Energy is the lifeblood of the ecosystem. In fact, the Encyclopedia Brittanica (LINK) description of an ecosystem begins with a topic on energy flow. Knowledge of biology is critical to understanding how the ecosystem functions. Bioenergetic models include biology and energy in the study of food webs.
The Wisconsin Bioenergetics Model was introduced in 1977. (LINK)
I personally prefer energy-based models, aka bioenergetic models, as they seem to be much more robust, and they get into much more detail on what is really going on in the ecosystem. By contrast, the biomass-based models are just numbers.
Following are examples of some bioenergetic studies:
A Bioenergetics Based Comparison of Growth Conversion Efficiency of Atlantic Cod on Georges Bank and in the Gulf of Maine (LINK)
A study using the Wisconsin Bioenergetics Model done in 2007 is very interesting. The Gulf of Maine is deeper and cooler, and the forage is low to medium quality. George’s Bank is shallower, warmer (near the upper limit of cod) than GB, and the forage is high quality. For GB, the study found that the fish consumed more food, their efficiency was lower, but their productivity was higher than the GOM. This suggests that with a better food supply the GB cod population can tolerate the warming waters or may have even adapted to the warmer waters.
Fish resist temptation from junk food: state-dependent diet choice in reproductive Atlantic cod Gadus morhua facing seasonal fluxes of lipid-rich prey (LINK)
A study on cod (LINK) was done in the straight between Denmark and Sweden using a model based on the Wisconsin Bioenergetics Model. This is the most detailed study that I have seen yet, and I strongly recommend reading it. The model is based on the law of conservation of energy, which is taught in junior high general science. The model tracks energy flow through the fish’s body and goes into detail how the components from different prey are important. They also did field validation of the model’s predictions.
Herring are migratory and appear in this area in September and remain for several months. The cod will feed heavily on herring for several weeks until their fat reserves are built up, and then they will go back to benthic prey, especially crabs, to get needed protein prior to spawning, even though there are still a lot of herring around. An example of Optimal Foraging Theory is given, In this case, the timing of spawning fits right in following a period of high forage availability, and the high forage availability improves the likelihood of spawning success. Foraging is a high-risk activity because of predation from seals. This could be part of the reason for the change of diet, back to benthic prey. Also, when feeding on herring, they only consume 2/3 the amount of herring as when they were feeding on benthic forage. This begs the question, “Who can swim faster, an overstuffed cod or a hungry seal?” It appears that the optimum foraging theory favors the seal. The diet change back to benthic prey is also important, now that the cod’s lipids reserves are built up, a higher ratio of protein is necessary to complete the development prior to spawning. In addition, another lipid, arachidonic acid (ARA), is available from the crabs, and ARA improves egg quality and offspring survival. The scientists also learned from the aquaculture industry about the “protein sparing effect of lipids” and put this in their model. “This mechanism is well known in aquaculture, where it has been shown that metabolic energy costs are to a larger extent covered by lipids than by proteins, if there are sufficient dietary lipids available. Hence, aquaculture researchers have experimented with feed formulas that optimize this mechanism without fattening the fish, to make sure the more expensive protein in the feed is retained as new tissue rather than being transpired. The high energy density of lipids makes it more suitable for storing energy.”
The energy density of the herring in this area was not mentioned. The area studied is between the Baltic Sea and the North Sea, which have herring densities of 7.28 kJ/g and 7 kJ/g respectively, for an average of 7.14 kJ/g which is only 8% higher than the energy density of the Atlantic herring in the GOM.
Energy-based ecosystem modelling illuminates the ecological role of Northeast Pacific herring (LINK)
Studies were done in Alaska with herring and its predators, which included birds, mammals and fish. Back-to-back studies compared a biomass model with an energy model and found that the biomass model underestimated the contributions of herring to the diet of seabirds, mammals and fish by 20% to 110% compared to the energy model (LINK). This paper states, “there is a clear need to reexamine the importance of energy rich forage fish, especially herring, in NE Pacific food webs.”
Predatory demand and impact of striped bass, bluefish, and weakfish in the Chesapeake Bay: applications of bioenergetics models. (LINK)
Abstract
We applied bioenergetics models for dominant Chesapeake Bay piscivores, striped bass (Morone saxatilis), bluefish (Pomatomus saltatrix), and weakfish (Cynoscion regalis), along with site-specific data on diets, growth, and energy density, to examine trophic linkages and the relationship of predatory demand to prey supply. Atlantic menhaden (Brevoortia tyrannus), bay anchovy (Anchoa mitchilli), and spot (Leiostomus xanthurus) accounted for 65–99% of the annual biomass of piscivore diets (excluding age-0 striped bass that ate mostly invertebrates). The diets of young piscivores were dominated by anchovy, but menhaden and spot became increasingly important to older fish. Young (age < 2) striped bass ate mostly benthic prey. Older striped bass fed increasingly on pelagic sources, primarily menhaden, but bluefish and weakfish increased benthic resource use from 10% at age 0 to 50% by age 2. Comparison of consumption (supply) to demand (potential consumption) measured the suitability of Chesapeake Bay for predator production. Bluefish came closest to achieving their demand for prey, suggesting that they are more successful predators than either striped bass or weakfish. Results suggest that Chesapeake Bay may be a better nursery than production area for older fish, and prey supply (not temperature) may account for the movements and use of the estuary by older piscivores.
Unfortunately, the rest of this document is behind a paywall and will cost $40 to read, unless you belong to an institution that has access.