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#food web

11 public questions tagged with this topic.

Controls Ecosystem

Collapse of intermediate trophic level species mainly causes:

“Drastic ecosystem changes at both higher and lower trophic levels” for collapse of intermediate trophic level species mainly causes. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Ecosystem processes are constrained by energy conservation and by the cycling of matter. Energy enters mainly through primary production, is lost as metabolic heat at every transfer, and therefore cannot be recycled in the way that carbon, nitrogen, phosphorus, or water can. The remaining alternatives—“Stability in all trophic levels”, “Increase in primary productivity”, “Reduced predation pressures”—refer to different states, processes, or scales and therefore do not express the same causal relationship. The relevant inference should follow the pathway from resource supply to organismal uptake and then to ecosystem-level flux. Productivity, trophic transfer, decomposition, and nutrient regeneration are connected, but each measures a different part of that pathway.

Ref: Fundamentals of Ecology, Odum & Barrett, 5th Ed., Ch. 4

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Controls Ecosystem

Biomass accumulation at lower trophic levels in top-down control is directly influenced by:

“Higher trophic level predation” for biomass accumulation at lower trophic levels in top-down control is directly influenced by. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Rates depend on temperature, moisture, substrate quality, consumer physiology, and the elemental balance between organisms and their food. These controls explain why the same process can differ among terrestrial, freshwater, and marine systems without changing its definition. The remaining alternatives—“Nutrient availability”, “Plant growth”, “Abiotic factors”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Ecosystem processes are constrained by energy conservation and by the cycling of matter. Energy enters mainly through primary production, is lost as metabolic heat at every transfer, and therefore cannot be recycled in the way that carbon, nitrogen, phosphorus, or water can. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors.

Ref: Fundamentals of Ecology, Odum & Barrett, 5th Ed., Ch. 4

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Controls Ecosystem

What is a characteristic of 'wasp-waist' ecosystems?

“Dominance at an intermediate trophic level” for what is a characteristic of 'wasp-waist' ecosystems. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Ecosystem processes are constrained by energy conservation and by the cycling of matter. Energy enters mainly through primary production, is lost as metabolic heat at every transfer, and therefore cannot be recycled in the way that carbon, nitrogen, phosphorus, or water can. The remaining alternatives—“High nutrient availability”, “Control by apex predators”, “Primary producers dominance”—refer to different states, processes, or scales and therefore do not express the same causal relationship. The relevant inference should follow the pathway from resource supply to organismal uptake and then to ecosystem-level flux. Productivity, trophic transfer, decomposition, and nutrient regeneration are connected, but each measures a different part of that pathway. This distinction matters because similar surface patterns can arise through different mechanisms, whereas ecological prediction depends on identifying the mechanism that actually changes rates.

Ref: Fundamentals of Ecology, Odum & Barrett, 5th Ed., Ch. 4

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Controls Ecosystem

Which type of ecosystem control involves a trophic cascade?

“Top-down” for which type of ecosystem control involves a trophic cascade. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. The relevant inference should follow the pathway from resource supply to organismal uptake and then to ecosystem-level flux. Productivity, trophic transfer, decomposition, and nutrient regeneration are connected, but each measures a different part of that pathway. The remaining alternatives—“Bottom-up”, “Wasp-waist”, “Abiotic”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Rates depend on temperature, moisture, substrate quality, consumer physiology, and the elemental balance between organisms and their food. These controls explain why the same process can differ among terrestrial, freshwater, and marine systems without changing its definition. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors.

Ref: Fundamentals of Ecology, Odum & Barrett, 5th Ed., Ch. 4

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Food Chain and Web

Connectance in food web is calculated by:

Food-web connectance is the fraction of possible feeding links that are actually realized, calculated as actual links divided by potential links. If directed links among S species are allowed, potential links may be S², S(S−1), or another denominator depending on whether cannibalism and basal species are included. Because conventions differ, comparisons require the same definition and sampling effort. Connectance influences possible pathways for energy flow and indirect effects, but observed values can decline artificially as more poorly resolved species are added. Energy budgets must distinguish stocks from rates: standing biomass can remain high or low even when production and transfer through that compartment are rapid. Matter can cycle repeatedly through producers, consumers, and decomposers, whereas usable energy requires continuous external input because respiration degrades it to heat. The amount reaching a consumer level depends jointly on resource production, the fraction consumed, assimilation efficiency, and conversion of assimilates into new biomass.

Ref: Fundamentals of Ecology, Odum & Barrett, 5th Ed., Ch. 3

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Ecosystem Ecology

Which is NOT correct about food web energy flow?

The keyed exception is “Herbivore efficiency higher in oceans.” In the context of which is not correct about food web energy flow, that statement differs from the governing ecological pattern and must be evaluated against the mechanism rather than accepted from wording alone. Rates depend on temperature, moisture, substrate quality, consumer physiology, and the elemental balance between organisms and their food. These controls explain why the same process can differ among terrestrial, freshwater, and marine systems without changing its definition. The remaining alternatives—“Herbivores enhance productivity in productive ecosystems”, “Detritus chains longer in productive systems”, “Carnivore production efficiency > herbivores”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Ecosystem processes are constrained by energy conservation and by the cycling of matter. Energy enters mainly through primary production, is lost as metabolic heat at every transfer, and therefore cannot be recycled in the way that carbon, nitrogen, phosphorus, or water can.

Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 17-19

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