Low on the food chain

Allow me to begin by asking what you think the four organisms below have in common? Diplodocus is in the upper left with the Whale Shark (Rhincodon) to its right. The Blue Whale (Balaenoptera) is on the bottom left and Brachiosaurus is adjacent.

If you thought that these four are some of the largest organisms that have ever existed here on planet Earth you would be right. Another commonality is that these largest-among-the-large are herbivores, or omnivores in the case of the two ocean-goers. The intention of this post is to marvel at these facts and to discuss how it is that such behemoths have always been found to make their living low on the food chain when logic may have suggested otherwise.

To begin to unravel this ecological puzzle one must recognize that the energy which drives all living things ultimately comes from the sun and that the only organisms capable of harnessing this radiant energy are green plants. In ecological terms we call the activities leading to the production of photosynthetic sugars, primary production and the plants that produce them primary producers. Those that make a living by consuming primary producers are called primary consumers (or herbivores), and those that consume primary consumers are secondary consumers, and so on. What’s fascinating about these trophic relationships is that the one-way movement of energy up the trophic pyramid is just 10% efficient. So, the internal combustion engine may be 20% efficient, a rocket engine 70%, an electric motor 85%, and a propane furnace may be more than 95% efficient and I’m telling you that nature, which has had several billion years to work it all out, is only 10% efficient? Right. But why? Because it costs to be an organism. There are costs associated with respiration and egestion and costs of tissues, organs, and structures that don’t transfer to the next trophic level (things like fur, bones, and claws which cannot be assimilated). So the total amount of energy available as primary production declines predictably at each transfer. If, for example, there are 100,000 calories in primary production in a certain patch of ocean, one can expect 10,000 calories in the bodies of primary consumers, which will support 1000 calories in the bodies of secondary consumers, which will ultimately support 100 calories in the bodies of tertiary consumers or top carnivores. The bottom line to our ecological puzzle is that very, very large bodies require very large amounts of energy and these energies are more easily obtained LOW on the trophic pyramid among primary producers and primary consumers. If an organism the size of a Blue Whale were to make the evolutionary shift to strict carnivory it would quickly discover that meeting the energy demands of such a large body wasn’t possible as a top carnivore; dropping to the bottom of the food chain, as it were, allows the omnivorous Blue Whale to more effectively and efficiently feed in what is essentially a continual food stream. [Living Lower on the Food Chain has other ecological implications as well, for human populations especially. But this is a topic for a future post.]

So why do I include the images below? I do so because I wanted to point out that I don’t believe Fay Wray really had to worry that King Kong was intent on consuming her. He wouldn’t have wanted to or even had the necessary dentition. At his monstrous size he was most probably a vegetarian. If Wray was going to worry about anything she should have been worrying about Kong dropping her from such a height. These trophic relations also explain why, in any particular landscape, plants will be most common, herbivores less so, things that eat the herbivores even less so, and big fierce animals will certainly be most uncommon.

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