Invasion of weeping lovegrass reduces native food and habitat resource of Eusphingonotus japonicus (Saussure)

To examine the relative importance and interactions of trophic and non-trophic effects of plant invasions on herbivores, we investigated how the invasion of weeping lovegrass Eragrostis curvula impacted Eusphingonotus japonicus, a food generalist grasshopper endemic to gravelly floodplains with sparse vegetation in Japan. Field observations and laboratory experiments showed that the grasshopper fed mainly on herbs endemic to the gravelly floodplains, which were negatively impacted by the alien grass. The alien grass was not consumed as food. Field censuses also showed that the abundance of the grasshopper was positively correlated with the coverage of endemic herbs in a plot where weeping lovegrass was not dominant. Dominance of the grass (i.e., habitat modification for E. japonicus) negatively impacted the grasshopper and weakened the positive relationship between the grasshopper and endemic herbs. These results suggest that an understanding of the relationship between non-trophic and trophic effects is essential to predict the impacts of plant invasions on herbivores.