And this is the biome chart for reference. The one on the left is for the land, and the right is for the seas.
Terrestrial BiomesJungleSavannaDunesTemperate ForestGrassland Desert Taiga TundraCold DesertAquatic BiomesWarm Shallow SeaWarm Deep SeaTemperate Shallow SeaTemperate Deep SeaCold Shallow SeaCold Deep seaHow The Biomes Work (Refer to the maps above)
Biomes work via simple arbitrary humidity and climate belt logic. Humidity is determined by the proximity of a tile to the western shore of the landmass it is a part of. Right now, in the default intermediate climate state, all squares that are directly next to the west coast are humid, ones behind them are intermediate, and the furthest away are dry. This applies in all 8 directions. Climate belts should be obvious. Closer to the poles, colder it is, and the same with warmth and the equator. The climate belts are also in intermediate state as well.
RegionsEach region supports a different amount of carnivores and herbivores, directly correlated with size. For each biome, one herbivore slot will be available for every two, and one carnivore for every three squares. For example, region 2 is 6 squares big, so it can support 3 native herbivore species and 2 native carnivore species. A single tile region, such as region 9 can only have a single indigenous species, an herbivore, and is too small for a carnivore to solely inhabit.
1-2 squares: 1 species of herbivore, no carnivores
3-4 squares: 2 species of herbivore, 1 species of carnivore
5-6 squares: 3 species of herbivore, 2 species of carnivore
...
Jungles, deep cold seas and shallow warm seas have a +1 in each indigenous species category, meaning a single tile of jungle can support two herbivores and 1 carnivore species, the same as the shallow warm seas.
Deep oceans contain one species of herbivore for each strip they possess, and one carnivore species for each two. Deep cold sea has a +1 on both.
While most coastal squares have shallow seas next to them, some may simply not. It is normal and a part of the game.
Predator Cross-SectionalityIf a biome is too small to hold an endemic predator of its own, then most suitable predator in the regions neighboring that one will be the occupier. The victor population will not be a distinct species of its own and cannot be used as a separate species, but will instantly become one if the said small region becomes large enough to fully support it, and will also have its climate and habitat preferences be automatically changed to fit in.
Habitat MultiplicityA species
can exist in 2 separate habitats at the same time, if those two habitats are the same exact type. And a species can also hang on if the habitat change isn't too severe - namely, a single notch of change in tempature. For example, a jungle species will survive if the habitat changes into a temperate forest, but will suffer significant penalties if the neighboring temperate forest species invades it.
Ocean CrossingYou can colonise an offshore territory with an already existing species if that piece of land is the same exact habitat that species is adapted to. You will roll a dice that depends on how far and large the target landmass is, and it can be influenced by your adaptations.