Bottom-up carbon subsidies and top-down predation pressure interact to affect aquatic food web structure

Body size is a major factor constraining the trophic structure and functioning of ecological communities. Food webs are known to respond to changes in basal resource abundance, and climate change can initiate compounding bottom-up effects on food-web structure through altered resource availability and quality. However, the effects of climate and co-occurring global changes, such as nitrogen deposition, on the density and size relationships between resources and consumers are unknown, particularly in host–parasitoid food webs, where size structuring is less apparent. We use a Bayesian modelling approach to explore the role of consumer and resource density and body size on host–parasitoid food webs assembled from a field experiment with factorial warming and nitrogen treatments. We show that the treatments increased resource (host) availability and quality (size), leading to measureable changes in parasitoid feeding behaviour. Parasitoids interacted less evenly within their host range and increasingly focused on abundant and high-quality (i.e. larger) hosts. In summary, we present evidence that climate-mediated bottom-up effects can significantly alter food-web structure through both density- and trait-mediated effects.

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Warming shifts top-down and bottom-up control of pond food web structure and function

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2012.0243 ◽

2012 ◽

Vol 367 (1605) ◽

pp. 3008-3017 ◽

Cited By ~ 158

Author(s):

Jonathan B. Shurin ◽

Jessica L. Clasen ◽

Hamish S. Greig ◽

Pavel Kratina ◽

Patrick L. Thompson

Keyword(s):

Food Webs ◽

Environmental Changes ◽

Lytic Cycle ◽

Top Down ◽

Food Web Structure ◽

Bottom Up ◽

Positive Effects ◽

Freshwater Pond ◽

Aquatic Food ◽

The Impact

The effects of global and local environmental changes are transmitted through networks of interacting organisms to shape the structure of communities and the dynamics of ecosystems. We tested the impact of elevated temperature on the top-down and bottom-up forces structuring experimental freshwater pond food webs in western Canada over 16 months. Experimental warming was crossed with treatments manipulating the presence of planktivorous fish and eutrophication through enhanced nutrient supply. We found that higher temperatures produced top-heavy food webs with lower biomass of benthic and pelagic producers, equivalent biomass of zooplankton, zoobenthos and pelagic bacteria, and more pelagic viruses. Eutrophication increased the biomass of all organisms studied, while fish had cascading positive effects on periphyton, phytoplankton and bacteria, and reduced biomass of invertebrates. Surprisingly, virus biomass was reduced in the presence of fish, suggesting the possibility for complex mechanisms of top-down control of the lytic cycle. Warming reduced the effects of eutrophication on periphyton, and magnified the already strong effects of fish on phytoplankton and bacteria. Warming, fish and nutrients all increased whole-system rates of net production despite their distinct impacts on the distribution of biomass between producers and consumers, plankton and benthos, and microbes and macrobes. Our results indicate that warming exerts a host of indirect effects on aquatic food webs mediated through shifts in the magnitudes of top-down and bottom-up forcing.

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Effects of changes in isotopic baselines on the evaluation of food web structure using isotopic functional indices

PeerJ ◽

10.7717/peerj.9999 ◽

2020 ◽

Vol 8 ◽

pp. e9999

Author(s):

Simon Belle ◽

Gilbert Cabana

Keyword(s):

Food Web ◽

Food Webs ◽

Horizontal Distribution ◽

Food Web Structure ◽

Web Structure ◽

Functional Richness ◽

Stable Isotopic ◽

Aquatic Food ◽

Set Up ◽

Functional Indices

Background This study aimed to assess whether ecological inferences from isotopic functional indices (IFIs) are impacted by changes in isotopic baselines in aquatic food webs. We used sudden CO2-outgassing and associated shifts in DIC-δ13C brought by waterfalls as an excellent natural experimental set-up to quantify impacts of changes in algal isotopic baselines on ecological inferences from IFIs. Methods Carbon (δ13C) and nitrogen (δ15N) stable isotopic ratios of invertebrate communities sharing similar structure were measured at above- and below-waterfall sampling sites from five rivers and streams in Southern Quebec (Canada). For each sampled invertebrate community, the six Laymans IFIs were then calculated in the δ -space (δ13C vs. δ15N). Results As expected, isotopic functional richness indices, measuring the overall extent of community trophic space, were strongly sensitive to changes in isotopic baselines unlike other IFIs. Indeed, other IFIs were calculated based on the distribution of species within δ-space and were not strongly impacted by changes in the vertical or horizontal distribution of specimens in the δ-space. Our results highlighted that IFIs exhibited different sensitivities to changes in isotopic baselines, leading to potential misinterpretations of IFIs in river studies where isotopic baselines generally show high temporal and spatial variabilities. The identification of isotopic baselines and their associated variability, and the use of independent trophic tracers to identify the actual energy pathways through food webs must be a prerequisite to IFIs-based studies to strengthen the reliability of ecological inferences of food web structural properties.

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The impacts of climate change on plankton as live food: A review

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/869/1/012005 ◽

2021 ◽

Vol 869 (1) ◽

pp. 012005

Author(s):

N Azani ◽

M A Ghaffar ◽

H Suhaimi ◽

M N Azra ◽

M M Hassan ◽

...

Keyword(s):

Climate Change ◽

Food Web ◽

Food Source ◽

Vertical Mixing ◽

Zooplankton Community ◽

Nutrient Cycle ◽

Aquatic Food Web ◽

Food Web Structure ◽

Aquatic Food ◽

Critical Components

Abstract Climate change is expected to warm up the ocean surface where majority of life inhabits. Ocean warming influences vertical mixing and stratification patterns, which alter nutrient cycle, plankton production, and aquatic food web. Plankton serves as the first food source for all larval organisms and the base of aquatic ecosystem. Zooplankton community is a crucial component of the aquatic food web. They are critical components in an ecosystem of aquatic and worldwide biogeochemical cycles. Zooplankton contributes as food source to economically valuable fishes, primary-production grazers, and carbon and nutrient cycle drivers. Climate change contributes to dire consequences by altering the baseline of aquatic food web structure. However, the ocean biota itself can influence climate change, and the implications of this are evident from the increase and decrease of wild fisheries production. This review highlights the effect of climate change on phytoplankton and zooplankton production.

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