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MagiMaster · 06-17-2010, 10:33 PM

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.

06-17-2010, 10:33 PM	#2
MagiMaster Join Date: Jan 2007 Location: Your imagination	Re: GURPS: Ecosystems and Evolution 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.