My planet is a tidally locked rocky planet (90% Earth surface gravity) orbiting an M-type star. This M-type star orbits a G-type star at roughly 1.5AU.
This means that it has a kind of day/night cycle determined by how fast the planet orbits the M-type. These "days" (both the day and night cycle together) last about 48 hours. On the side facing the red dwarf, days would be near Earth luminance, and "nights" would be lit by the red dwarf at approximately 60% Earth luminance. On the side facing away from the red dwarf, days would be lit by the yellow sun at approximately 40% Earth luminance (like days on Mars), and nights would be lit by whatever light refracts through the atmosphere from the other side of the planet.
Assume that the planet had liquid water oceans before terraforming and has since been terraformed sufficiently enough to have a breathable atmosphere, bacteria, plankton, algae, fungi, lichens, grasses, some trees/ferns, etc. (you know, the basics).
The planet has a band of habitability around its terminator (mostly on the warmer side of the planet) which is broadly suitable for humans (survivable, at least, if not exactly ideal). The only land masses in this habitable area are a series of large, volcanic islands (Iceland to Greenland in size). The general idea for this planet is that it is habitable in the broad sense, but harsh. Probably very windy, lots of storms, and broad temperature variation.
Once this base is established, animals are introduced. Building off of others' posts/answers that I have read, let's assume our terraformers sent the bare basics and intentionally didn't send any creatures harmful to humans unless they play an essential role in building the new ecosystem (i.e., nothing poisonous, venomous, crop-destroying, or disease-carrying, and no large apex predators).
I'll leave aside aquatic fauna for now because that's a whole 'nother barrel of fish (ha), but assume the aquatic ecosystem has been functionally stocked with fauna.
Turning to terrestrial fauna, our terraformers have introduced various forms of insects (especially pollinators), insectivore birds and rodents, pollinating birds, herbivorous rodents, small-to-midsize predatory birds, small-to-midsize carnivora, some small-to-midsize prey animals for hunting that may not fall into the above categories, and hardy/wild forms of domesticated animals (boars, goats/sheep, etc.).
Our terraformers give the animals time to adapt to this new environment so that any unfit animals have died off by the time humans arrive. What kind of new or surprising adaptations might we expect to see by the time humans arrive, and how quickly might we expect those adaptations to evolve?
To give some starting points for answers, maybe consider the following points in time for potential human arrival:
- 1000 years after animals arrive
- 25,000 years after animals arrive (this is the time frame I was originally thinking if enough interesting evolutionary changes would be plausible)
- 100,000 years after animals arrive
- 1 million years after animals arrive
To give some further starting points for answers, consider some potential adaptations that I have brainstormed and address them or respond with your own:
- Animals getting larger due to slightly lower surface gravity (especially birds??)
- Changes in the grazing or social habits of some animals due to environmental changes
- Heightened sensitivity to infrared light due to overall lower luminance and higher infrared radiance from the red dwarf
- small-to-midsize carnivora rapidly becoming larger to fill an apex predator niche
- along the same lines, general effects of both "island gigantism" and "island dwarfism" (i.e., the tendency for large animals introduced to an island to grow smaller, and small animals to grow larger)