Causes for Biodiversity Differences Between Local Neighborhoods?

I lived in the same area for 29 years now. In the neighborhood in which I grew up it wasn't uncommon to see slugs crawling around on sidewalks and porches. I'm living in a neighborhood now about 3 miles away where I never see slugs, but I do see snails just as often! I also see frogs or toads here where I've never seen them in my previous neighborhood. I've never seen a chipmunk in my current neighborhood but if I walk a half mile east, the chipmunks are almost as common as squirrels.

My questions is...what causes these minor differences in biodiversity within such short distances? Is there a name for this phenomenon? I am wondering if this could make a good topic for research...if anyone knows of research or articles or books regarding this or similar topics, please let me know!

Thanks!