Select "Threats" type in the menu, once you have picked on, click REFINE
Now, in "Taxonomy", select plants, animals or fungi, click REFINE
Each time you click REFINE, it narrows the list based on your selection.
To add "North America" click "Location" and select it, then click REFINE
Don't forget to clear your selections if you want to research something new. Look for a small, red X in a box to clear.