25. LAW OF AVAILABILITY 

The geographic distribution of plants and animals is limited in the first instance by their place and time of origin. 

At this year's Calgary Stampede
Alberta's mighty mastodon
Will not be taking up the lead
Because their day has come and gone.

Nor is the great Canadian moose,
Though they can run and swim all day,
Likely to show up down in Vera Cruz,
For it's too far out of their way!