Herbivory enhances the resistance of mangrove forest to cordgrass invasion

Abstract

The biotic resistance hypothesis proposes that biotic interactions, such as competition and herbivory, resist the establishment and spread of non-native species. The relative and interactive role of competition and herbivory in resisting plant invasions, however, remains poorly understood. We investigated the interactive role of competition and herbivory (by the native rodent Rattus losea) in resisting Spartina alterniflora (cordgrass) invasions into mangrove forests. In southern China, although exotic cordgrass numerically dominates intertidal mudflats and open gaps in mangrove forests, intact forests appear to be highly resistant to cordgrass invasion. A field transplant and rodent exclusion experiment showed that while the impact of rodent grazing on cordgrass was weak on mangrove forest edges and open mudflats, rodent grazing strongly suppressed cordgrass in mangrove understory habitats. A greenhouse experiment confirmed a synergistic interaction between grazing and light availability (a proxy for mangrove shading and light competition) in suppressing cordgrass establishment, with the strongest impacts of grazing in low light conditions that likely weakened cordgrass to survive and resprout. When both were present, as in mangrove understory habitats, grazing and low light acted in concert to eliminate cordgrass establishment, resulting in resistance of mangrove forests to cordgrass invasion. Our results reveal that grazing by native herbivores can enhance the resistance of mangrove forests to cordgrass invasion in southern China, and suggest that investigating multifactor interactions may be critical to understanding community resistance to exotic invasions.

Native herbivores enhance the resistance of an anthropogenically disturbed salt marsh to Spartina alterniflora invasion

“…, Zhang et al. ). Our results concluded that grazing by the native crab ( Helice ) effectively inhibited S. alterniflora invasion to anthropogenic ditches high marshes in northern China (Fig.…”

“…It is critical to better understand the mechanisms of a native ecosystem's resistance to exotic plant invasions in order to control invasions and mitigate their negative effects (Zhang et al. ). Biotic resistance plays a primary role in native ecosystems’ resistance to exotic invasions (Levine et al.…”

“…, Zhang et al. ) have indicated that native herbivores can exert significant negative effects on invader establishment and spread. However, how herbivory contributes to the resistance of native ecosystems to plant invasions in the face of various anthropogenic disturbances is still unclear.…”

“…Biological invasions have generated a range of ecological and economic impacts on ecosystems globally (Vil a et al 2010. It is critical to better understand the mechanisms of a native ecosystem's resistance to exotic plant invasions in order to control invasions and mitigate their negative effects (Zhang et al 2018). Biotic resistance plays a primary role in native ecosystems' resistance to exotic invasions (Levine et al 2004, Ricciardi et al 2013.…”

“…Consumptive resistance is constituent of these negative biotic interactions. Many investigations including meta-analyses (Levine et al 2004), literature reviews (Maron and Vil a 2001), and field experiments (Eschtruth and Battles 2009, Li et al 2014, Zhang et al 2018 have indicated that native herbivores can exert significant negative effects on invader establishment and spread. However, how herbivory contributes to the resistance of native ecosystems to plant invasions in the face of various anthropogenic disturbances is still unclear.…”