Natural Reality Check

Everything is Connected

So this is my last entry. I want to talk about what I know about the Food Web.

Most of us know about photosynthesis and the things at the top eat the things at the bottom. But it's not exactly that simple.

The truth is there are many bottoms to the food web. Every thing else relies on some form of life that derives its energy and building blocks from some inorganic form. With that in mind I'm going to explain a few definitions. Yes this is boring but it needs to be out of the way so what comes next is clearer.

Autotrophs don't eat other living things. This doesn't make them saints, it's just how they get by. To survive, they need to get stuff to make energy. There are two main types of autotrophs.

Chemo-autotrophs derive both their energy and nutrients from inorganic substances such as rocks, iron, sulphur or some other element. These types of organisms tend to be microscopic and are common around deep sea vents. In fact they are believed the basis for the ecosystem in the Marianas Trench.

Photo-autotrophs take light to make energy and gain nutrients from the soil. Pretty straightforward. This survival mode is used by cyanobacteria, algae(trust me not the same thing), plants and lichens.(I'll explain why they're not exactly autotrophs later.)

So anyways these organisms just sit around happily doing their thing until something limits their growth...or they get eaten. See living ecosystems have a limit. Unlike the old version of SimEarth, you can't sit with a field full of daisies and have their population grow forever. Eventually they run out of nutrients. When an organism dies and decomposes those nutrients return to the soil. But there's always one nutrient that gets scarce. That is called a limiting nutrient you can only have as many "daisies" as there is sufficient amount of that substance to go around. If that amount is exceeded, individuals begin dying off until the population reaches equilibrium.

Remember that because it comes up everywhere in the Food Web.

So populations of autotrophs are the basis of the food chain. No other forms of life can exist without them.

Why didn't life just stay all autotrophs? We're not sure, but somebody once said "Nature abhors a vacuum." Therefore, since there's something to exploit, something else comes along to fill that niche.

In a way this is good because that means two things. Not all the limited resources get turned into dead plants. That and if life hadn't gone beyond autotrophs, you wouldn't be reading this.(unless you're some weird, alien plant thingy with the equivalent of eyeballs and a brain. Thats unlikely though.)

Two more definitions here, heterotrophs and saprovores. Both equally important.

Heterotrophs gain energy and nutrients from eating other living things. Rabbits are heterotrophs; so are wolves, humans and a lot of unicellular and multicellular things. Including lichen. (believe me there's a huge reveal as to why I keep doing that. For those who already know, SHH! Don't spoil the surprise!)

Saprovores are a type of heterotroph that subsists on waste products and death. Without them we would be up worse than a poo river without a paddle. Everything dies and secretes waste. What happens to it? The answer is some microbe, fungi, insect, bird or other organism has to eat it. Gross but without them, the nutrients wouldn't cycle back through so they're vital too.
(All you living things who will eventually expire, the daisies and saprovores thank you for your sacrifice.)

For anybody who made it past the scatological and death talk, we're gonna start piecing this together.

The things that feed on the base of the food web are herbivores. The bunnies, deer, sea urchins and anything that doesn't eat animal flesh. Which is fine, but if it's just herbivores that's where we hit another bump.

Again we rub against limiting factors. For example if we have rabbits, just rabbits and plants, eventually there won't be any edible plants left in the area. The bunnies die a slow death from starvation.(Assuming there's enough water to go around.) Arrgh! That's a horrific idea, or at least it should be.

So again Nature, like the anti-hero it is, rescues the population of bunnies from starvation...by having a predator eating some. There are even predators that eat other predators. These are called apex predators.

But do you know what's neat about this? Predators are part of a healthy eco system. By keeping the herbivores from devouring all the plants they keep the ecosystem they exist in healthy.

When predators die, their remains are broken down by saprovores. Providing nutrients to grow plants to feed bunnies!(The circle of life completes...and cue that song from The Lion King!)

Robust ecosystems are not only pretty but help humans survive and stay sane.(see my entry on the importance of plants for why we need these. Oh yeah did I mention that, by and large, humans are omnivores? So having things to eat is just kinda a big deal.) Hey, look at that! It's all connected. Almost like a giant web.

Obviously this is a simple model with only "daisies", bunnies and wolves. In reality, there are thousands of species all competing for their piece of the web. The point I'm trying to make here is that everything depends on everything else. If one piece of the web, whether it's an autotroph, herbivore or predator, were to fail, it would have huge consequences for the rest of that ecosystem...and us.(Humans are not above this, we are a part of this web of life.)

Now for the ultimate reveal...what about lichens? Why did I include them crossed out in both heterotrophs and autotrophs? Because they're both. See a lichen isn't ever one organism. They have a photosynthetic algae or bacterium that lives in the moisture trapped by a heterotrophic organism, a fungus. In a way a lichen, by being symbiotic, is like the larger ecosystems. The microbe is dependent on the fungus for shelter and protection, the fungus in turn gets to eat some of the sugar produced by the microbe. Can these two organisms live without each other? Nope!

Without their partner, the individual organism would die. See? Even the bits we don't look at are connected.