So, I’ve been looking up a lot of science discussions about aliens for an upcoming project (you’ll see) and it’s a bit of a rabbit hole to say the least. There are countless examples of aliens out there from Star Trek’s various foreheads to the tongue-in-cheek aliens of Futurama. But for a hard sci-fi setting like Eclipse Phase that won’t work. So how do you make some interesting but realistic alien ecosystems? Here are some resources.
Research Online
First off, see what other people have done. I’ve been reading a lot of interesting pages including this Reddit thread of ideas, this thread of a 1001 alien elements, this extensive case study on the fictional alien life of Snaiad, and others. There’s also plenty of inspiration in novels; the best examples for me are Legacy by Greg Bear and Cibola Burn by James S. A. Corey.
Even aliens that are pretty unrealistic can be helpful when you pull them apart. Take, for example, the craziness that is the Ewoks. While attempts have been made to justify Ewok evolution they make zero sense. Even if you accept that they can look like living teddy bears they are wholly unsuited for their environments, as evidenced by needing help from the human characters to traverse their own natural habitat. They have stubby fingers that can’t climb the massive trees of the forest, they live in three dimensions but can’t turn their heads… The list goes on.
Ewoks are clearly not a good inspiration for a realistic alien species in an alien ecosystem, but why. They don’t make sense because the place they live doesn’t match their evolution. If they grew up in burrows on the plains they start to make more sense, but then why did they travel to the forests? Is there some massive ecological shift on Endor that is forcing all species to catch up? When this sort of thing happened on Earth it resulted in niches being strangely filled by unusual species. Apply this to a planet struggling to rebalance, you’ve suddenly got some good inspiration. Ewoks redeemed!
Evolutionary Parallels
It’s tempting to think that realistic alien worlds would be bizzaro lands of unimaginable ecosystems. No one has been to an alien ecosystem so maybe that’s true! Logically, though, it seems like there are probably some things you can count on. If the planet has lots of sunlight from it’s start then something is taking advantage of it. If those things taking advantage of it are converting sunlight into chemical energy, they probably have broad surfaces to soak up light (i.e. “leaves”). If there are things with leaves soaking up sunlight they probably don’t have to move too much and so would prefer to stay rooted in the ground… You get the idea.
Formally, this concept is known as parallel evolution but the simple explanation is, as Elvi Okoye puts it in Cibola Burn, species are “under the same selection pressures. Some things are just a good idea.” In a nutshell, don’t feel like you have to warp things out of all recognition. You can have forests and lakes and vegetation, just make sure they all seem alien. This is especially true if you want to have an alien world where your players feel uneasy and off-balance. Being in a technicolor world of jellies and bubble-seeds might be following some interesting biological ideas but it’s also numbing. Better to have things that seem like flowers and lizards but then the flowers start crawling and the lizards mimic words and speech. Now you’re toying with their heads.
Not Everything is a Threat
It’s hard to objectively look at Earth’s environments since we’re all familiar with them, but try for a second. Say you’re sending a group of D&D adventurers into a forest and you know that they are going to run into a big, angry bear. During their morning of walking to meet the bear they will pass dozens of plant species, countless bugs and insects, tons of scurrying creatures, a score of singing birds, and probably one or two big species like deer or badgers that just move away from them when they come by. Then there’s the bear, that’s a legitimate encounter in the “you might get pretty hurt” manner.
Alien worlds should also be like that. There should be scurrying, crawling, chirping, growing, smelly, pollinating, and hunting creatures all around but most of them are not going to be a threat to the player characters. They’re there as background color and scene-setting but more than that they are camouflage. If the PCs are trudging across a featureless plain for an hour and then happen upon a furry, burrowing creature they’re going to ready their weapons. Your plan to have the creature launch into a surprise frenzy is doomed from the start. On the other hand if this is one of a dozen creatures they’ve run into they won’t bother worrying until it’s a ball of fur and teeth headed for their face.
Mephit James Blog 
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