Role In Food Web Dynamics Research Articles

Changes in limpet diet according to habitat type

Limpets are a key taxon regulating the benthic community structure and serving as prey for various predators in rocky shores, however, their role in food web dynamics is still unclear. To determine environmental factors influencing the limpet diet, carbon and nitrogen stable isotopes in limpets and food sources were analyzed on three different coastal habitats. Sediment organic matter contributed the most (86 %) to the limpet diet in bedrocks around tidal flats with abundant sediment supply from the terrestrial matter inflow and the sediment resuspension. Microphytobenthos and macroalgae were the main food sources (57 % and 20 %, respectively) for the limpets around beaches, where benthic flora was abundant. Limpets in bedrocks, erosional habitat, primarily consumed relatively abundant phytoplankton (33 %) and microphytobenthos (28 %). Contrary to previous studies, habitat type, rather than latitude or seawater characteristics, was the most important factor determining the limpet diet. This result also suggests that limpets are non-selective scraper that consume abundant food sources.

An experimental framework for quantifying the degree of intraguild predation in omnivorous food webs in the field

AbstractIntraguild predation (IGP) is common in natural and human‐managed systems and plays a critical role in food web dynamics. Although studies have documented the occurrence of IGP across a wide range of predator taxa, quantitative understanding regarding the degree/intensity of IGP remains lacking. I propose an experimental framework combining controlled feeding trials and stable isotope analysis to quantify the degree of IGP in an omnivorous food web in the field consisting of a top predator, a mesopredator, and a shared prey. The degree of IGP is defined as the proportion (in number) of mesopredators consumed in the total diet (shared prey + mesopredator) of top predators. Feeding trials along with stable isotope analysis are used to construct a standard curve of the relationship between the diet composition of top predator and its nitrogen isotope signatures. The nitrogen isotope signatures of field‐collected top predator individuals are then analyzed and interpolated to the standard curve to estimate the degree of IGP in the field. The proposed framework leverages the strengths of different experimental approaches to study trophic interactions, providing a practical tool for quantifying IGP in a more accurate (controlled feeding trials and standard IGP curve) and realistic (stable isotope analysis of field samples) fashion. The current framework can be further extended to food webs involving more complex interactions (e.g., multiple shared prey) and complemented with other approaches (e.g., molecular gut content analysis) to capture a more complete picture of IGP dynamics in the field.

Assessing the distribution and variation characteristics of marine primary productivity in the coastal marine area of Vietnam South Centre

Primary production (PP) of phytoplankton plays an essential role in food web dynamics, biogeochemical cycles and marine fisheries. It is used as one of the basic information for evaluating marine ecosystems. In this paper, monthly composite PP data on a 4 km x 4 km grid for the period 2003-2020 was used to evaluate the distributional characteristics of PP in the coastal marine area of Vietnam South Centre. The statistical results show that the climatological average of PP in 18 years reached 449.2 mgC/m2/day, ranged from 272.1 to 14,205.4 mgC/m2/day. The PP has seasonal and spatial variations. In time, the lowest value of PP was in spring, and the highest was in winter; in space, PP tended to decrease from shore to offshore, PP was higher in coastal areas than in the open sea areas. During the northeast monsoon season, PP increased by more than 1000 mgC/m2/day in the coastal area. Meanwhile, in the southwest monsoon season, due to the ecological influence of the upwelling phenomenon, PP increased with a value greater than 1500 mgC/m2/day, distributed along the coastline of Ninh Thuan - Binh Thuan. Primary productivity positively correlated with chlorophyll content but negatively correlated with sea surface temperature with correlation coefficients of 0.9 and -0.6, respectively. There was a weak correlation between PP and ONI with correlation coefficients of -0.23. The temporal-spatial variation of PP was affected by the ENSO (El Niño-Southern Oscillation) phenomenon, the positive phase of ENSO (El Niño conditions) corresponded to lower PP, and the negative phase of ENSO (La Niña conditions) corresponded to higher PP. The research results from this paper can be used as a reference in marine ecosystem management.

On the Role of Biogeochemical Coupling Between Sympagic and Pelagic Ecosystem Compartments for Primary and Secondary Production in the Barents Sea

Primary production in the Arctic marine system is principally due to pelagic phytoplankton. In addition, sea-ice algae also make a contribution and play an important role in food web dynamics. A proper representation of sea-ice algae phenology and the linkage with the pelagic and benthic systems is needed, so as to better understand the ecosystem response to warming and shrinking ice cover. Here we describe the extension of the biogeochemical model ECOSMO II to include a sympagic system in the model formulation, illustrated by implementation in the Barents Sea. The new sympagic system formulation includes four nutrients (NO3, NH4, PO4, and SiO2), one functional group for sea-ice algae and one detritus pool, and exchanges with the surface ocean layer. We investigated the effects of linkage between the three systems (sympagic, pelagic and benthic) on the ecosystem dynamic; the contribution of the ice algae to total primary production; and how the changes in ice coverage will affect the lower trophic level Arctic food-web dynamics. To solve the scientific and technical challenges related to the coupling, the model was implemented in a 1-D application of the General Ocean Turbulence Model (GOTM). Results showed that the model simulated the seasonal pattern of the sympagic components realistically when compared to the current knowledge of the Barents Sea. Our results show that the sympagic system influences the timing and the amplitude of the pelagic primary and secondary production in the water column. We also demonstrated that sea-ice algae production leads to seeding of pelagic diatoms and an enhancement of the zooplankton production. Finally, we used the model to explain how the interaction between zooplankton and ice algae can control the pelagic primary production in the Barents Sea.

Quantitative food web modeling unravels the importance of the microphytobenthos-meiofauna pathway for a high trophic transfer by meiofauna in soft-bottom intertidal food webs.

Meiofauna are known to have an important role on many ecological processes, although, their role in food web dynamics is often poorly understood, partially as they have been an overlooked and under sampled organism group. Here, we used quantitative food web modeling to evaluate the trophic relationship between meiofauna and their food sources and how meiofauna can mediate the carbon flow to higher trophic levels in five contrasting soft-bottom intertidal habitats (including seagrass beds, mudflats and sandflats). Carbon flow networks were constructed using the linear inverse model-Markov chain Monte Carlo technique, with increased resolution of the meiofauna compartments (i.e. biomass and feeding ecology of the different trophic groups of meiofauna) compared to most previous modeling studies. These models highlighted that the flows between the highly productive microphytobenthos and the meiofauna compartments play an important role in transferring carbon to the higher trophic levels, typically more efficiently so than macrofauna. The pathway from microphytobenthos to meiofauna represented the largest flow in all habitats and resulted in high production of meiofauna independent of habitat. All trophic groups of meiofauna, except for selective deposit feeders, had a very high dependency on microphytobenthos. Selective deposit feeders relied instead on a wider range of food sources, with varying contributions of bacteria, microphytobenthos and sediment organic matter. Ecological network analyses (e.g. cycling, throughput and ascendency) of the modeled systems highlighted the close positive relationship between the food web efficiency and the assimilation of high-quality food sources by primary consumers, e.g. meiofauna and macrofauna. Large proportions of these flows can be attributed to trophic groups of meiofauna. The sensitivity of the network properties to the representation of meiofauna in the models leads to recommending a greater attention in ecological data monitoring and integrating meiofauna into food web models.

Interannual changes in zooplankton echo subtropical and high latitude climate effects in the southern East China Sea.

Climate variability plays a central role in the dynamics of marine pelagic ecosystems shaping the structure and abundance changes of plankton communities, thereby affecting energy pathways and biogeochemical fluxes in the ocean. Here we have investigated complex interactions driven a climate-hydrology-plankton system in the southern East China Sea over the period 2000 to 2012. In particular, we aimed at quantifying the influence of climate phenomena playing out in tropical (El Nino 3.4) and middle-high latitudes (East Asia Winter Monsoon, EAWM, and Pacific Decadal Oscillation, PDO) on pelagic copepods. We found that the EAWM and El Nino 3.4 showed a non-stationary and non-linear relationship with local temperature variability. In the two cases, the strength of the relationship, as indexed by the wavelet coherence analysis, decreased along with the positive phase of the PDO. Likewise, the influence of EAWM and El Nino3.4 on copepods exhibited a non-stationary link that changed along with the PDO state. Indeed, copepods and EAWM were closely related during the positive phase, while the link copepods–El Nino 3.4 was stronger during the negative phase. Our results pointed out cascading effects from climate to plankton driven by the positive phase of the PDO through its effect on temperature conditions, and likely through a larger southward transport of nutrient-rich water masses to northern Taiwan and the Taiwan Strait. We suggest a chain of mechanisms whereby the PDO shapes interannual dynamics of pelagic copepods and highlight that these results have implications for integrative management measures, as pelagic copepods plays a prominent role in food web dynamics and for harvested fish in the East China Sea.

Changes in food web dynamics of low Arctic ponds with varying content of dissolved organic carbon

ABSTRACT An influx of terrestrial dissolved organic carbon (DOC) into freshwater habitats can regulate a range of ecosystem characteristics, from water clarity to productivity. To understand the extent to which DOC can regulate ecosystem functioning, we conducted a survey to determine the source of DOC in low Arctic ponds close to the Arctic Circle (Kangerlussuaq, Greenland), including its role in food web dynamics. We used a multiple element (carbon, nitrogen, and hydrogen) stable isotope approach to examine the proportional contribution of different sources to aquatic consumers in nine arctic ponds that spanned a broad gradient of DOC (6.6–60.1 mgL-1). Our results show that benthic and pelagic primary production decreased along a gradient of increasing DOC content. Additionally, the changes in the organic matter pool with increasing DOC translated into changes in consumer resource use. We found significant differences in resource use between species. All consumers relied on benthic autotrophic material when DOC was low; but when DOC was high some consumers changed their diet. Collectively, our findings demonstrate how the concentration of DOC influences aquatic production and our study can be used as a baseline to predict how the aquatic food web may respond to regionally changing DOC concentrations.

Resource tracking in marine parasites: going with the flow?

Understanding how diversity interacts with energy supply is of broad ecological interest. Most studies to date have investigated patterns within trophic levels, reflecting a lack of food webs which include information on energy flow. We added parasites to a published marine energy‐flow food web, to explore whether parasite diversity is correlated with energy flow to host taxa. Parasite diversity was high with 36 parasite taxa affecting 40 of the 51 animal taxa. Adding parasites increased the number of trophic links per species, trophic link strength, connectance, and food chain lengths. There was evidence of an asymptotic relationship between energy flowing through a food chain and parasite diversity, although there were clear outliers. High parasite diversity was associated with host taxa which were highly connected within the food web. This suggests that energy flow through a taxon may favour parasite diversity, up to a maximal value. The evolutionary and energetic basis for that limitation is of key interest in understanding the basis for parasite diversity in natural food webs and thus their role in food web dynamics.

Biomarker assessment of spatial and temporal changes in the composition of flocculent material (floc) in the subtropical wetland of the Florida Coastal Everglades

Environmental context Flocculent material (floc) in freshwater and coastal areas of the Florida Everglades plays an important role in food web dynamics and nutrient cycling. Using biomarkers and pigment chemotaxonomy, we determined the organic matter composition of floc from different environments in the Everglades, and found that it is dominated by local biomass inputs and influenced by hydrological regimes. With the on-going restoration of the Florida Everglades, it is important to gain a better understanding of the biogeochemical dynamics of floc, including its sources, transformations and reactivity. Abstract Flocculent material (floc) is an important energy source in wetlands. In the Florida Everglades, floc is present in both freshwater marshes and coastal environments and plays a key role in food webs and nutrient cycling. However, not much is known about its environmental dynamics, in particular its biological sources and bio-reactivity. We analysed floc samples collected from different environments in the Florida Everglades and applied biomarkers and pigment chemotaxonomy to identify spatial and seasonal differences in organic matter sources. An attempt was made to link floc composition with algal and plant productivity. Spatial differences were observed between freshwater marsh and estuarine floc. Freshwater floc receives organic matter inputs from local periphyton mats, as indicated by microbial biomarkers and chlorophyll-a estimates. At the estuarine sites, the floc is dominated by mangrove as well as diatom inputs from the marine end-member. The hydroperiod (duration and depth of inundation) at the freshwater sites influences floc organic matter preservation, where the floc at the short-hydroperiod site is more oxidised likely due to periodic dry-down conditions. Seasonal differences in floc composition were not consistent and the few that were observed are likely linked to the primary productivity of the dominant biomass (periphyton in the freshwater marshes and mangroves in the estuarine zone). Molecular evidence for hydrological transport of floc material from the freshwater marshes to the coastal fringe was also observed. With the on-going restoration of the Florida Everglades, it is important to gain a better understanding of the biogeochemical dynamics of floc, including its sources, transformations and reactivity.

CAN WE IMPROVE MANAGEMENT PRACTICE OF FLOODPLAIN LAKES USING CLADOCERAN ZOOPLANKTON?

ABSTRACTNatural resource managers across Australia intend to promote healthy floodplain lake ecosystems with rich diversity and composition of biota because such ecosystems provide economically valuable services to society. However, management practice of these floodplain lake ecosystems is impeded by confounding effects of anthropogenic impacts and natural climate variability in recent decades. Yet, there are a few potential biological markers available that profoundly respond to ecological effects of climate change and human disturbances. Cladoceran zooplankton plays an intermediary role in food web dynamics. They show distinct responses to changes in temperature and environmental perturbations, such as acidification, nutrient loading and salinization. The effects of temperature and land‐use changes on food web dynamics and water quality, in particular, are major concerns for shallow lowland large river floodplain lakes management in Australia. Information on zooplankton assemblages and diversity can help increase our understanding of ecological processes in a wide range of environmental exposures. The study of cladoceran fossils and their ephippia preserved in floodplain lake sediment has substantially furthered our understanding of species–environment relationships at different temporal and spatial scales and allowed us to develop powerful inference models for degraded floodplain lake ecosystems. This consequently defines a benchmark of a shift from a naturally intact ecosystem to an ecologically poor regime. In this paper, I have made an attempt to persuade wetland managers through application of contemporary and palaeocladoceran communities to improve management practice of floodplain lake ecosystems in Australia by providing a range of examples. Copyright © 2011 John Wiley & Sons, Ltd.

Parasite-mediated allochthonous input: Do hairworms enhance subsidized predation of stream salmonids on crickets?

Energy and nutrients flow in diverse pathways across heterogeneous landscapes and tightly link the discrete food webs in local habitats. However, parasitism that enhances allochthonous resource input has not been previously documented. In a well-known example of parasite manipulation of host behaviour, crickets infected by mature hairworms (Nematomorpha) seek and jump into water when the worms reach the free-living stage. We found that a large number of trout (22%–61%), an aquatic predator, preyed on camel crickets (genera Diestrammena Brunner von Wattenwyl, 1888 and Tachycines Adelung, 1902) in September in five Japanese mountain streams where this host–parasite system exists. Trout (Kirikuchi charr, Salvelinus leucomaenis japonicus (Oshima, 1961); red-spotted masu salmon, Oncorhynchus masou ishikawae Jordan and McGregor, 1925) that preyed on crickets frequently ingested hairworms, whereas trout that did not prey on crickets did not ingest hairworms. Our results strongly suggest that hairworms enhance stream salmonid predation on camel crickets. This is the first documentation of parasitism enhancing allochthonous resource input in nature. Trout ingested a greater mass of crickets than other prey species in September, and this energy influx may play an important role in food-web dynamics in headwater streams.

Effects of dissolved organic matter and ultraviolet radiation on the accrual, stoichiometry and algal taxonomy of stream periphyton

Summary1. We investigated the effects of dissolved organic matter (DOM) and ultraviolet‐B (UVB) radiation on periphyton during a 30‐day experiment in grazer‐free, outdoor artificial streams. We established high [10–12 mg carbon (C) L−1] and low (3–5 mg C L−1) concentrations of DOM in artificial streams exposed to or shielded from ambient UVB radiation. Periphyton was sampled weekly for ash‐free dry mass (AFDM), chlorophyll (chl) a , algal biovolume, elemental composition [C, nitrogen (N) and phosphorus (P)], and algal taxonomic composition.2. Regardless of the UVB environment, increased DOM concentration caused greater periphyton AFDM, chl a and total C content during the experiment. Increased DOM also significantly increased periphyton C : P and N : P (but not C : N) ratios throughout the experiment. Algal taxonomic composition was strongly affected by elevated stream DOM concentrations; some algal taxa increased and some decreased in biomass and prevalence in artificial streams receiving DOM additions. UVB removal, on the other hand, did not strongly affect periphyton biomass, elemental composition or algal taxonomic composition for most of the experiment.3. Our results show strong effects of DOM concentration but few, if any, effects of UVB radiation on periphyton biomass, elemental composition and algal taxonomic composition. The effects of DOM may have resulted from its absorption of UVA radiation, or more likely, its provision of organic C and nutrients to microbial communities. The strong effects of DOM on periphyton biomass and elemental composition indicate that they potentially play a key role in food web dynamics and ecosystem processes in forested streams.

Fish Predation and Benthic Community Structure: The Role of Omnivory and Habitat Complexity

In population models, omnivorous predation (i.e., predation on >1 trophic level) generally has a destabilizing influence, whereas habitat heterogeneity tends to stabilize both predatory and competitive interactions. I experimentally evaluated the impact of a native omnivorous predator and of habitat structural complexity on the staegeri of a freshwater littoral macroinvertebrate community. Perch (Perca fluviatilis) were stocked at three densities (no fish, and low and high natural densities) into pond enclosures with dense submerged vegetation present or absent. Macroinvertebrate abundance, biomass, size structure, and diversity as well as gut contents of perch were monitored over a 2—mo summer period. Perch consumed both predatory and nonpredatory invertebrates except molluscs. In vegetation, perch consumed macroinvertebrates almost exclusively during the whole experiment, whereas in the absence of vegetation, perch successively increased their consumption of microcrustaceans. The biomass of predatory invertebrates and the abundance of the dominant predatory invertebrate Sialis lutaria (Insecta: Megaloptera) decreased with increasing perch density in both vegetation treatments. In contrasts, perch density had no effect on the biomass of nonmolluscan herbivores and detritivores. Vegetation increased the biomass of all macroinvertebrates and tended to delay the negative effect of perch on predatory invertebrates. Perch density had a negative effect on the mean size of total nonmolluscan macroinvertebrates, but not of predatory invertebrates and nonmolluscan herbivores/detritivores considered separately. While perch density had an effect on the diversity (Shannon evenness and Shannon diversity) of only nonmolluscan macroinvertebrates (i.e., potential prey), vegetation had a positive effect on species richness (but not on evenness) of all macroinvertebrates. The results suggest that perch disproportionally preyed on predatory invertebrates, but that characteristics other than size per se were responsible for their higher vulnerability to perch. Perch may have affected nonmolluscan herbivores/detritivores simultaneously through direct consumption and through indirect release from invertebrate predation, which could explain the lack of a perch effect on nonmolluscan herbivores/detritivores. Complex interactions between the omnivorous predator, intermediate consumers, and resource species (macroinvertebrate herbivores and detritivores) may explain the relationship between perch density and macroinvertebrate diversity. The reduction in foraging efficiency of perch in submerged vegetation, and the observed diet shift of perch towards microcrustaceans when predatory invertebrates were still fairly abundant, suggest that relatively large predatory invertebrates were still fairly abundant, suggest that relatively large predatory invertebrates can coexist with fish in the littoral of lakes to a higher extent than in the pelagic zone. Predatory invertebrates may thus play a more important role in food web dynamics of littoral than of pelagic communities.