The number of competitor species is unlinked to sexual dimorphism.

Meiri, S., Kadison, A.E., Novosolov, M., Pafilis, P., Foufopoulos, J., Itescu, Y., Raia, P., Pincheira-Donoso, D. 2014. The number of competitor species is unlinked to sexual dimorphism. Journal of Animal Ecology, 83 (6), pp. 1302-1312.

http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12248/abstract