Since your work is in game theory and population biology, do not forget Springer's
Journal of Theoretical Ecology. It's a newer journal (started in 2008) but already has an impact factor close to JTB, and has an open access option. Alan Hastings is the Editor in Chief of this journal (you'd have a hard time finding a more prominent figure in Theoretical Biology than him).
Unfortunately most journals in the subject don't have open access options (e.g. Mathematical Biosciences, Mathematical Biosciences and Engineering, Ecological Modeling, Journal of Theoretical Population Biology, Journal of Theoretical Biology)
Also don't forget Bio Journals, you can stick the more advanced math and proofs in an appendix, and often your work will get more exposure in these journals. I know Proceedings of the Royal Society Part B, the American Naturalist, Journal of Applied Ecology and PLoS BIO all have open access options and take modeling papers as long as the results are interesting from a biological perspective and aren't just a cool model that was fun to explore (a good intro and discussion is key for these journals as they all have very high impact factors).
If you prove things in your work also consider applied math journals like Nonlinear Dynamics (Springer) which has an open access option.