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I made an evolution simulator and observed that when a marginally competent predator appears, it quickly multiplies and hunts down all of the prey animals, which leads to their own extinction soon after. This seem unlike the real world.

About the simulator
The animals are controlled by neural networks, herbivores must consume spontaneously generated food particles to obtain energy, predators can sap energy out of a prey without killing it, but this significantly hinders the prey's well-being. Animals reproduce asexually with mutations.

There are about 50 animals when the predator appears. All herbivores tend to resemble one another.

The ideal result
This simulator was initially meant to explore the development of individual organism through evolution, but the phenomenon I observed made me aware of the importance of whole ecosystems. I want a modified simulator to produce a ecosystems with multiple niches and stable final state, in short, I want biodiversity.

Some proposed modification

  • Add different habitats: different habitats vary in naturally spawned food particle, and their difference can be detected by the animals
  • larger population
  • arbitrarily increase the reproductive period of predators (?)
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  • $\begingroup$ Please inform me if more information about the simulator is needed, I will also accept general guide lines to such a simulator. $\endgroup$
    – user289661
    Aug 15, 2016 at 6:10
  • $\begingroup$ have you set up so that individuals (both predator and prey) need to gather energy above a set rate to reproduce and survive? In the real world many predators would die of starvation as the prey population shrinks so dramatically, this allows the prey population to recover, and the predator population will recover with some lag $\endgroup$
    – rg255
    Aug 15, 2016 at 8:15
  • $\begingroup$ Just a point of ecology: a predator that "can sap energy out of a prey without killing it, but this significantly hinders the prey's well-being" sounds like a micropredator to me. Generally an organism will have one or the other feeding mode, it can't choose between them (although you could have a fixed probability of a mutation evolving that switches feeding mode) $\endgroup$
    – arboviral
    Aug 15, 2016 at 9:12
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    $\begingroup$ I may write a full answer at some point but you definitely need larger populations. It depends on the range they can move over, but if I put fifty rabbits into a sealed empty warehouse with randomly-placed bowls of food and then added a fox, I wouldn't expect the rabbits to last long. $\endgroup$
    – arboviral
    Aug 15, 2016 at 9:17
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    $\begingroup$ Don't forget parasites and disease. I took an ecology course and the that we used simulator was underwhelming... but the net result was that predator/prey population lags. Predators kill prey, until there are not enough to sustain the poulation. The fewer the prey, the more difficult they are to capture. After the predators population declines (starvation), the prey population blooms... and then the predator population increases again, like two sinusoidal waves with the predator population a couple years behind. $\endgroup$
    – Ben Welborn
    Aug 15, 2016 at 11:54

4 Answers 4

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What you're trying to do sounds really cool. I feel that you can do the following:

1) Increase reproductive period of predators

2) Increase prey to predator ratio (see Lotka-Volterra equation)

3) Make the reproductive speed/ ability of an individual to be in relation with the number of energy 'points'

What kind of set-up are you working with, a unicellular model or a larger scale?

Maybe you could start with a solely herbivorous setup, but give all individuals the ability to harm/sap a small amount of energy out of another individual.

Is there some way you could send me your project? I want to have a look at it

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I think the first thing to consider is adding immigration of prey animals from outside populations. In the real world if a predator hunts it's prey to extinction (or close to it), the predator will slowly die off. In that time period of low/no prey species and low predator density is a perfect opportunity for outsiders of the prey species to come in a fill that empty niche in that area.

Another thing is that predators eating prey is easy at first because prey numbers are large. As prey becomes rare they become harder to find and potentially smarter, so harder to catch once you do find them.

Also the fact that predators can "sap energy" out of prey makes them more of a parasite, not a predator. Just something to consider when you read about predator/prey dynamics.

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You have a parasite or parasitoid, since they dont kill and eat preys. Assuming real predators,I think that these need too:

  • add some kind of defense behavior or defense structure to preys. in real world this occurs as potential prey is capable to run, or have a thick skin.
  • add variation in both prey and predator, things like individuals faster then others, etc Good evolutionary novelties for predators (biger claws) drives selection of good evolutionary novelties for preys (thicker skin), that drives again selection of good evolutionary novelties for predators (group hunting), that selects good evolutionary novelties for preys (big horns and agressive behaviour) and so on...
  • add diseases, death and life spam to preys and predators
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Add the option of cannibalism and maybe increase predator mutation rate such that new species that feed of each other quickly evolve. Also insure that herbivores have the capacity to evolve defense mechanisms such as speed herd protection or the ability to harm predators back.

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