Efficacy : evolution and efficiency

these articles are a translation of those in the series on efficacy on 2000watts.org

An animal can be seen as a thermodynamic machine that transforms the chemical energy of food into mechanical, thermal and other forms of energy required for survival. Although biological processes are more complex than those of conventional machines, fundamental thermodynamic principles also apply to living organisms.

To win the game of evolution, animals must try to generate more surplus from the same energy source, using as little of it as possible, and so be more efficient than their little playmates.

So let's see why efficacy is important for efficiency and evolution, and what it means for the size of these animals.

The quest for efficiency

In the previous article, we looked at the profitability of a machine and its threshold (purple S).

But efficacy is not efficiency

·???????? Efficacy is the ability to achieve predefined objectives regardless of the means used;

·???????? Efficiency is the capacity of an individual, a group of individuals, a machine or a technique to obtain maximum results with minimum means, costs, effort or energy.

If an investment brings in more than it costs, it's profitable, but an investment that would bring in €10,000, depending on whether you invested €5,000 or €9,000, won't have the same flavor.

Efficiency is the net gain (gain - cost) divided by the cost.

·???????? Investment efficiency of €9,000 = 11% = (10-9) / 9

·???????? Efficiency of €5,000 investment = 100% = (10-5) / 5 = 9 times more efficient

After exceeding the break-even point S in purple, efficiency increases rapidly, slows down, reaches a maximum efficacy at 50% (in this theoretical case) and then decreases.

Put another way, going beyond an efficiency threshold is counterproductive, as efficiency diminishes. This is the law of diminishing returns postulated by the social sciences of economics.

The quest for efficiency: an analogy

Using the investment example above, the more efficient your investment, the more surplus financial resources you'll have for :

-?????? alleviate problems such as temporary job loss, accidents, rising living costs and climate change;

-?????? adapt your lifestyle, home, clothing, education to social norms or the technological context;

-?????? make other investments and diversify without taking too much risk;

-?????? access to quality food and care.

The higher the efficiency, the more resilient and competitive you will be in the game of natural selection, and for example, it's the richest households that have the most children.

Becoming efficient?

Let's take some of the world's biggest animals and find the odd one out: a blue whale, a polar bear, a mammoth and an African elephant.

The intruder is the African elephant, which, although comparable in size to the mammoth, doesn't live in a cold environment. In fact, there are quite a few big beasts living in Africa: hippopotamus, rhinoceros, giraffe, buffalo... the fact that it's cold is not the important factor that means you have to be efficient, because what's important :

It's the quantity of food available and its temporal scarcity.

-?????? the temporary "phytoplankton bloom" fattens the whales, which will eat nothing as they migrate to warmer waters to give birth.

-?????? Big bears make a killing during temporary salmon migration

-?????? Savannah animals gorge themselves during the very short rainy season.

-?????? The mammoth had little or no food during the harsher winter of this ice age.

Food production

Depending on the availability of what plants need to grow: water, sunlight and nutrients, they will produce more or less food per year. Let's take 2 illustrative cases of production of the same food over the course of a year, for which the total annual quantity produced is identical but with a different distribution.

Case 1: constant food all year round

Case 2: low production all year round, with peak production in summer.

To live in case 2, several strategies are possible, but the case of pausing the animals (hibernation and estivation) is not dealt with here.

Storage vs. no storage

If you want to use the surplus all year round, you need to stock up, because an animal has to consume a fixed daily minimum amount of food (basal metabolism) which cannot be filled with the little food available during the lean months.

The stock may be external, as squirrels do with their nut caches, or as humans do with their freezers, but in most cases the stock is internalized in the animal itself.

Keeping food implies an additional cost (extra effort) compared to food available all year round (case 1) to transform it into stock (fat), store it and/or move it when you carry it with you.

The animal in case 2 therefore costs more than the animal in case 1 to use the same amount of annual energy.

Cost and efficiency

This additional cost is added to the initial investment (red curve) to produce the orange curve below.

We can see that the blue zone of profitability is shrinking, but this also modifies efficiency in two ways!

Efficiency is falling (green arrow) and the efficiency maximum has shifted (black arrow) to the right, towards greater efficacy (from 50% to 55%).

The animal in case 2 will be less efficient and more effective than the one in case 1, which will have food available all year round.

If the food is identical apart from its availability throughout the year, it's important to understand that the animal in case 2, which would only consume the food available all year round (in dotted blue), would be identical to the animal in case 1 (in green).

The difference would be that there would be 3 times fewer individuals because there is 3 times less food.

More efficient and therefore bigger

The same logic applies here as for non-biological machines https://2000watts.org/index.php/home/thomas-norway/1389-efficacite-je-ne-suis-pas-gros-je-suis-efficace-2.html, because an animal is a volume made up of millions of cells that produce heat during operation, which is then evacuated through the surface of the skin.

Therefore, an animal that needs to become efficient needs to put on weight to maintain its internal temperature, because increasing efficacy reduces heat production in the animal's body.

Its only option, therefore, is to grow in size, in order to increase the total quantity of heat (greater volume) on the one hand, and to reduce the surface area of losses (the skin) per unit of volume on the other.

And we'll get to the dinos in the next issue, I promise.

Conclusions

Animals that want to occupy the ecological niche using a peak in food production have an additional cost induced by food storage.

This extra cost implies increasing its efficiency, making it more competitive in the "game" of natural selection.

But this increase in efficiency means the animal has to become bigger / fatter / more massive than its counterpart exploiting a year-round food source.

Column by Thomas Norway, energy systems specialist.? "I'm not for or against any technology, I'm for understanding the problem and democratically accepting the consequences of our choices."

?To conclude :

Many thanks to Jean-Didier and Fran?oise for their proofreading and advice.

"The rain of tears is necessary to the harvest of instruction." Tamil proverb