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3 predators cooperating 2 predators cooperating 2 predators herding

From left to right: 3 predators cooperating, 2 predators cooperating, 2 predators keeping a herd of prey

Multi-agent reinforcement learning on predator-prey aquarium environment - can sharks learn to cooperate? Or is the tragedy of the commons unavoidable?

Greedy agents in sustainable ecosystems need to refrain from over-exploitation. But are they even able to learn just from environmental influences (i.e. the response of the environment to over-exploitation) and not through reward shaping?

The environment this is analysed with contains a set of sharks as predators and fishes as prey. Sharks are controlled by a continuous set of actions that control speed and angle. Killing a fish gives a reward of 10. The observation only contains the nearest few fishes/sharks. Thus, this is a POMDP.

Previous work analyses a single-agent scenario using a DQN. We find that PPO performs much better, which enables emergent behavior such as cooperation or herding. We end up adding multiple features to the environment (multiple predators, starvation, stunning, no walls, varying difficulty of hunting in terms of view distance and maximum speed).

See the results section further below for a set of charts and results. A paper was published in ALIFE 2021.

Project Structure

File/Folder Purpose
contrib/ Helper bash files for the compute pool.
env/ Contains the aquarium environment with an API in accordance to OpenAI gym.
evaluators/ Evaluator scripts for each figure.
guide/ Contains a small guide to the environment.
models/ Trained models are saved here.
pickles/ Data created by evaluators.
plots/ Plots for the collected data.
profiles/ cProfile files used when I sped up the pipeline by using Cython.
runs/ Contains runs (for watching in Tensorboard). Builds the Cython project.
config.pyx Handles simulations.json. Can be executed directly to get all keys in simulations.json.
custom_logger.pyx Logging KPIs to Tensorboard. Entry point. MLP (norm/batchnorm) neural network models for baselines PPO. End to end training and evaluation of experiments from simulations.json. The meat of the project. For running cProfile. For showing cProfile results. Contains code to run deterministic shark algorithm.
simulations.json All experiments and configurations.

Note. This is a Cython project, which is why there are .pyx files everywhere. They still work with normal Python when executed directly (e.g. python3 config.pyx), because I didn't go deep into cythonization due to time constraints. It was simply a basically free 40% performance boost.

Installation and building

  1. Install all packages in requirements.txt: pip3 install -r requirements.txt
  2. Run This requires g++!


  1. Create a new experiment in simulations.json or re-use one. For instance, you could pick ma9_i5_p150_r10_s05_sp200_two_net_vd35_f.
  2. Run: python3 ma9_i5_p150_r10_s05_sp200_two_net_vd35_f single

Models are saved in models/ and runs (for checking them in Tensorboard, e.g. tensorboard --logdir runs) are saved in runs/.

To load and watch a model, run for example: python3 ma8_obs load models/ You can change the cfg_id to run the model in (ma8_obs) and you can change the model to run.


Accompanying blog post can be found here. The paper in a short summary:

  1. We find emergent herding. PPO learning is in three stages: First stage where sharks are not able to catch fish effectively yet, second stage where they are extremely good at it and destroy the population, third stage where they learn to restrain themselves and thus become sustainable.

Herding learnt over time

  1. We find that herding emerges much more in certain scenarios --- certain starving pressure and few starting fishes (thus inducing a sustainability scenario). Figure below shows from left to right the scenarios 10, 5 and 2 initial fishes.

Herding rate

  1. We find that cooperation also emerges, due to environmental influences --- number of initial fishes (from left to right in figure below), maximum shark speed (lower increases hunting difficulty), kill zone radius and view distance.

Avg cooperation rate

Avg cooperation rate

For more details check out the paper! TODO: Link it here.

Here you can find a few videos of some of the emergent behavior.


The corresponding publication can be found here: ALIFE 2021

To cite in publications:

    author = {Ritz, Fabian and Ratke, Daniel and Phan, Thomy and Belzner, Lenz and Linnhoff-Popien, Claudia},
    title = "{A Sustainable Ecosystem through Emergent Cooperation in Multi-Agent Reinforcement Learning}",
    volume = {ALIFE 2021: The 2021 Conference on Artificial Life},
    series = {ALIFE 2021: The 2021 Conference on Artificial Life},
    year = {2021},
    month = {07},
    abstract = "{This paper considers sustainable and cooperative behavior in multi-agent systems. In the proposed predator-prey simulation, multiple selfish predators can learn to act sustainably by maintaining a herd of reproducing prey and further hunt cooperatively for long term benefit. Since the predators face starvation pressure, the scenario can also turn in a tragedy of the commons if selfish individuals decide to greedily hunt down the prey population before their conspecifics do, ultimately leading to extinction of prey and predators. This paper uses Multi-Agent Reinforcement Learning to overcome a collapse of the simulated ecosystem, analyzes the impact factors over multiple dimensions and proposes suitable metrics. We show that up to three predators are able to learn sustainable behavior in form of collective herding under starvation pressure. Complex cooperation in form of group hunting emerges between the predators as their speed is handicapped and the prey is given more degrees of freedom to escape. The implementation of environment and reinforcement learning pipeline is available online.}",
    doi = {10.1162/isal_a_00399},
    url = {\_a\_00399},
    note = {74},
    eprint = {\_a\_00399.pdf},


Running RL algorithms on the fish/shark aquarium environment to find unexpected biological insights.







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