The american bullfrog is native to much of the eastern united states. this species has successfully begun to spread west as an invasive species. it is thriving in the western united states because of its large size, high mobility, and tremendous reproductive capabilities. american bullfrogs have very generalized eating habits and often eat the same food sources as the native frog species in the western united states, causing a reduction in the overall food supply. the relationship between the american bullfrog and native frog species in the western united states can best be characterized as

The relationship between species can be better characterized as competition.

Explanation:

Competition is an inharmonious ecological relation that can either occur between organisms of different species (interspecific), providing competition for one or more resources of the environment: water, food, luminosity and physical space, as well as between organisms belonging to the same species ( intra-specific), including, in addition to the other resources, competition from reproductive partners capable of proliferating fertile offspring. In this case, the species mentioned in the question are in relation of competition for food.