Japanese Stiltgrass Is an Invasive Plant That Was Accidentally Introduced

Japanese stiltgrass is an invasive plant that was accidentally introduced to the United States in the early 1900s. It can be found on roadsides and in forests, and it has many impacts on native plants and animals. Biologists Jayna DeVore and John Maerz studied the effect of Japanese stiltgrass on American toads in their natural habitat. They enclosed American toads in cages with lycosid spiders and/or Japanese stiltgrass. The four treatments were (A) lycosid spiders and Japanese stiltgrass, (B) lycosid spiders without Japanese stiltgrass, (C) lycosid spiders and Japanese stiltgrass, and (D) no lycosid spiders and no Japanese stiltgrass. They compared the survival of American toads across the treatments (left graph) . They also measured the density of lycosid spiders in different areas where Japanese stiltgrass was absent vs. present (right graph) .
Source: DeVore, J. L., & Maerz, J. C. (2014) . Grass invasion increases top‐down pressure on an amphibian via structurally mediated effects on an intraguild predator. Ecology, 95(7) , 1724-1730.
-What do their results demonstrate about the interactions between the species that they studied?

A) Lycosid spiders are predators of American toads.
B) American toads are herbivores of Japanese stiltgrass.
C) American toads are predators of lycosid spiders.
D) Japanese stiltgrass is a pathogen of lycosid spiders.