Let’s hash out a conversation using environmental tolerances categorically in accordance to the above logic. I say first order of business is agreeing upon some rough estimates for what environmental condition ranges should count for what categories by going through each one.
Then we might want to start a discussion regarding general principles for general principles regarding environmental conditions, which can help us answer questions like: how will the player have sufficient environmental tolerances as a single tile of cytoplasm? How will we be cognizant of the fact that different organism body plans require different coping mechanisms in face of the environment? How will we adequately balance patch movement if the player has to kill off their existing population to move into a different biome? That should then give us a pretty good understanding of how we can balance and integrate changing environmental tolerances within Thrive.
Some Environmental Factors to Consider
- Should we outright lock players off from moving to environments way out of their tolerance range? For example, should we block players adapted to temperate environments from going to extremely cold environments? Or should we make the player learn to organically avoid these areas? The latter would be a strong reinforcer of making the player be responsible for themselves, but it might be frustrating to spawn into the environment and have absolutely no chance of survival, quickly dying.
Pressure: Pressure will obviously differ depending on the depth at which your organism is adapted to live in.
I’d say pressure should have the following categories: Low, Medium, and High. Low pressure includes the Epipelagic and Mesopelagic Zones, which includes frozen shelves, estuaries, and tidepools. Medium Pressure includes the Pelagic Zone and Hydrothermal Vents. And High pressure includes the Abbysopelagic Zone. Caves will vary depending on their depths.
Eyeballing these estimates, perhaps adequate rough estimates of pressure ranges can be…
Light: 0-800 meters
Medium: 800-3000 meters
High: 3000+ meters
NOTE: we might introduce a “Very Low” pressure category if we implement high-elevation environments in the macroscopic stage, though this is very far away.
Temperature: Temperature can vary dramatically in an ocean across various depths. Seafloors can approach or even exceed freezing temperatures (a higher concentration of salt prevents deep seawater from freezing). Temperatures don’t vary too much in an ocean at the same depth as they might on land, though temperatures plummet as you approach the poles and increase as you approach the equator.
I’d say categories should include Very Cold, Cold, Temperate, Warm, Very Warm. Very Cold includes frozen regions, and perhaps some abyssopelagic zones. Cold includes the pelagic zones. Temperate can include epipelagic and mesopelagic patches. Warm includes shallow seas and estuaries. Very warm includes tidepools and hydrothermal vents.
With that in mind, these can be rough estimates…
Very Cold: Less or equal to 0 C.
Cold: Warmer than 0 C, colder than 13 C
Temperate: Warmer than 13 C, colder than 23 C
Warm: Warmer than 23 C, Colder than 33 C
Very Warm: Warmer than 33 C
Salinity: Salinity can vary across different regions of seawater. Though this variability is not enough to make certain regions of saltwater inaccessible to most aquatic animals, it can induce subtle osmoregulatory stressors on life. Surface waters are typically more salty than deeper waters due to evaporation - the same is true of cold, polar water and warm, equatorial/tropical waters.
We want to represent the switch between freshwater and saltwater. That can be pretty simple in the Microbe Stage, where we can just introduce a specific part or something which signifies a switch to freshwater.
Regarding this variability in saltwater bodies, I think it’s fine if salinity isn’t a huge constraining environmental factor for the Microbe Stage beyond the freshwater/saltwater divide. Salinity could just be represented by a value with some slight variation across different patches. A higher salinity can make osmoregulation more costly. However, this can be compensated by an increase in phosphate/ammonia within the patch, justified by the fact that a greater concentration of salt likely is paired by a greater concentration of other important nutrients. So it can be a choice for the player to make - is taking on more osmoregulatory costs worth the easier access to nutrients?
Oxygen: The evolution of oxygenic tolerance will be a very important phenomena to represent in our simulation; planets will begin anoxygenic, but photosynthesis will introduce oxygen, aerobic respiration, and thus, the need for oxygen tolerance.
I think oxygen is fine to represent numerically without diving into categories since I think it can be easier to keep track of. I also think that this oxygenation discussion should be its own thing since it will be so numerical and rather difficult to conceptualize without actually doing.
This is a list of currently described environmental conditions attached to different biomes. Note that a list of this can also be found in the Developer Wiki (Microbe Stage Appendices - Thrive Developer Wiki), but this list is more relevant to our current discussion. Also note that salinity isn’t described in every biome due to the fact that it will have some variance according to the above concept - I only mention salinity when I am noting which patches will likely have higher salinity on average.
Hydrothermal Vents: Very Warm. Medium to High Pressure. Average Salinity
Abyssopelagic (Ocean Floor): Cold. High Pressure. More Salty.
Bathypelagic (Mid-Ocean): Cold. Usually Medium, Sometimes High Pressure.
Mesopelagic (Sub-Surface): Temperate, Sometimes Cold. Light Pressure.
Epipelagic (Surface): Sometimes Warm, Sometimes Temperate. Light Pressure.
Coastal: Usually Warm, Sometimes Temperate. Light Pressure. More Salty.
Caves: Dependent on conditions of parent patch.
Shelves: Very Cold. Light Pressure. Less Salty
Estuary/River: Warm. Light Pressure. Freshwater or Minimal Salt.
Tidepool: Very Warm. Light Pressure. More Salty.
A question to consider: I previously thought that simulating sunlight tolerance would be a bit unnecessary since I felt that it would overlap a lot with pressure tolerance. But do you guys think we should include it? Looking at the list, I can see an argument for it.
Also, should we simulate acidity? It would probably be similar to how we deal with salinity if implemented.
As Mass Increases, Environmental Tolerance Range Decreases
Many of the most extremophilic organisms are small and simple, such as Archaea and other prokaryotes. For example, the vast majority eukaryotes inhabit relatively “average” environments and are anaerobic. The latter fact is largely to do with the fact that oxygenic metabolism is the most powerful form of energy production available to life. As to the former, @Bird notes that for more complex organisms, it can become a lot harder to specialize around extreme temperatures with so many moving parts. For example, eukaryotes have various incredibly complex enzymes and proteins necessary for functioning which have very specific preferences in terms of environmental conditions. Imagine this compounding for multicellular organisms, who must ensure that every part of the colony survives.
In terms of gameplay, this can mean that as your organism increases in size, you will have less of an inherent tolerance to certain environmental factors, hence necessitating the placement of more dedicated parts. This can effectively mean that eukaryotes will have to spend more energy adapting to an extreme than a prokaryote might, and the same for larger eukaryotes/multicellular organisms and smaller eukaryotes. This can also slide into how we deal with the fact that LUCA will have to have extreme environmental tolerances despite lacking any specialized adaptations.
Surface Area and Volume
More on this here: Surface Area, Volume, and Ratios - #8 by Buckly
While surface area and volume are still being brainstormed about, they have strong effects on environmental tolerances. A higher surface area to volume ratio means less resilience in the face of environmental extremes. Think of a deciduous leaf vs a coniferous leaf - it’s skinnier, meaning less captured light but less of a chance for a flimsy structure to freeze over.
What will this mean for Thrive?
We generally want smaller and more compact organisms to be a bit more resilient to environmental extremes. Organisms with less surface area in comparison to volume and organisms with less mass will do better in extreme environments, such as the depths, vents, and shelves than with higher surface area to volume ratios and larger organisms. In the Microbe Stage, this will effectively mean that prokaryotes will be more capable in adapting to the environment than eukaryotes. In the macroscopic stages, this will mean that players will have to adjust their morphology to live in their preferred habitats.
I think this can be simulated by just decreasing the “steepness” of the ATP debuff outside of a preferred environmental range for smaller, more compact organisms. For example, a tiny prokaryote slightly out of its preferred habitat will receive a +2 osmoregulation cost increase, while a large eukaryote would comparatively receive a +10 osmoregulation cost increase. This could part of how we address the Thrivian “LUCA having no adaptations yet being perfectly adapted to extreme environments” paradox.
This will probably mean that most players will drift towards the surface patches as they increase in complexity, which is completely okay. Complex macroscopic life probably started in shallow, oxygen-rich waters: Shallow Waters Allowed Early Fish-Like Creatures to Experiment With Evolution.
How Will We Deal With Patch Migration?
Here is an important question to answer: how will we address patch mobility when we begin simulating environmental tolerances? Right now, you move with a small population into a new patch, from which you can grow a new local population. If you die out in a local patch, you get to choose any of the patches your species currently inhabits.
How will this logic work with environmental tolerances? Wouldn’t the player basically be hurting their original population if they decide to change tolerances and biomes? I guess this would be balanced enough if you move between two similar patches, but what about transitioning from one extreme to another? For example, transitioning from a vent to an abyssal patch, or transitioning from a surface to a polar patch? Perhaps successfully reproducing in a new patch can give you the option of migrating the majority of your species in a former patch to the new one?
If we agree on things related to the above ideas discussed, then I think we will have a very solid understanding of how to simulate environmental tolerances for the rest of the “biology” part of Thrive. Then, we can focus specifically on exactly how players can adapt to these conditions. I think the question for that is considering whether or not we want to have environmental factors be completely dealt with via placing down parts, or have sliders in the membrane tab as well.
Once that is decided, I think we’ll finally have a cohesive plan for replicating a phenomenon as complex as simulating the ways in which life adapts to its environment.