Understanding the mechanisms by which the geomorphic structures affect habitat invasibility by mediating various abiotic and biotic factors is essential for predicting whether these geomorphic structures may provide spatial windows of opportunity to facilitate range‐expansion of invasive species in salt marshes. Many studies have linked geomorphic landscape features such as tidal channels to invasion by exotic plants, but the role of tidal channel meanders (i.e., convex and concave sides) in regulating the
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Abstract Spartina alterniflora invasion remains unclear. Here, we examined the combined effects of tidal channel meander‐mediated hydrodynamic variables, soil abiotic stresses, and propagule pressure on the colonization ofSpartina in the Yellow River Delta, China, by conducting field observations and experiments. The results showed that lower hydrodynamic disturbance, bed shear stress, and higher propagule pressure triggered by eddies due to the convex structure of channel meanders facilitatedSpartina seedling establishment and growth, whereas the concave side considerably inhibited theSpartina invasion. Lower soil abiotic stresses also significantly promoted the invasibility of the channel meanders bySpartina . Based on these findings, we propose a conceptual framework to illustrate the effects of the meandering geomorphology of tidal channels on the mechanisms that might allow the landward spread ofSpartina and related processes. Our results demonstrate that the meandering geomorphic structures of tidal channels could act as stepping‐stones to significantly facilitate the landward invasion ofSpartina along tidal channels. This implies that geomorphic characteristics of tidal channels should be integrated into invasive species control and salt marsh management strategies. -
Abstract Species range expansion induced by climate change and human activities threaten native populations and communities across the biosphere. Insect herbivores, important consumers of plants, are known to expand or contract their range under global change, with potential consequences to the newly reached environment. The selection of oviposition sites by herbivorous insects could notably impact offspring performance. However, the role of such effects in impacting the receiving ecosystem has been rarely explored. Here, we provide the first evidence showing that a terrestrial range‐expanding phytophagous wood‐borer moth (
Zeuzera leuconotum Butler) heavily attacked the saplings of a foundation plant species tamarisk (Tamarix chinensis ) in salt marshes. Long‐term field surveys and laboratory behaviour experiments revealed that the oviposition preference of adult females was beneficial to their larval performance. The preference to oviposit on young branches of the new host plants, which were often softer and contained enough nutrients for larval development, indicates that females could still make the right choice on novel host‐plants. This finding supports the ‘mother knows best’ hypothesis that female insects will evolve to oviposit on hosts on which their offspring fare best. Consequently, the survival of host‐plant saplings decreased dramatically under this top‐down control, revealing that herbivory of this range‐expanding insect has a profound negative impact on the recruitment and succession of coastal foundation species, thereby potentially leading to saltmarsh degradation. These findings highlight the importance of the maternal oviposition effects in range‐expanding insects and how these populations can establish using novel host‐plants and threaten coastal wetlands.