable nitrogen (N), an essential limiting nutrient. Despite their important role, the factors that control the distribution of diazotrophs and their ability to fix N2 are not fully elucidated. We discuss insights that can be gained from the emerging picture of a wide geographical distribution of marine diazotrophs and provide a critical assessment of environmental (bottom-up) versus trophic (top-down) controls. We expand a simplified theoretical framework to understand how top-down control affects competition for resources that determine ecological niches. Selective mortality, mediated by grazing or viral-lysis, on non-fixing phytoplankton is identified as a critical process that can broaden the ability of diazotrophs to compete for resources in top-down controlled systems and explain an expanded ecological niche for diazotrophs. Our simplified analysis predicts a larger importance of top-down control on competition patterns as resource levels increase. As grazing controls the faster growing phytoplankton, coexistence of the slower growing diazotrophs can be established. However, these predictions require corroboration by experimental and field data, together with the identification of specific traits of organisms and associated trade-offs related to selective top-down control. Elucidation of these factors could greatly improve our predictive capability for patterns and rates of marine N2 fixation. The susceptibility of this key biogeochemical process to future changes may not only be determined by changes in environmental conditions but also via changes in the ecological interactions. [ABSTRACT FROM AUTHOR]

The historical ecological paradigm of wetland ecosystems emphasized the role of physical or "bottom‐up" factors in maintaining functions and services. However, recent studies have shown that the loss of predators in coastal salt marshes can lead to a significant reduction in wetland extent due to overgrazing of vegetation by herbivores. Such studies indicate that consumers or "top‐down" factors may play a much larger role in the maintenance of wetland ecosystems than was previously thought. The objective of this study was to evaluate whether altering top‐down control by manipulating the presence of predators can lead to measurable changes in salt marsh ecosystem properties. Between May and August of 2015 and 2016, we established exclosure and enclosure cages within three New England coastal wetland areas and manipulated the presence of green crab predators to assess how they and their fiddler and purple marsh crab prey affect changes in ecosystem properties. Predator presence was associated with changes in soil nitrogen and aboveground biomass at two of the three field sites, though the magnitude and direction of these effects varied from site to site. Further, path analysis results indicate that across field sites, a combination of bottom‐up and top‐down factors influenced changes in measured variables. These results challenge the growing consensus that consumers have strong effects, indicating instead that predator impacts may be highly context‐dependent. [ABSTRACT FROM AUTHOR]

Elucidating the mechanisms of fluctuations in fish populations are key to sustainable fisheries management. However, limited data combined with climate variability and fishing further constrain our understanding of fish population dynamics. Fortunately, marine sedimentary archives of fish abundance and environmental changes in the past, may provide new insights into long-term fish population fluctuations. Here, we used 150-year sediment records of the abundance of Japanese anchovy (Engraulis japonicus) scales, phytoplankton, and zooplankton biomarkers, and δ15N data previously reported from the central Yellow Sea (YS). We discussed the linkages of the anchovy abundance to ecosystem structure and sea surface temperatures (SSTs). Principal component analysis (PCA) identified negative effects of strong stratification (higher δ15N) and high abundance of haptophytes (higher alkenone content) on the anchovy stock through our analytical period (~1860–2005 AD). In addition, we found positive relationships between the anchovy abundance and plankton productivity in proxies before the period of intense fishing (1860–1980 AD), indicating bottom-up processes affecting the anchovy stock. However, the bottom-up processes became unclear under excessive fishing. This was possibly due to overfishing becoming a major driver after 1980, thereby altering the cascading of the marine ecosystem towards a different structure. Climate variability seems to indirectly influence the anchovy stock through bottom-up control via a cascading effect from the changes in the North Pacific Gyre Oscillation (NPGO) or the Pacific North American pattern (PNAP). The impacts of these changes on the hydrodynamic features of YS in turn influence the productivity of plankton prey for the anchovy. Collectively, our findings suggest that synergistic effects of climate and fishing on the anchovy need to be paid greater attention. Our results also contribute to an improved understanding of fish population fluctuations in other seas. [ABSTRACT FROM AUTHOR]

Communities are shaped by a variety of ecological and environmental processes, each acting at different spatial scales. Seminal research on rocky shores highlighted the effects of consumers as local determinants of primary productivity and community assembly. However, it is now clear that the species interactions shaping communities at local scales are themselves regulated by large‐scale oceanographic processes that generate regional variation in resource availability. Upwelling events deliver nutrient‐rich water to coastal ecosystems, influencing primary productivity and algae–herbivore interactions. Despite the potential for upwelling to alter top‐down control by herbivores, we know relatively little about the coupling between oceanographic processes and herbivory on tropical rocky shores, where herbivore effects on producers are considered to be strong and nutrient levels are considered to be limiting. By replicating seasonal molluscan herbivore exclusion experiments across three regions exposed to varying intensity of seasonal upwelling, separated by hundreds of kilometers along Panama's Pacific coast, we examine large‐scale environmental determinants of consumer effects and community structure on tropical rocky shores. At sites experiencing seasonal upwelling, grazers strongly limited macroalgal cover when upwelling was absent, leading to dominance by crustose algae. As nutrients increased and surface water cooled during upwelling events, increases in primary productivity temporarily weakened herbivory, allowing foliose, turf and filamentous algae to replace crusts. Meanwhile, grazer effects were persistently strong at sites without seasonal upwelling. Our results confirm that herbivores are key determinants of tropical algal cover, and that the mollusk grazing guild can control initial stages of macroalgal succession. However, our focus on regional oceanographic conditions revealed that bottom‐up processes regulate top‐down control on tropical shorelines. This study expands on the extensive body of work highlighting the influence of upwelling on local ecological processes by demonstrating that nutrient subsidies delivered by upwelling events can weaken herbivory in tropical rocky shores. [ABSTRACT FROM AUTHOR]

Inland fisheries managers must account for multiple competing uses for aquatic resources; using methods such as ecosystem‐based management allows for different priorities for aquatic ecosystems to be accounted for. Declining abundance of kokanee salmon Oncorhynchus nerka (Walbaum) in Arrow Lakes Reservoir in the 1990s led to the use of large‐scale nutrient addition to improve productivity of kokanee and large piscivores. However, it is unclear what effect these measures had on the system given high discharge and highly variable annual flow regime throughout the watershed. An Ecopath with Ecosim model of the ecosystem was fitted to the available data and used to predict ecosystem structure and reservoir objectives under different nutrient addition strategies and varying annual flow regimes. Results from the model indicate that nutrient addition is an important driver in the system, with lower flows resulting in higher biomass for higher trophic levels. Decision analysis demonstrated the importance of maintaining nutrient additions to achieve management objectives despite losses in some high‐flow years. [ABSTRACT FROM AUTHOR]

Ecological stoichiometry seeks to understand the ecological consequences of elemental imbalances between consumers and their resources. Therein, the well‐accepted growth rate hypothesis (GRH) states that organisms exhibiting rapid growth have higher phosphorus (P) demand – and thus lower C:P and N:P ratios – than slow growing ones, due to a higher allocation to P‐rich rRNA. However, GRH has rarely been extended to other biological traits than growth, especially at the community level. In this study, we investigated whether macroinvertebrate stoichiometric traits (e.g. C:P and N:P ratios) can be linked to their development traits, and whether these stoichiometric traits are related to macroinvertebrate community assemblage under different nutrient conditions. We allocated more than 400 European taxa to different groups, defined using available information about three development‐related traits: 'life span', 'voltinism' and 'number of reproductive cycles per individual'. We sampled 18 invertebrate taxa in six streams exhibiting different levels of nutrient concentration and measured their stoichiometric traits. Further, we quantified invertebrate taxon abundances in these streams during an annual survey. Based on these data, we tested whether community composition regarding the developmental groups differs, depending on nutrient concentration. We found significant differences in the proportions of the developmental groups along a gradient of water N:P, in relation to their stoichiometric traits. Taxa with low C:P and N:P ratios were generally associated with faster development groups, and these taxa tended to occur at higher proportions in streams exhibiting low dissolved N:P ratios. In contrast, communities from P‐poor, high dissolved N:P streams, were dominated by slowly developing taxa with high N:P ratios. Our results highlight that extending the GRH to species development rate might give some insights about the mechanisms by which nutrient concentrations in ecosystems influence consumers' community composition. [ABSTRACT FROM AUTHOR]

• Temperature and nutrients alter the prevalence of top-down versus bottom-up control. • High synchrony and low grazing pressure in planktonic ecosystems facilitate bottom-up control. • Response mechanisms of planktonic ecosystems to warming and nutrients differ by ecosystems. Eutrophication and climate change may affect the top-down versus bottom-up controls in aquatic ecosystems. However, the relative prevalence of the two controls in planktonic ecosystems along the eutrophication and climate gradients has rarely been addressed. Here, using the field surveys of 17 years in a typical bay and estuary, we test two opposite patterns of trophic control dominance and their response to regional temporal eutrophication and climate fluctuations. It was found that trophic control of planktonic ecosystems fluctuated between the dominance of top-down and bottom-up controls on time scales in both the bay and estuary studied. The relative prevalence of these two controls in both ecosystems was significantly driven directly by regional dissolved inorganic nitrogen but, for the estuary, also by the nonlinear effects of regional sea surface temperature. In terms of indirect pathways, community relationships (synchrony and grazing pressure) in the bay are driven by both regional dissolved inorganic nitrogen - soluble reactive phosphorus ratio and sea surface temperature, but this drive did not continue to be transmitted to the trophic control. Conversely, trophic control in estuary was directly related to grazing pressure and indirectly related to synchrony. These findings support the view that eutrophication and climate drive the relative prevalence of top-down versus bottom-up controls at ecosystem and temporal scales in planktonic ecosystems, which has important implications for predicting the potential impacts of anthropogenic and environmental perturbations on the structure and function of marine ecosystems. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper looks at the value of second language students, teachers, and others interacting in very large groups of tens and even 100s of members of the same group. The paper begins by looking at disadvantages of these larger groups and then at their advantages, before providing advice on how to facilitate groups regardless of their sizes. This advice includes dividing resources and roles, promoting a common identity, encouraging rewards and celebrations, using groups of different sizes, taking advantage of communication technology, and paying attention to the development and use of collaborative skills. The authors’ conclusion is that very large groups can be beneficial if those involved carefully attend to the groups’ functioning, such as by dividing those very large groups into much smaller groups, including groups of 2-4 members.

Questions: Human activities are increasing the density of domestic grazers and global nutrient loads, modifying the main determinants of vegetation community dynamics. Grazing (top‐down control) and nutrient availability (bottom‐up control) may interactively modify plant biomass, which is particularly important in grasslands devoted to livestock production. Here, we aim to understand the interactive effects of grazing and fertilization on grassland plant biomass. We hypothesized that the joint effects of nutrient addition and domestic grazing on above‐ground plant biomass are not additive, but they modify each other through changes in ground‐level light, leaf nutritional quality, above‐ground net primary productivity (ANPP), and below‐ground plant allocation. Location: Flooding Pampa (Buenos Aires, Argentina). Methods: We carried out a factorial experiment of grazing exclusion and fertilization with nitrogen, phosphorus, and potassium + micronutrients during ​several years in a mesic grassland devoted to livestock production. Results: After four years, grazing reduced live above‐ground plant biomass by 52%, and when combined with fertilization this reduction was 70%. Nutrient addition in the grazed grassland increased ANPP and leaf nutrient concentration. These changes in turn intensified grazing pressure and cattle’s plant consumption. By contrast, fertilization did not produce any significant effect on plant biomass or ANPP inside the exclosures, where ground‐level light was low. A structural equation model revealed that the increase in ANPP fostered above‐ground and reduced below‐ground plant biomass. Conclusions: This is the first study conducted in the Pampas grasslands that evaluated the effect of cattle grazing and fertilization on plant communities under field conditions over several years. Grazing and nutrient addition synergistically controlled grassland plant biomass, as the reduction in above‐ground biomass by cattle consumption was greater in fertilized plots. Our results provided empirical evidence that leaf nitrogen and ANPP modulated plant biomass dynamics in grasslands devoted to livestock production in the context of increased nutrient loads in terrestrial ecosystems.Grassland ecosystems are used for livestock production and are exposed to the global alteration of nutrient budgets. We found that grazing reduced above‐ground plant biomass, but this reduction was greater when combined with nutrient addition. The observed changes in plant biomass across experimental plots were mainly accounted for by differences in plant quality and rates of above‐ground plant biomass production. [ABSTRACT FROM AUTHOR]

Changes in the composition of plant functional traits may affect ecosystem processes through influencing trophic interactions. Bottom‐up control by plant species through food availability to animals may vary with time. However, such dynamics and their consequences for deadwood turnover are poorly known for detrital food webs.We introduce a dynamic conceptual model of the feedback of tree functional traits, (deadwood‐feeding) termite populations and deadwood decomposition. We hypothesized that tree functional diversity (in terms of a wood resource economic spectrum [WES]) supports the sustenance of termite populations via complementary food supplied through time, as deadwood varies in traits both initially across species and because of different decomposition rates. Simultaneously, driven by this temporal dynamics of food quality, the consumption of deadwood by termites should hypothetically sustain deadwood turnover in a functionally diverse forest over time.We tested our hypothesis through an 18‐month termite‐exclusion decomposition experiment by incubating coarse (i.e. 5 cm diameter) deadwood of 34 woody species in two subtropical forests in East China. One site still sustained a healthy population of pangolins as the keystone termite predator, whereas another had lost its pangolins due to hunting and illegal wildlife trade.The results supported our hypothesis: in the first 12 months, termites amplified the positive linear relationship between % wood mass loss and initial wood quality (WES). In contrast, between 12 and 18 months, termite‐mediated consumption, and associated wood mass loss, showed a humpback relation with the initial WES. This shift in termite preference of deadwood species along the WES reflects complementary food availability to termites through time.Synthesis. Our findings imply that tree functional composition, with variation in deadwood quality through decomposition time, can help to sustain termite populations and thereby forest carbon turnover. Future studies need to test whether and how our conceptual model may apply to other detrital systems and food webs. In general, food web research would benefit from a stronger focus on temporal patterns for better understanding the interactions of basal resource functional traits and consumers on ecosystem functions. [ABSTRACT FROM AUTHOR]

Human‐caused loss of vertebrate and invertebrate animals, defaunation, is increasing, and potentially affects plant community structure of diverse grassland ecosystems world‐wide.We experimentally simulated defaunation using size‐selective fences to progressively exclude large‐, medium‐ and small‐sized mammals, and invertebrates from two subalpine vegetation types in the Swiss National Park (SNP): intensively grazed short‐grass and moderately grazed tall‐grass vegetation. We assessed plant community properties yearly from 2009 to 2013, and examined treatment effects on plant community structure in the two grassland types.In the short‐grass vegetation, the exclusion of large mammals increased total plant biomass, while the exclusion of large and medium‐sized mammals increased total, grass and forb biomass compared to when all animals had access. These increases became stronger when invertebrates were also excluded. The exclusion of all mammals and invertebrates increased biomass of grasses by 205%, forbs by 100% and total plant biomass by 118% compared to when all animals had access, hence enhancing relative biomass of grasses from 43.6% to 60%, changing plant species composition and lowering richness of forbs by 16%, the number of plant families by 13% and family‐level Shannon diversity by 23%. In contrast to these significant community‐level responses found in the short‐grass vegetation, there was no evidence that the size‐selective exclusion of animals altered the plant community structure of the tall‐grass vegetation. The contrasting results were due to the difference in plant community composition prior to our experiment, which were related to differences in quantity and quality of forage and in grazing intensities of herbivores between the two grassland types.Synthesis. Our results showed that different‐sized animals, in particular large mammals and invertebrates, contributed to maintain the plant community structure in the short‐grass vegetation, highlighting the importance of multiple, functionally different animal groups for ecosystem functioning and stability. In contrast to the short‐grass vegetation, we could not detect such a top‐down control by animals in the tall‐grass vegetation. Our results suggest that potential defaunation effects on grassland plant community structure depend on the degree of grazing pressure release and grassland vegetation type. [ABSTRACT FROM AUTHOR]

Top‐down and bottom‐up theories of trophic control have been fundamental to our understanding of community dynamics and structure. However, most ecological theories have focused on equilibrium dynamics and do not provide predictions for communities' responses in temporally fluctuating environments. By deriving the frequency response of populations in different trophic communities, we extend the top‐down and bottom‐up theories of ecology to include how temporal fluctuations in potential primary productivity percolate up the food chain and are re‐expressed as population variability. Moreover, by switching from a time‐based representation into the frequency domain, we provide a unified method to compare how the time scale of perturbations determines communities' responses. At low frequencies, primary producers and secondary consumers have the highest temporal variability, while the primary consumers are relatively stable. Similar to the Exploitation Ecosystem Hypothesis, top‐down effects drive this alternating pattern of variability. We define the top‐down effect of consumers on the variability of lower trophic levels as a variation cascade. However, at intermediate frequencies, variation cascades can amplify temporal variation up the food chain. At high frequencies, variation cascades weaken, and fluctuations are attenuated up the food chain. In summary, we provide a novel theory for how communities will respond to fluctuations in productivity, and we show that indirect species interactions play a crucial role in determining community dynamics across the frequency spectrum. [ABSTRACT FROM AUTHOR]

Many continental saline lakes are under the effects of salinity increase and anthropogenic eutrophication exacerbated by global change. The response of the food web to these drivers of change is not straightforward. To understand the consequences of salinity and eutrophication interactive effects on the food web, we studied the seasonal dynamics of zooplankton and phytoplankton and water quality parameters in 20 lakes of different salinity (from freshwater to hypersaline) and nutrient status (from oligotrophic to eutrophic) located in southern Siberia. We observed a pronounced bottom-up effect of nutrients, which induced an increase in the biomass of phytoplankton and zooplankton and a decline in water quality. A significant decrease in the species abundance of zooplankton was observed at a threshold salinity of 3 g L−1 and the disappearance of fish at 10 g L−1. The top-down effect induced by salinity manifested itself in an increase in the biomass of zooplankton with the disappearance of fish, and in the change of the size distribution of phytoplankton particles with an increase in the proportion of cladocerans in the zooplankton. Even though we observed that with the salinity increase the food web in saline lakes transformed from three-trophic to two-trophic without fish, we conclude that in the salinity range from 10 to 20–30 g L−1 this transition in most cases will not increase the ability of zooplankton to control phytoplankton. Interactive effects of salinity and eutrophication strongly depend on the size and depth of the lake, as deep stratified lakes tend to have a better water quality with lower biomasses of both phyto- and zooplankton. Thus, the salinity per se is not the driver of the decline in water clarity or the uncontrolled development of phytoplankton. Moreover, for deep lakes, salinity may be a factor affecting the stability of stratification, which mitigates the consequences of eutrophication. Thus, small shallow lakes will be the most vulnerable to the joint effect of salinity increase and eutrophication with the degradation of ecosystem functioning and water quality at moderate salinities of 3–20 g L−1.

We conducted microcosm experiments with two contrasting freshwater ciliates on functional traits (FTs) related to their growth rate (numerical response, NR) and ingestion rate (functional response, FR) over a range of ecologically relevant temperatures. Histiobalantium bodamicum and Vorticella natans are common planktonic ciliates but their abundance, swimming behavior, and temperature tolerance are different. In contrast to most sessile peritrich species, the motile V. natans is not strictly bacterivorous but also voraciously feeds upon small algae. We observed three main alterations in the shape of NR of both species with temperature, that is, change in the maximum growth rate, in the initial slope and in the threshold food level needed to sustain the population. Similarly, maximum ingestion rate, gross growth efficiency (GGE), and cell size varied with temperature and species. These findings caution against generalizing ciliate performance in relation to the ongoing global warming. Our results suggest that V. natans is the superior competitor to H. bodamicum in terms of temperature tolerance and bottom‐up control. However, the abundance of V. natans is usually low compared to H. bodamicum and other common freshwater ciliates, suggesting that V. natans is more strongly top‐down controlled via predation than H. bodamicum. The taxonomic position of V. natans has been debated. Therefore, to confirm species and genus affiliation of our study objects, we sequenced their small subunit ribosomal RNA (SSU rDNA) gene. [ABSTRACT FROM AUTHOR]

Context: Insectivorous birds are sensitive to forest disturbances that may limit the availability of food consisting mainly of invertebrates. However, birds and invertebrates may be differently affected by forest disturbances while invertebrates may interact with disturbances. Objectives: We aim to determine: (i) the effects of forest degradation on invertebrates and insectivorous birds; (ii) the effect of the availability of invertebrates as a food source on birds; (iii) interactions between food availability and forest degradation. Methods: We selected 34 1-km radius landscape units, where the abundance of birds and invertebrates was sampled in the canopy and understory. Bird density as well as the abundance and richness of invertebrates were considered as dependent variables and analysed using Generalized Linear Mixed Model and Structural Equation Models. Remote-sensing indices of forest degradation were included as predictors. Results: Eight indices of forest degradation affected canopy and understory invertebrates differently. Unlike invertebrates, bird abundance was affected by a smaller number of degradation indices, forest amounts as well as the cover of understory and canopy. Only two forest degradation indices had a comparable effect on bird abundance and invertebrates. We found causal relationships between understory invertebrates and the abundance of understory birds (all species and the small-sized ones), but also invertebrate abundance × forest cover interactions affected the abundance of a bird species. Conclusions: Our results indicate that birds and invertebrates respond differently to forest degradation, but also provide evidence for bottom-up control by forest degradation and suggest food limitation varies with forest amounts. [ABSTRACT FROM AUTHOR]

To seek how soil biotic and abiotic factors which might shape the Bdellovibrio -and-like-organisms community, we sampled paddy soils under different fertilization treatments including fertilization without nitrogen (Control), the nitrogen use treatment (N) and the nitrogen overuse one (HNK) at three rice growing stages. The abundances of BALOs were impacted by the rice-growing stages but not the fertilization treatments. The abundances of Bdellovibrionaceae -like were positively associated with soil moisture, which showed a negative relationship with Bacteriovoracaceae -like bacteria. High-throughput sequencing analysis of the whole bacterial community revealed that the α-diversity of BALOs was not correlated with any soil properties data. Network analysis detected eight families directly linked to BALOs, namely, Pseudomonadaceae , Peptostreptococcaceae , Flavobacteriaceae , Sediment-4, Verrucomicrobiaceae, OM27 , Solirubrobacteraceae and Roseiflexaceae. The richness and composition of OTUs in the eight families were correlated with different soil properties, while the evenness of them had a positive effect on the predicted BALO biomass. These results highlighted that the bottom-up control of BALOs in paddy soil at least partially relied on the changes of soil water content and the diversity of bacteria directly linked to BALOs in the microbial network. [ABSTRACT FROM AUTHOR]

Spatial dynamic theories such as source-sink models frequently describe habitat-specific demographies, yet there are surprisingly few field studies that have examined how and why interacting species vary in their dynamics across multiple habitat types. We studied the spatial pattern of interaction between a chewing herbivore and its primary larval host plant in two habitat types. We found that the interaction between an arctiid caterpillar (Platyprepia virginalis) and its host (Lupinus arboreus) differed in wet vs. upland dry habitats, as did yearly population dynamics for the caterpillar. In upland sites, there was a strong positive relationship between lupine cover and the abundance of caterpillars although this relationship was not apparent in wet sites. Additionally, in wet sites, caterpillar populations were larger and less variable across years. Caterpillars appeared to exhibit source-sink dynamics, with the time-averaged finite growth rate lamda > 1 in wet sites (sources), lamda < 1 in upland dry sites (sinks), and predominant source-to-sink movement of late-instar caterpillars. Populations in upland dry sites also went locally extinct in years of low regional abundance. Emigration from wet sites could potentially explain the lack of coupling of herbivore and host plant dynamics in these sites. These results indicate that movement and other factors affecting demography are habitat-specific and have important implications for trophic control. Acknowledging such complexity makes simple models of trophic control seem overly general but may allow us to formulate more broadly applicable ecological models.

Submarine groundwater discharge (SGD), the direct discharge of groundwater into the sea, is abundant around the globe. Fresh SGD can occur as focused flow in submarine springs. However, little is known on the impact of submarine springs on marine organisms. For a better understanding of the interaction between SGD and its surrounding organisms, the impact of SGD on the abundance of fish was investigated in a coastal lagoon of Tahiti, French Polynesia. The study is based on the assumption of an enhanced biological production due to increased amounts of nutrient input caused by terrestrial groundwater supply into the sea. Biofouling processes and zooplankton samples were used as indicators for elevated nutrient input due to submarine springs. The main objective was to investigate the effect on the abundance of fish assuming a higher fish abundance possibly caused by a bottom-up control. Presented data show a significantly higher abundance around a submarine spring as well as significantly larger growth of algal turfs exposed to groundwater discharge. Zooplankton evaluations suggest slightly higher abundances around the submarine spring. The results suggest elevated nutrient concentrations transmitted by submarine springs may cause a bottom-up control resulting in a higher abundance of fish around the investigated submarine spring.

The mechanisms of species coexistence make ecologists fascinated, although theoretical work shows that omnivory can promote coexistence of species and food web stability, it is still a lack of the general mechanisms for species coexistence in the real food webs, and is unknown how omnivory affects the interactions between competitor and predator. In this work, we first establish an omnivorous food web model with a competitor based on two natural ecosystems (the plankton community and fig–fig wasp system). We analyze the changes of both food web structure and stability under the different resource levels and predation preference of the generalist/top predator. The results of model analyses show that weak predation strength can promote stable coexistence of predators and prey. Moreover, the evolutionary trend of food web structure changes with the relative predation strength is more diverse than the relative competition strength, and an integration of both omnivory, increased competition, top-down control and bottom-up control can promote species diversity and food web stability. Our theoretical predictions are consistent with empirical data in the plankton community: the lower concentration of nutrient results in a more stable population dynamics. Our theoretical work could enrich the general omnivorous theory on species coexistence and system stability in the real food webs. [ABSTRACT FROM AUTHOR]

Questions: Meadows in montane forests have emerged as a global study system for the accelerating phenomenon of woody encroachment, particularly in the highly productive temperate rainforests of the Pacific Northwest. Study of woody encroachment into meadows in western Oregon, however, has been conducted almost entirely in the western and High Cascades, with only two extant observational studies of grassy balds in the Coast Range. This study evaluates evidence for factors limiting woody encroachment into meadows in the Oregon Coast Range, including bottom‐up control by soil properties, plant–plant interactions and top‐down control by large herbivores. Location: Coast Range, western Oregon, United States of America. Methods: The chemical and physical properties of soils to a depth of 50 cm in meadow and forest measured, and the community, density and browse pressure for shrubs, conifers, and deciduous trees ≤2 m tall from meadow into forest were recorded. A total of 20 Pseudotsuga menziesii (Douglas‐fir) seedlings were experimentally planted in each of five meadows and neighbouring plant presence and herbivore access manipulated. Results: Meadow soils were lower in C and C:N, slightly lower in N and similar in plant‐available water and pH relative to forest soils. Shrubs were most dense but experienced the lowest browse pressure near the meadow edge, while trees were sparse and varied by site (although at one site, browse pressure was heavier in meadow than forest). Seedling survival and growth varied by site and herbivory‐reduced growth; total soil N best explained residual variation in seedling growth among sites. Conclusions: These findings indicate that ungulate herbivores exert top‐down control on woody encroachment into temperate montane meadows, perhaps in concert with local N‐limitation. [ABSTRACT FROM AUTHOR]

BACKGROUND: The green peach aphids, Myzus persicae, are a predominant pest in peach orchards as they can alter fruiting and shoot development for several years. This aphid developed resistance against pesticides. Among the alternative control strategies is the reduction of the trees' attractiveness to aphids. In order to identify the plant variables related to plant susceptibility, young peach trees were submitted to various supplies of water and nitrogen, and then artificially infested with aphids. Shoot development, plant water potential and aphid abundance were then monitored on a weekly basis. The apex concentrations in total N, amino acids, soluble sugars and polyphenols were determined at infestation start and infestation peak. RESULTS: Until infestation peak, the thermal time requests for aphid development were independent of infestation severity. The aphid populations then collapsed more rapidly on the low infested shoots than on the high infested ones. Aphid abundances appeared to be positively related to shoot development (leaf expansion and secondary ramification), to shoot growth (stem length and diameter) and to apex concentrations in amino acids and non‐structural carbohydrates (NSC). Polyphenols had the opposite effect. CONCLUSION: Peach susceptibility to aphids depends on shoot development and apex composition, and could be lowered by decreasing the water and nitrogen inputs. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Excessive nitrogen (N) loading poses a substantial risk to soil biodiversity and disrupts carbon (C) flows within the soil food web. Intercropping with legumes is often considered a sustainable way to maintain soil N availability and mitigate the associated detrimental effects. However, it remains unclear whether and how legume crops restore energetic attenuation caused by N loading within the soil food web. Here, we conducted a two-year field experiment using randomized block design in a subtropic Camellia oleifera plantation with high wet N deposition. We examined the effects of applying N fertilizers at normal or half levels (168 or 84 kg N ha−1yr−1) and intercropping legumes (Arachis hypogaea or Cassia tora) on the soil nematode food web. We observed that N fertilization suppressed the majority of nematode trophic groups, weakened the stability of food web structure, and diminished the C flows across the bacterial and fungal energy channels. Conversely, intercropping with legumes (particularly with C. tora) bolstered the densities of bacterivore and fungivore nematodes. This enhancement facilitated interactions within the soil micro-food web, and subsequently augmented the C flows within their respective channels. Model predictions suggested that the detrimental effects of N fertilizers on the nematode food web are primarily linked to decreased soil pH resulting from soil N accumulation. Notably, higher soil organic C was found to mitigate these effects. Furthermore, N-enriched legume substrates played a beneficial role in stimulating soil microbial activities and facilitating C flows through bottom-up control. Our findings emphasize the positive impacts of legume crops on mitigating soil biodiversity loss and restoring energetic attenuation within soil food web under N-saturated soil conditions. These findings provide valuable insights for agroforestry management practices aimed at sustaining soil health and ecosystem resilience. Schematic representation of the effects of N fertilizations and legume intercropping on the soil nematode food web. Notes: (+) positive and (−) negative effects. [Display omitted] • The N fertilizers had negative impacts on carbon flows within soil nematode food web, whereas legumes had positive effects. • The detrimental effects of N fertilizers are derived from the decreased soil pH caused by soil N accumulation. • The beneficial effects of legume crops are determined by the N-enriched substrates that exert a bottom-up control. [ABSTRACT FROM AUTHOR]

Microbial food webs (MFW) play an indispensable role in marine pelagic ecosystem, yet their composition and response to abiotic variables were poorly documented in the oligotrophic tropical Western Pacific. During winter of 2015, we conducted a survey to examine key components of MFW, including Synechococcus , Prochlorococcus , picoeukaryotes, heterotrophic prokaryotes (HP), heterotrophic/pigmented nanoflagellates and ciliates, across water column from surface to 2000 m. Each MFW component exhibited unique vertical distribution pattern, with abundance ratio varying over six and three orders of magnitude across Pico/Microplankton (1.6 ± 1.0 × 106) and Nano/Microplankton (3.2 ± 2.8 × 103), respectively. Furthermore, HP was main component for MFW in the bathypelagic (>1000 m) zone. Multivariate biota-environment analysis demonstrated that environmental variables, particularly temperature, significantly impacted MFW composition, suggesting that bottom-up control (resource availability) dominated the water column. Our study provides benchmark information for future environmental dynamics forcing on MFW in the oligotrophic tropical seas. [Display omitted] • Heterotrophic bacteria was dominate component in microbial food web especially at bathypelagic zone; • Ratio of plankton abundance varied over 6 and 3 orders of magnitude across Pico/Microplanktons and Nano/Microplanktons, respectively; • Bottom-up control of HNF (resource availability) played a key role throughout the water column; • Present study will help assess future changes in oligotrophic tropical seas under rapid global warming. [ABSTRACT FROM AUTHOR]

1. Nutrient resource availability and host-plant foliar pubescence both influence arthropod food webs, but multifactor studies are needed to understand their interdependence and relative importance. Arthropods were sampled by clipping foliage from Metrosideros polymorpha (Myrtaceae) trees of pubescent, glabrous, and intermediate leaf forms on fertilised and unfertilised plots. 2. Fertilisation decreased leaf mass per area (LMA) but did not change the relative mass of pubescence within leaf morphological classes. 3. Fertilisation increased densities of individuals in four taxonomic orders, densities of individuals and species of all trophic levels, and the biomass of Collembola and Homoptera. Herbivore relative diversity (Shannon H') also increased with fertilisation, but detritivore diversity declined due to increasing dominance of Salina celebensis (Schaeffer) (Collembola). 4. Detritivore density, driven again by S. celebensis, increased with decreasing leaf pubescence, but Heteroptera and Acari were most abundant on the intermediate pubescence class, and Psocoptera density and biomass increased with increasing pubescence. Trophic-level species density did not change with leaf morphological class, but relative diversity of all arthropods and of detritivores increased with increasing pubescence. 5. Both resource availability and leaf pubescence affected Metrosideros arthropod communities. However, the pervasive positive influence of fertilisation did not translate to compositional shifts, and there were no interactions with leaf morphological class. In contrast, the effects of leaf pubescence on arthropod density, biomass, and diversity were more restricted taxonomically, and non-parametric MANOVA and redundancy analyses demonstrated significant differentiation in community composition on the pubescent morphology.

Small pelagic fish are key components of marine ecosystems and fisheries worldwide. Despite the absence of recruitment failure and overfishing, pelagic fisheries have been in crisis for a decade in the Western Mediterranean Sea because of a marked decline in sardine size and condition. This situation most probably results from bottom-up control and changes in the plankton community toward smaller plankton. To understand such an unusual phenomenon, we developed an original and innovative experimental approach investigating the mechanisms induced by a reduction in the quantity and size of sardine prey. While experimentations offer the unique opportunity to integrate behavior and ecophysiology in understanding key demographic processes, they remain rarely used in fisheries science, even more so on small pelagics due to the notorious difficulty to handle them. The results revealed that food size (without any modification of its energy content) is as important as food quantity for body condition, growth and reserve lipids: sardines that fed on small particles had to consume twice as much as those feeding on large particles to achieve the same condition and growth. Such a strong impact of food size (based on 100 vs. 1200 μm pellets) was unexpected and may reflect a different energy cost or gain of two feeding behaviors, filter-feeding vs. particulate-feeding, which would have to be tested in further study. As increasing temperature favors planktonic chains of smaller size, climate change might actually accelerate and amplify such phenomenon and thus strongly affect fisheries.

Arthropods in the leaf litter layer of forest soils influence ecosystem processes such as decomposition. Climate‐change models predict both increases and decreases in average rainfall. Increased drought may have greater impacts on the litter arthropod community. In addition to affecting survival or behaviour of desiccation‐sensitive species, lower rainfall may indirectly lower abundances of consumers that graze drought‐stressed fungi, with repercussions for higher trophic levels.We tested the hypothesis that trophic structure will differ between the two rainfall scenarios. In particular, we hypothesized that densities of several broadly defined trophic groupings of arthropods would be lower under reduced rainfall.To test this hypothesis, we used sprinklers to impose two rainfall treatments during three growing seasons in roofed, fenced 14‐m2 plots and documented changes in abundance from initial, pre‐treatment densities of 39 arthropod taxa. Experimental plots were subjected to either LOW (fortnightly) or HIGH (weekly) average rainfall based upon climate models and the previous 100 years of regional weekly averages. Unroofed open plots, our reference treatment (REF), experienced higher than average rainfall during the experiment.The two rainfall extremes produced clear negative effects of lowered rainfall on major trophic groups. Broad categories of fungivores, detritivores and predators were more abundant in HIGH than LOW plots by the final year. Springtails (Collembola), which graze fungal hyphae, were 3× more abundant in the HIGH rainfall treatment. Taxa of larger‐bodied fungivores and detritivores, spiders (Araneae), and non‐spider predators were 2× more abundant under HIGH rainfall. Densities of mites (Acari), which include fungivores, detritivores and predators, were 1.5× greater in HIGH rainfall plots. Abundances and community structure of arthropods were similar in REF and experimental plots, showing that effects of rainfall uncovered in the experiment are applicable to nature.This pattern suggests that changes in rainfall will alter bottom‐up control processes in a critical detritus‐based food web of deciduous forests. Our results, in conjunction with other findings on the impact of desiccation on arthropods and fungal growth, suggest that drier conditions will depress densities of fungal consumers, causing declines in higher trophic levels, with possible impacts on soil processes and the larger forest food web. [ABSTRACT FROM AUTHOR]

Rainbow smelt (Osmerus mordax) is a key planktivore and prey fish in Lake Huron. Given the declining offshore productivity in the lake since the early 2000s, we described the energy content of rainbow smelt in 2017 across five different regions (North Channel, Georgian Bay, Saginaw Bay, northern main basin, southern main basin) where phytoplankton and zooplankton productivity likely varied. To increase contrast across the productivity gradient, rainbow smelt energy content was also estimated from western Lake Erie. Within the North Channel where large fish (≥90 mm, total length) were sampled most frequently, mean energy density (kJ/g wet weight) varied seasonally: 4.29 in April (month of spawning), 3.86 in June, 3.99 in July, and up to 4.35 in September. Energy density of rainbow smelt from higher productivity western Lake Erie was 37% (large fish ≥90 mm) to 60% higher (small fish <90 mm) than that of fish from Lake Huron. Within Lake Huron, energy density of rainbow smelt from North Channel was slightly higher than those from other regions; rainbow smelt from Georgian Bay generally had the lowest energy density. Across regions, including western Lake Erie, energy density increased with chlorophyll a concentration. Compared with Lake Huron studies prior to 2004, when oligotrophication had not yet accelerated, energy density of rainbow smelt in 2017 was up to 31% lower. The decline in rainbow smelt energy density is likely the result of declining primary and secondary pelagic production and increased resource limitation for planktivorous fish. [ABSTRACT FROM AUTHOR]

Abstract Chinese milk vetch (CMV) is widely used as a green manure due to its efficiency for nutrient preservation and soil fertility improvement, as well for providing more organic substances for soil organisms. Detritus micro-food web drives carbon and nutrient cycling and maintains ecosystem productivity. The effects of CMV amendment on detritus micro-food web were investigated in a six-year field experiment. Compared to the mineral fertilizers (NPK) alone, the fertilizers combined with CMV (NPK + CMV) increased soil organic carbon content, and thus enhanced the biomass of microorganisms, as well as protozoa abundance, while did not change micro-feeding nematode abundance (MN). This indicates a substrate-driven bottom-up effect. However, the green manure application increased omnivores-predators (OP) abundance and the OP/MN ratio, suggesting a top-down effect. Higher F/B ratio indicates a shift of the food web energy structure towards to fungi-dominated channel in the manured soil. Here, the green manure amendment should be encouraged to improve soil detritus micro-food web. Highlights • Green manure promoted micro-food web development by the bottom-up and top-down effects. • Green manure shifted micro-food web energy structure towards to fungi-dominated channel. [ABSTRACT FROM AUTHOR]

The changes to physical and chemical ecosystem characteristics as a response to pervasive and intensifying land use have the potential to alter the consumer–resource interactions and to rewire the flow of energy through entire food webs.We investigated these structural and functional properties of food webs in stream ecosystems distributed across woodland, agricultural and urban areas in the Zagreb region of Croatia. We compared resource availability and consumer diet composition using stable isotope mixing models and tested how the isotopic variance of basal resources, primary consumers, macroinvertebrate predators and other food web characteristics change with different land‐use types.Combination of increased loading and altered composition of nutrients, lower water discharge and higher light availability at urban sites likely promoted the contribution of aquatic macrophytes to diets of primary consumers. Macroinvertebrate predators shifted their diet, relying more on active filterers at urban sites relative to woodland and agricultural sites. Urban food webs also had lower trophic redundancy (i.e. fewer species at each trophic level) and a more homogenized energy flow from lower to higher trophic levels. There was no effect of land use on isotopic variation of basal resources, primary consumers or macroinvertebrate predators, but all these trophic groups at urban and agricultural sites were 15N‐enriched relative to their counterparts in woodland stream food webs.The physical and chemical ecosystem characteristics associated with intensive land use altered the resource availability, trophic redundancy and the flow of energy to other trophic levels, with potentially negative consequences for community dynamics and ecosystem functioning. These empirical findings indicate that reducing nutrient pollution, agricultural runoffs and maintaining riparian vegetation can mitigate the impacts of land use on structure and function of stream ecosystems. [ABSTRACT FROM AUTHOR]

Fishery ecosystems are complex and influenced by various drivers that operate and interact at different levels and over multiple scales. Here, we propose a holistic methodology to determine the key mechanisms of fisheries, trophodynamics, and environmental drivers of marine ecosystems, using a multilevel model fitted to data on global catch, effort, trophic level, primary production, and temperature for 130 ecosystems from 1950 to 2012. The model describes the spatial‐temporal dynamics of world fisheries very well with a pseudo R2 = 0.75 and estimates the effects of key drivers of fishery production. The results demonstrate the integrative operation of bottom‐up and top‐down regulated trophic interactions at the global level and great variations in their relative importance among different types of ecosystem. The estimation of key drivers' effects on marine ecosystems provides practical mechanisms for informed ecosystem‐based fisheries management to achieve the sustainable objectives that are consistent with the needs of specific fisheries. [ABSTRACT FROM AUTHOR]