I was just browsing through tsuwm's lexicon, and came across a term for one who favors the underdog:

infracaninophile

I checked it out at onelook.com and didn't find anything to add to tsuwm's definition, so I looked up 'caninophile'; no go. But there did appear a botanical term that I thought was fairly interesting:

chianophile

"A plant that can endure long snowy winters, or one that requires snow cover in winter."

Here's a link to what appears to be a rich lexicon of botanical terms from which I quoted the above:

http://glossary.gardenweb.com/glossary/page1.html