What degree is necessary for a career in conservation?
The conservation, applied ecology, and natural resource management fields can be a tough job market depending upon your geographically location and what subfield you want to work in.  

For your undergraduate degree, any of the majors you listed would be reasonable. I would browse graduate programs you are remotely interested in and see what courses they require for admission. Some programs might requires 2-3 semester of calculus where others require none. Likewise, chemistry (e.g., organic) and physics requirements sometimes vary. As noted in a comment, your exact undergraduate degree does not matter if you plan on going to graduate school. However, some agencies (e.g., the US Federal government) have course requirements for jobs (e.g., a fish biologist). 

Academically, I suggest a double major or a minor in another field to give you technical skills to help you stand out. Possible examples might be chemistry, math or statistics, or something related to GIS.  

Outside of school, try to get as much experience as possible. Hopefully you can get payed summer job/internships. One great place to find these opportunities is the Texas A&amp;M Wildlife/Applied Ecology jobs board.  

The source for my information is my own experience. I am PhD-level research scientist working for a US natural resource research agency.