NetLogo User Community Models

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WHAT IS IT?

This model was inspired by the PBS Eons Youtube Video, 'Why Wasn't There A Second Age of Reptiles?', which explores how an asteroid impact ended the Age of Reptiles and ushered in the Age of Mammals, despite both mammals and reptiles surviving the catastrophe. The YouTube Video itself was inspired by papers by Arturo Casadevall and his colleagues.

This model simulates interactions between mammals, reptiles, plants, fungus, and scavenged meat on a patch grid. Mammals and reptiles wander, forage, hunt live prey, and reproduce. Plants and fungus grow and spread, competing for patches, while meat is produced when creatures die and may rot into fungus. The simulation explores how these agents' behaviors and environmental factors (e.g., light level, growth rates) influence ecosystem dynamics. The overall goal of the model is to explore how resistance to fungal infections (mammals) can help a species thrive even with weaker starting attributes (smaller size, smaller offspring litter sizes, and slower speed) than a species that is vulnerable to fungal infections.

HOW IT WORKS

**Agents**
- **Mammals** and **Reptiles** ("turtles") each have body size, energy, breeding mode, infection status, and timers (sprint, cooldown, immunity).
- **Patches** track plant-mass, fungus-level, meat-level, and meat-age.

**Movement & Foraging**
1. Agents eat food on their patch (meat x fungus chance, fungus for mammals, plants).
2. Sprint and cooldown timers govern chase and post-hunt rest.
3. Agents avoid fungus (reptiles) and flee larger threats.
4. Off-cooldown predators chase nearby prey; if within half predator's size, prey is killed (drops meat).
5. Agents detect meat, fungus, or plant patches within PERCEPTION-RADIUS, move toward them, and consume.
6. Random wandering when no other behavior applies.

**Reproduction & Infection**
- When an agents energy (body-size x tummy-size-factor), it enters breeding mode and seeks a same-breed partner.
- Offspring inherit sizes within a range around parents, enforcing MINIMUM-SIZE.
- Reptiles may become infected by fungus on their patch and can recover or die from infection.
- After predation, predators gain temporary immunity from infection (post-kill-immunity).

**Patch Dynamics**
- **Plants** spread randomly outward, replace fungus, and spread to neighbors based on PLANT-GROWTH-RATE x LIGHT-LEVEL.
- **Fungus** spreads randomly outward with FUNGAL-GROWTH-RATE x (1 - LIGHT-LEVEL).
- **Meat** ages each tick; rot chance ROT-CHANCE converts meat to fungus when depleted.

HOW TO USE IT

1. Adjust sliders and choosers: INITIAL-PLANT-SEEDS, INITIAL-FUNGAL-SPORES, INITIAL-MAMMALS, INITIAL-REPTILES, PLANT-GROWTH-RATE, FUNGAL-GROWTH-RATE, SEED-SPAWN-PERIOD, etc.
2. Press **SETUP** to initialize the world (also clears the last world).
3. Press **GO** to run the simulation.
4. Observe the Monitors for counts of mammals, reptiles, plant-covered patches, fungal patches, and meat.
5. Watch the Plots for population and resource level dynamics over time.

THINGS TO NOTICE

- How do plant and fungus distributions change with LIGHT-LEVEL?
- Do populations oscillate in response to prey/resource availability?
- How does meat rot into fungus and feed back into the system?

THINGS TO TRY

- Vary PLANT-GROWTH-RATE and FUNGAL-GROWTH-RATE to shift competitive balance.
- Increase PERCEPTION-RADIUS: does that stabilize or destabilize predator-prey cycles?
- Is there a LIGHT-LEVEL where both mammals and reptiles have a 50-50 chance of rising to dominance?
- Experiment with extreme initial size variability by varying INITIAL-SIZE-FRAC: do large initial mammal herds outcompete reptiles? Do "plagues" of mammals or reptiles take over and deplete all the fungus/plant resources?

EXTENDING THE MODEL

- Add a water resource and thirst mechanics for agents.
- Add hunger mechanics and starvation death.
- Implement seasonal light-level changes to vary plant/fungus growth rates and/or a pre-programmed light-level scenario such as a period of darkness after the KT-boundary followed by normal light-dark cycles.
- Model spatial heterogeneity (e.g., barriers, rivers) affecting movement and spread and potential for hiding/stalking.

CREDITS AND REFERENCES

Inspired by 'Why Wasn't There A Second Age of Reptiles?' (PBS Eons YouTube video), which explores how an asteroid impact ended the Age of Reptiles and ushered in the Age of Mammals:
https://youtu.be/EPXbSx17030?si=Fyxivy_RZ_QL0p5W

**Scientific Papers:**
Casadevall, A. (2005). Fungal virulence,vertebrate endothermy, and dinosaur extinction: is there a connection? Fungal Genet Biol 42: 98-106, avail. ttps://www.sciencedirect.com/science/article/abs/pii/S1087184504001938?via%3Dihub.

Casadevall, A. (2012). Fungi and the rise of mammals. PLoS Pathog.: 8(8):e1002808. Avail. https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1002808
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Casadevall, A. and Damman, C. (2020). Updating the fungal infection-mammalian selection hypothesis at the end of the Cretaceous Period. PLoS Pathog 16(7): e1008451. Avail: https://pmc.ncbi.nlm.nih.gov/articles/PMC7365386/

Additional inspiration from a YouTube video by Casadevall:
https://www.youtube.com/watch?v=eaNcTM-f5y8

HOW TO CITE

If you mention this model or NetLogo in a publication, please include:
Hoopes, D. (2025). NetLogo KT-Extinction-Survival model. http://ccl.northwestern.edu/netlogo/models/KT-Extinction-Survival. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

Wilensky, U. (1999). NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

COPYRIGHT AND LICENSE

Copyright 1997 Uri Wilensky

COPYRIGHT AND LICENSE

2025 Desmond Hoopes. CC BY-NC-SA 3.0 License.