Mangroves are vascular-plant-dominated coastal wetland ecosystems, and are characterized for complex spatial differences in structure and diversity along tidal gradients. Thus, Mangrove forests provide an idea system to examine the influence of habitat heterogeneity on insect herbivore communities. Meanwhile, the rapid, global, and anthropogenic alternation of species distribution in coastal wetland ecosystems necessitates a better understanding of how plant-insect interaction been shaped in natural communities for predicting and mitigating the herbivore impacts. Although many studies have investigated the responses of herbivores to climatic variability across a broad biogeographic range in mangrove forest, however, relative few studies available have often focus on mangrove seedlings rather than adults, especially across local intertidal elevation gradient. In this study, we evaluated patterns of insect herbivory on seedling of Kandelia obovata, the most widely distributed mangrove species in southeast China, across intertidal elevation, using a ‘marsh organ’ in Zhangjiang Estuary. We also examined the potential causes of variation in herbivory by monitored the plant growth and leaf traits of transplanted seedlings for two growing seasons.
Results/Conclusions
Damage to plants showed a hump-shaped relationship with the inundation time (ranged from 15 to 0 h/d), but varied with different feeding guilds. Across the tidal elevation gradients, damage by leaf-chewer (24-99% of damaged leaf number, 1-33% of leaf area consumption) and bud-feeding (0-84%) herbivores were greater that leaf-sucking (0-15%) herbivores, while few leaf-miners occurred. Herbivory with greatest values by leaf-chewer and bud-feeding herbivores occurred at higher mid-tidal elevations with inundation time of 1-2 h/d, while by leaf-sucking herbivores occurred at lower mid-tidal elevations with inundation time of ca. 9 h/d. Tidal inundation played an important role in mediating the relative importance and intensity of insect-plant interactions by directly inhibited the abundance and feeding activities of herbivores across mid- to low-tidal elevations, as well as constrained the seedling growth at low- and high-tidal elevations. Thus the best performance of mangrove seedlings and highest insect herbivory at mid-tidal elevations supported the Plant Vigor Hypothesis, but not explained by the leaf palatability in this intertidal plant-insect system. In view of the mangrove seedling, our findings were of scientific significance for regeneration and herbivory prevention in the process of mangrove restoration and afforestation in China.