GURPS: Ecosystems and Evolution
 

Originally, I had intended to write this up for Pyramid, but I didn't get everything together in time for the issue it was most suited to. It might still fit in the Monsters in Space, but I don't know how posting it here would effect that. Either way, since I still haven't worked out all the details, and I posted a good chunk in the Sewer Ecology thread already, I decided to go ahead and post what I have.

Whenever a GM is preparing an environment for an adventure to take place in, the question of "what are these things eating" always comes up. Depending on the setting, answering that question may or may not be important enough to bother with. This is for those times that it is. This information is meant to supplement the information given in chapter 6 of Space.

Table of Contents
Ecosystems
Trophic Levels
Food webs
Creatures
Worked Example

The second part was/will be Evolution which gives some guidelines for creating evolutionary trees using the alien creation rules, but I've got significantly more to do on them, so I'll put it off until later.

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Ecosystems
For world building purposes, a good definition of an ecosystem would be an environment and the things that live there. The first step in designing most ecosystems is to determine how big it is (in square miles for this system). Few creatures move between two different ecosystems, but those can be dealt with later.

For any ecosystem, the most important question is, where is its energy coming from. For most places, the answer would be the sun, but other answers exist (deep ocean vents and seeps, chemosynthetic life inside rocks, etc.). Where the energy comes from decides what the life will look like, but those details will be left to the GMs imagination. How much energy the ecosystem is receiving will determine how many creatures will live there. For all ecosystems, this can be boiled down to how much biomass (in pounds here) is generated at the first trophic level, the producers.

Sunlight
Earth ecosystems that depend on sunlight vary greatly in how much energy is converted into biomass, from about 50 lbs per sq. mile per day to about 40,000 depending on the water and other nutrients available. For comparison (from Wikipedia) -

• swamps and marshes: 37,500 lbs per sq. mile per day
• tropical rain forests: 30,000
• algal beds and reefs: 30,000
• river estuaries: 27,000
• temperate forests: 19,000
• cultivated lands: 10,000
• tundras: 2,100
• open ocean: 2,000
• deserts: 50

For planets other than Earth, pick a number based on similarities to the examples above, multiply it by the star's luminosity (in solar luminosities) and divide by the square of the orbital radius (in AU).

Other Energy Sources
On Earth, about 900,000,000 watts per sq. mile is absorbed by ground and water on the surface. This is averaged over the entire planet though, so it will be greater near the equator (about 25% more) and less near the poles (about 25% less). Of this, roughly 1% to 5% is converted by plants into chemical energy.

Combined with the numbers above, any energy source that can be rated in watts can optimally be converted to biomass at the rate of about 30,000 watts per (lbs per day). Unfortunately, not many energy sources can easily be expressed in watts.

Radiation, for example, is not directly measurable in watts, but some natural neclear reactors give us an idea of what to expect. These natural reactors only lasted for a few hundred thousand years and only produced an average of 100,000 watts, which would only support a few lbs per day. Fictional planets might have some geological processes that could increase this, but such places would be extremely dangerous to adventurers.

Thermal energy is probably a better place to look. While hot objects carry a lot of energy (in fact any object at about 75 F radiates about 40 watts per sq. foot), it's generally useless if everything's the same temperature. To get energy from heat, it has to be moved from somewhere hot to somewhere cold. Transforming a temperature differential into work is not straightforward. Currently, I have no idea how to transform a hot temperature, a cold temperature and an area into a maximum wattage.

Some forms of energy can be converted directly into biomass without worrying about watts. Things like chemical plumes and waste runoff from another ecosystem are best measured in weight per day. Simply assume that some portion of the input, depending on the type, is transformed into biomass at the first trophic level. I don't have numbers for hydrothermal vents or rainforest canopy refuse, but both would be appropriate examples.

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Trophic Levels
Trophic levels are a simplified view of how food webs work. If you assume that things only eat from the trophic level immediately below themselves, it basically works, but many real animals eat from multiple levels.

The first trophic level consists of the primary producers. In most Earth ecosystems, this consists of plants. The second trophic level consists of things that eat the primary producers. If plants are the first level, these would be herbivores. The third and higher levels are carnivores. How many levels can be supported depends on how rich the ecosystem is. Besides the main trophic levels, there are two secondary energy sources: excrement and dead bodies. Depending on how rich the ecosystem is, both of these sources can produce their own series of trophic levels.

At each trophic level, half of the biomass is lost to non-predatory deaths. This portion goes to the scavengers and decomposers. The consumers from the next trophic level eat the other half. Half of what is eaten is lost as excrement. Half of what's left is lost to respiration. This portion becomes various gasses and vapors and is generally unrecoverable on the small scale. (On a planetary scale, it's recycled as part of the conversion from energy to primary producers, in general.) Finally, the remaining portion is used for the growth and reproduction of the consumers. That means the each trophic level contains approximately 1/8 the total biomass of the trophic level below it.

The biomass at each level needs to be divided among the various species at that level. While there are no rules for this, a reasonable guess would be to give somewhere between 1/2 and 1/5 the biomass to the most abundant species, between 1/2 and 1/5 of what's left to the next, etc. until the biomass remaining is too small to support another population (see below for transforming biomass into populations).

The amount of biomass in the first trophic level has already been dealt with in the previous section. Use this to determine the biomass for each new level until there isn't enough left to support any populations within the new level. In some ecosystems, the levels might stop one short of this, but few ecosystems are likely to be short more than one level short in the long term. From the final trophic level, all of the biomass goes to scavengers and decomposers as there's nothing that hunts the creatures there.

Finally, determine the totals are for waste and corpses. As a shortcut, about the dead plant matter totals about 50% of the biomass of the 1st level, the dead animals total about 7%, and the animal waste totals about 28%. If these numbers are high enough, there might be creatures that prey on these creatures, so fill in any further levels there. I don't have any numbers, but it's reasonable to assume that both of these numbers should have some conversion efficiency factor applied to them. I'd guess that it'd be in the range of 1/10 to 1/2 for the waste and 1/4 to 3/4 for the corpses. After all, things are willing to expend the energy to avoid having to eat these things, so there must be a reason.

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Food webs
Trophic levels are a useful simplification, but a real ecosystem is rarely that simple. A better model is the food web. Most of the same ideas are useful in building a food web, but the process is a little more involved.

Start by making a list of all the primary producers in the area, and distribute the biomass among them. At this point, the scavengers and decomposers can be added using the percentages listed above to determine their biomass. (Ideally, it'd be possible to list all of the species before continuing, but it's very likely that add species as you go will be easier.) Add further species one at a time, drawing arrows from what they eat to them. (This is what makes it a food web.) Each of the arrows needs to be labeled with how much biomass is taken due to that particular predator-prey relationship. It's easiest to ignore the non-predatory losses for a second and say that all the arrows out of one species should add up to the biomass available to that species.

When deciding how much goes which way, a good rule of thumb is that a predatory gets most of its food from one or maybe two target species, but occasionally eats some other things. However things gets layed out, each species, besides the primary producers, gets a biomass of 1/8 the total of all the arrows coming in to it. It's possible that some of the species may end up with too little biomass to support a stable population and must be trimmed or find something else to eat.

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Creatures
Knowing that a species has 100,000 lbs of biomass available for growth and reproduction doesn't tell you much about the individuals making up that species.

First make sure that the creatures can eat what the diagrams say they should be able to eat. The evolutionary arms race necessarily leans in favor of the predators, though it's usually very close. Also, predators are rarely smaller than their prey by more than one or two SM.

The first thing we want to find out about the species is how individuals there are. The population of a species should be (how much food the species is eating)/(how much food an individual eats). The first will be 4 times the biomass for growth available to the species. The second is more difficult.

Bigger animals tend to require less food in proportion to their body weight, as do cold-blooded animals and animals with particularly efficient hunting methods. The alien creation rules from Space will be helpful in narrowing down the possibilites.

As a baseline, we should consider which Earth animals eat the most and the least compared to their body weight. On the high end, Hummingbirds can eat 5 times their bodyweight per day in nectar, and shrews can eat almost their bodyweight per day in insects. Both of these are small and warm-blooded. The hummingbird flies and the shrew digs. On the other end, large constricting snakes can eat around 1/200 of their body weight per day (on average).

Kleiber's law says that an animal's metabolic rate is proportional to the 3/4 power of its mass, meaning what the eat realted to their mass is proportional to the -1/4 power of body mass. Using this to correct for size, the flying, warm-blooded, gathering herbivore has a metabolism of about 1.25 while the slithering, cold-blooded, pouncing carnivore has a metabolism of about 0.0125. This suggests that the general formula would be 1.25 times (weight to the -1/4 power) times some correction between 1 for the most active animals and 0.01 for the least. The table below gives some guesses for this correction factor based on the alien creation categories from Space. Multiply the numbers from each subtable.

Tables to be added as I can figure out the numbers.

After working out how much an individual eats, get the population from 4*(biomass of species)/(consumption of individual). If the population is less than around 100 or so, it's almost certainly too low to survive in the long run. Either find something else for them to eat, or remove them from the area. If it's between 100 and 1000, they'll probably survive, but it'll be a struggle. Adventurers or settlers could wipe them out fairly quickly. Over 1000 and they'll probably be fine. No small group of adventurers passing through will significantly dent their numbers, though settled people can systematically eliminate them over time.

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Worked example

The worked examples are being saved for the final publication, at least for the time being.

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Logged as a reference thread :)

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I'm looking forward to seeing how this turns out.

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Thanks for the comments. There are still some holes in things that I might need some help filling in. Anyway, I'm going to be away from the internet for a week or two so it might be a bit before I get the worked example up.

Re: GURPS: Ecosystems and Evolution
 

...And I think this is exactly what I've been saying I wanted in every Beastiary thread...

While something official would be nice, this will do nicely for now. Thankyou.

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Just glancing through before bed, and, yeah, pretty much exactly what I was looking for, but leaves me with a couple of queries/suggestions:

Would eyeballed figures for how much biomass might be available at various mana levels for ecosystems where deriving energy from mana be reasonable?

At a guess, by analogy for your figures for different biomes: 0-50 at no mana, 2000 or so at low mana, 10,000-20,000 at normal mana, 20,000-30,000 at high mana and 30,000-40,000 at very high mana?

All extremely interesting and potentially useful, though something that I'd potentially find useful is reasonable energy expenditures for hunts in GURPS (i.e. fp) terms. Is that even possible to figure out or derive?

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I think originally intended to add something about mana, but I forgot. I'll fix that when I have more time. In the meantime, and without going through all the math to get a usable number for this system, the Heat spell generates 53000 watts per 2 FP when used on a 1 cubic yard object.

For the second question, yes, I think it'd be possible, though I haven't worked out the details yet.

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Participating is the best of all things. Elves can tell, the Yrth ones and Rudran's, too :) It is irrelevant if it's official or not, as long it is suffciently original and well thought-out. I'll keep this in my bookmark library. It's too good to be missed. May I copy-and-paste some or allt to a text file, printing it and reading it ofline?

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I think that something like this, probably with more detail, could well make its own stand-alone supplement, much like City Stats.

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Good idea! I'd gladly pay a few euros for that!

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Likewise, I would pay a few dollars for it. Even if it is posted in its entirety here first, I'd still buy it in support.

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And I'd gladly pay a few pounds for it.

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This would make an awesome Pyramid article or supplement and you should definitely submit it once it's finished.

I'm finding this paragraph difficult to understand and interpret. It would help if you could clarify how to calculate things. For example, is "3/4 power of its mass" = mass^(3/4)? And what are the proportions based on? For one thing, "cold-blooded" and "warm-blooded" are actually short-hand for a number of different metabolic traits that can each have a variety of values. Even the GURPS advantages and disadvantages related to them should really be divided up.

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(I'm still away, so I haven't really gotten any actual work done on this yet.)

Thanks for all the support. If I can make this fit into either format, I'll submit it and see how it goes.

Yeah, 3/4 power of mass means mass^(3/4). I'm not sure of a better way to put that, but maybe I should just do what Space does and write out the equations.

I'm not sure what you mean by "what are the proportions based on". For most things like "warm-blooded" and "cold-blooded" I intend to use the alien rules, which covers things with a little more granularity than the disadvantage does. (I suppose for a standalone publication, I'd need to make it so that it doesn't really too much on Space, but for a pyramid article, you'd probably have to have that book to use this.)

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This may belong in a separate thread, but I've never learned if the 4th ed. Space rules for aliens are the updated version of the rules for aliens in Uplift, or an entirely new set of rules.

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Wikipedia isn't always the best source for information.

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@Vaevictis, I don't have Uplift, so I can't tell. Wherever they came from, they're very well done though.

@Ragitsu, can you be more specific? Wikipedia may not be the best source, but it's almost always good enough, and if I need more there are references at the bottom to get me started. For this project though, I think everything I've found has been good enough for use in a game.

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No you're not. You're right there. I see you. ;)

Allow me to duplicate the "This could make a great article/supplement" sentiment.

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Wikipedia reflects people's common knowledge of what they remember from something they read, and so articles can get changed from actual information to reflect common knowledge instead of actual reality.
So if you can't see the real sources, anything on the Wiki needs to be taken with a grain of salt due to what the freshmen who updated the article misremembered from class.

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Essentially, yes. Then, there are the petty motivations of the moment that interfere with long term objectivity.

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thanks, will be looking forward to the write up.

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Those of you bashing Wiki, can I ask how that's relevant to this thread? Is there a particular article or factoid from an article that yall feel is incorrect? On one hand, I do want my information to be somewhat accurate. On the other hand, it's just a game and the results need to be simple enough to be useable in that context, so little differences aren't going to matter. (Also, I haven't noticed a significant number of technical articles that are wrong. Poorly worded or incomplete sometimes, but rarely wrong outright.)

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Actually to simply settle sources, its better to check the sources used to make the wiki article than just the wiki article itself.

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Bookmarked, and eagerly anticipating more.

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Well if this doesn't find a home as an article/supplement it welcome a home over on the GURPS Wiki

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Another good idea. Wyh didn't I bookmark this link?

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I still need some help converting a temperature gradient over an area to (maximum) watts, if anyone knows which equations I should be looking at.

Anyway, for mana, normal levels probably shouldn't be worth too much biomass, since it'd be in addition to the energy from sunlight in most places. Very high mana should probably be a little less than the maximum for sunlight, so a pitch black cave with very high mana will be about as lush as a rain forest or reef, but not as overgrown as a swamp. This would also mean that a swamp in a very high mana area will be oveflowing with life. Normal mana should probably not even support as much life as cultivated lands without some other energy source or it'd start to (more than) significantly raise the overall abundance of life.

Are there any other interesting energy sources I'm overlooking? Kinetic energy (in wind, water, whatever) sounds too far out there. Electricity, lightning specifically, might deserve a paragraph, even if it's already in watts.

(Note to self: add a paragraph about taking away energy sources.)

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In some sci-fi universes, maybe psionic? (Thinking about Planet in Alpha Centauri here)

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I don't think that the psionic powers in Alpha Centaur actually fed the life there, just connected it. On the other hand, treating it like mana would be pretty easy.

Another question I need to write down: If you have four animals, A consumes its body weight per day, B is just like A but has trait X and consumes 3/4 its body weight, C is just like A but has the (non-conflicting) trait Y and also consumes 3/4, and D has traits X and Y. How much should D consume?

Let's see:
A has a modifier of 0.8
B has a modifier of 0.6
C has a modifier of 0.6
D probably has a modifier of either 0.4 or 0.45 (additive or multiplicative)

Hmm... I can't currently see any good reason to pick one over the other and I can't think of any RL animals that fit so nicely into the kind of lists I need.

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Well, rethinking the problem with converting heat to watts, I think I have a first draft of an answer. The Stefan-Boltzmann law says that a hot surface emits energy at a rate of emissivity * constant * (temperature in Kelvin)^4 in watts per sq. meter. The Carnot efficiency is the maximum theoretical efficiency a heat engine can attain, though the endoreversible efficiency gives slightly more reasonable numbers. Multiplying the two gives an answer that's not completely unreasonable, but may be somewhat too big. For a hot temperature of 200 F and a cold of 50 F, I get about 290,000,000 watts per sq. mile, which converts to about 9,500 lbs of biomass per day, which seems high. Either I've got the wrong equation, or there needs to be a conversion efficiency on top of everything else (1% - 5% probably).

Anyway, can someone else play with the equation a bit and see if there are any cases where it gives really obviously wrong results?

Th equation is: 5.67*10^-8 * e * Th^4 * (1 - sqrt(Tc/Th)) * 86
Where: e is emmisivity of the surface (0.9 is an average for rock), Th is the hot temperature in Kelvin and Tc is the cold temperature in Kelvin. (5.67*10^-8 is the Stefan-Boltzmann constant, and the 86 is converting watts per square meter to lbs of biomass per square mile per day.)

Edit: I can't decide if it'd be Th^4 to Tc^4. On one hand, the hot side is what's supplying the energy. On the other hand, if more energy is being transfered than what the cold side is radiating away, it wouldn't stay cold. Also, if you use Tc^4, lowering the cold temperature while keeping the hot the same would lower the power produced. I'm not sure that makes much sense.

Edit again: Oh yeah. My wife also mentioned adding belief to the list of energy sources. I'm not quite sure where to start with that one.

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That's mostly not a useful value (it depends on the design of your heat engine); for any real source what matters is the rate at which the temperature gradient recreates itself when consumed, as the total energy of a reasonable temperature gradient is not large.

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I'm looking for the maximum possible wattage. I know that any real system will be below that. Anyway, how would I estimate how quickly the gradient is being consumed? I'm assuming that the temperatures don't actually change significantly over time, since it's stable enough for life to evolve around it.

(Note to self: Add a comment on energy cycles.)

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Depends on the efficiency of thermal transport; theoretical max is insanely high.
You can assume that anything in an equilibrium state is consuming heat as quickly as the heat is generated. Thus, you really just need to figure out how fast the heat is being generated, and assume that the maximum percentage of that heat which can be captured to do useful work is equal to the carnot efficiency.

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If it's in equilibrium, then the heat generated and the heat radiated should be the same (though conduction is more efficient than radiation, which is what most hat engines would use). The Stefan-Boltzmann law gives heat radiated, and that's what I've got above. It still seems like I'm doing something wrong, but I can't figure out what.

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The easy answer would be (3/4)^2, but it's probably also wrong. Trait X and trait Y are presumably biological traits, and how they interact with each other in the body of animal D depends entirely on the animal's physiology and what exactly the two traits do to the animal's metabolism, and to its other bodily functions that ultimately impact its energy budget. I think the question is just too complex to answer, except by conducting in-depth studies of real animals.

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While I agree that this is a gross oversimplification of real metabolisms, I'm just wondering which of the two options (or what other options) produce the least bad results. Bad results in this case don't mean just unrealistic, but ungameable too. Currently, neither seems to win out on either simplicity or obviousness, and I don't know what else to go on. I can't study this on real animals without another degree and some significant grant money.

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Of course, I know you probably can't study it that way. I wasn't suggesting you should. I was just saying, that's what it would take to find a realistic answer.

For an answer that seems plausible and simple enough to use in a game, I think multiplicative makes more sense. But if X and Y are Advantages, I don't know whether multiplication or addition would be more fair and balanced.

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The Xs and Ys from Space are a combination of advantages, disadvantages and 0-point features.

The equation was 1.25 * factor * mass^(-1/4) for fraction of body weight eaten per day. So if factor can be broken down into (factor1 * factor2 * ...), each factor needs to be between 1 and some number depending on how many factors there are (and their relative importance). For the moment, imagine there are four factors that coud be either 1 (most active), 0.6 or 0.3 (least active) each. Are there any combinations of mass and factors that gives really weird answers?

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I'm working on the factors some and I was wondering whether anyone else thinks that the IQ of the species has anything to do with how much they need to eat. I can seem a number of arguments in both directions (from more efficient hunting to more energy spent on brainpower), so maybe it just balances out. Either way, it would be a small effect and may not worth bothering with.

Also, how would special abilities, such as projectiles or invisibility change things? Would those also tend to balance out?

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I've heard convincing arguments that brain power is correlated with calorie budget. Basically, brains are energy intensive organs that cost fuel whether they are used or not. Creatures with a large energy budget can afford to spend some of that on a big brain with lots of processing power. As the metabolism gets lower, the same brain costs a correspondingly larger amount, and is a correspondingly larger drain on the animal's available resources. This is borne out by trends seen in animals. Mammals and birds tend to be smarter than reptiles. The smartest reptiles - monitors and crocodillians - also have the highest aerobic metabolism among reptiles. Reptiles in general tend to have more complex behaviors and learn faster than amphibians (which have a corespondingly lower metabolism), and snakes (which have a low metabolism) seem fairly stupid compared to more active lizards. Many of the warm blooded "fish" (such as the lamnid sharks) are noted as having sophisticated behavior that would correlate with higher intelligence than expected for typical fish.

Luke

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Thanks for the info. So far I've got the following categories of factors (sorted by my guess at relative importance):
- Trophic level (Aliens II)
- Locomotion (Aliens III)
- Temperature control (Aliens VI)
- Intelligence (Aliens IX)
- Skin (Aliens VI)
- Strategy (Aliens VII)
- Gestation (Aliens VII)
- Organization (Aliens IX)
- Mating (Aliens IX)

I think the first three are the biggest factors, the next three are medium ones, and the last three are fairly small.

Some of these lists are kind of long and complicated, so I don't have numbers to attach to them yet. I might can generalize Skin by the DR and TT it grants, but I'm not sure anything else generallizes easily. (IQ could be used, but it's a small enough range either way.)

Edit: Oh yeah. I'm also not sure if autotrophs fit into this scheme or not, but I guess I'll have to wait until it's more complete and see.

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lwcamp is right about the brain being a hungry organ. The theory about human evolution is that our ancestors couldn't have larger brains until they started eating significant amounts of meat. Meat has denser energy than plants and is also easier to digest, allowing us to have smaller guts and shorter intestines.

Well pure autotrophs shouldn't consume anything, right? Even an Earthly carnivorous plant will only consume what it needs for minerals it can't get in the soil. So it should only matter for mixed autotroph/heterotroph creatures like lichen, and then I think a big factor is what % of their carbon is primary production and what % is consumed.

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For this system, I have a given biomass equivalence of the primary energy source, and I'm using consumption to estimate the population, so I think I'll have to come up with some kind of figure for autotrophs, but it may not us the same formula. I think I remember reading that the power of mass for plants is different.

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Talking about a larger equilibrium -- the system containing the heat difference and the life form is presumably persistent, which will only happen if there's a heat source and a heat sink and the two are in balance.

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There's also the recent evidence of an island-bound goat, now extinct, that adapted to a poor and restricted environment by reducing metabolic rate more and more and more... and one of the primary casualties was its brain, which was reduced to reptilian proportions. They're guessing it actually became virtually ectothermic by the end, before IIRC human sailors showed up and ate it.


EDIT: Good source:
http://www.physorg.com/news177755291.html

Humans settled and ate it. Also they reduced eye size significantly, another complicated organ.

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Ok. I'm finally back at my own computer.

Does anyone disagree with my assessment of the relative strength of the various factors, or the inclusion or exclusion of certain factors?

Also, I've been trying to rate the traits within each category on a scale from giant snake at 0 to hummingbird at 10 (meaning some things might be higher or lower than that). Since some of these tables get pretty big, I'll just do one or two at a time for now.

The first one would be from Alien Creation III, locomotion. (I would do II first, but it's really hard to work out good numbers for that one.)

• Immobile - -7
• Slithering - 0
• Swimming - 5
• Digging - 8
• Walking - 5
• Winged Flight - 10
• Floating - -4
• Bouyant Flight - -4
• Climbing - 8
• Solar Sail - -4
• Rocket - 20

(Note to self: Don't forget FP for hunting and what things eat.)

Edit: Another note to self: Don't forget about creatures existing in multiple ecosystems.

Edit again: Actual numbers for consumption per body weight (or just consumption and body weight) are hard to find for real animals. The really low and high end species get noted as being special, but in between no one bothers to write it down if they know at all. Anyway, if anyone runs across any actual numbers, can you let me know?

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Hmm... I'm working on the numbers for those tables, and something got me wondering. There are two entries for warm-blooded: warm-blooded and warm-blooded with 2 levels of metabolism control. Which one would need more food on average? I'd guess the one with the metabolism control, but not by much.

Anyway, I've almost got the tables ready, but I'm going to need some help looking them over and making sure they make sense.

Edit: Oh yeah. I'm guessing that a large snake does have the cold-blooded disadvantage, but a hummingbird doesn't have metabolism control.

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IANAB [Biologist] but, I'd assume that since controling metabolism takes energy (in exchange for better survival if you can keep fed), the one that would need the more food is the one with the metabolism control.

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Being able to lower one's metabolism to suit times of lean would reduce the amount of food needed not increase it.

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...I really should start reading the book text before making comments like that, aheh.

Re: GURPS: Ecosystems and Evolution
 

Been lurking on this thread, but I thought I should mention three things which may be relivant. I will point out that I am not a fauna expert, and even my knowledge of flora and the vegetation related aspects of ecology are constrained to a couple of geographically specific examples of a few biomes.

Firstly, reproductive strategies and rates. The conditions underwhich a population of a particular organism can reproduce can have dramatic impacts upon it population size. However, if these are very specific or rare, it can be dovetailed with a dormancy strategy. The crustacea which appear within the ephemeral Lake Eyre in Central Australia are an example of this.

The other point relates to food sources. The koala and the panda are both very specific about what sort of food they eat. In Australia some macropods will graze tussock grasses, whilst feral goats will eat the weedy patches of blackberries which grow next to them, as they contain less silicates.

Finally there are the impacts of symbosis. A wallaby which grazes on fungi that occurs in woodlands and forests, and thusly spreads the fungi spores around, can be elimated by colonising carnivores, such as dogs. This could have an impact upon the growth of the trees which rely upon the fungi for nutrient transfer. However the imput of another omnivore, say feral pigs, could possibly reverse this.

IMHO, there could be utility in defining the 'stamp collection', as opposed to the component 'stamps'.

Re: GURPS: Ecosystems and Evolution
 

I found the data very interesting, but I have to admit that I have no idea on how all this could be useful in a game (or even in worldbuilding).

Sure, designing a believable food web when creating the fauna for an alien world could add some "realism" in a very hard-sf game...
But I fail to see how calculating "total lbs of biomass produced per day" for a given space could impact a game.

Re: GURPS: Ecosystems and Evolution
 

@Flyndaran, I agree, but would they need (a little bit) more food on average to be able to do that? I think so, but I have no evidence either way. Do you think camels or bears would qualify for metabolism control?

@Luke, thanks for the info, but I don't know what you mean by stamp collection vs stamps, or what you were trying to point out with the picky eater examples. I know the simple method doesn't single out exactly what eats what, but that's why it's simple. The more complicated method answers that question at the expense of taking more time and effort. Also, for the moment, this is all for a stable ecosystem, not one dealing with invasive species or colonization. (Though I should comment on such things elsewhere.)

@Lupo, I agree that the pounds of biomass per day isn't that interesting by itself, but it's what the whole food chain is based on. Together with some other numbers (which I'm still working on) you can get things like the population in the area, and what eats what and how. Those kind of details are interesting to a world builder. (For example, this can answer the common question of how can such a place support such a big predator.)

Thanks for the interest. Please keep asking questions. I'll post the tables for consumption per day soon. I've got them mostly worked out even though they look a little off in places. I'll have to get yall to help me look over them.

Re: GURPS: Ecosystems and Evolution
 

Okay. Here's some numbers to play with. These are still in need of some simplification, so don't bother commenting too much on the fact that there are too many digits in most of these. Anyway, to reiterate, the procedure here is, take the product of all the relavent numbers, multiply that by 1.25* (mass in lbs)^(-1/4). I'll get to autotrophs later, since I think they don't follow the same formula. In the mean time, let me know if any of these numbers seem off to you. Thanks.

Niche

• Decomposer - 0.305
• Scavenger - 0.205
• Omnivore - 0.205
• Gathering Herbivore - 1
• Grazing/Browsing Herbivore - 0.305
• Pouncing Carnivore - 0.115
• Chasing Carnivore - 0.45
• Trapping Carnivore - 0.0675
• Hijacking Carnivore - 0.205
• Filter Feeder - 0.027
• Parasite/Symbiote - 0.0675

Locomotion

• Immobile - 0.26
• Slithering - 0.44
• Swimming - 0.505
• Digging - 0.76
• Walking - 0.505
• Winged Flight - 1
• Floating - 0.34
• Buoyant Flight - 0.34
• Climbing - 0.76
• Solar Sail - 0.34
• Rocket - 3.95

Temperature

• Cold Blooded (w/ disadvantage) - 0.225
• Cold Blooded (w/o disadvantage) - 0.37
• Partial - 0.605
• Warm Blooded - 1
• Warm Blooded (w/ metabolism control +2) - 1.2

Skin

• Soft Skin - 1.15
• Normal Skin - 1.1
• Hide - 0.925
• Thick Hide - 0.795
• Armor Shell - 0.735
• Blubber - 0.54
• Scales - 1.1
• Heavy Scales - 1
• Fur - 0.925
• Thick Fur - 0.735
• Thick Fur over Hide - 0.63
• Spines - 0.855
• Feathers - 1
• Thick Feathers - 0.795
• Feathers over Hide - 0.68
• Light Exoskeleton - 0.925
• Tough Exoskeleton - 0.795
• Heavy Exoskeleton - 0.735

Reproduction

• Spawning/Pollinating - 0.79
• Egg Laying - 0.975
• Live-Bearing - 1.25
• Live-Bearing w/ Pouch - 1.35
• Brood Parasite - 0.925
• Parasitic Young - 0.875
• Cannibalistic Young (parent) - 0.875
• Cannibalistic Young (siblings) - 0.925

Strategy

• Strong K - 0.97
• Medium K - 1
• Median - 1.05
• Medium r - 1.05
• Strong r - 1.1

IQ

• Mindless - 0.66
• Preprogrammed - 0.745
• Low - 1
• High - 1.15
• Presapient - 1.2

Mating

• No bond - 1.05
• Temporary bond - 1
• Permanent bond - 0.985
• Harem - 0.945
• Hive - 0.89

Society

• Solitary - 1.05
• Pair-bonded - 1
• Small Group - 0.97
• Medium Group - 0.945
• Herd - 0.89

Re: GURPS: Ecosystems and Evolution
 

Someone on a different forum said that a tarantula fed 25% of its body weight once a month would grow, so that's about 1% per day on average. The tables above give about 6.5% per day. (I'm assuming the tarantula weighs 0.15 lbs.) So these numbers don't quite work right, but I don't know which ones need the most work. Does anything look off to anyone else?

Edit: Updated the tables with some better numbers. Tarantulas get about 3% now, which is probably close enough, even though using this would predict about 1/3 the population. I need to look back over things and see what's left. I'm getting some help on another forum for the thermal to watts question. I still need to write up the FP used to hunt question, but I have some ideas there. Is there anything else I need to add?

Edit again: I think the right equation for thermal energy is 1,700,000*(Th - Tc)*(area in mile^2)/(height in ft)*(1-sqrt(Tc/Th)). So the previous example of 200F to 50F would give about 47.5 million watts now (with a 20 ft ceiling), instead of 270 million. I think that's a bit more reasonable. I might need to find some way to simplify that though.

Re: GURPS: Ecosystems and Evolution
 

Ok, if there's nothing else missing, I think I have enough to write up an e23 submission. I think I'll leave the worked examples for the submission.

One other question: would anyone be interested in the Evolution section on suggestions for making the life on a planet look like something that could have evolved there instead of something placed there? I'll probably include it anyway, unless I run out of space. I'm just curious how much effort to spend filling it out.

Thanks for all the interest so far. I hope that the finished product lives up to the expectations. :)

Re: GURPS: Ecosystems and Evolution
 

Mostly these numbers look reasonable to me.

Grazing/Browsing Herbivore should be much larger, indeed larger than 1, unless you want to make separate categories for "in an ecosystem where plants/krill/whatever are easy to digest" and "in an ecosystem where plants/krill/whatever are hard to digest."

I am interested in the other section you mentioned, though I can't afford any e23 products until I find a job so maybe I'm not the person to ask. But it does sound like a worthwhile thing to include if there's room.

Re: GURPS: Ecosystems and Evolution
 

Yeah, that makes sense. Would 1.2 be about right? (I should look up some details for some RL grazers and see what that'd suggest.)

Edit: Hmm... I found some info on whitetailed deer that suggest they eat about 3% of their body weight per day. For a 200 lbs deer, that'd give a factor of 0.09. My current numbers give 0.18. If I raised grazers to 1.2, it go up to 0.71. Either grazing is roughly right (grazers may eat low energy food, but they don't spend much energy getting it) or some of my other numbers are really far off.

(I should point out that I'm probably going to just accept an error of a factor of 2. I don't think such a simple formula can really do better than that.)

Re: GURPS: Ecosystems and Evolution
 

I don't think you can combine browsers and grazers together. In fact, I don't know that you can combine ruminants and non-ruminants together. Cows, hippos, and elephants eat different proportions of their body weights each day, for example. It depends on how generic you want to be, but I would at least separate browsers and grazers, or better yet provide a "high-efficiency browser/grazer" and a "low-efficiency browser/grazer" so that the categories aren't Earth-specific.

Re: GURPS: Ecosystems and Evolution
 

I'm trying to stick to the categories in GURPS Space, which combines grazing and browsing. BTW, what would a high-efficiency grazer be? That sounds a lot like a gathering herbivore. Also, the day-to-day intake is below the resolution of this. All I care about is long-term averages.

Anyway, like I said, the current numbers predict the value for a whitetailed deer pretty well, so either the numbers I have for grazers is about right, or everything is off in a way that balances out for that one example.

I should mention the examples I've got so far, just to make sure I'm not doing something wrong with them:
- Anaconda, 215 lbs, eats about 0.3% body weight daily, Pouncing carnivore, Slithering, Cold-blooded (w/ dis), Scales, Egg-laying, Medium r strategy, Preprogrammed, No bond, Solitary
- Hummingbird, 0.0044 lbs, eats about 500% daily, Gathering herbivore, Winged flight, Warm-blooded, Feathers, Egg-laying, Medium K strategy, Low intelligence, Temporary bond, Pair-bonded society
- Tarantula, 0.15 lbs, 1% daily, Pouncing carnivore, Walking, Cold-blooded (w/o dis), Tough exoskeleton, Egg-laying, Strong r strategy, Preprogrammed, No bond, Solitary
- Deer, 200 lbs, 3% daily, Grazing herbivore, Walking, Warm-blooded, Fur, Live birth, Medium K strategy, Low intelligence, No bond, Small group

Re: GURPS: Ecosystems and Evolution
 

Well elephants are much less efficient than ruminants, of which the cows are significantly less efficient than hippos. And AFAIK grass is more difficult to digest than broadleaf plants, so I'm surprised that the writers collapsed grazers into browsers.

In Uplift, (assuming the Space system is based on the Uplift version from 3E) herbivores are divided into grazers (low-energy food, time-intensive), browsers (mid-energy food, less time-intensive), saprophytes (very low-energy food and time-intensive), and gatherers (high-energy food). Maybe saprophytes correspond to 4E decomposers?

Baleen whales and anteaters are listed under both grazers and gatherers, clearly a mistake. Krill and insects are meat, so gathering seems a more appropriate category. Perhaps they became the 4E filter-feeder category.

The other Uplift diet categories are pouncer (incl. trapper), stalker, chaser, herder, carrion scavenger, gatherer/hunter, opportunist browser, hunter/browser, pure ergivore, mixed ergivore, plant, and tapper.

Out of curiosity, what are hijacking carnivores?

Re: GURPS: Ecosystems and Evolution
 

They are big carnivores that can just scare off other predators from thier own kill. Of course, they have the ability to hunt themselves.

Re: GURPS: Ecosystems and Evolution
 

Space describes both grazers and browsers as consumers of lots of low energy food, with grazers as eating grass and browsers as eating leaves. Filter-feeders are described as generally sessile. I'd probably call a baleen whale a trapping carnivore, and I'm not too sure about an anteater, but they're probably closer to trappers than anything else.

Hijacking carnivores are described as fierce chasing or pouncing carnivores that get at least a portion of their diet by taking it from other carnivores. Lions might qualify.

Wiki has stats on elephants, so I can add them to my list of test points. My system predicts that a 20000 lbs elephant would eat about 1.8% per day, and the actual numbers come out to about 3% per day. That's within my factor of 2 margin of error. It seems like my numbers may not be too far off.

Anyway, just in case I made a mistake, here are the stats I'm using for an elephant:
- 20000 lbs, 3% per day, Grazing/browsing herbivore, Walking, Warm-blooded, Thick hide, Live-bearing, Strong K strategy, Presapient, Temporary bond, Medium group

Re: GURPS: Ecosystems and Evolution
 

Dang. I keep forgetting to write up my thoughts on FP used to hunt. I'm not sure whether or not I'll include it in the final version, but I did have some thoughts:

• Most animals would avoid going below 1/3 FP, since that'd put them in danger from other predators. They'd only burn past that if they were being chased by something already, or otherwise in mortal danger. Let's say most animals will avoid spending more than 1/2 FP at once. Since Basic gives every animal between 10 and 13 HT, they'd have 5 or 6 FP to spend on a hunt.
• It's below the resolution of GURPS, but increasing average FP expenditure should increase consumption. I'm going to make a wild guess that an average creature can expend up to its maximum FP in total per day without losing weight/increasing consumption.
• Pouncing carnivores probably spend this FP one or two at a time for extra effort.
• Chasing carnivores probably spend between 2 and 6 FP sprinting in a few chases per day. (Cheetahs: "Only half of the chases, which last from 20-60 seconds, are successful.")
• Trapping carnivores probably spend the FP building the traps. For creatures as small as spiders, it'd be reasonable to assume that making the webs costs FP, though only slowly. Trapping carnivores probably don't use up as much FP as most other carnivores.
• Hijackers spend FP as per their primary hunting technique, plus one or two for sprinting or extra effort when stealing a kill.
• Scavengers spend FP to sprint in, extra effort some food away, then sprint out (hyenas), or they spend FP hiking to food saving a bit to sprint away from trouble (vultures).
• Grazing/browsing herbivores spend some FP hiking and some for defences. They eat very low quality food, but spend very little effort to collect it (lots and lots of it.)
• Gathering herbivores spend some on extra effort to reach juicy bits of food, and some on defences.
• Decomposers (the moving kind) spend some on hiking or sprinting to get to their next meal, but then save everything else for defences.
• Omnivores do pretty much all of the above depending on the exact animal.
• Filter-feeders, autotrophs, sessile decomposers, parasites and symbiotes don't spend FP except on special defences, or hiking or sprinting while in a mobile form (larva or whatever).
• Of course, any animal might spend some FP on other things. These are just what I think the main expenditures would be.

Did I miss anything? Do you think this info would be useful to a worldbuilder using the rest of the system?

Re: GURPS: Ecosystems and Evolution
 

Mainly the FP estimates, I think - I was mainly wanting that for 'If in this ecosystem animals have evolved the ability to cast some spells, how much FP could be justified for a hunt'? - You've given enough to work from for that, I think.

Re: GURPS: Ecosystems and Evolution
 

Cool. I think cutting it down to that could make a useful info box.

Re: GURPS: Ecosystems and Evolution
 

Has the resulting article of this thread been published or has the info concerning autotrophs moved to another thread? If so could some post/share a link for it here or tell me where I would find it? I am extremely interested because I recently tried something similar only based on the number of species on earth per miles diameter. It would obviously be of different chemical basis for almost any planet based the world generation system from Space, but nonetheless it was still fun to imagine the possibilities. Anyways this post seems to have presented a more realistic way of generating an ecosystem.

Re: GURPS: Ecosystems and Evolution
 

I'd appreciate if everyone forgave the thread-necromancy, as well. This is fascinating, for me, as a world-builder, and I missed it, the first time around.

Also, a friend of mine is working on a space campaign, and I just sent him the link to this thread. :)

Re: GURPS: Ecosystems and Evolution
 

So, I have some questions as to what some equations go where, and how they relate to eachother.

My first is about the population of a species per their biomass. After following the thread back and forth several times, I have come to understand that the equation for the population of a species is either

4*(biomass of species)/(consumption of individual)

or

4*(biomass of species)/[1.25* (mass in lbs)^(-1/4)]

My question then is, am I correct?

My next couple questions have to do with generating the starting biomass for a world and some confusion garnered from Google research.

First I discovered some information concerning the conversion of solar luminosity into biomass via produced wattage;

According to

http://www.astro-ecology.com/Astroec...man_Future.htm

"Assuming a power requirement of 100 Watt/kg biomass"

and

https://www.cfa.harvard.edu/~dfabric...145/units.html

"1 Solar Luminosity = 1 Quadrillion Watts"

so our sun should be generating 140 trillion biomass, but I feel I may have misread something previously in the thread, and so therefore I moved onto this equation;

1,700,000*(Th - Tc)*(area in mile^2)/(height in ft)*(1-sqrt(Tc/Th)

and what I'm wondering is how to convert this for an entire world?
Maybe using the Average Surface Temperature or the blackbody temperature, but more likely the former.
I'm guessing based on your world type and the AST you could determine Th and Tc as extremes for the world, but then I begin to question the height portion.

So I humbly inquire;
Am I overthinking this?
If so is there a simpler way to approach problem that someone would be willing to share?