A BEDTIME STORY FOR US ALL
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Putting things in boxes.
Greek philosopher Aristotle was a forerunner in categorizing types of species, mainly by the way they gave birth. This I admit is an interesting approach to putting things into boxes. He declared that there are five levels of animal categories, and of course he placed man at the top. Today, when deciding on animal groups, we involve a field of biology called taxonomy. (This has nothing at all to do with tax. Humans are the only creature on earth that charge one another for things.)
Taxonomy is the science of naming, defining, and classifying organisms into groups based on shared characteristics. For example, the ‘chief’ taxonomic rank name is called Domain. This is all about cellular organization and genetics. There are three documented areas for ‘Domains’: Archaea, Bacteria, and Eukarya. I know this part of the story has some complicated words, but don’t panic, you don’t have to remember all of this, just be in awe of the diversity of life we have and the fact that we have had to come up with so many names.
Excluding humans, there are about 3 trillion plants on planet earth, 10 quintillion (10^19) insects, hundreds of billions of fish and also hundreds of billions of birds. Mammals, amphibians, and reptiles still need to be added to these numbers, but their category groups and numbers are less compared to bugs. Suffice to say, this planet has a lot of life!
Another taxonomic rank, and the one I use the most, is called the ‘Animal Kingdom’, which decides by organizing the critters based on fundamental traits. There are Animalia, Plantae, Fungi, Protista, Archaea, and Bacteria. Another one is when we categorize and sort by Phylum. This is all about body plan characteristics. An example would be Chordata which is a phylum that includes animals with a spinal cord. We could also sort by Class, Family, and Genus. Deciding on a group based on what organisms can interbreed is another way to group critters who might share some indifferent characteristics but can still produce offspring.
If you have met me in person, you will know I absolutely love my food, so I want to do things differently and group animals in the order of their food energy efficiency, basically what they eat and absorb. This is an important distinction because we don’t actually absorb everything we put in our mouths. If we did, we would have none of that nasty stuff that comes out the other end, or certainly less. I am also not suggesting that this category puts creatures into an order of who poos the least, but if I were to pick a winner, it might have to be the Thorny Devil Lizard or perhaps even the Koala. Something odd I learned at a Games evening at the time I was writing this is that a wombat is known for producing cube-shaped poo. How odd! The hummingbird is known to be one of the animals that eats most frequently and Sloths the least.
Trophic levels are basically the spot a creature has in the food chain and also a great way to describe the flow of energy through an ecosystem. The flow is never linear but more of a web. We are talking about categorizing animals by energy efficiency. First, we have the Producers. These are plants and algae that produce their energy through photosynthesis. They gobble sunlight! Then we have the Primary Consumers (Herbivores) who eat Producers. Next are the Secondary Consumers (Carnivores); these animals eat Primary Consumers. They are followed by Tertiary Consumers who are also predators that feed on secondary consumers. Now things get a little dirty. Next up are Decomposers. These are creatures like fungi and bacteria that break down dead creatures and recycle nutrients back into the ground.
Out of these categories, who is the most energy-efficient? To answer this, we need to use an ‘energy thermometer’ measurement called trophic efficiency. Trophic efficiency is fascinating on its own, so let me quickly share a few nuggets on the subject.
Trophic efficiency is about the transfer of energy from one trophic level to the next in the natural food web. For example, Producers to Primary consumers, or let me put it another way: a Plant absorbs some sun, then a cow comes along and eats that plant, but then a human eats that cow, but the human dies a few days later and fungi and bacteria decompose the human. The ‘energy thermometer’ can help us work out how much of the sun’s energy in that process actually got to the bacteria at the end.
The average is that about 10% of the energy moves from one trophic level to the next. There is a name given to this too: ‘Lindeman’s efficiency’. Humans love naming things!
Here is a working example of Lindeman’s efficiency: if Producers (plants) capture 1000 units of energy from sunlight, only about 100 units will be available to primary consumers (herbivores). The next level will only get 10 units, the next 1, and the little bacteria, I think, is left with a very sad 0.10. (Don’t feel bad for them; they are not very hungry critters anyway).
Understanding trophic efficiency helps ecologists work out the energy budgets in an ecosystem. I want to conclude this section of the story by explaining the ways living things actually obtain their energy from the bits and bobs they are eating. To do this, we also put things into categories through the process of Metabolic Classification.
Our classification, and all animals, are in the category called Heterotrophs. This is when we obtain both energy and carbon by eating organic (meat or vegetable) compounds. We need carbon because it is a foundational element in all living things molecules. Carbon is an element perfect for forming complex molecules necessary for life because of its brilliant bonding capabilities. The second group is Photoautotrophs. This group likes to take selfies. Sorry, that is such a dad joke, this category is actually organisms like plants and cyanobacteria which use sunlight to produce energy and carbon compounds from carbon dioxide.
Finally, there are Chemoautotroph organisms that obtain energy by oxidizing inorganic substances using CO2 as a carbon source. Did you see that rust on the car outside? That is literally ‘life’ having dinner using this process and obtaining some energy.