The effect of invasive fall armyworm abundance on native species depends on relative trophic level

Abstract

Fall armyworm (FAW) has posed a significant threat to Chinese agriculture and native species since its presence was first reported in 2019. To better understand the impacts of FAW, however, information on how FAW abundance affects native abundance and communities and whether these effects are dependent on the trophic level of native species relative to FAW is needed. Here, we studied the direction, strength, and shape of the relationship between FAW abundance and responses of native abundance and community-level metrics (mean value of unit-scaled richness, diversity, and evenness). We then tested how relative trophic position influenced these relationships. Across 25 study sites in Yunnan province, we recorded FAW abundance ranging from 0 to 715 individuals per 2666.8 m2. Across this range, native abundance declined nonlinearly by 14.6%, on average, and community metrics declined linearly by 18.1%. For lower trophic levels, FAW caused a significant nonlinear decline in native abundance (20.7%) and community metrics (28.6%), with the greatest declines occurring at low FAW abundance. At the same trophic level, native abundance (9.1%) and community metrics (14.5%) declined nonlinearly and linearly, respectively. In contrast, FAW had no significant impact on native abundance or community metrics at higher trophic levels. At the community level, negative impacts were stronger for evenness and diversity than for richness. The results of our analyses suggest native responses to FAW invasion rely strongly on FAW abundance and trophic position. The FAW abundance–native response relationships reveal how FAW impacts may develop during the invasion process and when to best manage them.