It was called a trophic cascade. In an ecosystem, predators ate prey, and those prey in turn ate prey of their own, and so on until you were dealing with the smallest prokaryotes. Big fish ate little fish which ate plankton which ate bacteria which ate smaller bacteria, or something like that. However, if any stage of that process was interrupted, the rest of the process would be altered. In a complex ecosystem with dozens of organisms depending on each other, the entire system could be disrupted.
By wiping out one food source, I could wipe out every organism that depended on that resource, and then what would follow was a cascade where everything that depended on those organisms died, and then everything that depended on the organisms that depended on those organisms, and eventually you had a complete collapse of an ecosystem.
This was the big thing that every biologist back at home worried about the most, a worldwide trophic cascade that would eventually make the world unlivable to all life, including humans. Trophic cascades could be caused by many things. Weather change, the introduction of a new invasive species, or the destruction of an environment could all cause such an event. Ironically, humans accomplished all three of these things, causing countless trophic cascades.
I wasn't even a human, although I liked to think I still possessed the mind of one, and I was causing my trophic cascade. My hunting had caused enough destruction across the body of water I resided in that it was starting to affect the populations. I had wiped out all of the food, and the results were that the fish died in droves.
I found this out after finding a sudden aggressive surge in algae species. Tracing them back to their source, I found an ocean of dead fish. The kingfish and a few of the other great fish still survived, but a good portion of the mid-fish had been all but wiped out. Furthermore, oxygen was being overused, creating dead zones where even my cells struggled to remain alive.
This is how I realized how my aggressive leveling had nearly wiped out all my life. Unlike humanity, I had the power to stop it. I began to start taking over nutritional functions for my water mass. If I wanted to continue to live here, I had to put my thirty-three million cells to good use. Some cells became oxygen makers, while others made nutrition. At first, I used my cells to make food for other creatures to feed on, but constantly being gnawed at by fish was irritating and I eventually managed to regrow the population of their previous food source.
My aggressive leveling campaign was forced to come to an end, and instead, I started to have to deal with countless struggles, such as the amount of available nutrients. If there were too many nutrients, protists would spike, and then overbreed and cause an epidemic. Meanwhile, if it got too scarce, this would cause the population to plummet, which caused the predator population to plummet. I found myself no longer able to go along senselessly killing. Instead, I hunted periodically followed by seasons of allowing the populations to regrow.
It took about five years, by my best estimate, for the population to restore to a normal state, although it was hard to say what the world was like back when I was a prokaryote. Most of my time was taken up by my management. They say that when someone becomes a manager, they usually keep getting promoted until they reach the limit of their abilities. At that point, they'd no longer be promoted. In the same way, I felt like I had reached the limit. Would this be my life from now on?
Congratulations! You have reached level 8.
You have unlocked the skill, Electrogenesis.
Hmm? The ability to make electricity? An attack? How long had it been since I last leveled? Ten years? I couldn't remember anymore, but I had long since stopped counting days or even seasons since there were just too many and they all blurred together. I had fallen into a rhythm, managing this world. In some ways, I almost felt like a god. I felt a bit of ownership over this body of water.
Although the great fish had still been outside of my ability to defeat, I could have killed them if I wanted to. By removing their food sources, all of the fish would have died from it. Of course, that would have left me in an empty world and no path of evolution. Yet, now, I think I could do it. Rather, I had to do it.
The great fish and the kingfish had become the lords of the sea by living longer than anyone else. In all of these years, I hadn't seen their population grow by a single fish. They would likely die off from old age at some point. It would be better if I killed them myself and took their experience. I calculated it, and the great fish should be enough to bring me to level 9. At that point, if I could defeat the kingfish, then I could evolve.
Multicellular. I could finally become a creature. Perhaps, I might even be able to leave the sea and lord over the ground as well. I could use all of my abilities and become ruler of the entire world. That was certainly a thought. For now, I just wanted to reach that fabled multicellular realm.
After doubling up my population to over sixty-six million, I began hunting again. Of course, I had countless cells serving other roles, maintaining a perfect sea environment as I knew it. However, my combat units all began to seek out the kingfish. I used Gastrulation to create long strands of fibrinous tissue, which I used to create a net. These nets caught normal fish with ease, but the great fish were strong and quick.
I worked fast. As soon as I had one in my net, I delivered an electrical shock. The first time I did it, I wasn't sure how much I should use. Considering the water boiled and the fish was partially fried black, and instantly killed, I think I might have overdone it. I managed to practice my Electrogenesis on the next great fish, refining my ability. Without such an effective ability, I'd have no chance of defeating these guys.
The way the sea was laid out, the kingfish went everywhere, but the great fish each had a territory. They rarely minded me unless I used Gastrulation within their territory and started gathering too much of my body. At that point, they'd attack aggressively and scatter that portion of me. This time, I wasn't going on the offensive. One territory after another fell as I began to systematically knock off the great fish.
These guys weren't like the bottom feeders whose populations I controlled. They were intelligent, and they could smell the blood in the water. The status quo had changed, and the stalemate these creatures had maintained since likely before I had even reincarnated was being usurped systematically. They panicked, and some of them grouped for protection.
Those fights were long and difficult, but with so many cells at my disposal, along with my mutated cells designed for attacking, Toxins, and a few well-placed suicide bombers… I was able to take out a group of fish. The remaining ran to the kingfish for help, but he was too arrogant. He ended up chasing them away. As a result, they were easy pickings. When I killed the last great fish, a familiar text appeared in my vision.
Congratulations! You have reached level 9.
You have unlocked the skill, Adaptation.
Adaptation was a knowledge skill. If Mutation was the driving force of evolution, then adaptation was the driving force of individual survival. Adaptation flooded my mind with understanding. It showed me how I could optimize all of my cells. It was similar to Homeostasis in that regard, although while Homeostasis worked passively, Adaptation was a skill I had to manually apply. It only gave me the recipes, but it was up to me to apply them to cells.
It was hard to explain exactly what it did, but I instinctively knew that with Adaptation, I had taken a qualitative leap in ability, and the final step necessary to become a multicellular organism. After another mitosis, I had 1.3 billion body cells. With such an amount, I no longer feared the kingfish. Since killing the great fishes and freeing the territories, the kingfish had sunk low into his territory. It was like he was waiting for me.
After making ample preparation, I formed a tissue-like body, sinking into the depths of the sea. I wasn't a multicellular organism, resembling something more like a tumbleweed or seaweed. At the deepest point, a dark zone inhospitable to most other forms of life, I came before the kingfish. It looked at me at I stared right back.
"So, you've finally come to kill me." The kingfish declared.
Eh? It speaks?