Bottom-up Control Research Articles

Food web modeling indicates the potential impacts of increasing deforestation and fishing pressure in the Tapajós River, Brazilian Amazon

In the Tapajos River, Brazilian Amazon, fishing is an important activity, especially for low-income riverine populations. Unfortunately, the Tapajos River fish diversity and abundance are threatened by several anthropogenic drivers, including deforestation and overfishing. We modeled the lower Tapajos River's food web and simulated changes in biomass compartments as a response to increases in deforestation (loss of floodplain forest habitat) and on artisanal fishing pressure over 30 years. According to our simulations, the large-bodied species could be reduced drastically while small-bodied and fast-growing species could be favored by fishing effort increasing. The loss of floodplain forest is expected to cause a general decline (23%) of the total standing fish biomass. This reduction could reflect greater losses on species that are directly dependent on resources from the floodplain forests, such as fruits and seeds. These results indicated that the food web of the lower Tapajos River is structurally characterized by bottom-up control, through the use of basal resources, such as detritus (mostly from decomposing plants), fruits, seeds, terrestrial, and aquatic invertebrates. Furthermore, the simulations’ results highlight that the protection of the floodplain forest through the existing protected areas will be of essential importance in the future to maintain fish biomass, sustainable artisanal fishing, and improve the food security of Amazonian riverine inhabitants.

A Canonical Laminar Neocortical Circuit Whose Bottom-Up, Horizontal, and Top-Down Pathways Control Attention, Learning, and Prediction.

All perceptual and cognitive circuits in the human cerebral cortex are organized into layers. Specializations of a canonical laminar network of bottom-up, horizontal, and top-down pathways carry out multiple kinds of biological intelligence across different neocortical areas. This article describes what this canonical network is and notes that it can support processes as different as 3D vision and figure-ground perception; attentive category learning and decision-making; speech perception; and cognitive working memory (WM), planning, and prediction. These processes take place within and between multiple parallel cortical streams that obey computationally complementary laws. The interstream interactions that are needed to overcome these complementary deficiencies mix cell properties so thoroughly that some authors have noted the difficulty of determining what exactly constitutes a cortical stream and the differences between streams. The models summarized herein explain how these complementary properties arise, and how their interstream interactions overcome their computational deficiencies to support effective goal-oriented behaviors.

COCO-Search18 fixation dataset for predicting goal-directed attention control

Attention control is a basic behavioral process that has been studied for decades. The currently best models of attention control are deep networks trained on free-viewing behavior to predict bottom-up attention control – saliency. We introduce COCO-Search18, the first dataset of laboratory-quality goal-directed behavior large enough to train deep-network models. We collected eye-movement behavior from 10 people searching for each of 18 target-object categories in 6202 natural-scene images, yielding sim 300,000 search fixations. We thoroughly characterize COCO-Search18, and benchmark it using three machine-learning methods: a ResNet50 object detector, a ResNet50 trained on fixation-density maps, and an inverse-reinforcement-learning model trained on behavioral search scanpaths. Models were also trained/tested on images transformed to approximate a foveated retina, a fundamental biological constraint. These models, each having a different reliance on behavioral training, collectively comprise the new state-of-the-art in predicting goal-directed search fixations. Our expectation is that future work using COCO-Search18 will far surpass these initial efforts, finding applications in domains ranging from human-computer interactive systems that can anticipate a person’s intent and render assistance to the potentially early identification of attention-related clinical disorders (ADHD, PTSD, phobia) based on deviation from neurotypical fixation behavior.

Integrated computer-aided engineering and design for DNA assemblies.

Recently, DNA has been used to make nanodevices for a myriad of applications across fields including medicine, nanomanufacturing, synthetic biology, biosensing and biophysics. However, current DNA nanodevices rely primarily on geometric design, and it remains challenging to rationally design functional properties such as force-response or actuation behaviour. Here we report an iterative design pipeline for DNA assemblies that integrates computer-aided engineering based on coarse-grained molecular dynamics with a versatile computer-aided design approach that combines top-down automation with bottom-up control over geometry. This intuitive framework allows for rapid construction of large, multicomponent assemblies from three-dimensional models with finer control over the geometrical, mechanical and dynamical properties of the DNA structures in an automated manner. This approach expands the scope of structural complexity and enhances mechanical and dynamic design of DNA assemblies.

Effects of Climate Change in Marine Ecosystems Based on the Spatiotemporal Age Structure of Top Predators: A Case Study of Bigeye Tuna in the Pacific Ocean

How top predators behave and are distributed depend on the conditions in their marine ecosystem through bottom−up forcing; this is because where and when these predators can feed and spawn are limited and change often. This study investigated how the catch rates of immature and mature cohorts of bigeye tuna (BET) varied across space and time; this was achieved by analyzing data on the Taiwanese longline fishery in the western and central Pacific Ocean (WCPO). We also conducted a case study on the time series patterns of BET cohorts to explore the processes that underlie the bottom-up control of the pelagic ecosystem that are influenced by decadal climate events. Wavelet analysis results revealed crucial synchronous shifts in the connection between the pelagic ecosystems at low trophic levels in relation to the immature BET cohort. Many variables exhibited decreasing trends after 2004–2005, and we followed the Pacific Decadal Oscillation (PDO) as a bottom-up control regulator. The results indicated that low recruitment into the mature cohort occurs 3 years after a decrease in the immature cohort’s food stocks, as indicated by a 3-year lag in our results. This finding demonstrated that, by exploring the connection between low-trophic-level species and top predators at various life stages, we can better understand how climate change affects the distribution and abundance of predator fish.

Green more than brown food resources drive the effect of simulated climate change on Collembola: A soil transplantation experiment in Northeast China

Bottom-up or resource control is one of the most important aspects that determine the effects of climate change on soil fauna. It remains unclear whether the response of soil fauna to climate change is detritus-based or producer-based resource driven. Soil transplantation, from Heilongjiang to Jilin and Liaoning provinces, was used to simulate the effects of climate change on Collembola through different green or brown food resource treatments, which were represented by soybean cultivation (hereafter SC), land abandonment (LA), and vegetation removal (VR).The results showed that soil southwestward transplantation to warmer region, Jilin and Liaoning, significantly increased density and biomass of Collembola in plant growth but not withered period. Structural equation modeling and redundancy analysis showed increasing food resources, such as plant biomass, microbial biomass, and soil organic carbon, during the warm or higher food-quality treatments directly increase the density and biomass of Collembola. Soil southwestward transplantation to warmer region, Jilin and Liaoning, significantly increase the density of Collembola in SC and LA. VR buffered the effect of soil transplantation on Collembola. It was concluded that the effects of soil transplantation on Collembola mainly occurred through the green but not brown food resource pathways.

An experimental investigation of the acquisition of Nd by authigenic phases of marine sediments

The neodymium isotope composition (ɛNd) of authigenic phases in marine sediment is widely used to reconstruct the origin and mixing of water masses of overlying seawater through time. However, at some locations in the modern ocean, the ɛNd of authigenic phases in surface sediment is not consistent with that of local seawater, raising concerns about its current interpretation as a paleotracer of water masses. To further investigate this question, we conducted a laboratory-based incubation experiment with a Mn-oxide phase placed at the sediment–water interface of multicores to assess the extent to which the authigenic phase records seawater ɛNd.Multicores were collected from the Strait of Georgia (SoG), which is a relatively deep coastal waterway with high sedimentation rates, oxygenated surface sediments, and active macrofauna, separating the mainland coast of British Columbia and Vancouver Island. Manganese oxide-coated XAD resin beads were placed at the sediment surface and the cores were incubated for 6 months in a tank filled with SoG seawater spiked with 150Nd. While the ɛNd of the Mn-oxide coated resin (−4.0) was similar to that of SoG seawater used for the incubation (−3.7), the 150Nd/144Nd of the Mn-oxide phase measured after the incubation indicates that, under our experimental conditions, a minimum of 83% of the Nd associated with the Mn-oxide phase is not sourced from seawater, but from pore water. The 150Nd/144Nd ratio of the Mn-oxide resin is necessary to determine the predominant source of Nd to the resin because the ɛNd of SoG pore water (−3.9) is within analytical error of seawater (−3.7). Using field data and constraints from the Nd mass balance during the incubation, we conclude that the similarity of ɛNd in pore water and seawater in the SoG is fortuitous and not a result of a top-down or bottom-up control. Although the setting of our sediments is not directly comparable to open ocean locations, this study raises concerns about the use of ɛNd in paleocirculation studies, and points to the necessity of elucidating the factors controlling local lithogenic dissolution in pore waters as a prerequisite for the correct interpretation of ɛNd in the authigenic phases of marine sediments.

Predictors of Biofilm Biomass in Oligotrophic Headwater Streams

Biofilm forms the base of food webs as an autochthonous resource in nutrient-poor, heavily shaded headwater streams. However, we know little about the influence of bottom-up and top-down controls on the standing stock of biofilm biomass in headwater streams. We used spatially extensive stream surveys and pre-existing stream chemistry data to assess the influence of potential bottom-up and top-down controls of biofilm biomass in the oligotrophic headwater streams of the Hubbard Brook Experimental Forest (HBEF), NH. The potential bottom-up controls we considered were canopy cover and aspect (determinants of available radiation at the stream surface), available nutrients (e.g., nitrogen, phosphorus), physical habitat characteristics (e.g., stream width, substrate), and physicochemical properties of water (e.g., water conductivity, pH). The potential top-down controls we examined were benthic macroinvertebrate biomass and stream salamander occurrence. Salamanders may affect biofilm biomass indirectly by preying on benthic macroinvertebrate consumers. We used stepwise multiple linear regression to assess the relative importance of these variables in predicting biofilm biomass and found that biofilm increased with light availability (as indicated by canopy cover and aspect), nutrient availability, and lower acidity, suggesting that the autotrophic components of biofilm may be particularly important. Our top-down control indices were unrelated to biofilm biomass; however, more intensive studies on top-down controls are needed in these systems.

Understanding the factors controlling biofilm as an autochthonous resource in shaded oligotrophic neotropical streams

Light and nutrients are bottom-up factors in controlling biofilm in tropical shaded oligotrophic streams. Regardless of the predominant resource source (autochthonous or allochthonous), greater availability of light and nutrients favors the development and, later, grazing (top-down factor) of the biofilm, with reflections on the trophic structure of these ecosystems. The increase in primary productivity in lotic ecosystems may reflect the fractionation of dissolved inorganic carbon (DIC) by the algal cells contained in the biofilm. A global meta-analysis showed that an increase in primary productivity leads to enrichment of the carbon isotope ratios of biofilm. The objective of this study was to evaluate how top-down (grazing) and bottom-up (light and nutrient) factors act on the biofilm and whether algal biomass determines the isotopic fractionation of δ13C in headwaters of Central Brazil. The density of grazing macroinvertebrates was controlled with electric pulses. Electrified (excluding grazers) and non-electrified grids were implemented in open and shaded areas in each stream. The biofilm ash-free dry mass (AFDM) doubled in nutrient-enriched streams. The effect of grazing on the biomass of the biofilm was significant for the nutrient-enriched streams, with a 50% reduction in the AFDM. Additionally, shading influenced chlorophyll-a even in pristine streams, as the concentration increased approximately ten-fold under open canopy conditions. There was a significant negative relationship between chlorophyll-a concentrations and δ13C values. Our study provides evidence that biofilm biomass increases as a result of changes in bottom-up controls. Top-down control significantly reduced biofilm in the food web based on autochthonous organic matter.

A test of the provisioning hypothesis of recruitment control in Georges Bank haddock

The haddock (Melanogrammus aeglefinus) stock of the Georges Bank region of the US Northeast Continental Shelf displays a pattern of large, episodic recruitments. Among the hypothesized controlling mechanisms is the idea that recruitment events are related to provisioning of prespawning haddock by the fall bloom the year before. With the occurrence of a recent large recruitment event in 2013, it would be prudent to retest this hypothesis. Fall bloom magnitude was positively correlated (r = 0.645, p = 0.005) with haddock survivor ratio (recruits per spawning biomass), including data from the 2013 recruitment. This relationship identifies a pathway of bottom-up control of a resource species, thus focusing concern over recent changes in lower trophic-level productivity.

Teatime in Kruger: Tailoring the application of the Tea Bag Index approach to an African savanna

Attempts to obtain standardised decomposition data to determine potential drivers of carbon release have evolved from the use of cotton strips and standardised leaf litter mixtures to the most recent Tea Bag Index (TBI). The TBI is an internationally standardised method to collect comparable, globally distributed data on decomposition rate and litter stabilisation, using commercially available tea bags as standardised test kits. As this index was developed as a citizen science project in the northern hemisphere, we aimed to highlight the potential value – and pitfalls – of its application in a subtropical African savanna. We furthermore aimed to expand on existing protocol details and propose amendments to achieve an enhanced understanding of decomposition dynamics across temporal and spatial scales in African ecosystems. Proposed adaptations include extended incubation periods for long-term monitoring studies, the burial of more tea bags to account for potential losses, and the use of additional equipment to enhance effective sampling. These adaptations provide a system-specific protocol which can facilitate studies aimed to understand the interactions between top-down drivers (e.g. herbivory, fire, climate variability) and bottom-up controls (e.g. decomposition) in carbon flux dynamics of savanna ecosystems. Application of the proposed extended protocol in a semi-arid savanna provided results which reinforce the potential value of the TBI in an African context.
 Significance:
 
 The TBI is a relatively easy and cost-effective approach to gather globally distributed data on potential decomposition rate and inherent carbon flux, yet it was developed and primarily tested in boreal and temperate ecosystems.
 The use of more paired tea bag replicates and additional equipment is a viable means to mitigate tea bag losses to several savanna-based agents of disturbance, while enabling confident conclusions made from statistical results and improved estimates of the TBI. High recovery success across disturbance treatments and incubation periods suggest that the TBI can be applied successfully to spatial and temporal decomposition studies.

Are we on the cusp of a new paradigm for biology? The illogic of molecular developmental biology versus Janus-faced control of embryogenesis via differentiation waves

The logic of molecular developmental biology fails to explain embryogenesis. A new approach, Janus-faced control, involving both top-down control by differentiation waves and bottom-up control via the mechanical consequences of cell differentiations, may be needed. This obviates problems inherent in reductionism with an explicit, testable mechanism.

Persistent blooms of filamentous cyanobacteria in a cormorant-affected aquatic ecosystem: Ecological indicators and consequences

Globally, the establishment of protected reserves contributes positively to species protection but also presents a real threat of unexpected changes. A few reports showed that progressively increasing the number of roosting and breeding cormorants across Europe was associated with food-rich water bodies. Our studies concerned detailed and novel research on annual cyanobacterial growth against other ecological factors, that is, biotic (ciliates, rotifers, cladocerans, and copepods) and abiotic (temperature, nutrients) factors, in a lake where the piscivorous great cormorants evidently affects the water quality. Mass development of cyanobacteria lasted throughout the whole of the ice-free months (March–December). However, in the under-ice period they also formed a relatively high biomass, suggesting an annual persistence. The potentially toxic filamentous Pseudanabaena, Aphanizomenon, Planktothrix, and Limnothrix were constant dominants in the cyanobacteria-dominated phytoplankton almost year round. Water temperature played a major role in stimulating the growth of filamentous cyanobacteria. However, nitrogen, phosphorus, and even some zooplankters were significantly related to cyanobacteria. A very low trophic efficiency suggested a reduced energy flow at a lower food-web level starting from dominant cyanobacteria. Our results also suggest that numerous breeding colonies of great cormorant contributed to bottom-up (nutrients) and top-down (predation on fish) controls and consequently to the formation of a site-specific refuge for filamentous cyanobacteria. This affects the functioning of the water ecosystem by disturbing the energy flow in the classical food webs, which is important in water management and warming-induced global problems with cyanobacterial dominance and water quality.

Response of bats and nocturnal insects to urban green areas in Europe

Animal biodiversity in cities is generally expected to be uniformly reduced, but recent studies show that this is modulated by the composition and configuration of Urban Green Areas (UGAs). UGAs represent a heterogeneous network of vegetated spaces in urban settings that have repeatedly shown to support a significant part of native diurnal animal biodiversity. However, nocturnal taxa have so far been understudied, constraining our understanding of the role of UGAs on maintaining ecological connectivity and enhancing overall biodiversity. We present a well-replicated multi-city study on the factors driving bat and nocturnal insect biodiversity in three European cities. To achieve this, we sampled bats with ultrasound recorders and flying insects with light traps during the summer of 2018. Results showed a greater abundance and diversity of bats and nocturnal insects in the city of Zurich, followed by Antwerp and Paris. We identified artificial lighting in the UGA to lower bat diversity by probably filtering out light-sensitive species. We also found a negative correlation between both bat activity and diversity and insect abundance, suggesting a top-down control. An in-depth analysis of the Zurich data revealed divergent responses of the nocturnal fauna to landscape variables, while pointing out a bottom-up control of insect diversity on bats. Thus, to effectively preserve biodiversity in urban environments, UGAs management decisions should take into account the combined ecological needs of bats and nocturnal insects and consider the specific spatial topology of UGAs in each city.

Warming-driven shifts in ecological control of fish communities in a large northern Chinese lake over 66 years

Warming, land-use change, and habitat loss are three major threats to aquatic biodiversity worldwide under the influences of anthropogenic disturbances. Positive feedback between warming and bottom-up regulation may cause irreversible ecological regime shifts. Threshold dynamics of interspecific interactions have been rarely studied in freshwater fish communities using threshold community models. Here we use 66 years (1950–2015) of data to link four ecological regime shifts of 9-species fish communities to climatic and land use changes in Lake Hulun, the largest freshwater lake of Northern China. Overfishing caused the collapse of piscivorous fish populations and an ecological regime shift of Lake Hulun in the late 1950s. The first recorded algal bloom of Lake Hulun took place in 1986, with accelerated warming and rapid increases in livestock grazing. The dominance of planktivorous minnow populations reduced fish biodiversity in a nonlinear, threshold manner when annual mean ambient temperature was >0.12 °C. Multivariate environmental vector regression demonstrated that warming, eutrophication, and water-storage reduction (i.e., habitat loss) were related to three ecological regime shifts of Lake Hulun from 1960 to 2015. Multivariate autoregressive models (MAR) did not detect predation by piscivorous fish in Lake Hulun after 1960. Threshold MAR models indicated that dominant minnow populations and other prey fish populations switched from top-down to bottom-up control during the 1980s. Sustained positive feedback between warming, the dominance of planktivorous fish populations, and bottom-up regulation caused predator-prey role reversal, and probably resulted in three regime shifts of Lake Hulun over 56 years. This study provides a comprehensive analysis of ecological regime shifts in Hulun Lake fish communities, and has potential implications for fish species living in similar environments that are subject to global warming, land-use changes, and overfishing.

Impulsivity as Early Emerging Vulnerability Factor-Prediction of ADHD by a Preschool Neuropsychological Measure.

Impulsivity, comprising deviations of brain-based bottom-up and top-down control processes, has been regarded as a crucial, early emerging marker of a developmental pathway to attention-deficit/hyperactivity (ADHD) and externalizing disorders. In two independent studies (a cross-sectional study and a longitudinal study), we analyzed the concurrent and predictive validity of a task-based neuropsychological impulsivity measure for preschool children. The sample of Study 1 comprised 102 3–5-year-old children (46% boys). In Study 2, 138 children (59% boys) with elevated ADHD symptoms were recruited and assessed at the ages of 4–5 and 8 years. In both studies, preschool impulsivity was measured by a summary score of neuropsychological tasks on approach motivation and hot inhibitory control. For Study 1, the impulsivity measure was significantly associated with symptoms of ADHD and oppositional defiant disorder (ODD) (χ2(1) = 9.8, p = 0.002; χ2(1) = 8.1, p = 0.004). In Study 2, the impulsivity measure predicted the 8-year-olds’ ADHD diagnoses over and above concurrent ADHD symptoms (χ2(1) = 10.0, p = 0.002, OR = 5.0, 95% CI: 1.8–14.0). The impulsivity measure showed good concurrent and predictive validity. The measure can be useful for the early identification of children at risk for developing ADHD and externalizing disorders.

Effects of <i>Carassius auratus</i> on water turbidity, nutrient levels and plankton biomass in shallow lakes: A mesocosm experiment

鲫（Carassius auratus）是我国各类淡水水体的优势鱼类之一.作为底栖杂食性鱼类，一方面，鲫可以通过排泄和扰动沉积物影响湖泊营养和光照水平，通过上行效应促进浮游植物生长；另一方面，鲫也可以捕食浮游动物，通过下行控制影响藻类生长以及营养盐循环.对于浅水湖泊，两种途径对于生态系统影响的相对重要性仍有待研究.本研究设计了一个两因素户外中宇宙实验，通过在沉积物表面添加隔网的方式，比较两种情况下（能、否接触沉积物），鲫对水体浊度、营养盐和浮游生物生物量的影响.实验在16个大型钢化玻璃桶（400 L）中进行，持续36 d（2019年8月6日-9月11日）.研究结果表明：1）在能接触沉积物的条件下，鲫显著促进了沉积物再悬浮，表现为水体的总悬浮物（TSS）和无机悬浮物（ISS）浓度大幅升高；水体的光衰减系数（K_d）增加，总氮（TN）和总磷（TP）浓度明显升高；2）在不能接触沉积物的条件下，鲫对水体悬浮物（TSS和ISS）浓度和K_d的影响不明显，但是显著降低了水体TN和TP浓度；3）在两种情况下，鲫对浮游植物叶绿素a浓度以及浮游动物生物量的影响均不显著.本研究表明鲫只有在能够接触沉积物的条件下，才会显著提高水体浊度和营养水平.因此，在缺乏沉水植被的浅水湖泊中，鲫扰动沉积物产生的上行效应可能是其对生态系统产生负面影响的主要途径.;In China, crucian carp (Carassius auratus) are dominant fish species in various freshwater ecosystems. As an Omni-benthivorous fish, on one hand, crucian carp may affect water nutrient and turbidity levels via sediment disturbance and thereby enhance phytoplankton growth, a bottom-up route. On the other hand, crucian carp may also affect algal growth and nutrient cycling via predation on zooplankton and thereby reducing zooplankton grazing on phytoplankton, a top-down process. For shallow lakes, the relative importance of both mechanisms remains to need to be elucidated. Here, we designed an outdoor mesocosm experiment to compare the effects of crucian carp on water turbidity, nutrient and phytoplankton growth between mesocosms with (via adding a sieve above the sediments) and without sediment disturbance. The experiment was conducted using 16 armoured glass tanks (400 L) and lasted for 36 days (from August 6 to September 11 in 2019). The results showed that:1) in mesocosms with sediment disturbance (without sieve), crucian carp caused severe sediment resuspension, reflected by the large increases of total suspended solids (TSS) and inorganic suspended solids (ISS). Correspondingly, light attenuation efficient (K_d), total nitrogen (TN) and total phosphorus (TP) concentrations were significantly higher in mesocosms with crucian carp than ones without fish. 2) In mesocosms without sediment disturbance (sieve present), the effects of crucian carp on suspended solids (TSS, ISS) and K_d were both insignificant. However, TN and TP concentrations were significantly reduced by crucian carp. 3) no significant effects of crucian carp on chlorophyll-a concentration and zooplankton biomass were observed. Our study suggested that crucian carp promote water turbidity and nutrient levels only when they could access the sediments. Thus, in shallow lakes without submerged macrophytes, bottom-up control may be the main mechanism of crucian carp affecting water quality adversely.

Functional Ecology of Two Contrasting Freshwater Ciliated Protists in Relation to Temperature.

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.

Weak Predation Strength Promotes Stable Coexistence of Predators and Prey in the Same Chain and Across Chains

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.

Nearshore ecosystems on seabird islands are potentially influenced by invasive predator eradications and environmental conditions: a case study at the Mercury Islands, New Zealand

Seabirds maintain island ecosystem function by providing rich marine-derived nutrients to the islands where they nest. These nutrients are returned to the sea through runoff, fertilizing the nearshore environment. Invasive predators disrupt this bottom-up control by decimating seabird populations. While invasive predator eradications lead to terrestrial recovery on seabird islands, there is little information on the nearshore impact. We determined how nearshore macroalgae communities and seabird-derived nitrogen concentrations are influenced by predator eradications and environmental parameters (sampling depth, season, wave exposure, and runoff). This case study examined 4 islands in the Mercury Islands archipelago, representing 3 eradication histories: never invaded by mammalian predators, eradicated over 30 yr ago, and eradicated 2 yr ago. Macroalgal diversity was highest at never-invaded islands, followed by islands in order of eradication year (eradicated 30 and 2 yr ago). The amount of seabird-derived nitrogen (δ15N) in algae was higher during the rainy season and decreased with sampling depth and wave exposure. Sampling near high runoff points resulted in increased δ15N in red algae alone. Never-invaded islands had the highest δ15N in most species. With species found at both eradicated islands, the recently eradicated island had unexpectedly higher δ15N than the island eradicated over 30 yr ago. This discrepancy may be a result of the recently eradicated island’s large size and presence of streams, estuaries, and sheltered bays. Studying nearshore habitats is crucial in understanding the extent to which seabirds act as a conduit of the land-sea interface and the marine impacts of island management.