Can't change the screenshot directory because "com.apple.screencapture: command not found"
The error message is telling you that the shell (bash) is expecting the first expression on the command line to be a program, script, or shell built-in. com.apple.screencapture is none of those.

The command you are missing is defaults, with a sub-command of write, like so:

defaults write com.apple.screencapture location /Users/mac/Documents/Zoology/edited\ screen\ shots