Habitat preference. How should this look on the card?

i.e. Can we limit habitat types to a certain number - good for icon development for the cards. How should this be shown. Is there a way to show it, so that gradients can be illustrated? i.e. first row below image has icons showing preferred habitats, followed by icons (in different shape or something) of possible habitats, etc.

This might be best done by trying to stick to the concept of biomes (http://en.wikipedia.org/wiki/Biome). Unfortunately, this can get pretty detailed, but there's quite a few education type places of information that attempt to simplify the number of biomes. Anyway, the simple classifications tend to have the following:

Freshwater

Marine

Desert

Forest

Grassland

Tundra

I also propose adding an "Urban"

Maybe a good way to show this, is to have an icon for each of these "biomes" and then a color indicator for the preferred temperature (as in red for hot, blue for cold, and green for temperate).

I'd definitely include an "urban" since there's lots of species that do really well in urban environments and are actually the ones kids are most likely to encounter! It prevents kids from going "but if this animal likes Forest why is it on my lawn?"

However icons are laid out they should probably designed so that you can include more than one on the card without squishing. That'll then allow things that are found in multiple environments to be in those environments instead of just pigeonholed in one.

I presume you guys are thinking along these lines:
http://www.discoveringpoetry.co.uk/habitat-icons.jpg

I've actually seen this problem solved pretty handily another way, with iconic illustrations of the habitats drawn in blocks from a side-on view. If the ground is the same number of pixels high at the border of each tile, then they can be seamlessly placed together, indicating a transition from one to the next. You could probably overlay a color gradient pretty easily. For example (forgive the ASCII):

Desert: ..::..::.. (that's sand dunes)
Forest: _||||||||_ (pretend these are stylized tree trunks)
Plains: .:;;;;;;:. (stylized grasses)

So the "habitat" slot on the card of a critter that lives in any of these three could look like this:


Each habitat blends into the next. Plus, it's from the point of view from which we normally experience the world; it doesn't require any sort of bird's-eye-view processing.

Think of a mountain range cross-section illustration, a lá this example, only reducing things to a handful of categories instead of a smooth gradient.

I love the side view idea. There's actually a few graphic artists that have contacted me about working on things like this (as well as logo, etc). Will pass it on.

Urban, by the way, would probably be best exemplified in the general synanthropic spp.