Food web structure of a subtropical headwater stream
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The food web structure of a headwater stream (Hapen Creek) in subtropical northern Taiwan, which is subject to regular typhoon disturbances, was characterised using stable isotope techniques. δ13C and δ15N signatures were used to examine (i) the relative contributions of allochthonous versus. autochthonous sources to the web, and (ii) the trophic organisation of the community including the predominant feeding guilds and the most prevalent feeding mode. This study presents food web attributes for one of the very few food webs studied to date in a subtropical region. Consumers utilised allochthonous and autochthonous carbon sources differently depending on their trophic positions. The majority of consumers exploited more autochthonous carbon sources. Consumers at higher trophic positions in the food web had more direct and greater association with benthic algae. Higher-order consumers also consumed allochthonous carbon in an indirect manner by assimilating lower-order insects. The results reveal the importance of invertebrate consumer snails and aquatic insects in the transfer of organic matter. Omnivores predominated in the food web; this may reflect an opportunistic foraging strategy that enables them to adapt to hydrological disturbances and a fluctuating food supply.Keywords:
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Abstract In the field of ecology, habitat loss and fragmentation are the two main characteristic forms of habitat destruction and the main drivers of species extinction, resulting in the gradual loss of biodiversity. So far, many scholars have made some progress in the theoretical research of the spatial food web, but research on the effect of introducing an invasive species in an omnivorous food web is very rare. In order to explore the impact of invader on the persistence of species in omnivorous food webs, we constructed a model framework to describe the patch occupation of each species in omnivorous systems. Our model results show that invasive species is a prey of species in omnivorous food webs is easier to invade than invasive species is a predator of species in original omnivorous food webs on habitat loss and fragmentation. One conclusion also can be drawn is that when an invasive species is a prey of species in omnivorous food webs, no matter what trophic level the invasive species is invade, it is more successful. But when invasive species is a predator of species in different trophic levels on omnivorous food webs, they show different coexistence patterns. The invasion of a species has little effect upon the stability of original omnivorous food web for habitat loss and fragmentation, and will only make the original omnivorous food web more stable and more complicated. Therefore, we have proved that the omnivorous food web is stable and is not easy to destroy this ecological fact . Some examples to illustrate the reliability of our model results are discussed.
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Microbial loop
Microbial food web
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Abstract Pelagic copepods often couple the classical and microbial food webs by feeding on microzooplankton (e.g. ciliates) in oligotrophic aquatic systems, and this consumption can trigger trophic cascades within the microbial food web. Consumption of mixotrophic microzooplankton, which are both autotrophic and heterotrophic within the same individual, is of particular interest because of its influence on carbon transfer efficiency within aquatic food webs. In Lake Baikal, Siberia, it is unknown how carbon from a well‐developed microbial food web present during summer stratification moves into higher trophic levels within the classical food web. We conducted in situ experiments in August 2015 to test the hypotheses that: (a) the lake's dominant endemic copepod ( Epischura baikalensis ), previously assumed to be an herbivore feeding on diatoms, connects the microbial and classical food webs by ingesting ciliates; and (b) this feeding initiates top‐down effects within the microbial food web. Our results supported these hypotheses. E. baikalensis individuals consumed on average 101–161 ciliates per day, obtaining 96%–98% of their ingested carbon from ciliates and the remainder from small diatoms. Clearly, E. baikalensis is omnivorous, and it is probably channelling more primary production from both the microbial food web and the classical food web of Lake Baikal to higher trophic levels than any other pelagic consumer. Most ciliates consumed were a mixotrophic oligotrich and such taxa are often abundant in summer in other oligotrophic lakes. Consumption of these mixotrophs is likely to boost substantially the transfer efficiency of biomass to higher trophic levels with potential implications for fish production, but this has seldom been investigated in oligotrophic lakes. Feeding of E. baikalensis initiated a three‐link predatory cascade which reduced the abundance of ciliates and elevated growth rates of heterotrophic nanoflagellates but did not affect abundance or growth rates of autotrophic picoplankton. This demonstration of a potential trophic cascade in Lake Baikal indicates that investigations at larger spatial–temporal scales are needed to identify the conditions promoting or precluding trophic cascades in this lake.
Microbial food web
Microbial loop
Autotroph
Mixotroph
Trophic cascade
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Trophic state index
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Abstract Diet was examined in four species of marine herbivorous fishes in northeastern New Zealand, which for three species represents the southern end of their range. Aplodactylus etheridgii (Aplodactylidae) and Girella cyanea (Girellidae) are restricted to the subtropical southwest Pacific region, whereas Kyphosus bigibbus (Kyphosidae) is distributed antitropically in the Indian and Pacific oceans. The temperate Australasian herbivore A. arctidens was also examined for comparative purposes. Aplodactylus etheridgii and A. arctidens predominantly consumed rhodophytes (91.22% ± 4.12 SE and 72.50% ± 6.63 SE, respectively), with A. arctidens also consuming a significant proportion of chlorophytes (22.65% ± 6.91 SE), mainly Viva spp. Kyphosus bigibbus consumed predominantly phaeophytes (91.50% ± 2.69 SE), mainly Carpophyllum spp., with the remainder consisting of rhodophytes. Girella cyanea was omnivorous, consuming some animal material (12.45% ± 7.29 SE), mainly sponges and hydroids.
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Dissolution of anthropogenic CO2 into the oceans results in ocean acidification (OA), altering marine chemistry with consequences for food web primary, secondary and tertiary producers. Here we examine how OA could affect the food quality of primary producers and subsequent trophic transfer to second and tertiary producers. Changes in food quality induced by OA are often related to secondary metabolites in primary producers, such as enriched phenolics in microalgae and iodine in brown algae. These biomolecules can then be transferred to secondary producers, potentially affecting seafood quality and other marine ecosystem services. Furthermore, shifts in dominant functional groups of primary producers under the influence of OA would also impact higher trophic levels through food web interactions. It is challenging to understand how these complex food chain effects of OA may be expressed under the influence of fluctuating environments or multiple drivers, and how these effects can be scaled up through marine food webs to humans.
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Ocean Acidification
Marine ecosystem
Whole food
Primary (astronomy)
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Abstract Biological oceanographers generally distinguish between two contrasting trophic pathways in the pelagic environment, i.e. the herbivorous and the microbial food webs. The former goes from large phytoplankton and zooplankton to fish, whereas the latter comprises small eukaryotic algae and cyanobacteria as well as heterotrophic bacteria and protozoa. The present paper describes a continuum of trophic pathways, between systems dominated by the herbivorous food web and those dominated by the microbial loop (i.e. almost closed system of heterotrophic bacteria and zooflagel-late grazers, the latter releasing dissolved organic matter used as substrate by the bacteria). It is proposed that the continuum goes from the herbivorous web (or chain) to a "multivorous food web", to the microbial web, and finally the microbial loop. Characteristics of the various pathways maybe summarized as a series of interconnected ratios. It is hypothesized that systems dominated by the herbivorous food web or the microbial loop are of transient nature and thus inherently unstable, whereas the multivorous and microbial food webs have higher stability and are thus longer lasting. This view is supported by a review of properties of several systems, that include herbivorous webs of the spring phytoplankton bloom and in upwelling areas, the multivorous web in the "high nutrient low chlorophyll" region of the North Pacific Ocean, a microbial web at a retreating ice edge off Antarctica, and the microbial loop in oligotrophic waters where the biomass of bacteria significantly exceeds that of phytoplankton.
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Total inorganic carbon
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In theory, food chain length and omnivory are pivotal elements of food web structure that can affect the population dynamics of species within the web. Long food chains are thought to be less stable than shorter food chains, and omnivores are thought to destabilize food webs, although populations of omnivores may be more stable than populations of nonomnivores. In three of four simple food webs assembled from bacteria and protists in laboratory microcosms, the abundance of bacterivorous protists varied more over time when the species occurred in longer versus shorter food chains. The abundance of protists attacked by omnivorous top predators was either more or less temporally variable than in webs where top predators fed only at one adjacent trophic level, depending on the particular combination of interacting species. The abundance of omnivorous top predators varied less over time than the abundance of top predators restricted to feeding only at an adjacent trophic level. Observations of increased temporal variation in prey abundance in longer food chains and low temporal variation in omnivore abundance agree broadly with several predictions of food web theory. The observation that different species in similar trophic positions can exhibit very different dynamics suggests that stability may depend on complex interactions between species-specific life-history traits and general patterns of food web architecture.
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